The difference between astronomers and biologists


The debate about intelligent, extra-terrestrial aliens goes on, with the usual divide: astronomers insisting that the galaxy must be swarming with alien intelligences, which is popular with the media, and the biologists saying no, it’s not likely, there are probably swarms of single-celled organisms, but big multicellular intelligences like ours are probably rare. And the media ignores us, because that answer simply is not sufficiently sensational.

But we will fight back! Here’s an interesting review of the alien argument. There is actually a historical and conceptual reason why astronomers think the way they do.

In response [to a paper arguing that SETI was a waste of time], Sagan co-wrote a paper with William Newman “The Solipsist Approach to Extraterrestrial Intelligence” which right from the title attacks Tipler for believing Earth to be unique. Sagan is of course citing the Copernican Principle, which roughly states the Earth is NOT the center of the heavens. The Copernican Principle is the modern foundation for Astronomy, Cosmology and Relativistic Physics. Sagan thought anyone claiming the Earth to be special must be doing bad science. Here’s a typical quote: Despite the utter mediocrity of our position in space and time, it is occasionally asserted, with no sense of irony, that our intelligence and technology are unparalleled in the history of the cosmos. It seems to us more likely that this is merely the latest in the long series of anthropocentric and self-congratulatory pronouncements on scientific issues that dates back to well before the time of Claudius Ptolemy.

It’s all about our perception of the rules. Astronomers see a universe with uniform laws that set up similar patterns everywhere: stars, rocks, gas. Life is lumped in with rocks as a phenomenon that just pops up everywhere, and with their limited idea of biology, just see all life as life like ours. Biologists also see universal laws, but we know from our experience that those laws generate endless diversity — there are millions of species on this planet, and each one is unique.

Now unlike Astronomy, the discipline of Biology takes a highly favorable view of uniqueness. Evolution constantly discovers quirky and highly contingent historical paths. Biology takes it for granted that everybody is a special snowflake. In fact the third sentence of Tipler’s 1980 paper calls this out:

The contemporary advocates for the existence of such [extraterrestrial intelligent] beings seem to be primarily astronomers and physicists, such as Sagan (2), Drake (3), and Morrison (4), while most leading experts in evolutionary biology, such as Dobzhansky (5), Simpson (6) Francois (7), Ayala et al. (8) and Mayr (9) contend that the Earth is probably unique in harbouring intelligence, at least amongst the planets of our Galaxy.

And as quoted in Mark A. Sheirdan’s book, we have eminent Evolutionary Biologist Theodosius Dobzhansky (“Nothing in Biology Makes Sense Except in the Light of Evolution“) joining the fray:

In his article Dobzhanksy turned Sagan’s argument on its head. Dobzhansky cited the fact that of the more than two million species living on Earth only one had evolved language, extragenetically transmitted culture, and awareness of self and death, as proof that it is “fatuous” to hold “the opinion that if life exists anywhere else it must eventually give rise to rational beings.”

And here’s a nice, short table to summarize the differences.

intellife2

I have to add that it is probably another of those universal laws that Darwinian replicators will expand to fill an empty ecosystem, but that there are many ways to do that. It’s also a rule that the replicators are exploiting short term advantages to supplant competitors — there is no teleological imperative that says Strategy X is a good one, because while it slows our species down for the next billion years, there’s a chance we might build spaceships two billion years from now. Spaceship building is never going to be a selectively advantageous feature — it’s only going to emerge as a spandrel, which might lead to a species that can occupy a novel niche. And that means that spaceship builders are only going to arise as a product of chance, which will mean they’re going to be very rare.

On the other hand, a species that does successfully exploit space as an ecosystem is going to have a phenomenally fascinating future history of radiating forms. Think of the first space colonizers as equivalent to the first cells that evolved a metabolism that allowed them to exist outside the coddled, energy-rich environment of a deep-sea vent. It’s only the first step in a long evolutionary process that’s going to produce endless forms most beautiful…and also unexpected variations. It’s silly to expect that the successful, thriving interstellar life forms will be bipeds adapted to life on a planetary surface, living in large metal shells as autonomous agents crewing a spaceship. The real thing would be alien, and probably terrifyingly incomprehensible.

Comments

  1. says

    I always thought a reasonable answer to Fermi’s paradox is that Einstein was right – there really isn’t superluminal travel, and that space’s size means that intelligent life develops general relativity and their version of a Hubble space telescope, takes a look around, says their equivalent of “fuck” and eventually dies.

  2. urbanwitch says

    I’ve always held the opinion that if there is life out there travelling through space, the junk that has been beaming out there from our radio and television will have led to a quarantine of this sector; until we develop some taste. BBC nature programmes just can’t be enough to counteract the rest.

  3. says

    I’m reminded that the astronomer’s definition of “metal” is every element that isn’t hydrogen or helium.

  4. mykroft says

    So essentially astronomers and physicists are frequentists, and biologists are Bayesians?

  5. machintelligence says

    Space is an incredibly hostile environment for “moist robots.” If we are visited by alien species, I predict that they will be — wait for it — machine intelligences.

  6. dingojack says

    The difference between astronomers and biologists
    Astronomers study stars; biologists study living organisms? :)

    There’s a Youtube video of a lecture by Dr. James Kasting (a astronomer) called how to find a habitable planet [it’s nearly an hour long so I won’t link to it] in which he discusses this tangentially. He comes down a little closer to Sagan (but less optimistic). The upshot is if you want to find life, look for thermodynamically unbalanced pairs of reduced/oxidised gases (such as carbon dioxide and methane) in planetary atmospheres.

    (Oh and astronomers think silicon and oxygen are METALS…. don’t get me started!)

    Dingo

  7. johnhodges says

    If a planet had no fossil fuels, but DID have an intelligent species, would they ever develop space travel? Most “alternative” forms of energy good enough to power a high-energy civilization (high-tech photovoltaic, advanced wind turbines, nuclear fission via U-235, plutonium, or thorium, and deep-rock geothermal) seem to require a high-energy civilization to develop them.

    Assuming that Einstein was correct, that FTL travel is impossible and near-C travel is extremely (astronomically) expensive and difficult, and given that habitable planets are few and very far between (and likely already have indigenous life far better adapted to them), would any intelligent species ever attempt interstellar travel? What profit would there be in it?

    We humans may someday visit “in the flesh” some of our solar system, but really, will we ever COLONIZE anyplace but Earth? Given the inhospitable environments there, I doubt we ever could, and I doubt we would ever want to.

    The “habitable-zone” exoplanets we have found so far are all larger than Earth; if an intelligent species developed on a “super-Earth”, getting from the ground to orbit would be even more difficult and expensive for them than it was for us.

  8. Kevin Kehres says

    Good grief. You missed the most important third option.

    They’re already here. And our tiny human brains can’t comprehend the observational machinery.

    My dog doesn’t believe my shoes exist. Every morning, he competes for attention with my tying my shoes so we can go for a walk, even though going for a walk is the most important thing EVER. Because poop.

    Same thing with humans. Aliens are here. We don’t notice them. Because they’re hidden as poison ivy — or dogs.

    /snark (because that was a pretty good Poe)

  9. alkisvonidas says

    Yes, there probably is no other intelligent life in our Galaxy.

    No, SETI is not a waste of time.

    Or money, for that matter, at least compared to other modes of wasting money we have devised (like producing movies about going to outer space, which probably costs more than actually going into space)

    So, we allocate some of our signal-processing time to listening on the off chance that we might be wrong and there’s someone/thing out there. So what? If we were to take a purely utilitarian approach, most of basic science research should be considered a waste of resources.

  10. Holms says

    I’m reminded that the astronomer’s definition of “metal” is every element that isn’t hydrogen or helium.

    I hope you realise, this simply means ‘metal’ has a different definition in astronomical use?

  11. says

    Considering the size of the universe (hang on, my brain just imploded again), even something improbable as intelligent life should be widespread. Even if we are alone in our galaxy there are a few hundred billion galaxies out there.

    Do I believe in a Star Wars universe with life on every other planet and FLT? No, Fermi’s paradox pretty much rules that one out. So for all practical purposes I think we’re alone in our corner of the world, although I would love for SETI to prove me wrong.

  12. alkisvonidas says

    @ Marcus Ranum:

    I always thought a reasonable answer to Fermi’s paradox is that Einstein was right – there really isn’t superluminal travel

    Superluminal travel (at least, some modes of it) would NOT mean Einstein was wrong! The Alcubierre drive, for example, is based on Einstein’s field equations of General Relativity, coupled with some “exotic matter”. If I ever believed that FTL travel would require Einstein being wrong, I’d plain disbelieve FTL.

    Furthermore, it would be possible for an intelligent species with a lifetime comparable to ours to spread through the Galaxy using only near-lightspeed travel. They would have to find a means of producing comfortable (to their biology) acceleration for years; they’d have to build mini-ecosystems to cart around in space, in order to survive and replenish their supplies; and they would have to get used to the idea of never going back, except to meet a race of distant descendants who would consider them a half-forgotten legend.

    Some rogues might actually do it. Humanity might some day do it, if the current fossil fuel crisis is resolved in a way allowing us to retain a high-tech civilization.

  13. diego says

    I guess it kind of depends on two things; the power of selection versus constraint and contingency to explore morphospace and also the number of niches in morphospace. We can’t really estimate either but we could look at instances of convergence and parallelism to get some idea of the relative probabilities. Of course with no real examples of convergence on human-type intelligence in our planet’s history it certainly doesn’t give us much confidence in the inevitability of humans (contra Simon Conway Morris et al.).

  14. colnago80 says

    Interestingly enough, there was an Internet debate back in the 1990s between Carl Sagan and Ernst Mayr on the prevalence of intelligent live in the universe, with Sagan arguing that it might be fairly prevalent while Mayr argued that it might be rare. Obviously, this is a question that is sheer speculation as we sit here today as we don’t have evidence either way.

  15. says

    Internet debate? What?

    There was a published exchange between Sagan & Mayr. I believe you can find it in Mayr’s Toward a New Philosophy of Biology.

  16. dianne says

    According to the Fermi paradox, we don’t exist because we’re not everywhere in the galaxy. Maybe extraterrestrial intelligence species haven’t gotten around to it yet either. Or maybe it really is just too much trouble. Or maybe it’s hard to get a species that can survive long enough to get the tech. Or maybe life and/or intelligence really is a >1 in 300 billion event. Or maybe they’re here but so different that we don’t notice each other. There’s just not enough data to say anything at all for sure.

  17. Mark Foley says

    I’d like to point out that you switch between two completely different arguments apparently arbitrarily in the post: that life is common throughout the universe (amongst which some unknown proportion will be intelligent), and that intelligent life is common thoughout the universe. The first is easy to defend, the second most definitely not, and you only seem to devote any energy to arguing against the second point, which is unrepresentative of what people in the field actually believe.

    If you completely misrepresent the other side, it is very easy to make them appear foolish. This is something you should be well aware of, considering how often creationists do it, but that’s apparently not enough to make you be careful in your own writing.

  18. birgerjohansson says

    Discussions in literature:

    The SF aithor Stanislaw Lem, when striving to explain the Silentium Universii, was of the opinion that life like ours is very rare. There may of course be many species who acquire intelligence and technology, but what they do with this is inherently unpredictable and contac t attempts may be vain because the gulf is too huge.

    The sentient ocean in Solaris is a very successful -even godlike- organism, but it lacks the tools to directly communicate with humans. Instead it attempts indirect communication, with partially disastrous results.

    The Strugatsky novel “Wayside Picnic”(filmed as “Stalker”) is another story of indirect contact, also with partially bad results for humans who enter the zone where something once happened, attempting to comprehend.

    Lem’s short novel “His Master’s Voice” is both a satire of the terror balance and the futility of SETI. After many years of herculean efforts, the varipous teams decode fragments of the message, but apa rt from some amateur magician-trick stuff, there is no revelation.

    Strugatsky’s novel Beetle in the Anthill is another example of pessimism. This time we have humans produced by zygotes kept in storage since before technology developed on Earth. They develop normally and become ordinary humans (unawaye of their unique origin),, but are cover tly watched by the authorities. They seem to be part of an experimen of how humans interact with the alien. Once again there is no breakthrough for the scientists trying to unravel a mystery beyond their grasp.

  19. aziraphale says

    My feeling is that before an intelligent species gets anywhere near building a starship they will have built machine intelligences smart enough to explore new planets at least as well as their makers. Given that, why explore in person? The machines, not needing life support, can do it faster for a given expenditure of energy. They would probably be programmed not to interfere with any ecosystem they found, including us.

    It’s obvious, I think, that interstellar flight will never be an answer to population pressure. They will have to solve that problem at home.

  20. alkisvonidas says

    @ aziraphale

    Any machines intelligent enough to operate for years in total isolation would have to repair themselves, therefore they’d need raw materials and tools/low-tech machines. They would need to replenish their power, which is a task as demanding as feeding for living organisms. They’d need to reproduce, because at some point repairs would become infeasible/impractical.

    At which point, we’re faced with the task of providing them with an artificial ecosystem, or the means to build one. I don’t see how this is any less of a daunting task than sending organic life forms into space along with a natural ecosystem.

  21. pikaia says

    Even if a planet did produce an intelligent species it doesn’t follow that they would be able to go into space. If dolphins had developed human intelligence they would not produce technology because it is rather hard to smelt metal underwater. If elephants, then they would not be able to do much with only a trunk instead of a pair of hands. If orangs, they would not have a society that you need to do technology on an industrial scale. So space-faring life is likely to be much rarer then intelligent life, and even that took Earth 4.5 billion years here.

    And how would anyone emigrate to another star system, a journey that would probably take centuries? It is so expensive, difficult and dangerous that I doubt if we will ever try it, even if we identify a suitable planet to go to, which is another problem.

  22. twas brillig (stevem) says

    Life is **probably** very common throughout the universe. Where there’s water there’s probably life. BUT intelligence is much harder to define. I’ll just say it: What. Is. Intelligence? My answer: that our definition of intelligence is only how we define it, we will define it to be what we think intelligence is [Turing Test anyone?].
    That Fermi’s Paradox is just pointing out that ET intelligence might be very different than ours and not conform to what we expect and limit ourselves to only looking for what we expect. So, yes, I think intelligence, while not COMMON, is certainly elsewhere. ‘Our_intelligence’ may be unique, but Intelligence is not unique to ours.
    Are dolphins intelligent? Whales? ET intelligence is here, in our oceans. We need to think about it harder.

  23. alkisvonidas says

    @20: However, I can picture some future civilization building a small fleet containing intelligent Von Neumann machines, which would slowly spread out exploring first our solar system and then the Galaxy. They would make frequent stops on the Moon, the asteroid belt, etc., where they would mine for the minerals necessary to build more machines and spacecraft. They could then venture longest trips, perhaps on “sleep mode”, retaining only the functions necessary to detect a nearby mineral source, and so on and so forth.

    In short, we could probably afford to send out some “artificial spores” to explore and colonise the galaxy on our behalf. But we could hardly expect to hear from them again. If they ever returned, our (very distant) descendants would probably think they were making “first contact” with an alien intelligence!

  24. Jason Dick says

    Minor correction: we can’t develop interstellar spaceships two billion years from now, because if it takes that long, we’ll almost certainly be dead:
    http://io9.com/earth-will-turn-into-a-venus-like-hell-earlier-than-pre-961194748

    While the estimate the article is about is quite short for a runaway greenhouse effect, earlier estimates ranged between 1.1 – 2 billion years. So either way we shouldn’t procrastinate for two billion years.

    Anyway, given the Fermi paradox, one can show that there are three possibilities for civilizations besides us:
    1. Civilizations are exceedingly rare.
    2. Interstellar travel is really really hard, so hard that it is effectively impossible.
    3. Civilizations aren’t that uncommon, and interstellar travel isn’t horribly difficult, but we just happen to be the first.

    The third option seems pretty unlikely. So we’re left with either one or two.

  25. says

    It seems rather presumptuous to assume that it’s even possible to expand to fill the galaxy (less so to think intelligent machines could spread throughout the galaxy) though in both cases I think we’re probably expressing profound ignorance of the sheer scale involved. It’s entirely possible that the trip between stars is simply too long and difficult for even complex machinery to complete it in a useful/productive way.

    Just as one might naively assume traveling faster than 300,000 kilometers per second is possible, or that it is possible to sort 1000 random songs into two equal-length playlists — in both cases the assumptions seem so reasonable until one learns more about the problems, and now we’re quite confident that both are forbidden by the structure of the universe.

    I was surprised when Stephan Hawking suggested if alien intelligence exists it’s probably a threat to us. A friend once asked me if aliens could come for our resources, and given the distances involved I told him it’s kinda like driving from the southern tip of Chile up to the Yukon to get the last gallon of gas on Earth. If you can get between star systems you’ve already figured out how to sustain yourself alone in interstellar space indefinitely.

    Also, what’s with the assumption of unlimited expansion? Isn’t anyone paying attention to global reproductive trends? There are very good reasons to think human population could level off within a century or two, purely by choice.

  26. Al Dente says

    Alpha Centauri is 4.3 light years away. That’s over 3.9×10¹³ km (271,000 AU). Voyager 1 is traveling away from the Sun at a rate of 17.3 km/s. If Voyager were to travel to Alpha Centauri (which it isn’t, it’s going in a different direction) it would take over 73,000 years to arrive.

  27. says

    The debate about intelligent, extra-terrestrial aliens goes on, with the usual divide: astronomers insisting that the galaxy must be swarming with alien intelligences, which is popular with the media, and the biologists saying no, it’s not likely, there are probably swarms of single-celled organisms, but big multicellular intelligences like ours are probably rare.

    We know from the fossil record that life arose shortly after the formation of the Earth, suggesting that the origin of life might be an inevitable chemical process on countless Earthlike planets throughout the cosmos. But on the Earth, in nearly four billion years, life advanced no further than algae. So, maybe, more complex forms of life are harder to evolve, harder even than the origin of life itself. If this is right, the planets of the galaxy might be filled with microorganisms, but big beasts and vegetables and thinking beings might be comparatively rare.

    — Carl Sagan, Cosmos: A Personal Voyage (1980), episode 2: “One Voice in the Cosmic Fugue”

  28. Gerard O says

    There’s also another possibility: A life-form that is smart enough to create brilliant technology, but is too stupid to use it to escape its own climatological prison.

  29. Sunday Afternoon says

    It’s silly to expect that the successful, thriving interstellar life forms will be bipeds adapted to life on a planetary surface, living in large metal shells as autonomous agents crewing a spaceship.

    Seems to me your objection is with Star Trek, not astronomers.

    I was part of the astronomical community in the late ’90s when astrobiology was becoming popular. This was mainly a consequence of realising what might be accomplished with the next generation of space telescopes given that extra-solar planets were being detected. If measuring a spectrum of a planet were possible, what could be looked for that might suggest life of some sort?

    SETI is working at the other (Star Trek) end of the life-on-other-planets probability function. I think the odds are very long against SETI finding anything.

  30. Trebuchet says

    I’m really surprised no one’s mentioned that YEC’s really, Really, REALLY like to expostulate on the uniqueness of Earth.

    I’m inclined to think that there are probably many, many, many forms of intelligent life out there. Intelligent life that looks like us, not so much. But Space is Big. Really big. There’s other intelligent life but it’s spread incredibly thin. So thin that we’ll never detect in the 20-30 years remaining in my lifetime, nor in the 100 years of those just being born.

  31. Marleen says

    As Nick Lane stated, the formation of the first eukaryote by means of symbiosis between an archaea and a α-proteobacterium was an extremely improbable event. Therefore, life as we know it must be quite rare in the universe.

    Eugene Koonin suggested even, by calculating the rate of RNA-synthesis in the hypothetical RNA-world, that the probability of life is extremely low and that we need to postulate multiverses in order to explain the appearance of life on Earth.

  32. says

    Oh come on. everybody knows that all alien life forms are common fall into one of two categories: mammals capable of physically mating and often reproducing hybrids with humans, and vicious killers who see humans as a food source. The second category often doesn’t have the digital dexterity to manipulate machinery to the degree necessary to develop spaceships capable of FTL travel.

    I suppose given an infinite universe, intelligent life capable of, and interested in, space travel is possible, but even if it did exist, the probability of it being close enough to interact with us would be ridiculously small.

  33. Monsanto says

    It seems ironic that Sagan was once married to Lynn Margulis and that at least Dorion Sagan had some sense of proportion. If Sagan was such a polymath, why didn’t some of Margulis’s work rub off?

  34. Monsanto says

    Besides that, everyone knows from countless Star Trek adventures that all life eventually converges to humanoid form.

  35. newenlightenment says

    Here’s an alternative to the Drake equation:

    1)So far as we know, the human race is the only species capable of producing civilisation to have evolved on earth. There are an estimated 3o million species on earth, which represents an estimated 1 percent of all species that have ever lived. So, approximately 1 in 3 billion species is intelligent.

    2)We know that there are approximately 400 billion planets in our galaxy. We then need to estimate what percentage of these are earthlike, assuming that an earthlike planet would also support around 30 million species we can the get a total sum of the number of species inhabiting earthlike worlds, divide this sum by 3 billion and come up with a number for the total number of intelligent species in the galaxy.

    Of course, an intelligent species might not develop a civilisation, there could be some insurmountable biological, environmental or geographic obstacle to development, for instance, imagine if earth’s trees had been a kind of land coral made of limestone, it is likely that humans would never have invented spears or tamed fire, and consequently n matter how smart we were, we would now be at the same technological level as homo erectus

  36. madtom1999 says

    Life (carbon based) couldn’t develop for the first few billion years because if there was any carbon it would probably be in very hostile zones. Once the universe generated enough ingredients for life – by maybe 8 billion years old then it probably started quite frequently – once every billion years in each galaxy. And supernovae wiped it out just as frequently – some of these things are powerful enough to sterilise whole galaxies.
    The Fermi paradox only existed before the big bang became evident – 10 years after Fermi died.
    Once you take the big bang and the impossibility of FTL travel then the Fermi paradox evaporates any credibility.

  37. dianne says

    @25: There’s at least one other possibility: The aliens have gotten at least close to Earth, know perfectly well that we’re here, and don’t want to make contact for some reason. Maybe something benign like the “prime directive” or maybe because we’re too disgusting to deal with or maybe because they don’t want to ruin the science experiment that we really are. Again, we simply don’t have enough information.

    Personally, I’d be thrilled to find some non-Earth origin bacteria on Titan or Europa or somewhere. Of course, having the Vulcans show up would be even better, but just finding new microscopic life would be incredibly significant.

  38. says

    Aloha PZ…

    I work for one of the world class astronomical observatories in Hawaii (and also on the NASA Mars Habitat site). While I am not an astronomer (I’m a computer scientist) – I’ve absorbed enough astronomy and cosmology to feel that I can comment on this.

    While I can’t speak to the differences between Biology and Astronomy (at least not in an appreciable way), I think the astronomical view presented is more of what people used to think, and not so much what they think today.

    You might look to Phil Plait on this subject, as he has penned a number of pieces on intelligence elsewhere.

    My simple thoughts are this…

    First, yes – strictly statistically speaking, the odds for advanced life (similar to ours) elsewhere in the universe is almost certain.

    The answer to “why have we not discovered them” is more complex:

    * Our own expanding electromagnetic bubble has only had time to extend in light years from earth, the amount of time of the source (eg. beginning of radio/tv transmission). So, is there intelligent life within 100 to 200 light years of earth? Perhaps, but that is a pretty tiny part of the universe – AND, any answer from them would take just as long to get back to us (though we hope to pick up their transmissions as well).

    * Our own electromagnetic bubble is quickly closing as we turn to non-radio-wave-based, and encrypted forms of communications. Do other civilizations also have a short time frame before technology turned to other forms of communication (light, quantum, etc)?

    * Do other civilizations WANT to be found? Perhaps they are more intelligent (or paranoid) than we are and realize that shouting loudly attracts unwanted attention.

    * However, the biggest one… the universe is an incredible cruel and hostile place. It is very easy for a civilization to be destroyed – either from its own troubles, or from events outside of their control (such as a massive collisions, or gamma ray burst, etc).

    So the answer may not be “are there intelligent civilizations elsewhere” – but moreover, “how many intelligent civilizations survive long enough to find other intelligent civilizations”.

  39. Ryan Ellingson says

    This seems like a lazy generalization of what astronomers think about this topic. Here’s a response from friend and UCLA astronomer James Larkin, posted as a comment to the other publication of this post on ScienceBlogs (http://scienceblogs.com/pharyngula/2014/06/28/the-difference-between-astronomers-and-biologists/#comment-841706):

    “I am an astronomer working on instruments to directly image planets around nearby young stars and have a variety of colleagues working in a variety of astrobiology topics all the way up to SETI. This is a horrible characterization of astronomers and focuses on only the most optimistic views of some astronomers from 40 years ago. All astronomers working in these fields are well aware of the possible rarity of life, especially advanced life. In fact there have been conferences trying to come up with answers to the Fermi paradox since the 1960′s and a recurring theme is that life may be quite rare. Yes, the popular media loves picking up the optimistic view of aliens everywhere, and there are astronomers like Sagan and Drake who were once very optimistic. But even Frank Drake has commented recently that all the failed SETI searches imply that there at least are not lots of civilizations out there communicating with radio waves. Astronomers are discovering many planets that are getting closer and closer to Earth-like conditions suggesting that Earth is not particularly special in terms of temperature and size. But we all realize that it may be quite a rare event for life to sustain itself for billions of years on a planet and evolve into intelligence. I see no reason to focus on the optimistic (and often old) popular views and slam a field that is very sober to the realities of a relatively sterile universe.”

  40. says

    The thing about the ‘It’s a big universe out there’ argument is that it cuts both ways. We could be sharing our galaxy with thousands of planets occupied by tool users of roughly comparable technology to ours, and neither we nor they would have any way of knowing it. Most of the galaxy is thousands or tens of thousands of light-years from us, which means that for us to see anyone else out there, they’d need to have been putting out large amounts of powerful signals for several millenia (by contrast, we’ve been putting out signals that are distinguishable from cosmic background noise at significant distance for about 50 years now, and even allowing for all of our radio traffic ever, our signal covers this much of the galaxy. That’s not even considering all the other galaxies out there.
    pikaia

    If orangs, they would not have a society that you need to do technology on an industrial scale

    This is another point to consider. The hell with orangutans, 99% of human history was spent in small tribal bands with stone tools who weren’t generating any particular signal. It’s quite possible that that’s the baseline state for tool users unless something happens to force a change.
    alkisvonidas

    At which point, we’re faced with the task of providing them with an artificial ecosystem, or the means to build one. I don’t see how this is any less of a daunting task than sending organic life forms into space along with a natural ecosystem.

    Because the mechanical nature of the constructs allows you to use radically different values for ‘ecosystem’. You don’t need to worry about ensuring that they have free oxygen, liquid water, atmospheric pressure, an ambient temperature above freezing, and things of that nature. Interstellar Von Neumann machines could be made to cannibalize asteroids for raw materials, and ‘feed’ off sunlight and magnetic fields (maybe hydrogen from comets or gas giants, if anyone ever gets the bugs ironed out of fusion).
    Jason Dick #25
    or, as noted above 4. It’s a really, really long way between places that actually have tool users on them, so even if interstellar travel is feasible, the odds of anyone being home when you get there are basically nil.

  41. ragarth says

    There’s a lot of ragging on Star Trek’s casting every intelligent species as biped. While its true this was originally the product of budget limits and the nature of the entertainment industry (I see movies and tv series as high budget plays: We use culturally understood indicators to define traits of characters and these indicators are collected to build a story.), ST:TNG explored this phenomena and worked it into the actual star trek mythos.

    The thing is, the fact that all encountered space faring species in star trek are biped is artificially created. The first ‘intelligent’ species to develop in the galaxy never encountered any other intelligent life. Instead they seeded the galaxy to produce life like their own:

    http://en.memory-alpha.org/wiki/Ancient_humanoid

    This was a star trek: the next generation story arc that spanned several episodes.

  42. says

    Assuming there are alien life out there at roughly the same technological level as us, how far away could they detect our radio signals?
    Considering the challenge of just listening for signals, imagine the challenge of transmitting strong signals to any noticeable portion of the sky. That’s going to take a lot of commitment from a pretty advanced civilization…

  43. Nathan Taylor says

    Just had to comment. Awesome to see PZ Myers citing my praxtime post. Carry on.

  44. pikaia says

    @45 I understand that our unbeamed signals are only detectable to a fraction of a light-year. As for beamed transmissions, there aren’t any! We put virtually all of our effort into detection, not transmission, so there is virtually no chance of aliens finding us. If they have the same attitude then we can never detect them either, so the galaxy might actually be teeming with techno civilisations that we will never know about.

  45. aziraphale says

    @47 I believe some of our Cold War era radars would have been detectable with our own receivers at 60 light years distance. If we ever take the threat of asteroid impact seriously we might start using even more powerful radars. No message (unless we chose to modulate them!) but it would certainly indicate that there was technology here.

  46. says

    @47: Thanks, that’s what I suspected. The actual distance will of course depend on both signal strength and receiver sensitivity, but that puts things in perspective. Even with vastly superior receivers we’re still talking about the “local neighborhood”.
    As for beamed signals, there are always limits. Afaik you cannot get 0 divergence, and empty space still contains matter that could affect the signal. Nevertheless, unless one assumes a technological level waaaaay beyond ours any detectable signal would be a beamed one. And beaming signals to all corners of the galaxy would be an undertaking of astronomical proportions.

  47. P. Zimmerle says

    I think it’s rather hilarious to assert that it will be biological people (or even biological humans) that expand beyond the solar system. Most likely we’ll cut biology out of the mix entirely before we get anywhere near an interstellar starship.

  48. observer15 says

    One can make arguments until the sun burns out but the only way to know anything is to look. It is not a waste of time to look at things that have not been looked at before.

  49. lochaber says

    Granted, I think there are quite a few flaws and problems with it, but I kinda like some of the ideas brought up in the Olduvai theory: http://en.wikipedia.org/wiki/Olduvai_theory

    One adaptation/variation/explanation I had run into made the claim that any planet has pretty much a 1-shot attempt to go from an industrial civilization to a sustainable/space faring civilization. Bio fuels need to be exploited to build the technology capable of extracting and using fossil fuels. Fossil fuels need to be exploited to build the tech for extracting/using nuclear fuels and sustainable energy sources. If at any point in that chain after bio fuels, the civilization fails to make a transition to the next step, they will exhaust the resources of their current step, and then collapse back into a pre-industrial civilization. And I don’t think that’s even getting into issues like climate change, environmental degradation, wars, disease, etc.

    I have no idea what some alien culture/society would be like, but I don’t think it’s unreasonable to suspect that some of those that build industrial societies will also encounter similar problems we are, and face a societal collapse before they manage to obtain an off-planet foothold.

  50. Nick Gotts says

    I recorded a BBC programme on the “Drake equation” recently, but gave up halfway through because it was such bilge. First, it greatly over-estimated the cotnribution Drake made to scientific discussion of the possible existence of extra-terrestrial civilizations capable of communicating with us: it was a marginally useful way of breaking down the question into sub-questions, but relied on unstated assumptions (life only develops on earthlike planets, does not travel between star systems) and a lot of pure guesswork. More annoyingly, it had that tedious self-publicist Paul Davies yakking on about the supposed discovery of a possible independently involved life-form (bacteria that supposedly used arsenic in place of the phosphorus in nucleic acids). I gave up when the presenter went to talk about the “discoverer” of these bacteria.

    It’s not true to say we have no evidence about the existence of extra-terrestrial civilizations.
    1) We have the negative evidence that led to Fermi formulating his paradox: no sign of them anywhere. Of course it’s possible we wouldn’t recognise their signs, but if there are any such civilizations, they are likely to be millions of years older than ours, which is plenty of time to be far more technologically advanced, and to make their presence obvious. I’ll come back to this.
    2) We have the timeline of terrestrial life. This seems to have got started fairly early in Earth’s history, which suggests (but does not prove) that on a planet like ours, it’s likely to appear – although we don’t know what “a planet like ours” means in this context. However, it then took some 3 billion years for motile macroscopic organisms (animals in this case) to evolve. That suggests this is not at all easy, let alone inevitable. Of course there could be other paths to intelligence, but we have no evidence to support that speculation. It’s at least highly plausible that the development of eukaryotic cells was both an essential step, and a very improbable one, involving symbiosis, maybe with more than two partners. But unicellular eukaryotes are thought to have appeared at least a billion years before animals, so it looks as though there was at least one other improbable step. Once there were motile macrobes (Is this a word? If not, it should be!), I’m inclined to disagree with PZ and think the evolution of high behavioural complexity and flexibility was very likely, as long as no extra-terrestrial catastrophe intervened, (a) because we have examples in at least two phyla (maybe three if we count social insects), and two classes within one of those phyla, (b) because there do seem to be successively brainier holders of the “brainiest animal” title* over time and (c) because we don’t need to assume any general selective force in the direction of greater behavioural complexity: a branching random walk with one absorbing or reflecting barrier will do to produce successive record-holders at the other end of the distribution over time.

    However, the random walk, if that’s what it was, took a long time to produce a species capable of cumulative and accelerating technological change.** And presumably, a rather larger asteroid or comet than did for a lot of species at the Cretaceous-Tertiary boundary, or a nearby supernova, could have halted the process.

    Put these two sources of evidence together, and I think it’s a reasonable hypothesis that technolgical civilizations either very rarely arise, or don’t last long when they do – or, of course, both.

    Going back to (1), I’m strongly inclined to think that it should not be that hard for a civilization a few centuries in advance of our own to colonise the galaxy over a period of not more than tens of millions of years – and if civilizations arise frequently and don’t reliably destroy themselves, there should be lots of them hundreds of millions or billions of years old. I give no credence whatever to “Alcubierre drives” and other FTL travel fantasies. Apart from the requirements for supplies of unobtanium in the Alcubierre drive case, FTL travel would allow backwards travel in time, which raises the Fermi paradox to the nth degree: where are all the time travellers from the future? Even travel at a respectable portion of the speed of light is perilous, because at (say) 1% of light speed, hydrogen atoms become hard radiation, and encountering a grain of dust would result in a spectacular explosion. Nevertheless, sending out lots of small, relatively cheap von Neumann (i.e. self-replicating) probes, allowing for a high failure rate, probably pushed by lasers or particle beams, and using stellar or planetary gravitation for braking, should be feasible within mere centuries. Once you have something capable of tapping local supplies of energy and materials in another star system, turning as much as desired of that system into material for further expansion would be the work of a moment, on a cosmic timescale.

    One more point: I’m surprised by how often the human lifespan is raised as an insuperable objection to schemes for galactic colonisation: surely, it is said, no-one would begin a project that would take thousands of years to complete. I’m not suggesting actual travel by people (broadly defined), but this is still raised with regard to von Neumann probes. But does anyone really think that, if our civilization (unlikely as this currently seems), survives another few centuries and continues to advance technologically, that our successors won’t refashion themselves, biologically andor via cyborgization, to live far longer than we do?

    Finally, I recommend David Brin’s Existeance, which takes the Fermi paradox as its starting point, even though I think its main idea – that interstellar probes are already here – is extremely unlikely.

    *I’m aware no single measure will give an unambiguous ranking.

    **Although Dobzhansky was surely wrong about ours being the only species with nongenetic cultural inheritance, partly because we now know a lot more about non-human cultures than was known when he wrote.

  51. Nick Gotts says

    First paragraph of #53, last line: “talk about” should be “talk to”.

  52. Holms says

    And here’s a nice, short table to summarize the differences…

    Oh hey, I skipped over this the first time I read this, but wow, this table bugs me. Hell, even before getting to this bit the entire post was patronising, but this takes the cake. PZ, do you honestly believe this to be a reasonable, non-smarmy summary of astronomical thought?

    “Earth life is unique.”
    This statement can be read in at least two ways.
    1: Earth life is unique in the sense that none of the species here will be repeated on another planet with another evolutionary history. It’s possble that organisms occupying a similar ecological niche might have some similarities through convergent evolution, but they will still be different in other ways.
    2: Earth is unique in that it harbours life at all.
    In my reading of the respective summaries from biologists and astronomers, the biologist is answering reading #1, while the astronomer is answering #2.

    Thus, I think these comparisons are unequal, but this disagreement has nothing on the astronomy caricature in response to the second proposition.

    “Can’t be. If this is true, then the aliens should already be here.”
    Loads of reasons why this is not a necessary conclusion, several of which are astronomical / physics in nature: space is big, FTL is probably impossible, sublight travel is inadequate etc etc.
    “And since they aren’t this implies Earth is unique.”
    No, that’s a stupid conclusion given the variety of reasons why an alien visit is unlikely; and given that plenty of those reasons are well known to astronomers, the author of this image is basically calling astronomers idiots.
    “Copernican violation. Error. Error…”
    And from here on it gets nakedly insulting.

    Given the very basic nature of the logical errors masquerading as a summary of astronomical thought, it follows that A) you (and the author) think the state of astronomical thought has not changed since Sagan (which is similar to saying evolutionary biology has remains in lockstep with what [famour biologist] said 40 years ago), or B) your appraisal of astronomy is overly simplistic.

    I can only imagine the scorn you’d give to an equivalent summary of biology / evolution from an astronomer / physicist. Except, I don’t have to imagine that at all, because that is a frequent refrain.

  53. Sunday Afternoon says

    Thanks ragarth @44: I remember that story from watching TNG from way back and had been meaning to look into it again. Until your reminder, I couldn’t remember if it was TNG or DS9.

    My comment wasn’t to knock Star Trek, merely to point out (as others did too) that there are more credible things going on in astrobiology than PZ alluded to in the OP.

  54. Holms says

    @47 I believe some of our Cold War era radars would have been detectable with our own receivers at 60 light years distance. …

    I strongly doubt this. Are you aware of just how vast this distance is? 60 ly is 567,643,828,354,848km, or 44,549,036,913,738 earth diameters. YOu might be thinking of an idealised scenario, where this distance is a perfect vacuum with no competing electromagnetism? Even so, that seems unlikely.

  55. brett says

    Space isn’t a friendly environment for machines, either, and especially not for machines with delicate on-board instruments and the need for a lot of computing power. That’s why the actual computing capabilities on Mars Curiosity are very limited compared to what we have on Earth – they have to be durable enough to last for years against physical damage and the non-stop cosmic ray radiation damage that any computer will take unless it’s under a lot of shielding (or like on Earth, beneath a thick atmosphere).

    That’s why the whole “self-replicating Von Neuman probes” idea feels so incredibly glib to me. There are so many unknowns involved with interstellar travel, not least of which is whether we can actually engineer intelligent machines that can survive the transit along with enough resource harvesters and fabrication equipment to build the factories they’ll need to build additional self-replicating probes.

    @PZ Myers

    I have to add that it is probably another of those universal laws that Darwinian replicators will expand to fill an empty ecosystem, but that there are many ways to do that.

    It gets rather complicated when we look at creatures as intelligent and capable as humans, too. At least from what we can see of Rich Country humans, maximum reproductive success doesn’t seem to be at the forefront of our desires, since we no longer directly need lots of children to take care of us in old age, run our farms with us, and simply survive the high early childhood mortality rates. In fact, we’re pretty much in some unknown territory here since we now have reliable contraception and abortifaecents, and can thus have child-bearing to whatever degree we individually desire within the limitations of our bodies aging.

    Machines make that even more complicated, since they’re effectively immortal as long as you replace the parts over time, and what they desire could be wholly different from what humans do. A machine intelligence might find the idea of actually colonizing other solar systems to be bizarre – why would you do that when you could just send explorers and have the exploring probe send back a digital copy of itself by tight-beam radio broadcast to “sync” with the copy back home when they’re done with the mission?

  56. brett says

    @Holms

    I strongly doubt this. Are you aware of just how vast this distance is? 60 ly is 567,643,828,354,848km, or 44,549,036,913,738 earth diameters. YOu might be thinking of an idealised scenario, where this distance is a perfect vacuum with no competing electromagnetism? Even so, that seems unlikely.

    You’d need very large radio telescopes (as in multi-kilometer diameter) just to pick up our television and civilian radio signals inside of a single light-year, never mind around another star. The only stuff that would be detectable over interstellar distances would be military radar and high-powered radio telescopes like Arecibo, which use very tightly-focused broadcasts – meaning that it’s incredibly unlikely that you’d accidentally pick up on such a signal around another stuff unless they were deliberately trying to “ping” you with it.

  57. Nick Gotts says

    sublight travel is inadequate – Holms@55

    But that has to be argued, not just asserted. It has to be not just very difficult, but so inadequate that none of the supposed swarms of extra-terrestrial civilizations has done it. Also, none of them can have set up a signalling system we would yet have detected. Given the technological advances we might expect over the next few millennia if we manage to avoid destroying our civilization, how plausible is this, if technologically advanced civilizations are in fact common and don’t reliably destroy themselves?

  58. Nick Gotts says

    Machines make that even more complicated, since they’re effectively immortal as long as you replace the parts over time, and what they desire could be wholly different from what humans do. A machine intelligence might find the idea of actually colonizing other solar systems to be bizarre – why would you do that when you could just send explorers and have the exploring probe send back a digital copy of itself by tight-beam radio broadcast to “sync” with the copy back home when they’re done with the mission? – brett@58

    But that would be colonizing other solar systems!

  59. Jason Dick says

    Well, it’s not at all surprising that we wouldn’t have detected extra-terrestrial civilizations through observing their communications. The issue is that any sufficiently-advanced communications technology is likely to conserve energy, and broadcasting a signal in all directions is a really poor way of conserving energy.

  60. Amphiox says

    Even if a planet did produce an intelligent species it doesn’t follow that they would be able to go into space. If dolphins had developed human intelligence they would not produce technology because it is rather hard to smelt metal underwater. If elephants, then they would not be able to do much with only a trunk instead of a pair of hands. If orangs, they would not have a society that you need to do technology on an industrial scale. So space-faring life is likely to be much rarer then intelligent life, and even that took Earth 4.5 billion years here.

    If dolphins (or any other aquatic species) had human level intelligence, and they were able to domesticate an amphibious species, they would eventually possess the means to get into the air, and they would be able to figure out smelting metal from their. The discovery of fire would simply be a late rather than early development in their technological trajectory. They could also likely do it if they learned to farm something that formed floating mats on the water surface, like kelp. (Cephalopods might have a better shot than dolphins in the long run, though…)

    If oranges had human level intelligence, there is no saying that somewhere in their history they would not be able to change their social structure, just as humans have many times over in our history.

    Do not underestimate the dexterity of an elephant’s trunk! (And their enormous strength would compensate for a lot of things.) Though I shudder to think about how costly an elephantided space program would be for them in terms of the energy demands for getting into orbit!

  61. doublereed says

    Okay so you need a hospitable planet to support basic lifeforms and cellular life. Then you need them to evolve in more complex forms of multicellular life. Then animals (or animal-like things). Then socialization. Then intelligent life?

    Isn’t this still arguing over statistical likelihoods then? Humans aren’t exactly good at handling things at such large and small magnitudes of probability. I think you actually need to crunch out the numbers.

  62. consciousness razor says

    Nick Gotts:

    Apart from the requirements for supplies of unobtanium in the Alcubierre drive case, FTL travel would allow backwards travel in time, which raises the Fermi paradox to the nth degree: where are all the time travellers from the future?

    Heh. These are bad times. They all wanted to go to some other time, instead of this one. You might think that they’d want to go to a time when the entropy was much lower, to make the most of the available resources (and take the “best” jobs, away from the cavemen/bacteria/whatever), but that means we should expect all of the most advanced civilizations to end up at the earliest possible times, not now, and to have already exhausted the resources they would need in the distant future in order to begin this process. Of course, this was all after they killed their grandfathers (and Hitler).

    Nevertheless, sending out lots of small, relatively cheap von Neumann (i.e. self-replicating) probes, allowing for a high failure rate, probably pushed by lasers or particle beams, and using stellar or planetary gravitation for braking, should be feasible within mere centuries. Once you have something capable of tapping local supplies of energy and materials in another star system, turning as much as desired of that system into material for further expansion would be the work of a moment, on a cosmic timescale.

    I’ve never really understood the appeal of von Neumann replicators. What exactly would be useful or interesting about them? Maybe they’re not supposed to be. If I built one, what would I (or somebody else) get out of it? I’m sure they would have a grand time exploring the universe and filling it up with their robot goodness, but why would anyone expect me (or people like me) to do something like that?

    But does anyone really think that, if our civilization (unlikely as this currently seems), survives another few centuries and continues to advance technologically, that our successors won’t refashion themselves, biologically andor via cyborgization, to live far longer than we do?

    I strongly doubt the “far longer” part, but probably at least somewhat longer. Long enough to (individually) survive trips that take tens or hundreds of thousands of years — in other words, longer than all of recorded history? That’s a pretty huge leap to make. We’re going to hit some kind of a limit, no matter how fancy our “cyborgization” might get. But I still wouldn’t say that’s a good argument against it, because people already take on lots of projects that they have every reason to believe will last longer than their own lifetimes. They (generally) care about the next generation and the next, and so on. I don’t see what difference it would make, if “we” are capable of surviving indefinitely in such a trip, over however many generations.

  63. Amphiox says

    Even at sunlight speeds, even at non-relativistic sunlight speeds, even giving 5000 years between colonization events, an intelligent species could colonize a galaxy in a few hundred million years with exponential growth.

    BUT, doing so means creating spacecraft with self-sustaining artificial habitats that endure of hundreds of thousands of years. Once you can do that, you don’t need no stinking planets anymore (indeed you would consider colonizing the surface of a planet to be an inefficient waste of resources). If you spread out in that fashion, living in autonomous habitats scattered about the galaxy, with distances between habitats ranging from hundreds of millions of kilometres to light years, I don’t think your activities would be detectable from earth at all, if you were in the Milky Way. (If you lived in another galaxy, and your population density and general activity were large enough, we just might notice something funny about the light coming to us from your galaxy (your waste heat still has to go somewhere!) but whether we would recognize that activity as the product of intelligence, or simply be puzzled by what appears to be a strange natural phenomenon, it’s hard to say).

    I actually think the above scenario is the most likely pathway for humans to colonize space. We’ll build habitats, first in orbit, starting with things like space hotels, and moving up to full on orbital colonies. We can then stick an engine on those habitats, even a relatively slow and low powered one, and those colonies become spacecraft. They can move through the solar system and harvest resources they need from things like asteroids and comets and KBOs. They can self-replicate by parking by an asteroid or two harvesting some materials, building a second habitat from them, and moving some of their surplus population into the new habitat. (At this point things are starting to look a lot like cells. And maybe that WILL be the form of alien spacefarers – the habitats themselves will become the autonomous organism, and the biologicals within them will evolve into something akin to organelles….)

    Eventually, such habitats will diffuse through the solar system and get into the Oort Cloud, and from there the jump into a nearby star’s Oort Cloud would not be that big a leap. (Sol’s Oort Cloud extends past 1ly, and if the Centauri systems’ is similar in extent then that’s potentially less than 2 ly away, rather than 4). Rinse and repeat.

  64. Amphiox says

    Another thing to remember is that evolutionary contingency will not just be at play on the development of the intelligent species itself, but in the entire biosphere of the alien world. Because the first source of the critical resources necessary to develop technology will come from that biosphere, and ALL of it will be contingent.

    Where would human civilization have gone if earth’s biosphere never evolved lignin and there was no wood? What if there were no domesticable species equivalent to horses? We would never have even gotten to the fossil fuel stage of development without first having animal horsepower….

  65. Amphiox says

    Send out a generation ship on a mission to Alpha Centauri, and you have no guarantee that halfway there and a dozen generations later the people aboard won’t go “fuck Centauri, we’re turning around and going back to (conquer) earth!”.

    Or any number of other scenarios…

  66. lochaber says

    Amphiox>

    I think the limiting factor is an energy source. In Earth orbit, (maybe within most of the solar system?), this could probably be handled by solar panels. But once you get to the outer solar system, or manage to leave the system entirely, you’d have to carry an energy source.

    I imagine there are all sorts of ideas proposed for this, but I imagine most of them are going to require ridiculously large ships to be able to carry enough energy to sustain the trip just to the nearest star. (and hope they can do something once there…)

  67. consciousness razor says

    Isn’t this still arguing over statistical likelihoods then? Humans aren’t exactly good at handling things at such large and small magnitudes of probability. I think you actually need to crunch out the numbers.

    Sure. But which numbers? For one thing, if the universe is infinite, getting some kind of a meaningful and informative probability out of that, for any event whatsoever, is not exactly a trivial task. And even if it’s finite, it’s very, very, very, very large; and we’re going to be limited to talking about a region much smaller than the observable universe, if we don’t assume violations of relativity. So no matter what, you just can’t say anything so grandiose about probabilities for life in the whole universe or even the observable part of the universe. We should at most talk about our own galaxy and nearby galaxies, but even then, does anyone seriously believe there’d be a reason to travel/communicate between distant galaxies? It’s hard enough getting to the very closest star system, which probably contains nothing interesting. I don’t think people really appreciate just how mindbogglingly big these distances (and times) are.

  68. madscientist says

    I agree with #70. I always marvel at claims that we or any other species can travel the great void between the stars. It doesn’t even make sense from a physical point of view. We’re sustained by the energy from a nearby star; where does heat, food, etc come from on an interstellar voyage? We have no means of generating sustained propulsion essentially indefinitely, so how do we even begin our journey? Some of our earliest space probes are at or approaching the so-called heliopause after over 30 years of traveling (though admittedly for most of the journey they hardly used their tiny motors). Our largest structure in space is the ISS, and it’s hardly large enough to sustain the most meager of crews on an interstellar journey. Even mere 1-way communication is unlikely; we need to create beacons as bright as the stars and hope that after thousands or even millions of years someone can somehow detect the signal.

    Intelligent ETs: no fundamental reason to rule out their existence, but no good reason to state that they must exist.

  69. Nerd of Redhead, Dances OM Trolls says

    An interesting factor to consider is the effect of our large moon on life here on Earth. One of the theories of abiogenesis use clay in tidal pools, where the effects of drying/wetting cause biopolymers to form and replicate (citation behind a paywall). Asimov in his essay “Triumph of the Moon” (found in Tragedy of the Moon), speculated that tides were necessary to help multicellular life to evolve onto land, and speculated that without a moon large enough for sizable tides, life may not be able to break the land barrier.

    If having a planet in the “life zone” with a moon large enough to be considered a “double planet” is necessary for life, it could rare in the universe, or it could take much longer to evolve than here on Earth.

  70. eigenperson says

    “Where is everybody?”

    Well, based on a sample size of one, I figure they’re probably sitting relatively quietly on their home planets, burning through their nonrenewable resources and lamenting that their government isn’t putting enough effort into funding space travel.

  71. says

    I agree that while life could be abundant in the Milky Way, the evidence tends towards intelligent life being rare. However, I disagree with this:

    It’s silly to expect that the successful, thriving interstellar life forms will be bipeds adapted to life on a planetary surface, living in large metal shells as autonomous agents crewing a spaceship. The real thing would be alien, and probably terrifyingly incomprehensible.

    If there are intelligent space-faring aliens out there, then we do, in fact, share a lot in common — namely the Universe and the laws by which it is governed. That is a lot of common ground to start with, and there is a lot to be said for the benefits of community and cooperation between intelligent beings when it comes to getting off the ground and into space.

    Therefore, while there is every chance that appearances may be wildly different, my bet is that if we ever meet another intelligent species in this galaxy, we’ll have a lot more in common than you might think.

  72. says

    My own dystopian paranoid fantasy on this issue is that the alien invasion is already here. It arrived several hundred thousand years ago in the form of microscopic viruses that arrived by comets and meteorites from interstellar space. The viruses infected our ancestors with intelligence. This intelligence has led our species to dominate the Earth and exploit resources to their fullest. In so doing we are in the process of terraforming the Earth to be a more friendly environment for our future masters who will arrive to stake their claim once we have annihilated ourselves or are sufficiently weakened so as to put up little resistance. …. but I could be wrong.

  73. Amphiox says

    I think the limiting factor is an energy source. In Earth orbit, (maybe within most of the solar system?), this could probably be handled by solar panels. But once you get to the outer solar system, or manage to leave the system entirely, you’d have to carry an energy source.

    The energy source could be fusion. Hydrogen is abundant in icy bodies beyond the snow line in the solar system, in the form of water and other volatile compounds. (Directly mining hydrogen from the atmospheres of gas giants is also possible, though the technology required boggles the mind to even contemplate. However there doesn’t seem to be anything in the laws of physics to say that it is impossible.)

    So it may depend on whether or not economically feasible fusion is possible and can be engineered on a scale small enough to fit into a spacecraft. As the old joke goes, fusion tech here on earth has been “30 years away” for the last 30 years…

  74. Amphiox says

    I imagine there are all sorts of ideas proposed for this, but I imagine most of them are going to require ridiculously large ships to be able to carry enough energy to sustain the trip just to the nearest star. (and hope they can do something once there…)

    The ships will indeed need to be ridiculously large. If we’re talking generation ships/self-sufficient habitats, they have to be big enough to house a genetically viable population with enough space to make quality of life reasonable.

    I imagine genetic screening and engineering can reduce the number needed for a genetically viable population, and directed mutagenesis could in theory be used to ensure the population remains healthily genetically diverse, but humans still need elbow room for psychological reasons….

    Of course, to our ancestors who pioneered the dugout canoe, an aircraft carrier is rather ridiculously large.

  75. brett says

    @Nick Gotts

    But that would be colonizing other solar systems!

    Think about it, though. If you knew you could just cycle through the solar system every few million years, why even bother having a machine mind sit out there doing mostly by itself, separated by light-years of lag-time in communications from other people? Once it gets there, does a couple hundred (or thousand) years of exploration, it could then send a copy of itself along with the data back to a “home” solar system to sync with the version back home.

    It would especially make sense if you didn’t try and build a probe-manufacturing station in every solar system you went through. You could target solar systems with large amounts of accessible space resources and energy, then launch one-way-missions to a bunch of nearby stars from them once the infrastructure is built. They’d explore the system for a while, send back their digital copy and data, then shut down. Rinse, cycle, repeat every few million years or so, more if the system has something that might actually change into something more interesting in the next few hundred thousand years.

    And we’d never know, especially if the destination probe sent to our solar system, say, 35 million years ago was relatively small and eventually got “grabbed” by either the Sun or one of the gas giants to burn up after shutting down.

  76. Amphiox says

    If there are intelligent space-faring aliens out there, then we do, in fact, share a lot in common — namely the Universe and the laws by which it is governed. That is a lot of common ground to start with, and there is a lot to be said for the benefits of community and cooperation between intelligent beings when it comes to getting off the ground and into space.

    One would imagine they would need a method of communication, in order to cooperate to build spaceships, and govern themselves. They would also need an appendage or something equivalent to manipulate the world around them and build stuff.

    But here on earth, organisms that cooperate, communicate, and build stuff range as widely as slime molds to ants to cetaceans to cephalopods to primates. That’s a rather wide range of diversity right here on a single world that shared a LUCA.

    I would assume bilateral symmetry is likely to be shared, but even that I wouldn’t bet too much on.

  77. says

    @madscientist (#71) when thinking about these things one must surpass the limitations imposed by the technological state that exists in the now and think instead about what science has shown us to be possible in principle. Larry Kraus has explored this concept in his Physics of Star Trek and Beyond The Physics of Star Trek. The conclusion that Larry came to on interstellar travel is that it would cost several years worth of global GDP provided we had mastered the techniques of fusion energy production. Most likely that expenditure of wealth would not be allocated to such a venture except in the most dire of predicaments, such as some global environmental or astronomical catastrophe … escape from the Solar System! In turn, this should lead us to suspect the motivations of possible alien visitors. They most likely will not arrive with return-trip ticket and are here as desperate nomads from a dead home-planet.

  78. brett says

    I don’t quite understand the appeal of a colonizing expedition, unless you absolutely had to get away from some calamity back home (either political or physical) and had no way to do that other than leaving your home solar system. Even the most “Earth-like” alien world is going to be vastly different than Earth and whatever you can build in a space habitat, and going across interstellar distances permanently means you’re stuck with long light-speed communication lag times with the people back home.

    At least, that’s why we usually see proposals to send robots instead.

    @Amphiox

    Even at sunlight speeds, even at non-relativistic sunlight speeds, even giving 5000 years between colonization events, an intelligent species could colonize a galaxy in a few hundred million years with exponential growth.

    You don’t really need interstellar travel to be impossible to resolve Fermi’s Paradox on that level. It would be enough for it to simply be so incredibly difficult that only, say, 1 in 100 alien civilizations ever achieves it. If there are only 50 alien civilizations in the entire Milky Way Galaxy, then maybe none of them would – the nearest interstellar civilization might be over in Andromeda Galaxy.

    But here on earth, organisms that cooperate, communicate, and build stuff range as widely as slime molds to ants to cetaceans to cephalopods to primates. That’s a rather wide range of diversity right here on a single world that shared a LUCA.

    You’d probably need

    1. Intelligence
    2. Tool-using capabilities
    3. Recursively better tool-creating-better-tools tool creation
    4. Social organization
    5. Transmission of complex cultural information and technology between generations
    6. Social capabilities for large-scale social organization (like kingdoms, cities, nation-states) far beyond whatever social groups they evolved in, unless they’re hive creatures.

    That’s a lot of targets to line up in evolutionary terms. I can think of lots of creatures that get some of those – chimps have limited tool-using, intelligence, cultural transmission, social groups, for example, but they’re still stuck as small groups of creatures eeking out a living in the African rain forests.

  79. consciousness razor says

    madscientist:

    Intelligent ETs: no fundamental reason to rule out their existence, but no good reason to state that they must exist.

    I would say that there’s no good reason to state that they must be observable. If they do exist, but they’re not very close to us (in our own galaxy or even a small part of it), the Fermi “paradox” isn’t very paradoxical. Life could be super-extremely rare or just extremely-rare, in the big scheme of things, and we would not notice the difference. The thing is, I’ll give it to you for free, that the universe is infinite and that according to some kind of probabilistic argument, they “must” exist. That still does not give you anything in terms of an actual observation that you ought to expect (or that the lack of it should be “paradoxical” or unlikely).

    Allen Everhart:

    @madscientist (#71) when thinking about these things one must surpass the limitations imposed by the technological state that exists in the now and think instead about what science has shown us to be possible in principle.

    That argument, and my argument, isn’t about our current limitations. There are lots of things that you just can’t do.

    They most likely will not arrive with return-trip ticket and are here as desperate nomads from a dead home-planet.

    Fine. Just build a really big, really slow spaceship for your alien nomads/refugees. What they don’t need to do, simply to survive their planet’s destruction, is travel through intergalactic space using whatever magical technology you want to dream up, so we have no reason to believe aliens from such a distance are likely to be observed. They have plenty of planets/moons/locations where they could go, which are much closer and don’t require the equivalent of “magic did it” or “it’s extremely unlikely and unreasonable but possible” to make it happen. This is just parsimony. Galaxies are also generally moving away from each other, so in the future this situation will only get worse (for them or us). They are stuck more or less where they started (somewhere in their own galaxy), not showing up at our doorstep or “communicating” with us over vast timescales. They can’t do anything about that. Period. Then comes heat death. The end.

  80. says

    Do not assume that alien visitors will arrive in a “mother” ship. Large vessels powered by huge energy sources are not the way of interstellar travel. Rather, I expect that an alien species would send something like a seed. They would compress all the experience and knowledge that their emissary would need to know into a few DNA-like molecules with just enough environment for it to reconstitute on arrival at its destination. Think pea-size. They could already be here in our solar system and we are just too insensitive to notice.

  81. consciousness razor says

    Why bother? Seriously.

    I can imagine wanting to continue existing (because the sun’s going to explode or whatever). And I can imagine, even without such a disaster forcing it on me, that it might be fun to explore the galaxy, Star Trek style. So I’d build a ship that I can “travel” in. That’s what “travel” means to me. That’s what “survival” means to me.

    I just don’t get why I would ejaculate into a tiny spaceship and send it off on its way. I get nothing out of that. I don’t have a reason to care. If the sun’s going to blow, that is not the first thing, nor is it even within the first million things, that I would consider doing with myself. Maybe it’s just me or my personality, but in any case, I don’t think you can justify the claim that this is just “the way of things,” or that it’s what’s likely to happen, or that it’s the behavior I would expect to see from some generic intelligent being.

  82. says

    @pikia (#47) There have been several “beamed” transmissions from Earth. There were several high-power radar probes of the moon and the planet Venus in the 60’s and 70’s. These ought to be detectable by a radio telescope in a remote planetary system in the right direction. Also there is the Aerocibo message that was intentionally beamed into space: http://en.wikipedia.org/wiki/Arecibo_message

  83. says

    I for one am a biologist who agrees with the astronomers, to a point. When I look at the diversity of life on this planet, I see a lot of convergence happening, and I see several lineages increasing their cognitive capabilities in parallel. In those cases where something has only happened once (as far as we know–it might be that other attempts haven’t fossilised well), such as the evolution of eukaryotes, it seems more plausible to me to assume that the first to achieve the trick competetively excludes all late-comers while they are still only half there rather than that it is something highly unlikely to happen.

    Because here we run into a major intuition issue: Solutions that are unique on Earth just seem unlikely because we are poorly equipped to contemplate the deep time and the many worlds on which the experiment presumably runs in parallel. Indeed the argument that sentience is highly unlikely to arise on other planets has shades of creationist fallacies.

    As for why the aliens aren’t here, that one I consider to be easily answered: If we drop our unwarranted SF-induced optimism, it sure looks a bit as if it might be physically impossible to travel to other star systems and survive. If you go fast, even being hit by a single atom floating in the void will blow up your spaceship. If you go slow (travelling hundreds or thousands of years), all the air inside your ship will have dissipated long before you arrive at your destination. And that is before we mention cosmic radiation and suchlike. We do know enough about physics now to flinch at suggestions that “somebody will somehow come up with a force shield” or some such nonsense.

  84. says

    @c-razor, first of all there is a considerable difference between intergalactic travel and interstellar travel. Like the difference between millions/billions of light years and several-to-100k light years. It is somewhat disingenuous to conflate these two. If we are to contact alien species it would have to be somewhere on our Orion Spur of the Milky Way, at least if we were to hold out the tenuous possibility of two-way communication.

    Secondly, the Sun will balloon up in some 5 billion years as its burns through the sequence of elements in its core. The Earth will be incinerated then. That is a long time and likely the human species will not exist anymore, anyway. However, it is my conceit that whatever intelligent species is around near the end will want to propagate/relocate itself any way it can.If that means jacking-off in a tin-can I suspect it will be done!

  85. says

    The problem with the astronomers’ view is that it creates unrealistic expectations in the public’s mind (e.g. “finding ET is inevitable”). The public often aren’t scientifically educated enough and they expect immediate results. And when those results don’t come quickly (enough), they assume science (one or all fields) to be wrong, and possibly wrong about everything. That’s partly why creationists are anti-evolution, and it can easily happen with OECs and other sciences.

  86. says

    @77:Amphiox
    I would assume bilateral symmetry is likely to be shared, but even that I wouldn’t bet too much on.

    I wasn’t talking about appearance, I was talking about our outlook on the Universe–our wants, our needs, our goals, our desires, etc.

    No matter where an intelligent species evolves, they all have to play by the same rules (i.e. the laws of physics), and all face the same challenges when it comes to becoming a space-faring civilization. We have to have the curiosity to explore, the determination not to give up, the cooperation to work together, and the empathy required not to destroy each other along the way.

    So, no matter what they look like, I expect we will have more than enough in common with other intelligence space-facing species that should we ever encounter them, they might appear strange, but they won’t be incomprehensible.

  87. Menyambal says

    Well, as for life, all we know is it seems to be limited to carbon in water, up to now. Anything else may be impossible, or, to us, so different as to hardly count.

    We also can’t deny that life may only be possible on a planet with a large moon and plate tectonics. We haven’t enough to go on to discuss the possibilities.

    Based on our sample of one, we can say that life takes a honking long time to develop complexity, and complexity takes a long time to develop intelligence, and intelligence takes a long time to develop technology. And all of that is unpurposed and accidental and wildly contigent.

    We are talking about space travel, and that has only been a viable topic for the past hundred years, out of the billions our ancestors have been on this planet. And I will bet you a Reichsmark that we wouldn’t have space vehicles at all if Adolf Hitler hadn’t stumbled into the beginning of the Nazi party, and if Werner von Braun had been less ruggedly handsome.

  88. says

    @85: Allen Everhart

    Aliens won’t be looking for technological beacons. The planets themselves are the beacons. Given the prohibitive cost of interstellar travel, the next step in our exploration of the galaxy is to build ever larger, ever more powerful telescopes–here on Earth, on the Moon, and eventually whole fleets of them in the outer reaches of the Solar System.

    Even a fleet of space-faring telescopes would cost next-to-nothing compared with a single interstellar mission, and we will likely have cataloged millions of planets this way before we ever set foot in another solar system.

    Assuming they are within range, once you can detect planets, you can begin to detect their atmospheres (we already can in some very limited circumstances). If life is rare in the galaxy, then Earth has stuck out like a sore thumb from dozens, possibly hundreds of light years away, for hundreds of millions of years already, given its oxygen-rich atmosphere, and the other life-bearing signatures it gives off.

    And assuming their instruments are sensitive enough, pollutants in the atmosphere, and other rapid changes in the biosphere would be strong clues that an intelligence was at work. Again, such changes on Earth may have been detectable from many light years away for several thousand years already.

    That’s why I believe there is no point in stopping people from beaming signals out into space in case of the remote possibility that it might attract the wrong type of alien. If they’re out there and close enough to detect the signal we broadcast, then they already know we’re here, and have done for a very long time.

  89. says

    Based on our sample of one, we can say that life takes a honking long time to develop complexity, and complexity takes a long time to develop intelligence, and intelligence takes a long time to develop technology. And all of that is unpurposed and accidental and wildly contigent.

    Yep, that’s pretty much my conclusion. The only realistic hope of making contact with another alien species in the near future is that out of the possible handful of planets to become host to intelligent alien life, one of them saw their inhabitants bloom into an advance space-faring civilization that has already spread out through the galaxy. After all, if we are not the only intelligent species in the galaxy, and we’re not the first intelligent species in the galaxy, then it would only take one successful species to be, say, a few tens of thousands of years ahead of us technologically, for them to spread out across the stars and happen across us.

  90. says

    Lifeboat scenarios are weird. There are, what, trillions of pounds of living humans on earth; they will not ever leave the gravity well. Escape is not an option. Sending a tiny few off planet might be, but humand off earth are – something else, and humans that leave billions of their kind behind to die are something even different. The very action of getting into the lifeboat changes you, any humans that escape earth are (at the very least) antisocial and have abandoned their humanity.

  91. says

    The problem with the astronomers’ view is that it creates unrealistic expectations in the public’s mind (e.g. “finding ET is inevitable”). The public often aren’t scientifically educated enough and they expect immediate results.

    Not so sure about that. There’s a good number of under-educated people who believe that we’ve already made contact with the aliens, because they are here, only they are being kept hidden by the government because everyone would freak out if their presence was known, or something.

    You’re kind of right about the instant gratification part, fed by the wealth of science fiction movies and books we consume, but as often as not, that tends to lead people to suspect someone is covering things up since reality can’t be that boring.

  92. consciousness razor says

    @c-razor, first of all there is a considerable difference between intergalactic travel and interstellar travel. Like the difference between millions/billions of light years and several-to-100k light years. It is somewhat disingenuous to conflate these two.

    I’m not conflating the two. You were responding to madscientist, who responded to me, and that was basically the line of argument we were talking about. (At least, that is what I was talking about.) My point is exactly that there’s an enormous difference between those scales, and that people thinking we should expect to see alien life, right here on the smallest scales (cosmologically speaking), because that’s the only scale we could observe such things with any confidence, are failing to appreciate how big of a difference that makes.

    However, it is my conceit that whatever intelligent species is around near the end will want to propagate/relocate itself any way it can.If that means jacking-off in a tin-can I suspect it will be done!

    Very well, but I don’t think that’s what it means. There are lots of other options that could and would be pursued first. You could mine resources from other planets/moons/comets/asteroids in our solar system (plenty of time to work on that). You wouldn’t need to go all that far, simply to avoid the danger posed by the sun (and if “we” were orbiting a quasar or something, we’d already be fucked). You could try to make your way to the next habitable planet eventually; but that’s a lot of work (to put it mildly) that you won’t necessarily need to do. As Marcus Ranum said, it’s a big enough problem just thinking of how we’d get a significant number of people off of this tiny little planet, much less “off” of the whole fucking solar system. There’s also no reason to think that in the meantime you’d also do the extra work of sending out enormously powerful signals in every direction to advertise yourself to the rest of the galaxy. Intelligent beings don’t tend to do things simply to make sure your observational/selection bias works out the way you wish it would — they tend to have reasons of their own.

  93. PaulBC says

    The probability of finding intelligent life on earth at any instant in time is low if you take a uniform sample over the period when earth has had some form of life until the present. So I think I agree with the “biologist” position that intelligent life would be very uncommon if you could select a planet at random in the galaxy, even with the precondition that it has some life.

    However, there may be an unstated assumption that once intelligent life occurs on a planet, it tends to persist, so maybe the relevant question is the probability of finding intelligent life on earth at any instant from the first appearance of life until the planet becomes uninhabitable, (and another unstated assumption is that intelligent life does not lead rapidly to the planet becoming uninhabitable). So in that case, the probability of finding intelligent life on earth at some instant selected uniformly from the first occurrence of life until the destruction of the planet might be better than even odds.

    I don’t really see the speed of light as a serious objection to Fermi’s paradox. If intelligent life was sufficiently motivated to replicate throughout the galaxy, they could send fairly small replicators at high speeds to use available resources. The limit of reproduction would be cubic, not exponential, but a sphere expanding at 90% of the speed of light would have a noticeable influence throughout the galaxy and eventually reach us.

    My guess is that there are many planets with life, but no intelligent life, and no particular reason to predict its eventual occurrence on these planets. Of the ones that develop intelligence, it’s not clear how long this would exist as organic intelligent life. I take it as given that we’re living in a very unusual period of time in the history of life on earth. What happens in the next thousand years will look nothing like what happened in the last 30 thousand years. While intelligence might continue to exist, there might not be the same motivation to marshal all the resources of multiple star systems that we see in science fiction. Properly managed, the resources of this solar system could support orders of magnitude more sentient beings than it now does.

    That alone doesn’t answer why at least one intelligent life form with the technological capability would not have expanded rapidly due to some compulsion rather than actual need for resources and eventually reached us. I could accept a variety of explanations. The simplest might actually be that we’re alone in the galaxy, but not in the universe (That would make me sad, but I don’t see any clear refutation.) It could also be that there are more intelligent life forms opposed to “Fermi” expansion than favor it, and these expanding spheres actually get quashed once they become large enough to notice. Or maybe expanding life forms expand selectively based on the type of solar system they encounter, and ours doesn’t look that appealing to extraterrestrials who originated under quite different conditions. (You might pick some spot on earth in the Sahara desert or Antarctica and ask why the humans haven’t gotten there yet–well, they probably did get there but didn’t stay long because there were more appealing places.)

  94. says

    Both answers cannot be reached with any reasonable result. First of all our scope of knowledge in science is too limited to answer either question with any accurate falsifiable evidence.

    We don’t know if light travel is achievable, the wall we hit is there is a point when no matter how much energy is expended it just seem to increase the mass of the object. We do know that there are things that travel at or faster than the speed of light but these objects are instantly accelerated to their speed.

    Given the age of our world only planets within 4.5 billion light years could have any knowledge that there is a planet here, but it would only be 4 billion light years away that there is a possible life supporting world. We as an intelligent life have only been around 100,000-200,000 years so only those worlds 100,000-200,000 light years away could even establish a life with any intelligence exists here. So it could be possible that only just outside our galaxy is all that knows we are here. And this would be the very beginning of our species. So Given such a small scope how could anyone assert a yes or no on life throughout the universe. So even if there is another life in our galaxy how far would you have to travel would your own species be extinct by the time you arrive? Could you sustain an entire species flying through space for a hundred thousand years? It could simply be that there is no feasible form of attainable travel to interact this way.

    Even if you could establish an atmosphere on another planted through artificial means how long would it take? And what of planets that don’t have water or the essentials for life, how long would that take? It is possible in the mere 13.5 billion years of our universe that there is no feasible way for the second to happen.

  95. Nick Gotts says

    I just don’t get why I would ejaculate into a tiny spaceship and send it off on its way. I get nothing out of that. I don’t have a reason to care. – consciousness razor@84

    Fine, that’s the way you feel. But if you’re using this as an argument defusing the Fermi paradox, it’s completely worthless. You’re assuming everyone in all technological civilization shares this lack of interest, when it’s obvious that many people even in your own don’t!

  96. Nick Gotts says

    I strongly doubt the “far longer” part, but probably at least somewhat longer. Long enough to (individually) survive trips that take tens or hundreds of thousands of years — in other words, longer than all of recorded history? That’s a pretty huge leap to make. We’re going to hit some kind of a limit, no matter how fancy our “cyborgization” might get. – consciousness razor@65

    How do you think you know that? If all parts are replaceable, why is an indefinite lifespan not possible?

  97. Nick Gotts says

    consciousness razor,

    #65

    people already take on lots of projects that they have every reason to believe will last longer than their own lifetimes. They (generally) care about the next generation and the next, and so on.

    #84

    I just don’t get why I would ejaculate into a tiny spaceship and send it off on its way. I get nothing out of that. I don’t have a reason to care.

    Is there perhaps some inconsistency there?

  98. Nick Gotts says

    You’d probably need

    1. Intelligence
    2. Tool-using capabilities
    3. Recursively better tool-creating-better-tools tool creation
    4. Social organization
    5. Transmission of complex cultural information and technology between generations
    6. Social capabilities for large-scale social organization (like kingdoms, cities, nation-states) far beyond whatever social groups they evolved in, unless they’re hive creatures.

    That’s a lot of targets to line up in evolutionary terms.You’d probably need
    brett@81,

    1. Intelligence
    2. Tool-using capabilities
    3. Recursively better tool-creating-better-tools tool creation
    4. Social organization
    5. Transmission of complex cultural information and technology between generations
    6. Social capabilities for large-scale social organization (like kingdoms, cities, nation-states) far beyond whatever social groups they evolved in, unless they’re hive creatures.

    That’s a lot of targets to line up in evolutionary terms.

    But they’re not all separate targets. The ones specific to humans are 3, 5 and 6 (1, 2 and 4 are quite widely distributed, if you don’t define intelligence to include 3, 5 and 6) and they are clearly closely related. Human intelligence develops in individuals, and almost certainly evolved, in the process of manipulating tools and interacting in social groups. I can’t conceive how human-level intelligence could evolve in organisms unable to make and use tools, or extensive social networks. It’s expensive in energetic terms, so to evolve, it has to have a considerable payoff.

  99. Nick Gotts says

    Alex SL@86

    In those cases where something has only happened once (as far as we know–it might be that other attempts haven’t fossilised well), such as the evolution of eukaryotes, it seems more plausible to me to assume that the first to achieve the trick competetively excludes all late-comers while they are still only half there rather than that it is something highly unlikely to happen.

    But why did it take so long – something like 2 gigayears – to produce eukaryotes, and then another gigayear or more to evolve motile macrobes?

    If you go fast, even being hit by a single atom floating in the void will blow up your spaceship. If you go slow (travelling hundreds or thousands of years), all the air inside your ship will have dissipated long before you arrive at your destination. And that is before we mention cosmic radiation and suchlike.

    All that makes the wholly unjustified assumption that what would be travelling is fragile, squishy, planet-evolved organisms, not entities designed for the rigours of interstellar travel, and probably in a state of deep freeze. BTW, I think you exaggerate a bit in “a single atom floating in the void will blow up your spaceship”. at, say, 1% of light speed an atom could certainly do some damage, but not, I think, blow up a spaceship. Do you have a reference that shows otherwise?

  100. Nick Gotts says

    tacitus@91

    the next step in our exploration of the galaxy is to build ever larger, ever more powerful telescopes–here on Earth, on the Moon, and eventually whole fleets of them in the outer reaches of the Solar System.

    David Brin’s SF novel Existence, which I mentioned above, suggests that using the sun as a gravitational lens would greatly increase our observational capacity.

    And assuming their instruments are sensitive enough, pollutants in the atmosphere, and other rapid changes in the biosphere would be strong clues that an intelligence was at work.

    Stanislaw Lem, I think somewhere in Star Diaries, suggests that the successive signs of intelligent life are trash, noise, and spots: “trash” in the form of junk in orbit around their planet, then “noise” as an increasing amount of this trash is made up of obsolete AIs, and finally “spots”, as this noise becomes so annoying to the locals that they coerce said obsolete AIs to plunge into their star.

  101. consciousness razor says

    Nick Gotts:

    You’re assuming everyone in all technological civilization shares this lack of interest, when it’s obvious that many people even in your own don’t!

    Read on, Nick, for some (obvious) elaboration on what I think of this “assumption” of mine:

    Maybe it’s just me or my personality, but in any case, I don’t think you can justify the claim that this is just “the way of things,” or that it’s what’s likely to happen, or that it’s the behavior I would [read: “we should”] expect to see from some generic intelligent being.

    If the argument goes from “look at that, somebody actually has such interests” to “this is a basis for our expected observations of an advanced space-faring civilization,” I think you have lost the plot. It’s “obvious” that many people have foot fetishes too. Should we expect to see signs of that? And if we don’t, should that itself have some kind of groundshaking consequences for our beliefs about the nature of reality? I hear some people are rrrreeealllly interested in it.

    Is there perhaps some inconsistency there?

    I don’t think so. It occurred to me to bring that up earlier, but I didn’t think the similarity was convincing enough to worry about it. Compare/contrast actual living people (including future generations) who are capable of having experiences, with stuff like this:

    #75:
    It arrived several hundred thousand years ago in the form of microscopic viruses that arrived by comets and meteorites from interstellar space. The viruses infected our ancestors with intelligence. This intelligence has led our species to dominate the Earth and exploit resources to their fullest.

    #83:
    They would compress all the experience and knowledge that their emissary would need to know into a few DNA-like molecules with just enough environment for it to reconstitute on arrival at its destination. Think pea-size.

    Let’s leave aside the logic of this, of how DNA, experience and knowledge/intelligence seem to be lumped together as essentially one thing. (What would even mean for a virus to “infect with intelligence”?) Presumably, you could say these are “information” in some really vague sense, and pretend that’s enough to make the magic happen. But who knows how these are supposed to be definite ideas, much less practical possibilities, much less expectations we ought to have (or even might have) based on some sort of data.

    It reminds me of claims about “teleporter”/cloning machines and personal identity, but maybe I’m reading too much into it. To address your first quote above again, in these terms, I don’t think it’s at all “obvious” that when people look for immortality in such fantasies, they care only just enough that a clone of themselves exists. (Yet they also care so very, very much that vast resources will be dedicated to the cause.) That’s not satisfying. At the very least, they want the clone, or whoever the beneficiary is, to be a real experiencing subject, not a virus or a molecule or some bits of “information.” How exactly that’s still supposed to be the end result, in something the size of a pea that’s traveling through outer space to some alien environment, I have no idea. I leave that to you, if you believe it’s a serious proposal.

    One more thing:

    How do you think you know that? If all parts are replaceable, why is an indefinite lifespan not possible?

    I wouldn’t say that it is, in principle. I’ve got zero data here, so how exactly are you making such predictions? In any case, you would have to deal with the practical and political reality too, not just technology. We’re going to have billions of long-lived cyborgs who aren’t reproducing — is that it? Who’s paying for that?

  102. says

    Marcus Ranum #93

    Sending a tiny few off planet might be, but humand off earth are – something else, and humans that leave billions of their kind behind to die are something even different. The very action of getting into the lifeboat changes you, any humans that escape earth are (at the very least) antisocial and have abandoned their humanity.

    Seriously? Because we can’t save everyone, we shouldn’t save anyone? Unless everybody makes it, we shouldn’t even try to save the ones we can? Please tell me I’ve misunderstood you.

  103. Amphiox says

    If you go fast, even being hit by a single atom floating in the void will blow up your spaceship.

    Cosmic rays, which ARE atomic nuclei, already exist that travel close to light speed. When they strike the earth’s atmosphere, they do NOT strike with enough force to blow up a spaceship. The most powerful hit with the force equivalent to that of a thrown baseball. Which is mighty impressive for something that has a rest mass of an atomic nucleus, but not spaceship shattering, unless you make spaceships as fragile as pigeons.

    Note the dearth of cosmic ray detectors spontaneously exploding due to “spaceship shattering” collisions, here on earth and in orbit.

    If you go slow (travelling hundreds or thousands of years), all the air inside your ship will have dissipated long before you arrive at your destination.

    What? No.

  104. Amphiox says

    Escape is not an option. Sending a tiny few off planet might be, but humand off earth are – something else, and humans that leave billions of their kind behind to die are something even different. The very action of getting into the lifeboat changes you, any humans that escape earth are (at the very least) antisocial and have abandoned their humanity.

    The Titanic survivors abandoned their humanity because they left the majority of their fellow passengers behind to die?

  105. Amphiox says

    Based on our sample of one, we can say that life takes a honking long time to develop complexity, and complexity takes a long time to develop intelligence, and intelligence takes a long time to develop technology. And all of that is unpurposed and accidental and wildly contigent.

    Based on our sample size of one, one out of one habitable planets developed a technologically competent intelligent species after 4.5 billion years of existence.

    This is consistent with the accidental and contingent odds of technological intelligence being low.

    But how low is low. It could mean that the odds are SO low that only one planet in the entire galaxy, in the entire history of the galaxy, has ever had such a technologically competent species on it.

    BUT, it could it ALSO mean that the odds are just low enough that, with the diversity of the biosphere of earth, and rates of evolution of new diversity in the biosphere of earth, the likelihood for the production of at least one technological competent species is approaches INEVITABILITY by the time the biosphere gets to 3.5-4.0 billion years of age.

    And thus another habitable planet with a biosphere that has only half of earth’s average diversity and rate of evolution of new diversity would take 8 billion years of existence before the odds of producing at least one technologically competent species asymptotes to 1.0, while a habitable planet with a biosphere that has on average TWICE earth’s diversity and rate of evolution of new diversity would take less than 2 billion years for the odds of producing at least one technologically competent species to approach 100%.

    Because, sure, here on earth out of billions of species and over 4 billion years, just one technologically competent intelligent species ultimately emerged. But would we not expect that many, if not most, alien biospheres would similarly produce billions of species and endure for several billion years?

    With a sample size of one we can’t really make odds arguments, because the arguments go equally forcefully in both directions.

  106. Amphiox says

    I wasn’t talking about appearance, I was talking about our outlook on the Universe–our wants, our needs, our goals, our desires, etc.

    How many of your wants, needs, goals or desires do you share with an ant?

    No matter where an intelligent species evolves, they all have to play by the same rules (i.e. the laws of physics), and all face the same challenges when it comes to becoming a space-faring civilization. We have to have the curiosity to explore, the determination not to give up, the cooperation to work together, and the empathy required not to destroy each other along the way.

    How certain are you that there is just ONE way to be curious to expore, ONE way to be determined not to give up, ONE way to cooperate to work together, ONE way to have empathy required not to destroy each other along the way, allowed by the laws of physics, and that if OTHER such ways exist and aliens employ them, we humans, familiar only with OUR way of doing these things, would recognize those other ways?

  107. Amphiox says

    Secondly, the Sun will balloon up in some 5 billion years as its burns through the sequence of elements in its core. The Earth will be incinerated then. That is a long time and likely the human species will not exist anymore, anyway.

    Within 1 to 1.5 billion years, the natural evolution of the sun will mean an increase in solar brightness that will push the earth into a runaway greenhouse state, like Venus. Whatever life still exists on earth at that time, whatever intelligent species, if any, descendants of humans or otherwise, they will have to be vamoosing off-planet a lot earlier than 5 billion years if they want to survive.

    Though with really advanced geoengineering technology they might be able to avert or compensate for the increased solar irradiation, at least for a time.

  108. Amphiox says

    And we’d never know, especially if the destination probe sent to our solar system, say, 35 million years ago was relatively small and eventually got “grabbed” by either the Sun or one of the gas giants to burn up after shutting down.

    If the destination probes arrived in our solar system 35 million year ago or so, did their thing, completed their mission, then had their energy sources run down or wear out, and fell inert/died, falling into a stable quiescent orbit somewhere in the Outer Solar system, Kuiper Belt, or Oort Cloud, we would not currently know, or be able to know, that they are there.

    We haven’t even finished cataloguing the near-earth asteriods, and have only just begun searching for KBOs. We haven’t even found a SINGLE Oort Cloud object yet (in an Oort Cloud orbit, rather than one of the ones that get nudged into a sun-falling orbit and become a comet we can see).

    The alien probes could easily be smaller and darker than the average asteroid/KBO/comet.

    Hell, if there was such a probe that was out there in the Kuiper Belt, which was still ACTIVE, and communicating with its builders, but using a narrow beam method of transmission that points outwards, away from the inner Solar System, I’m not sure we’d be able to detect it right now, if its energy usage was relatively frugal.

  109. Amphiox says

    If you go fast, even being hit by a single atom floating in the void will blow up your spaceship. If you go slow (travelling hundreds or thousands of years), all the air inside your ship will have dissipated long before you arrive at your destination. And that is before we mention cosmic radiation and suchlike. We do know enough about physics now to flinch at suggestions that “somebody will somehow come up with a force shield” or some such nonsense.

    Take an average icy KBO. Hollow out an interior space. Put an engine on the surface somewhere. The tens of meters, or even kilometers of water and other ices of the KBO will effectively shield the inhabitants from all cosmic radiation and cosmic rays. It will also significantly reduce if not eliminate atmospheric dissipation. You can also use the material to make new atmosphere to replace any you lose along the way. The water ice and other organics (you’ll of course want to be choosing a KBO to start with that has these resources already in place) will also provide a continuous supply of resources that should last your crew from at least several hundred thousand years, and even allow them to have children and increase their population somewhat. The KBO may even have a good supply of iron and other metals if it has a metallic core. Hydrogen dissassociated from water ice and other volatiles provides fuel. Oxygen (if you need oxygen to breath like humans do) similarly comes from the same process.

    The KBO would likely not have the structural strength to endure extreme accelerations, so this is strictly for slow missions, but there is absolutely nothing in the laws of physics or biology that precludes this kind of thing from working.

    (If you are talking about REALLY technologically capable civilizations, they could dispense with the KBO and turn their whole home PLANET into such a generation ship, with a variety of gravitational slingshot manipulations with local asteroids to kick their planet out of stellar orbit and slingshot it on a trajectory to another star system. This in fact would be one way a civilization could escape their sun’s Red Giant phase, and if they have several hundred thousand years of advance warning to do the necessary underground engineering, they could save a large portion of their population this way.)

    All this of course requires fusion technology, and also requires a civilization to be able to endure for timescales on the hundred-thousand-year range, as well as enact and complete plans that go on for that long, as well.

  110. aziraphale says

    I do like large-scale thinking. I think, though, you would need more than asteroids to get the Earth completely away from the solar system. A planet would be better. Larry Niven, in A World Out Of Time, used Uranus for his slingshot manoeuvres.

  111. Nick Gotts says

    consciousness razor@104,

    If the argument goes from “look at that, somebody actually has such interests” to “this is a basis for our expected observations of an advanced space-faring civilization,” I think you have lost the plot.

    No, it’s you who have lost the plot, because your personal lack of interest has to apply to every such civilization if it’s to be an escape from the Fermi paradox. If it’s feasible for a civilization to send out self-replicating probes, then there only has to have been one such civilization that chooses to do so for the galaxy to be full of the things.

    To address your first quote above again, in these terms, I don’t think it’s at all “obvious” that when people look for immortality in such fantasies, they care only just enough that a clone of themselves exists. (Yet they also care so very, very much that vast resources will be dedicated to the cause.) That’s not satisfying. At the very least, they want the clone, or whoever the beneficiary is, to be a real experiencing subject, not a virus or a molecule or some bits of “information.”

    I’m not sure what this stuff about clones has to do with the current issue. People may look for a form of immortality (or at least, long-term continuation) not only for themselves, but for their civilization. It may not interest you, but not everyone is exactly like you in their desires and interests, oddly enough.

    How exactly that’s still supposed to be the end result, in something the size of a pea that’s traveling through outer space to some alien environment, I have no idea. I leave that to you, if you believe it’s a serious proposal.

    Well since you ask: the pea-sized object builds a wireless-receiving station, builds a hardware copy of a machine intelligence, then downloads a copy of the internal state of such an intelligence from the home system into the hardware. Not that I think this is necessarily the most likely way to spread intelligent “life” (using that term to include AIs) between systems, but I can’t see why it should be considered impossible, or even implausible, given a few millennia of technological advance. And if there are lots of technological civilizations and it is technically possible, some of them would probably do it.

    I wouldn’t say that it is, in principle. I’ve got zero data here, so how exactly are you making such predictions?

    Relying on the principles that intelligence and consciousness aren’t magic, and that there appears to be nothing that rules out intelligent, conscious beings all of whose parts are replaceable.

    In any case, you would have to deal with the practical and political reality too, not just technology. We’re going to have billions of long-lived cyborgs who aren’t reproducing — is that it? Who’s paying for that?

    The billions of long-lived cyborgs who aren’t reproducing, one would hope, although it could also be their trillions of short-lived slaves – that I see something as likely to happen, given certain conditions, does not imply that I think it would be without its problems. I would point out that by the standards of a few centuries ago, there are now at least hundreds of millions of long-lived cyborgs who aren’t reproducing (much) around.

  112. doublereed says

    @70

    So no matter what, you just can’t say anything so grandiose about probabilities for life in the whole universe or even the observable part of the universe. We should at most talk about our own galaxy and nearby galaxies, but even then, does anyone seriously believe there’d be a reason to travel/communicate between distant galaxies? It’s hard enough getting to the very closest star system, which probably contains nothing interesting. I don’t think people really appreciate just how mindbogglingly big these distances (and times) are.

    So make a bunch of assumptions and go. And then make a bunch of other ones and go. Again and again. We don’t need precise numbers. It’s better than doing this touchy-feely kind of statistics that reminds me of people arguing whether infinity/infinity is 0, 1, or infinity. The correct answer is facepalm.

    And the whole point of mathematics is that people don’t appreciate the mindbogglingly large numbers involved. That’s why we USE arithmetic for large numbers. So our minds aren’t boggled. Humans can’t conceive of geologic time either, but we can do exponential and logarithmic equations.

  113. says

    Okay, two stray thoughts on this:

    1)
    If an alien species detects life, would it bother to investigate further?

    If life is relatively common, but intelligence is rare, then a star traveling species would run into many life signs that amount to little more than amoebas, Why bother with them? Unless it’s clear that there’s intelligent life, what’s the motivation?

    Moreover, an argument could be made for actively avoiding planets with life. An alien ecosystem is unpredictable and possibly dangerous. You have no way of knowing if your existing medicines are effective against infections from another planet and no matter the precautions, it’s possible that some microbe you’ve never thought of has evolved a unique ability that can defeat your defenses.

    So, unless there’s a very specific reason for going down to the planet, it makes more sense to stick to the ones that are predictably dead. If they’re just cruising around for more resources, they’d probably just leave us alone. They’ll only come if they clearly see that there’s another intelligent species here. That leads us to the next point.

    2)
    What will an alien species consider a sign of intelligence and what’s the window of discovery?

    If an alien probe came by a million years ago, it would have noticed nothing especially interesting. If it came by a thousand years ago, it might have looked at houses and fields and considered them no more interesting than ant hills and bird’s nests.

    Depending on the criteria, the aliens might not even consider our current state to be worth bothering with. This is similar to the old idea that the aliens are waiting for humanity to grow up as a species before we can be part of the galactic council.

    On the flip side, if multicellular life is the bottleneck and only occurs on one in a million life-bearing planets (to pull a number out of my rear) then a probe swinging by a million years ago would have popped a circuit in excitement and sent a message home that it hit the jackpot.

    The aliens could be on their way right now with a big bottle of Romulan Ale to say hello. Or a bomb, to wipe out the competition. Whichever.

  114. PaulBC says

    Marcus Ranum #93

    The very action of getting into the lifeboat changes you, any humans that escape earth are (at the very least) antisocial and have abandoned their humanity.

    I think a more likely scenario for interstellar expansion is to send off a probe capable of first replicating whatever environment is needed, and seeding it with an initial population of the sentient beings that constructed it with bootstrap educational materials. There doesn’t need to be anyone along for the ride to feel survivor’s guilt.

    It also seems unlikely that these sentient beings will be organic humans, because by the time the above technology develops in this solar system (if it does) the whole idea of populating the galaxies with humans as we know them today won’t have any obvious practical purpose.

  115. says

    As I see it, pond scum is probably fairly commonplace in the universe. Multicellular life is probably much less common. Intelligent life that can develop technology is probably quite rare and spread out. It’s not unreasonable to expect civilizations to die out or stunt their advancement before they solve the resource issues of interstellar travel.

    I don’t have quite as much trouble imagining humanity sending out a self-replicating probe as a last gasp with the message, “To whom it may concern, we apologize for the inconvenience of our probe landing on this planet and strip-mining the region. Once it’s done launching copies of itself, help yourself to these instruction manuals to aid in reverse engineering its technology. We hope you will find it useful. Please remember us. If you have a concept of music, we hope you’ll enjoy this piece composed by Mozart. If not, we hope you’ll at least enjoy analyzing our concept of music.”

    Of course, we’d need some very clever linguists to make the message translatable and hope they can challenge enough assumptions not to leave any probed species confuddled.

  116. says

    Great out-of-the-solar-system thinking in this thread. There is a sort of misunderstanding of how special relativity works wending its way throughout this thread that I should like to clear up. The misunderstanding is implied by statements that the human lifespan is inadequate for interstellar travel, that some new longevity break-through is required. Or that FTL travel is required. Both of these are not true within the framework of SR. Near light speed travel is sufficient and within principles. This is due to the effects of time-dilation and space contraction that occur at NLS. Relative to an earth-observer the on-board clock of an interstellar spaceship runs slow. At .87c the on-board clock runs at half speed.At .995c it runs at 1/10th speed. To the spacetraveler the experience is one of space contraction. At .995c the distance to alpha centauri contracts 10-fold, if that is the direction of travel. With sufficient energy resources it is entirely within principle to travel to the stars within a human lifespan. Granted that’s a big IF since current technology is only capable of accelerating individual protons to such high speeds but it does not violate physical law.

  117. PaulBC says

    Fermi’s paradox isn’t easy to dismiss, but it does require many assumptions about the detectability of intelligent life that has advanced far beyond human technology, the motivation of these advanced extraterrestrials, and the actual feasibility of von Neumann probe expansion in a galaxy already populated by other advanced intelligences.

    Specifically, technology far in advance of humans could do more with the space and energy that we use on earth today than we could do on a hundred worlds using the sort of technology envisioned in space opera SF. A nearby “post singularity” star system populated with artificial intelligence could be carrying out science, philosophy, and art without creating any obvious evidence of its existence from this distance.

    However, this isn’t an answer either. It certainly goes against the assumption in economics that nobody is ever satisfied. If one solar system is as good as a million earths, why not expand to nine more, and get the equivalent of ten million earths. At this point, you can speculate all you want about the motivations of extraterrestrials, but there might be at least some extraterrestrials that choose expansion.

    If this expansion made it as far as this solar system, then it might be hard to stop us from noticing, but a Fermi/von Neumann probe colonization attempt might be noticeable from far away before it ever got going (sending anything of significant size at close to the speed of light requires an enormous amount of energy). If the civilizations weren’t detectable, the trails of their probes might be hard to hide. On the other hand, if we could see this with today’s human technology, it would be detectable much sooner by more advanced technology. Maybe this kind of unchecked expansion is always stopped early by the galactic equivalent of the EPA and that’s why we don’t see it.

    I don’t see anything implausible about the above. On the other hand, the idea that we are alone in the galaxy is also consistent (could we tell the difference between a “colonized” galaxy and any other). This is a simpler, though less interesting explanation.

  118. says

    Regarding SETI – there were a number of posts bashing SETI as being unlikely to produce a positive result. I should like to refer to Carl Sagan on this matter – a thorough SETI search that comes up empty handed is also an extremely valuable piece of information. It would tell us that Earthlings are in-fact unique and explain the Fermi paradox. It may well tell us that exo-planets with billion-year stability are extremely rare and not to expect to find another pale blue-dot once we screw this one up. Perhaps governments will become better stewards of this rare and unique environment. Or not……..

  119. PaulBC says

    Has anyone developed a more detailed mode for “Fermi paradox” colonization than assertions like “Even at the slow pace of currently envisioned interstellar travel, the galaxy can be completely colonized in a few tens of millions of years.” (wikipedia)?

    What I’m thinking of is a few parameters. What is the smallest reasonable mass for a self-replicating probe? What speed is it traveling at? What is its propagation strategy and how much total distance is involved (e.g. expanding on a minimum-radius spanning tree of stars in the galaxy centered at the originating star system).

    The energy requirements vary tremendously depending on the parameters. E.g., a Bussard ramjet with life-support for a self-perpetuating colony of organic lifeforms accelerated close to the speed of light (where it needs many time its rest mass in energy) is a very different proposition from a refrigerator-sized payload of nano replicators that cruises along at, say 0.05c until it reaches a convenient source of matter to begin constructing additional replicators. The latter could still colonize the galaxy, though it would be 20 times slower (but it would still take just a few million years at this rate).

    I don’t think that energy requirements could possibly answer Fermi’s paradox, but it would be interesting to see what they are and how they relate to detectable sources of energy use. I am kind of picturing the acceleration of a Bussard ramjet to 0.99c as something that would leave a highly visible “contrail”-like signature (anyone know?). On the other hand, at 1/20th this speed, it might be undetectable until it actually starts modifying the planets around stars.

    There is also an unstated assumption in Fermi’s scenario that the civilization that started this colonization will continue it as planned. In fact, later seeded planets might develop entirely new viewpoints about the wisdom of this program. The desire for such unchecked expansion by advanced intelligence could be so improbable that more of the seeded colonies (on average) would opt to prevent it than to continue it. So they could send out a new wave of slightly faster probes to stop the original wave.

    This is still pure speculation, but it seems more likely to me than a “galactic EPA” scenario (as I suggested above). In short, you can talk about the feasibility of Fermi paradox colonization in purely engineering terms, but it may be inherently unstable as carried out by sentient beings.

  120. Amphiox says

    I do like large-scale thinking. I think, though, you would need more than asteroids to get the Earth completely away from the solar system. A planet would be better. Larry Niven, in A World Out Of Time, used Uranus for his slingshot manoeuvres.

    Jupiter is the obvious candidate. But it is, I would think, a tad easier to use asteroids to move the earth into an orbit that would take it towards a slingshot with Jupiter, than the other way around!

    (The maneuver might require several major planet flybys, with each boosting to the next….)

  121. Amphiox says

    …has to apply to every such civilization if it’s to be an escape from the Fermi paradox. If it’s feasible for a civilization to send out self-replicating probes, then there only has to have been one such civilization that chooses to do so for the galaxy to be full of the things.

    All such exclusivity arguments are feasible if the number of alien civilizations in the galaxy are small. If there is just a handful of such civilizations in a given time span, then it becomes more likely that the one exception to the exclusivity argument has not (yet) arisen.

    One could model self-replicating probes as one would model an organism. But even here on earth we are not certain that every abiogenesis event resulted in complete colonization of the planet. There could have been several that actually failed and went extinct.

    Thus we should not assume that only one alien civilization producing self-replicating probes will inevitably lead to the dispersal of such probes throughout the galaxy. The descendants of the probes may well go extinct before completely spreading through the galaxy, and it may take several civilizations making several such attempts before colonization of the galaxy could be considered a reasonably likely outcome.

  122. Amphiox says

    If an alien species detects life, would it bother to investigate further?

    If life is relatively common, but intelligence is rare, then a star traveling species would run into many life signs that amount to little more than amoebas, Why bother with them? Unless it’s clear that there’s intelligent life, what’s the motivation?

    Would we expect the individuals that make up an alien intelligence capable of starflight to be monolithic? When we get to the level of a starfaring species that has traveled enough to consider life on other worlds a routine finding, we are looking at something in the K2-K3 range at the least, and when we get to such levels of technological sophistication, we are looking at scenarios were individuals or small private groups may have access to the means to explore solar systems like ours, and, relative to the output of the civilization as a whole, the resources required to do so would be trivial. If so, even if the main civilization has little interest in pond-scum worlds (and even if they consider we humans just another variant of a pond-scum world), we would expect that there will be curious individuals who WOULD be interested at least taking a look-see of a world like ours.

    Our civilization does not care a great deal, or spend much collective effort or time, investigating ants. But we DO have entomologists, and curious children with sticks.

    So perhaps when we get our first contact situation, and we roll out the red carpet for the presumed alien dignitaries, it will turn out to be their equivalent of a first grader doing a science project.

    And all those alien invasion movies where it seems so improbable for the humans to have actually won in the end? Those were not wars with any alien military, those were simply the alien equivalent of the foolish drunk dude who got himself bitten and killed by a blue ringed octopus.

  123. says

    …when we get to such levels of technological sophistication, we are looking at scenarios were individuals or small private groups may have access to the means to explore solar systems like ours, and, relative to the output of the civilization as a whole, the resources required to do so would be trivial

    That’s a possibility I hadn’t considered. The fewer individuals required to travel, the more likely that random hobbies and curiosity would determine the destination. Interesting idea.

  124. a_ray_in_dilbert_space says

    The issue of cosmic radiation is not one that can be brushed glibly aside. To merely halve the galactic cosmic ray flux, you’d need 13 cm of aluminum or 37 cm of water or ice. If your space vessel were a 200 meter sphere, that would give a weight of over 46000 tonnes just for shielding. All that extra weight means more fuel, which means more weight AND slower acceleration–therefore more time to get where you are going and longer exposure to radiation. And that is just to cut the flux of GCR down by a factor of 2! The highest energy cosmic rays have an energy equivalent to a 100 mph fastball for a single nucleus! There is no way you will shield that. And to top it off, once you leave the protective heliomagnetic field and solar wind, the fluxes increase by about a factor of 3.

    What is more, the high-energy, high atomic number ions characteristic of GCR damage tissue and especially DNA over a large radius, causing damage even to multiply redundant and highly critical genetic information. Even storing the genetic information electronically likely would not work given the high radiation exposure. I do not see any way that an organism with its genetic information coded chemically could survive a long space trip. And even if you were to reach a far-off habitable planet, it is highly unlikely you would find any sort of crop or other energy source to sustain yourself–you’d likely be confronted with a poison world.

    Stories of interstellar travel should be filed under fantasy. There’s not enough reality there to even call it science fiction.

  125. PaulBC says

    a_ray_in_dilbert_space #127

    Even storing the genetic information electronically likely would not work given the high radiation exposure.

    This is a solved problem, and maybe one of the few instances in which “information theory” can be referenced for legitimate reasons on this blog. If you know, for example, that every bit has a 10% probability of being flipped by radiation (which is quite high) you can still construct an error-correcting code to reduce the probability of losing any original bit to whatever value is desired by using a redundant representation. So maybe you put 1000 terabytes of raw bits in the probe in an attempt to send 1 terabytes without errors (way more than needed, but information is compact, so why not?).

    For that matter, you could send the information as a separate laser signal following the probe, which would render it safe except for transient gaps caused by very rare occluding objects (again, easily solved by redundancy). You could actually have the probe itself request a retransmit after it finds its destination, because the transmission propagates at c, whereas the probe may have traveled at a much smaller fraction of c, so this will not add much time to the total time between launching and starting self-replication. E.g., maybe it took 1000 years to get to its destination at 0.05c. Next it will request instructions. The request will be received 50 years later, and it will begin receiving the instructions 50 years after that. So it takes 1100 years to get started instead of 1000.

    And even if you were to reach a far-off habitable planet, it is highly unlikely you would find any sort of crop or other energy source to sustain yourself–you’d likely be confronted with a poison world.

    Given. I don’t think that organic lifeforms tooling around in starships is a very likely scenario, and the probability that they will find immediately usable living environments is statistically negligible. You have to assume that it is possible to send something robust enough to survive an interstellar trip that is capable of transforming whatever resources are available into copies of itself when it gets there. The technology needed is far beyond what we have today, but I don’t see how it would be ruled out. The probe might have most of its mass in shielding and contain a payload of nanotechnology that would survive intact. In fact, the shielding might make a good set of starter resources for the replicator, since the radiation damage won’t necessarily have rendered it unusable.

    So step 1 is a compact “smart” machine surrounded by dumb but carefully selected material. Step 2, it converts this to a massive “xenoforming” machine that is robust to the environment of the star system it has reached. Step 3, that machine starts converting available resources (e.g. local star radiation plus asteroids, etc.) to an industrial base capable of constructing any technology. Step 4 it sends off its own probes.

    This is starting to veer so much into metaphors of an actual egg or seed that I’m nervous about taking it any further. But long story short, if you don’t have to send all that much functioning hardware and you can draw new resources as you go, it doesn’t seem implausible at all.

    Stories of interstellar travel should be filed under fantasy.

    If you mean organic life traveling in spacecraft, I agree. If you mean the propagation of technology and post-organic intelligence to other star systems, I don’t think that background radiation is a blocker.

    However, I will add that another answer to Fermi’s “Where are they?” is simply that colonizing with von Neumann probes is actually much harder than it sounds. If technology doesn’t exist at present to do something (or even come close), it is at least a little reasonable to stay skeptical about whether such technology will ever exist.

  126. says

    @ray #127 – great problem to bring up.

    I think the 3x increase you speak of was reported by Voyager when it was thought to detect the heliopause. Voyager will continue to report radiation levels as it continues into interstellar space. http://voyager.jpl.nasa.gov/

    Does that level of radiation preclude interstellar robotic missions? If so that may explain the Fermi paradox – theyr’e out there but they can’t leave their star system in any meaningful way.

  127. says

    Yeah, technology is one of those areas that we all may be way too optimistic about. All one has to do is look at the ongoing quest for workable fusion power, which has been a “decade or two away” for my entire life. We have no idea what the limits to various technologies will be until we reach them.

  128. Nick Gotts says

    Near light speed travel is sufficient and within principles. This is due to the effects of time-dilation and space contraction that occur at NLS. – Allen Everhart@119

    I think it’s unlikely people are missing that: enough of those in discussion are SF readers or reasonably familiar with the phenomenology of SR. Specifically, most will have read stories and thought experiments involving time dilation. Rather, it’s that near light-speed travel for macroscopic objects, while physically possible, runs into its own serious problems. If you get time dilation, you also get mass increase, which not only means you have to push harder, but also increases the damage from anything not travelling at close to c itself, as well as the difficulty of avoiding it.

    All such exclusivity arguments are feasible if the number of alien civilizations in the galaxy are small. If there is just a handful of such civilizations in a given time span, then it becomes more likely that the one exception to the exclusivity argument has not (yet) arisen. – Amphiox@124

    Agreed: all my arguments have been aimed at the notion that there are lots of alien civilizations out there.

  129. Nick Gotts says

    Has anyone developed a more detailed mode for “Fermi paradox” colonization than assertions like “Even at the slow pace of currently envisioned interstellar travel, the galaxy can be completely colonized in a few tens of millions of years.” – PaulBC@

    Wikipedia’s artcle on “self-replicating spacecraft” says Robert Freitas was the first to do so in 1980.
    Here’s a version of his paper, which I haven’t read yet.

    Here’s a more recent, non-quantitative but classificatory essay on self-replicating probes. And here’s one on a SETI search for signs of von Neumann probes and specifically, their communication systems.

  130. says

    Nick Gotts #102,

    No idea what the time to evolve has to do with the probability of it happening elsewhere. Why did it take thousands of years to develop agriculture? Well, maybe it just takes that long. Was still invented six or seven times in parallel.

    You make the wholly unjustified assumption that we can actually invent entities designed for instellar travel and cryonics. This is not the 15th century any more, we actually know a few things about physics and biology now. One could just as well say, maybe somebody invents the philosopher’s stone and a way to summon the spirits of the dead! Ha, somebody else already brought up the singularity I see – beyond that point we are really just talking “wouldn’t it be nice if there was magic”.

    If you go with 1% of light speed you need hundreds of years even to the next star, and there goes all your oxygen. And it is reasonable to assume that you need to travel much further than to the next star before you find a habitable planet.

    Amphiox #106,

    Yes, on both counts. The void is not totally empty, and being hit by what little is in there will tear you apart at high speeds. And in our laboratories, gases dissipate out of their containers over the years – do you really think one would be able to build a massive, structurally complex space ship that is better sealed than a three feet bottle optimised to the sole purpose of storing a gas?

  131. Menyambal says

    I think that if we get fusion working, and mountable in a spacecraft, we will find the ideal location for such a technology is out in the Oort Cloud. There’s ice out there, and metals and carbon, all floating free between the stars. All a solar system has is light and gravity wells, which a fusion craft doesn’t need and isn’t built for.

    Such a space-faring society would scavenge the cloud in a gradual fashion, capturing objects and using them for materials, fuel and reaction mass, moving them about as they were harvested. That society would spread across the space between the stars but never need to venture down near the stars.

    We, here, would never notice them. Sure, they might fumble an Oort object now and then, and we’d see a comet. We would get cosmic rays off their exhausts, and sometimes particles, but we wouldn’t know what we saw. And we might notice that we haven’t seen our Oort Cloud, but we’d blame our telescopes.

    They would have so much more volume of space than our little hell-hole of sunlight and gravity, and materials just drifting around to be caught. Why would they come say hello to us?

    So there’s a space society that would spread across the galaxy, that we would not know about. It could have happened already.

  132. unclefrogy says

    why does anyone think we can keep up interest in any particular interstellar travel either by those who remain or those who do the traveling? Even if the engineering is possible, affordable and practical, which is a big if. What evidence do we have of anything we do lasting that kind of time without repeated alteration. I do not mean things like pyramids or other such things. I mean ideas, cultures or society and its ordering and priorities changing.
    how many generations are we stable.
    The development of warp drive change everything as would faster than light communication.
    While the engineering . may be possible I do not see how we could maintain interest in any project involving these kinds of time frames.
    Unless of course it takes on some the attributes of a religion
    uncle frogy

  133. Amphiox says

    why does anyone think we can keep up interest in any particular interstellar travel either by those who remain or those who do the traveling? Even if the engineering is possible, affordable and practical, which is a big if. What evidence do we have of anything we do lasting that kind of time without repeated alteration.

    Alteration isn’t necessarily a showstopper. Launch a generation ship to colonize the stars, and you know you have no ultimate control over what the crew will decide to do a few generations down the line. But they’ll be out there, in space, and whatever they choose to do, of all the options (some which you doubtless cannot even envision) available to them, only one would really thwart the process of space colonization, and that would be the crew deciding to turn around and go home.

    But this is also why I foresee a “comet-jumping” stepwise progression through Oort Clouds and Kuiper Belts as more likely than a home-run style shot into another star system. For a society on board a generational ship, going from one icy Oort object to another is merely a hop from one, possibly depleting, source of resources, to a newer, fresher one. Add replication of habitats into the mix, and you get a kind of natural diffusion outwards as each habitat merely seeks the resources it needs to sustain itself, and you almost just naturally fall into the next star’s Oort Cloud in the process.

    I’m pretty sure the British did not foresee the possibility of the American Revolution when they invested the time and effort into settling the New World. The reality of that unknown did not deter them.

    We, here, would never notice them. Sure, they might fumble an Oort object now and then, and we’d see a comet. We would get cosmic rays off their exhausts, and sometimes particles, but we wouldn’t know what we saw.

    It’s the proverbial anthill beside a superhighway. The ants will detect the activity in the superhighway. They will feel the vibrations transmitting through the ground into their next. They may notice strange odors interfering with their pheromone trails. They may notice a few of their number going missing from being stepped on. But they are unlikely to recognize that these phenomena are due to the activities of a cooperative, technological intelligence far in advanced of themselves.

  134. Amphiox says

    Amphiox #106,

    Yes, on both counts. The void is not totally empty, and being hit by what little is in there will tear you apart at high speeds.

    No, on both counts.

    We already have the empirical evidence of what the energy of being hit by an atom at relativistic speed will do, and we already know that it would barely dent a car, let alone an advanced spacecraft. An asteroid is a different matter, but that first post specifically said ATOM, and if you’re moving on to “any object” now you’re moving the goalposts of that discussion. And asteroid sized things are actually ASTOUDINGLY RARE in space. Space is very big.

    And in our laboratories, gases dissipate out of their containers over the years – do you really think one would be able to build a massive, structurally complex space ship that is better sealed than a three feet bottle optimised to the sole purpose of storing a gas?

    Yes. Absolutely. And I’ve already described how. You would expect and accept some leakage, but you can replenish what you lose, if you start with a KBO-based spacecraft as I described. Even with reasonable loss rates an average icy KBO will be more than enough to supply a nominal crew population for hundreds of thousands of years.

    Or there could be any other engineering solutions to the problem.

    There is no law of physics that says it is impossible to produce a seal with a gas-loss rate low enough to support a journey of several hundred thousand years. It is an engineering problem. It is unwise, ever, to bet against something that is just an engineering problem not prohibited by any law of physics.

  135. PaulBC says

    Alex SL #134

    If you go with 1% of light speed you need hundreds of years even to the next star, and there goes all your oxygen. And it is reasonable to assume that you need to travel much further than to the next star before you find a habitable planet

    This sort of comment has come up enough times that I have to call it out as a strawman. Maybe someone out there believes in space-opera style galactic colonization, but ruling out the (admittedly small) likelihood of biological humans spreading beyond the solar system, and then calling it a day is not a serious answer to Fermi’s question “Where are they?”

    One could just as well say, maybe somebody invents the philosopher’s stone and a way to summon the spirits of the dead! Ha, somebody else already brought up the singularity I see – beyond that point we are really just talking “wouldn’t it be nice if there was magic”.

    If we’re going to speculate at all about technology millions of years in advance of our own, then saying “Wouldn’t it be nice if they were also bound the same technical limitations that we are?” is not much of a starting point either. I’ll accept fundamental limitations like the speed of light or conservation of energy. But the level of radiation shielding feasible with today’s human technology probably isn’t very relevant.

    If you find the idea of a singularity comical, that’s fine (the rapture for geeks, fair enough). Note that I’m not holding my breath for it to happen in my lifetime. However, I find it comical for a 21st human to imagine themselves to be living at a sort of all-done-now-close-the-patent-office apex of scientific understanding.

    I agree that it’s not the 15th century anymore, and we know some things we didn’t know them. Do you think that the amount of new things we learn between now and the 27th century will be more or less than in the previous 600 years? Possibly (I emphasize possibly!) there will be fewer new fundamental laws of physics to discover, but our computation ability will at least increase to where it dwarfs anything imaginable today. We’re smart enough to take the principles we understand now and cobble together a few little things that apply them. It doesn’t mean we’re really at a vantage point where we can make pronouncements about ultimate limitations of technology any more than someone hundreds of years ago could make accurate predictions about today.

    In fairness, we’re in no position to declare things essentially solved in the future if they’re clearly infeasible today. There’s a reasonable 15th century analogy there too, because some things, like chemical transmutation of elements would have seemed more plausible than they do today. On the other hand, much of today’s technology would have been thought impossible. The analogy may be flawed if you think we have already passed some other singularity in scientific understanding since the 15th century and are in a better position to understand the limits of future discovery. In some areas, our understanding is much better, but I still think that we’re quite ignorant compared to what is possible to know.

  136. Amphiox says

    The claim that gas loss is an insurmountable problem for space travel is very much akin to the contention that the radiation of the Van Allen belts would have made a moon mission impossible, or supersonic flight is impossible because the human body would not be able to take the strains.

    It is simply not a credible argument whatsoever.

  137. Amphiox says

    In the Oort-Cloud-hopping scenario I and a few others have suggested, you can literally TOW a million-year-supply of frozen atmosphere with you wherever you want to go.

  138. a_ray_in_dilbert_space says

    PaulBC,
    I know about error detection and correction codes. And, yes, we can come up with unmanned probes (e.g. Voyagers I and II) that will last decades, albeit with very limited technological capability. There is no way most advanced electronics will last that long–we’re having trouble finding advanced parts that will last the 15 year life required of many GEO birds. There’s no way we have electronics lasting hundreds of years. There would have to be fabrication capability on the probe and the ability to replace failed systems. That is an absolutely huge overhead.

    People grossly underestimate the threats and difficulties associated with space travel even within the solar system–hell, even in low-Earth orbit. When it comes to interstellar travel, people don’t have a clue.

  139. PaulBC says

    Nick Gotts #114

    If it’s feasible for a civilization to send out self-replicating probes, then there only has to have been one such civilization that chooses to do so for the galaxy to be full of the things.

    Another possible answer to Fermi’s paradox is that the galaxy is full of these probes.

    The self-replicators wouldn’t necessarily convert the entire mass of every solar system they encountered, and would probably go for the most readily available resources. We may think that the best part of our solar system is a planet an earth-like orbit, and for all I know it may even be the most likely place for life to originate. That still doesn’t mean it’s the best place for an advanced intelligence to colonize.

    Who knows, maybe the Oort cloud is full of self-replicating alien robots. I would personally want to be closer to the sun for energy, but maybe they have their own fusion power, rendering this less of an advantage than it seems.

    I mean, I doubt it, but would we definitely know? They would be better at not leaving obvious waste products. What exactly they would want out of another solar system isn’t even obvious. Suppose large parts of the far outer solar system have been converted into a server farm as as part of a massively distributed form of Douglas Adams’s “Deep Thought.” We might not have any awareness of this until we take a much closer look than we can we telescopes. Meanwhile, it could be policing the territory for competing self-replicators (which we might not notice until they start operating).

  140. cm's changeable moniker (quaint, if not charming) says

    The issue of cosmic radiation is not one that can be brushed glibly aside.

    Aww, c’mon. If we can imagineer an interstellar fusion drive, an artificial heliosphere is a mere bagatelle.

    :-)

  141. PaulBC says

    a_ray_in_dilbert_space #142
    Actually, I don’t rule out the hostile interstellar environment as a potential answer to “Where are they?” It just doesn’t sound very likely to me.

    There is no way most advanced electronics will last that long–we’re having trouble finding advanced parts that will last the 15 year life required of many GEO birds.

    And could this be explained by the fact that we have a lot left to learn about interstellar travel, and some of these problems might be solved given another thousand, or maybe a million more years of technological development? I’m having trouble accepting “equipment failure after 15 years using today’s technology” as a fundamental obstacle.

    I agree with you that interstellar travel is not only hard, it may be infeasible in some fundamental way that I don’t understand. But the only issues proposed so far sound more like engineering problems than proofs of impossibility. I do have a lot of confidence that our ability to solve engineering problems will increase significantly in the future.

  142. fjgiie says

    If the nearest planet with intelligent life is one to two billion light years away, seems like we will never see ET at all. A trip that last more than a billion years is a problem. For instance the salt would be all gone after only a thousand years; a shake per day. My guess is that there are only 125,000 planets with intelligent life in the universe. There may as well be none.

  143. says

    Amphiox,

    No, I wasn’t talking asteroids but I admit that “one atom” was hyperbole on my part. There is stuff out there, it is a long journey so you will hit a lot of stuff, and you will hit it with a lot of impetus. I guess we will just have to agree to disagree on what happens when you fly into cosmic dust at those high speeds. And that is assuming that one could even accelerate that much with any realistic amount of fuel, of course.

    Yes, it is an engineering problem, but sorry, the idea that you can build a spaceship that remains operable after hundreds of years (let alone thousands) is just not very plausible. We don’t even appear able to build houses that remain functional that long without constant renovation. Will the computer you comment from still work in fifty years?

    Just as many creationists fail to appreciate the deep time that life has had on this planet to evolve, so I guess many techno-optimists fail to appreciate the enormous distances between stars, the minuscule volume of the universe that even under most charitable assumptions will be suitable for colonisation, and the ludicrous amounts of energy needed to do anything about either.

    PaulBC,

    Perhaps the difference is that I see technological and scientific progress not primarily as us finding out how to do cool things, although there is certainly some of that too, but mostly as us realising that certain things do not actually exist and other things are not actually possible or feasible. Yes, we can fly using hot air balloons or airplanes (as long as we can afford sufficient amounts of high-density fuel, something that may not be the case in another 200 years) but we know for certain now we cannot fly by flapping wings. Yes, we can shoot people into space using rockets but we cannot do so using Jules Vernes’ idea of a cannon, at least if we want the passengers to survive.

    And yes, I do believe that this limits the number of things that can still be invented in the future. Sure humans will probably come up with innovations currently unimagined in the future if we don’t fall back into another dark age first – but that is just another point. SF from a few decades ago had easy space travel that suspiciously looked very much like ocean travel or fighter planes but it didn’t have the internet. Assuming that future innovations will deliver precisely the stuff one would need to fulfill one’s dreams instead of something else sounds a bit too much like wishful thinking. Actually, doing something about the telomers shortening sounds much more plausible to me than us or any other sentient species figuring out economically feasible fusion power, survivable cryonics or survivable interstellar flight.

    But in the end I don’t know if these things are really unachievable. I am merely advancing that as the most plausible explanation for the Fermi Paradox given that the alternative of us being unique seems like a very arrogant and implausible explanation.

  144. Menyambal says

    Well, we sent out a radar beam that was getting contours off a .4 kilometer rock at 1.4 million kilometers away. Somebody might notice that.

    http://www.slate.com/blogs/bad_astronomy/2014/06/26/asteroid_2104_hg124_radar_imaging_gives_size_and_shape.html

    =====

    If you are out in the Oort Cloud, scavenging, you latch on to an object, push it in front of you, and let it take any impacts. Tunnel inside a bit and Bob’s your weightless uncle. All the stuff you dig out falls into your nets, you feed the fusion engine with the good stuff and drop the scrap overboard.

  145. Amphiox says

    I guess we will just have to agree to disagree on what happens when you fly into cosmic dust at those high speeds. And that is assuming that one could even accelerate that much with any realistic amount of fuel, of course.

    I only object to your seeming insistence that it is impossible. It may well not be feasible, but at our currently technological level I don’t think we should be making blanket declarations about impossibility on things like this.

    The Oort-Cloud-Object-Generation-Habitat scenario does not actually require very fast speeds or significant accelerations. And when one has a self-sustaining habitat one does not need to limit oneself to straight A to B trajectories. Gravitational slingshot maneuvers of all kinds become possible.

    A trip that last more than a billion years is a problem. For instance the salt would be all gone after only a thousand years; a shake per day.

    You would recycle your salt, just like you would recycle everything. It’s not like the Sodium and Chloride ions will just up and disappear into the ether.

    (A billion years is an extreme number. Our own solar system, moving at significantly non-relativistic speeds, has circled the entire galaxy some four times in that span of time….)

  146. Amphiox says

    Actually, I don’t rule out the hostile interstellar environment as a potential answer to “Where are they?” It just doesn’t sound very likely to me.

    Most of the “hostile interstellar environment” and “galactic habitable zone” and such-like arguments are really only valid for life arising on star systems in those so-called prohibited areas. The challenges suggested really wouldn’t bother a technological civilization capable of interstellar travel at all.

    The range of environments that can be colonized with sophisticated technology is far, far, far wider than the range of environments that can support the evolution of life through the non-technological phases.

    One could talk about galactic regions with high rates of sterilizing gamma ray bursts as being places where life would have a hard time evolving. But a technological civilization that evolved away from that danger zone should have little trouble moving in and colonizing that region, if they have the wherewithal to do interstellar colonization in general.

  147. Amphiox says

    If you are out in the Oort Cloud, scavenging, you latch on to an object, push it in front of you, and let it take any impacts. Tunnel inside a bit and Bob’s your weightless uncle. All the stuff you dig out falls into your nets, you feed the fusion engine with the good stuff and drop the scrap overboard.

    You can throw the scrap overboard directionally for added thrust….

    And if you can tunnel deeper than a few hundred meters you’re basically safe from cosmic radiation.

  148. PaulBC says

    Alex SL #147

    But in the end I don’t know if these things are really unachievable. I am merely advancing that as the most plausible explanation for the Fermi Paradox given that the alternative of us being unique seems like a very arrogant and implausible explanation.

    The notion of intelligent life being rare enough to have <1 such planet per galaxy on average doesn't seem arrogant. It's far from saying humans are unique, just an example of a rare phenomenon. (I leave open whether it's implausible.) In a sense, that strikes me as the most plausible explanation for the Fermi Paradox, but admittedly not the one that makes me happiest to believe.

    Another reasonably plausible explanation to me is that by the time an extraterrestrial intelligence is advanced enough to send out von Neumann replicators, they've lost any rational incentive to do so. Our own solar system is almost unfathomably resource-rich compared to what's currently available to humans, and our use of matter and energy will continue to grow more efficient (yes, assuming no new dark ages).

    There might be scientific interest in sending out probes, but in purely practical terms, if the question is what to do next to "produce more stuff we want" (whatever that means in the far future) the answer may almost never be "start expanding into the galaxy with replicators." Even if the entire mass of some star system (other than its star) has been converted to machines sentient and otherwise, it may seem more reasonable to start recycling the matter from obsolete parts than to expand further.

    Granted, even if unchecked replication is unreasonable, it just takes one planet to start it. So then it turns into a question of odds. Maybe the odds are a thousand to one against, and there are less than a thousand planets with intelligent life in this galaxy. Neither of these numbers are available to me, but a combination of low odds for intelligent life and low odds for actually carrying out Fermi's suggestion could easily explain why we don't see evidence of it happening around us.

  149. lpetrich says

    I’ve checked on watching our TV shows from interstellar distances, and one would need a planet-sized radio telescope. Not VLBI, but a radio telescope with an area comparable to a planet’s cross section. That’s necessary because a TV signal is spread over a few megahertz, meaning that most of it is very easily drowned out by noise. It’s much easier to pick up the carrier signal, however, and that could make possible some interesting inferences.

    Even if one did pick up a TV broadcast, how much could one infer from it? One could easily infer that it’s an analog raster-image system, but beyond that is rather difficult. The closest thing to a “Rosetta Stone” might be educational kiddie TV shows.

    How might one tell left from right? One might have to look for some astronomy TV show that shows that the stars look like from the Earth.

  150. lpetrich says

    It’s worth noting that the era of analog broadcasting is coming to an end. Digital broadcasting offers much less by way of interpretation cues, and it’s even worse when it’s encrypted.

    As to interstellar travel, that’s VERY difficult. One needs nuclear energy to get a reasonable travel time and to power one’s spacecraft. Chemical energy isn’t dense enough, and antimatter is energetically expensive to make and very difficult to store, despite its even greater releasable energy. That’s because antimatter is just like ordinary matter except for some flipped signs and the like. Bulk antimatter would be just like the corresponding bulk ordinary matter. The easiest bulk antimatter to make would be antihydrogen, but the properties of ordinary hydrogen indicate that it would be rather difficult to store. One would have to keep its temperature below a few K to keep it from evaporating. Hydrogen is diamagnetic, so antihydrogen could be stored with strong magnetic fields, however.

  151. says

    PaulBC,

    <1 such planet per galaxy on average

    But as you just wrote yourself, the techno-optimist scenario underlying the paradox part in the Fermi Paradox is that it doesn’t matter if there is only one civilization arising every fifty million years because it is assumed that they stay and spread out, just like winged insects needed to arise only once but are still plentiful.

    As for your alternative explanations, they are not so different from mine then, variants on why even if intelligent life would arise repeatedly it would still not spread out. Really the two meet in “not being interested in expansion” if instead of not being technically utterly impossible it would turn out that interstellar travel was merely unaffordable.

    But still we must have a very different view of things. I have no idea why anybody would ever have an incentive to send out replicators; what good does it do you? It is a bit like scratching “I was here” into a bus seat only the “knife” may cost you $5 trillion or so. Anything that doesn’t either carry colonists or at least a probe that sends back information within ca. 100 years is pointless, and most likely would be equally pointless to other intelligences because they would face the same evolutionary imperatives and resource constraints as humans.

    It also seems as if our past history was mostly one of becoming ever more wasteful; I do not foresee us changing those habits and becoming more efficient unless forced to do so, and the circumstances that force that efficiency upon us will be the same that make space flight unaffordable.

    Third, I have repeatedly seen the claim in this thread that the solar system has a lot of resources that we could mine. What are those resources? If we only had enough energy we would probably never need more metal or water than just what we find on earth because given enough energy we can clean and recycle everything. Energy is the main problem. But we will not find any additional oil, coal or gas on the other planets or moons. So what could interest us about space instead? Well, living space. The only resource worth having outside of our home planet is other habitable planets and those would have to be outside the solar system. (And while there might be lots of planets that potentially could harbor some form of sentient life, planets that could carry specifically us humans might be much rarer. What good is a planet with lots of water in the Goldilocks zone around an orange star if it has 5x Earth gravity?)

    So really travel that goes no further than the solar system itself may be scientifically rewarding but will always remain uneconomical.

  152. PaulBC says

    Alex SL #155

    It is a bit like scratching “I was here” into a bus seat only the “knife” may cost you $5 trillion or so.

    You’re right that we differ in outlook. I have a “too cheap to meter” assumption about the distant future (I admit past predictions of this nature have been premature.)

    A monetary figure is only meaningful when there is competition over resources. I’m assuming the existence of abundant AIs for solving the hard problems of interstellar travel, abundant automated offworld production, and abundant energy. Constructing the probe will not be depriving anyone else, nor need it occupy the attention of any sentient beings who aren’t interested in it. So I don’t think “expense” is the blocking issue as much as “why bother?”.

    E.g., you said something about how we don’t build machines that fly by flapping wings. But with sufficient technology, we probably could build some machines larger than birds that flew by flapping their wings and carried a significant payload. We just don’t do it because there isn’t much point if we can achieve flight by other, simpler, means. Analogously, Fermi’s paradox suggests a particular solution to a problem that may seem to make sense now, but may make very little sense at the point in the future where it is feasible.

    Beyond that, you can question why people bother to do anything in particular. It’s not clear how much satisfaction I would get knowing that I may have biological descendants at interstellar distances. Even sending off an old-fashioned starship with regular humans on board is a fairly pointless gesture. They would have an entirely new and independent trajectory to ours here on earth.

    Starting with the assumption that machines can be sentient and may carry some record of their human originators, having them propagate outside the solar system is at least as interesting to me as sending biological humans.

    But we will not find any additional oil, coal or gas on the other planets or moons. So what could interest us about space instead?

    I don’t expect distant future technology to use significant chemical energy (and we’d run out anyway, and sure couldn’t power an interstellar ship that way). Solar energy is more readily available and constant in space. I’m assuming self-replicating machines using solar power to transform, e.g. the asteroid belt into more usable materials. I’m also assuming that most sentient beings in the solar system would not be biological humans (who might continue to live on earth). Just transforming “dumb” mass into additional components supporting sentience would occupy such a civilization for a long time, and it’s not clear what benefit would come from interstellar expansion.

    This is all vaporware of course, and maybe there’s some good reason why it cannot possibly happen that way. But it is the kind of scenario I envision as the future of technological civilization. Current use of resources on earth is unsustainable. If I’m going to be any kind of optimist, it might as well be a techno-optimist, because I don’t see a lot of optimism about people simply learning to scale back their appetites.

  153. Amphiox says

    But we will not find any additional oil, coal or gas on the other planets or moons. So what could interest us about space instead?

    Oil, gas, coal, any fossil fuel, and indeed, any source of energy that requires combustion would be useless in space. Your oxygen is WAY too precious to be burning it away like that. And the cost of getting it in space to use on earth will be highly unlikely to be competitive with other energy generating means. You could practically synthesize the stuff straight from atmospheric CO2 for better cost-effectiveness.

    The biggest resource out there in space is living room. Earth is getting close to its human carrying capacity already. Given the choice between moving elsewhere versus restraining their own reproductive impulses, at least some humans always choose the first.

    And all the resources one might talk about in space are for use in space, to support living in space and using that one key resource of living room. It is highly unlikely that ANY space resource will be economically competitive with earth-harvested resources for use on earth, up to the point (if we ever get there) where our technology allows us to tap out the planet’s core for its metals. But the flip side is that space harvested resources will be very likely quite cost-competitive for use in space, versus earth harvested resources you have to boost into orbit.

    There is little incentive right now for human civilization to venture into space on a scale that would require a large output of cooperative societal engagement. The incentives that exist will likely be the ones that appeal to small groups of individuals who simply want to leave this planet. As such, space colonization for our species will not be likely to happen until we reach a level of technological and economic development wherein small groups of private individuals would be expected to have access to the technology and resources needed to venture into space.

    If we get to such a point, where a planetary spaceship is an investment akin to a luxury yacht, then personal eccentricity will be enough to spur colonization. If we do not or cannot get to that point, then it is less than 50:50 that we will ever get off this rock.

    This is why I think the stepwise scenario starting with orbital pleasure habitats for the wealthy is the most likely sequence that would get us into space as a species.

    An alternative to that, that would possibly produce a grand, civilization-spanning attempt to colonize space at a time before achieving the technology level that would allow small private groups to do it would be if we detected some unavoidable cosmic disaster that would render earth uninhabitable, but with sufficient lead time (like several centuries) that we would have a fighting chance of getting off planet. Something like detecting a rogue star or neutron star or black hole on collision course with our solar system. Though in such a scenario it is still possible that our civilization would waste all its time arguing over what to do, and end up doing nothing, and dying.

  154. mrjonno says

    Well any advanced species is not going to tolerate dying for a start (human beings certainly don’t), most likely solution is going to be some sort of computer based life form highly unlikely to resemble anything organic on Earth.

    Not being organic whether these species are going to need oxygen, water or carbon is highly debatable

    There is a chance that is far from zero that some babies born today will still be alive in 1000 years. A baby born in a 100 years time is highly likely that it will not die at all bar major accidents

  155. PaulBC says

    Amphiox #157

    The biggest resource out there in space is living room. Earth is getting close to its human carrying capacity already. Given the choice between moving elsewhere versus restraining their own reproductive impulses, at least some humans always choose the first.

    I’m not convinced that there will ever be a large population of biological humans living off earth, or that space is really the limiting factor. I.e., by the time it is feasible to support humans off earth, there might be little interest in doing so.

    I also think that matter and energy outside earth are more significant resources than space, though space is important in the sense that some industrial processes may only be safe to attempt far away from earth.

    Our current resource use on earth is incredibly wasteful compared to what’s possible, and continues to get more efficient. If we perceive it as getting worse (e.g. deforestation, ocean pollution, rising atmospheric CO2) it’s because growth in production outstrips improvements in efficiency. E.g., how much iron could we produce using charcoal from trees without causing irreversible deforestation?

    That doesn’t mean we’re not on the path to ruin, just that if it’s inevitable, it will happen because production continues to grow faster than improvements in efficiency, not because efficiency is theoretically impossible. Earth can support more people, but not many more people in single family houses who commute by car. It’s also unlikely that billions more can fulfill that dream by moving into space. However, if it is just a question of how much matter, energy, and space are needed to support a large population of sentient beings, there are no obvious limits. It may not even be that appealing to move off earth into the solar system relative to developing greater efficiencies.

    None of this is guaranteed or even necessarily likely to happen. We might destroy the earth rapidly and catastrophically, or hit a Malthusian limit, or even come up with a way to reach sustainable resource use, preserving something like human life recognizable to us in the 21st century. Of these, I would consider the third option least likely, but it’s worth a try.

    So to put in context my comments about somebody out there constructing a self-replicating interstellar probe, it is conditional on (1) not screwing up their own planet to the point where future progress is impossible (2) developing autonomous means of production including self-replicating robots (3) achieving a high level of control over resources in their own star system, (4) solving the admittedly difficult problems of building such a probe. I have no views about whether this is remotely possible, or even desirable, for humans.

    Step 4 comes so far beyond anything imaginable to me, that disproofs of an interstellar probe sound to my ears like: “The steam-driven abacus will never replace the idiot savant for computing log tables. There is simply not enough coal.” In fairness, my views probably sound like I’m saying in the future we’ll have rainbows and unicorns, and everyone gets a pony. I do tend to feel that predictions about what’s ultimately impossible are more likely to be wrong unless there is a very simple reason for the limit based on physics. But predictions about what is ultimately possible can also be wrong, and predictions about what will actually happen are almost always wrong.

    The timeline is also very hard to guess. There might be very little incentive in the next thousand years even to do much besides scientific observation far beyond earth’s orbit. There is a lot more incentive for now to figure out how to get the most out of earth-based materials than merely acquire possession of more unstructured matter.

  156. a_ray_in_dilbert_space says

    PaulBC: ‘And could this be explained by the fact that we have a lot left to learn about interstellar travel, and some of these problems might be solved given another thousand, or maybe a million more years of technological development? ‘
    Basically…no. Not only are we never going to travel the galaxy. I seriously doubt we will ever leave Earth in any significant numbers. Even if we survive the environmental hell we are creating on this planet, space is quite simply too hostile to life for long-term survival therein.

    Space exploration is my day job, so I’m pretty confident when I say there is a limit to what we can explore.

  157. PaulBC says

    a_ray_in_dilbert_space #160

    Space exploration is my day job, so I’m pretty confident when I say there is a limit to what we can explore.

    As a former academic computer scientist (now software engineer) I’m not confident enough to say there is no polynomial time algorithm for the traveling salesman problem (though I would be astounded if there were).

    Proofs of infeasibility are very rare and usually limited in scope (false analogy between mathematical proof and empirical science, I know, but it may explain why pronouncements of limits strike me as a red flag).

    In context, I was referring to your statement about a 15 year lifetime for a particular component. Are you really going to tell me that you can set a limit within two orders of magnitude for the lifetime of such a component or its equivalent using unspecified future technology? That is a remarkable degree of confidence, and I’m curious to see your basis for belief.

    I also agree that the putative interstellar craft would probably need some form of self-repair, but I’m picturing an active payload about the size of a kitchen appliance, mostly inert in transit, heavily shielded. It could travel as slow as 1% lightspeed and still fit the parameters of Fermi’s paradox. It would not need to use active propulsion for much of its trip.

    Obviously there would be no biological lifeforms on board. I’ll accept that technology to produce such a thing won’t be coming around any time soon, but I don’t see how you rule out what is possible in a million years of sustained technological development.

  158. Rob Grigjanis says

    Amphiox @137:

    But they [ants] are unlikely to recognize that these phenomena are due to the activities of a cooperative, technological intelligence far in advanced of themselves.

    Yes, that’s why they’re still debating the Formi paradox.

  159. a_ray_in_dilbert_space says

    PaulBC,
    This has nothing to do with proof. It’s physics–specifically the physics of failure and of radiation in matter–and the emptiness of interstellar space. After about 10-100 Mrad(in Silicon) of radiation dose, plastics and other polymers turn to powder. After 10s of Grad(Si), even metals start to lose integrity. You can certainly give up using any sort of advanced technology–these rely on control of matter at the near-atomic level, and that gets hosed by radiation and failure mechanisms on timescales of years. So you are left with a need for a repairable system–but with what is the system to repair itself when interstellar space has a density of about 1 atom per cubic centimeter? I prefer to confine my speculations to future developments that would not require the violation of at least one well established law of physics.

  160. Rolan le Gargéac says

    Erlend Meyer @ 49

    And beaming signals to all corners of the galaxy would be an undertaking of astronomical proportions.

    Groan

  161. PaulBC says

    a_ray_in_dilbert_space #163:
    Thanks for the clarification. I think I understand your position better and I also agree that the infeasibility of interstellar travel is one possible explanation for Fermi’s paradox. (and said as much as early as my post #128)

    I still think you have made a lot of unstated assumptions about how such a probe would be implemented, how fast it would have to travel, and what the payload would be.

    First off, speed: Doing a little bit of web searching/back of the envelope calculation, I feel safe in saying that even the Voyager 1 probe is moving along at faster than 1/20000 c, and a replicator at that speed could propagate copies across the galaxy in 200 million years. It’s possible that some other planet in the galaxy could have a 200 million year head start on earth in the appearance of intelligent life; earth already had dinosaurs. My point is not that we should be expecting slow-moving von Neumann probes any day now, but that you don’t need futuristic propulsion technology to invoke the time scales needed for Fermi’s paradox.

    Shielding: I’ll accept your expertise on this, but you seem to assuming the active part of the probe is exposed and not embedded deep in an asteroid-sized lump of inert matter. Granted, the more mass, the more energy needed, but there is definitely need for shielding, so it probably won’t be a lightweight spacecraft like Voyager. The active part ideally won’t need much self-repair, but it should be able to use some surrounding material that is also shielded by the exterior layer. When it arrives safely in another star system, it would begin by converting the inner material of the probe into a much larger craft. The highly damaged, irradiated external layer would be discarded with great caution as hazardous waste.

    So what is the maximum speed attainable by propelling an asteroid-size lump chemically, slingshotting it like Voyager and sending it off without propulsion into interstellar space? I don’t know the answer to that, but my rough understanding of Newtonian physics suggests that the slingshot will work as well on an asteroid as a smaller probe, and whatever energy is expended from the orbits of planets used as a slingshot will be small enough that the trick can be done a few times without any serious repercussions to life in the solar system (and it only needs to be done a few times per star system).

    Payload: I said it already, but repeating for emphasis. Obviously, sending biological people off in a spacecraft with life support for 100 years or more is a very, very unlikely scenario. The payload would be some form of self-replicating technology. The actual hardware protected in transit would only need to replicate in a controlled environment, but it would use the surrounding material to build a robust replicator that would use material available where it arrives. Information loss doesn’t strike me as a serious objection (compared to hardware malfunction) but it is also the easiest part to solve because the bulk of the information needed by replicators can be sent at the speed of light (e.g. as a focused laser signal received on arrival).

    So… yeah, rainbows and unicorns and a pony for everybody, but it doesn’t strike me as all that implausible. The main “magic” is the assumption of compact replicators (i.e. nanotechnology). I can’t claim that such a thing is definitely possible, but I don’t see the obvious counterargument either.

  162. PaulBC says

    me #165

    OOPS, off by an order of magnitude

    First off, speed: Doing a little bit of web searching/back of the envelope calculation, I feel safe in saying that even the Voyager 1 probe is moving along at faster than 1/20000 c, and a replicator at that speed could propagate copies across the galaxy in 200 million years.

    I guess that would actually be 2 billion years, which makes a lot of my argument specious. A 2 billion year head start is not as believable. So the slowest reasonable speed would probably need to be about 10 times as fast as Voyager 1. Still, a lot slower than most starship enthusiasts would like to assume.

  163. Rolan le Gargéac says

    madscientist @ 71

    Even mere 1-way communication is unlikely; we need to create beacons as bright as the stars and hope that after thousands or even millions of years someone can somehow detect the signal.

    Er, what about technological advances ? Quantum entanglement perhaps ?
    Also, why could we not gene-tailor variants of pan narrans for different ecosystems, environments ?

  164. a_ray_in_dilbert_space says

    PaulBC,
    Have you done the math on how much energy would be required to accelerate an asteroid-sized chunk of matter to a significant fraction of the speed of light? Have you given any thought to how you’d get rid of all that waste heat in the vacuum of space? And you do realize that your radiation dose will increase roughly linearly with time, right? And that as you slow down particles in matter they give off bremsstrahlung photons, which, essentially, you cannot shield? Over millions or even thousands of years, the dose from even these feeble sources will add to the point where they cease to operate.

    And of course, this doesn’t even start to consider other wear-out mechanisms. A colleague of mine has a sign on his door: “Failure is not an option. It is a standard feature.” Everything fails, and in a hostile environment like space, it happens a lot faster.

    And no, I don’t think this is the answer to the Fermi Paradox. Radio contact would still be possible. The more likely answers to the Fermi Paradox are:

    1)They just don’t want to bother with us out here in the exurbs of the galaxy, preferring to concentrate on the galactic center, where probability of making contact is greater.
    2)Any species that attains sufficient technology to modify its environment on a planetary scale winds up killing itself off.

  165. Rolan le Gargéac says

    tacitus @ 91

    Aliens won’t be looking for technological beacons. The planets themselves are the beacons.

    That’s very clever, oi wish oi’d fort of that ! Oi bloody should have, oi’s a git.

  166. Rolan le Gargéac says

    Marcus Ranum @ 93

    Lifeboat scenarios are weird. There are, what, trillions of pounds of living humans on earth; they will not ever leave the gravity well. Escape is not an option. Sending a tiny few off planet might be, but humand off earth are – something else, and humans that leave billions of their kind behind to die are something even different. The very action of getting into the lifeboat changes you, any humans that escape earth are (at the very least) antisocial and have abandoned their humanity.

    Oh right, the boat is sinking so tie the childrens to the mast we should all stick together ! You’re a very sick puppy Marcus.

  167. Rolan le Gargéac says

    Amphiox @ 112

    Take an average icy KBO. Hollow out an interior space…..

    Oh yes ! Lovely ! And, and have extended families of about 150 members (for the ideal village ) in a, er, a ‘pod’. Have 5 pods in a cluster, because in a group of five one will always betray the others and this will engender some interesting politics (have as many clusters as you can fit on the KBOship) and hence give the bastards something to do while their degenerate progeny bleat “are we there yet?”

  168. says

    And then film the whole thing and beam it back to earth. Then use the advertising revenue to fund the next round of pods.

  169. PaulBC says

    a_ray_in_dilbert_space #168

    Have you done the math on how much energy would be required to accelerate an asteroid-sized chunk of matter to a significant fraction of the speed of light?

    I’m not sure what you count as “significant”. I’d accept something like 1/1000 c as a reasonable minimum speed for purposes of Fermi’s paradox. Then a planet with a head start of 100 million years should have been able to reach us with a self-replicating probe.

    Have I done the math? Short answer, no, but we can stick to classical physics at these speeds. A typical planetary orbital velocity (e.g. Jupiter’s) is around 1/23000 c, which has the same classical kinetic energy as a body around 529 (23*23) times less massive moving at 1/1000 c, and an asteroid is far less massive than that. Obviously all that energy isn’t immediately available for a gravity assist of an asteroid, but I think I have some perspective on the amount of energy needed.

    You wouldn’t have a chance of doing it with chemical propellants, and most other suggestions are vaporware for now. I don’t know your take on solar sails or something like (SF author) Robert Forward’s suggestion of a light sail powered by lasers fixed at the source. Back in the day, he was considered a credible source of ideas about interstellar flight (and had physics and engineering background). But I think I’m asking for something pretty modest here.

    I just want to send an asteroid out of the solar system at about 1/1000 the speed of light. I don’t need propulsion for most of the trip. I don’t care much about where it ends up, though I would like it to reach some other star system in 10000 years or so. We can disagree on whether it is capable of doing anything when it gets there.

  170. Amphiox says

    Oh yes ! Lovely ! And, and have extended families of about 150 members (for the ideal village ) in a, er, a ‘pod’. Have 5 pods in a cluster, because in a group of five one will always betray the others and this will engender some interesting politics (have as many clusters as you can fit on the KBOship) and hence give the bastards something to do while their degenerate progeny bleat “are we there yet?”

    Some will surely fail, and internal conflict is one likely mode of failure. The key is that you never send one. If Britain had stopped after Jamestown failed, there might not be a United States today (for better or worse).

    So you are left with a need for a repairable system–but with what is the system to repair itself when interstellar space has a density of about 1 atom per cubic centimeter?

    Using a KBO/Asteroid based craft means you are carrying all the raw materials you need for continuous repair with you.

  171. Rolan le Gargéac says

    Alex SL @ 155

    I have no idea why anybody would ever have an incentive to send out replicators; what good does it do you? It is a bit like scratching “I was here” into a bus seat


    And on the pedestal these words appear:
    “My name is Ozymandias, king of kings:
    Look on my works, ye Mighty, and despair!”

  172. Rob Grigjanis says

    PaulBC @173:

    Obviously all that energy isn’t immediately available for a gravity assist of an asteroid

    The asteroid’s mass being negligible wrt to Jupiter’s, the maximum speed it can get from a slingshot is

    v + 2V

    where v is the asteroid’s initial speed at Jupiter approach, and V is Jupiter’s orbital speed, both speeds relative to the fixed solar frame. Enough to escape the sun, with v plus a few km/sec to spare. In other words, what you get from the slingshot is only about 1/40,000 c after subtracting the escape velocity at Jupiter, plus what you provide (v).

  173. David Marjanović says

    macrobes (Is this a word? If not, it should be!)

    It is! It’s rare, but I’ve seen it used before.

  174. Rolan le Gargéac says

    Amphiox @ 157

    There is little incentive right now for human civilization to venture into space on a scale that would require a large output of cooperative societal engagement.

    Oligarchic Dominance and
    it’s already happening.

  175. Amphiox says

    I have no idea why anybody would ever have an incentive to send out replicators; what good does it do you? It is a bit like scratching “I was here” into a bus seat

    And yet people do scratch “I was here” on bus seats.

    If the technology required to send a small replicator, which would be much cheaper than a full on mission with squishy boologicals ever dropped to the point where private individuals can afford it, someone is going to do it on vanity alone.

    (We almost have the technology to do a primitive version of that right now. Make a radiation shielded canister, or even just a porous rock, inoculate it with bacterial spores, and launch it on a solar system escape trajectory like Voyager probes, aimed at some star system of your choice. It would cost less than the Voyager missions themselves, and is almost in the range of what super rich eccentric could afford to do right now.)

  176. a_ray_in_dilbert_space says

    PaulBC, solar sails only work where there is a sun–sat the first 0.0001% of your trip, and a solar sail would have to be ginormous to accelerate an asteroid. Believe me, it is not that I haven’t looked at this problem. Rather it is because I have that I am so pessimistic. It’s not a matter of inventing technology. It’s a matter of defying physics.

  177. Rolan le Gargéac says

    a_ray_in_dilbert_space @ 160

    Space exploration is my day job, so I’m pretty confident when I say there is a limit to what we can explore.

    Insert your own phrase here , MUch?

    It’s the new AngryAstronomers !

  178. PaulBC says

    Rob Grigjanis #176

    Enough to escape the sun, with v plus a few km/sec to spare. In other words, what you get from the slingshot is only about 1/40,000 c after subtracting the escape velocity at Jupiter, plus what you provide (v).

    Yeah, I concede that a slingshot won’t get you to 1/1000 c. But I’m not sure where you are getting 1/40000 c. Shouldn’t 2V be closer to 1/12000 c? Maybe I’m not following one of your steps.

    In theory, could you do a cascade of slingshots? Slingshot a big mass around Jupiter, then slingshot a smaller mass around that, etc.? Doubling each time. I’m not claiming there is any reasonable way to do it, just wondering if there is an actual limit.

    I can imagine having a cascade of colliding hockey pucks, diminishing in mass by a constant factor at each step. Hockey puck 0 (traveling at v) hits hockey puck 1 sending it off at nearly 2v, which hits hockey puck 2, sending it off at 4v. Ultimately hockey puck k (which must be very light at this point) is sent off at 2^k v. That is easier for me to analyze than orbital mechanics, though I realize you can’t bounce planets like hockey pucks. But it seems like for k>=4, you could get speeds > 1/1000 c.

    I’m also thinking there are more reasonable ways to go about it. It’s admittedly a tall order (shoot a small asteroid at 1/1000 c into interstellar space) but doesn’t seem like something that violates any reasonable assumptions about available energy.

  179. PaulBC says

    I wrote:

    then slingshot a smaller mass around that, etc.

    Eh, never mind. I do realize that moving a planetary mass into the right position is probably a lot harder than just propelling the asteroid, so this is a silly suggestion, which I retract.

    There are suggestions of slingshotting around stars, in which V is the speed of the star traveling around the galactic center, e.g. http://arxiv.org/abs/1307.1648 but the maneuvers used for something like Voyager would not be sufficient to attain a reasonable minimum speed.

  180. Rob Grigjanis says

    PaulBC @183:

    Shouldn’t 2V be closer to 1/12000 c?

    Yes, and it’s about 26 km/sec. But you’ll lose some of that, because the escape velocity at Jupiter’s distance is about 18.5 km/sec. To find out what you’ve got left in interstellar space, you can use conservation of energy. The number I gave (1/40,000) was a not very good guess. A quick calculation says it’s actually more like 1/17,000 if v=0. Anyway, the point remains; a slingshot isn’t going to help getting 1/1000 c.

  181. aziraphale says

    There is at least one reason for sending out replicators if you’re sufficiently paranoid. That is, to destroy any other technological civilisation before it can become a threat to you. This was the idea of Greg Bear’s “The Forge Of God”, one of my favourite hard SF novels. And also, it occurs to me, another possible solution to the Fermi paradox.

  182. Rob Grigjanis says

    aziraphale @186:

    That is, to destroy any other technological civilisation before it can become a threat to you.

    Shades of Fred Saberhagen’s Berserker books/stories.

  183. says

    Why is it so hard for us to imagine that humans might be the ‘first’ ???

    A Ray – i have read all your posts with great interest. However, I am not convinced by the nay-saying. I understand that there are problems with radiation and what not but I am not hearing from you that there is a principle of physics violated by instellar travel, just that it is very difficult and expensive. These are significant engineering problems to be sure but I should not project our current technological backwardness as a limitation to what future generations might achieve. A mere 114 years ago, most people could not conceive heavier than air flight much less the idea of man landing on the moon! Yet there it is. I do not mean to minimize the magnitude of the challenge of interstellar flight but clearly there is no law of physics that precludes the possibility. That which is not impossible becomes highly probable given enough time.

    Just sayin’ …

  184. says

    That is, to destroy any other technological civilisation before it can become a threat to you.

    Makes for good scifi, but I suspect that most space-faring species will quickly discover that the Universe is a very empty place — seen a million solar systems, and you’ve seen ‘em all — and would welcome the discovery of another technological civilization as a long hoped for break from the monotony of barren planets.

    After all, if there is one thing that is sure to be unique about our planet, it’s the history and culture of the species living on it. (Well, that’s two things, but hey.)

  185. Nerd of Redhead, Dances OM Trolls says

    These are significant engineering problems to be sure but I should not project our current technological backwardness as a limitation to what future generations might achieve.

    And why you presupposing without evidence these present real problems will be overcome if no new technology to do so is developed? Why don’t you do a reality check on your “optimism”, and only then complain about reality as it is at the moment? Star Trek is fiction. Never forget that.

    Just saying…..

  186. PaulBC says

    Another random thought… I wonder if a more cost-effective method of interstellar expansion would be some form of “social engineering” (in the computer security sense).

    It only works if there are advanced sentients out there, and they’re also kind of gullible (or susceptible to letting their curiosity get the better of them). And we would also have to invent some kind of Galactic Esperanto.

    But, OK, with these little snags out of the way, we don’t need to send replicators at all, just the plans for replicators. We sell the ETs on how cool it would be to build their own copies of Sol technology, and maybe even clone real live biological humans. The DNA is easy enough to encode and serialize. Probably a high-res 3D scan of a zygote would be a good thing to include too, and little bit of theory about how to piece it all together (smart ETs will fill in the details). Followed of course by all the information needed to reconstruct human culture.

    Then just start beaming it out like crazy in every direction using high powered laser bursts for a few thousand years. The signal actually will travel at c unlike most of the other proposals, making this one of the fastest ways to send the essence of human civilization across the galaxy. Who knows, there might be some takers, and some of them might be nice to their simulated human pets instead of engaging in large scale vivisection.

  187. Amphiox says

    One problem with the laser sail idea, apart from the engineering and physics of it, is also sociological. What happens if the planetbound types decide one day they don’t want to fund the continuing operation of that big honking expensive laser? Or if something happens and they can’t anymore?

  188. says

    @aziraphale #181 – thanks for that wiki link on interstellar travel, that was a very enjoyable read and settles many of the issues our posters were discussing. There was a small paragraph on “nanoprobes” which is how I envision the exploration of nearby star systems will be first carried out. These are nanoscale robots that are easily accelerated to high speeds and because of the much reduced cross-section are relatively immune to radiation and particulate collisions.

    I noticed there were scant references to pB11 fusion as propulsion which may soon need revising.

  189. PaulBC says

    Alex SL #194
    Thanks for the link. In case there’s any question about my views, I don’t take it as given that there will be a significant presence of human technology outside earth in 500 years (*), and I don’t expect large numbers of biological humans out there ever.

    I would answer the survey differently, because astronauts did travel to the moon in my lifetime, but it’s sad to see to the general lack of understanding on the subject (though the misconception that the space shuttle could have gone to the moon is as old as the shuttle itself, and kids who haven’t taking a class in physics may be forgiven for failing to appreciate the difference in energy involved, since it’s counterintuitive).

    (*) The only reason for space technology on a large scale is if it has economic value. The only way it could have economic value initially is if it is entirely autonomous including self-replication, and it is able to extract resources more cheaply than possible on earth and produce and deliver something of economic value to earth. I expect that in 500 years, there will be major advances in automation, but I don’t know that there will be any incentive to move industry off earth. Our need for bulk materials may be reduced substantially and total recycling of some kind may be the norm, aided by technological advances. The limiting factor would be available energy, and fossil fuel won’t get us that far.

    However, Fermi’s paradox applies to intelligent life in advance of ours by maybe tens of millions of years. While I agree that this doesn’t mean they can do magic (Clarke’s law aside), many arguments relevant for the next 500 years of human technology are inapplicable.

  190. aziraphale says

    PaulBC, that makes sad (if possibly true) reading for one who followed the development of the space colony idea in the 1970’s. There was then a credible* program for using lunar materials (aluminium, silicon, titanium) to build large habitats in space, which would justify their cost by building solar power satellites to beam energy to Earth as microwaves.

    If we had followed that path, we might now have:

    A clean source of energy enough for a large fraction of our needs

    A large population living in space, able to support much more research than our current space station and satellites can do

    Technology in place to prevent disastrous asteroid impacts (of which the question is not whether they will happen, but when)

    * Well I thought so, anyway. So did my professor.

    See http://en.wikipedia.org/wiki/Gerard_K._O'Neill

  191. a_ray_in_dilbert_space says

    Allen Everhart,
    Please explain to me how making a space probe small would make it immune to radiation? You would have zero shielding, so you would be exposed to the full radiation environment. You wouldn’t even make it out of the solar system! What is more, how do you plan to propel your nanosat? The smaller the satellite, the less space for propellant. How do you plan to power your satellite? Solar panels aren’t much use beyond Jupiter’s orbit, and radioactive sources are inefficient to begin with and decay exponentially.

    Perhaps you missed my # 168 where I pointed out the inevitability of wear out and radiation degradation for very long missions–and this one would last centuries! The smaller your satellite, the less ability it would have to repair itself, so once your parts wear out, you’re just another piece of space junk. It isn’t that it is “expensive”. It isn’t that it is “difficult”. It is that it is flying in the face of known physics.

    To compare the problem of interstellar space travel to that of heavier than air flight is a joke. There was no physics making heavier than air flight impossible. In fact, the physics had been known since the 17th century! One could specifically answer critics of attempts to fly with physics showing it was possible. No one has provided even the most rudimentary sketch of how you design hardware that lasts thousands of years in a high-radiation environment with no possibility of repair. All they do is airily wave their hands and mumble about Galileo and the Wright Brothers. Your argument is not with me, but with physics, and when you argue with physics, you lose.

  192. PaulBC says

    aziraphale #196
    I had friends in college in the 1980s that were into the L5 society’s vision of the future, which is very similar (spaced-based solar and human settlements in orbit).

    I agree that’s it’s exciting and even potentially achievable in a modest timeframe. My feeling is that it is just answering the wrong question, or at least not the questions that most people are interested in.

    What I wouldn’t have foreseen at the time was ongoing improvements in manufacturing productivity, and no obvious end in sight to the availability of fossil fuel. This cannot continue forever, but I’ve given up predicting when it will end. Immediate limiting factors today are not energy and mineral resources, but the cost of human labor and indeed consumer demand (in the current world economic slump). These aren’t solved by lunar mines and orbiting solar plants.

    From this perspective the L5 vision looks to me like a solution in search of a problem (an awesome solution, sure). Even earth-based solar can supply many times more energy than it does now, and it keeps getting better. We’re not likely to run out of fossil fuel before our use of it destroys the environment. Environmental impact rather than scarcity is the medium-term limiting factor.

    Now if we envision a future of orders of magnitude greater manufacturing capacity, sufficient to build things like interstellar probes, and consistent with a sustainable environment for living things on earth, then it starts to make sense to consider lunar and asteroid mining. But this needs to be considered in economic terms, not merely engineering terms. It won’t happen until enough people are willing to invest in it.

    Occasionally I read about ideas that pique my interest. There was a suggestion that the lunar surface could be covered with low-efficiency solar arrays manufactured in place by robots out of available material. Not sure how much of this is real and how much is vapor, but plans that seem likely to me to work are those that involve a small, autonomous payload that can produce something of more value than the cost of sending it. By contrast, plans involving colonies of human workers in space (like the movie Outland) seem about as likely to me as the space pirate holding a sliderule between his teeth.

  193. PaulBC says

    I wrote:

    What I wouldn’t have foreseen at the time was ongoing improvements in manufacturing productivity

    And back then, I didn’t appreciate the stubborn resistance to spend public funds on pencils for school kids, let alone for orbiting solar plants. Maybe you should try holding a bake sale.

  194. aziraphale says

    PaulBC #198

    Yes, I was a member of the L5 society for a while.

    And yes, the limit to fossil fuel will not be how much there is, but how much we can burn without completely wrecking the climate. It frustrates me beyond measure that we have known the physics of global warming* for over a century and still listen to those who say it’s controversial.

    * http://en.wikipedia.org/wiki/Svante_Arrhenius

  195. PaulBC says

    a_ray_in_dilbert_space #197

    You have made a lot of valid points, and certainly enough to reconsider the feasibility of something like Robert Forward’s “Starwisp” http://en.wikipedia.org/wiki/Starwisp which does seem to go against fundamental physical laws (and makes me wonder why this wasn’t obvious to him).

    One specific question about interstellar radiation. Is your main blocker the radiation exposure to a probe traveling near the speed of light (say 0.1 c or greater) or are you referring to any radiation exposure outside the heliosphere for a probe traveling at any speed? I assume the latter is also quite high, but doesn’t pose the same issues.

    I still think you are missing the distinction between requirements and implementation. Comments like this do nothing to change my view:

    No one has provided even the most rudimentary sketch of how you design hardware that lasts thousands of years in a high-radiation environment with no possibility of repair.

    No one will provide such a sketch, because it does sound impossible. So the hardware will need to be shielded. Point taken. And the shielding will add to its mass. This presents other problems, but it is still a logical fallacy to start with a particular solution to a problem and point out its impossibility as proof that no other solution exists.

    I agree that the issue is nothing like heavier than air flight, or Columbus, or Galileo and have never found these metaphors appealing.

  196. says

    @a_ray: #197 – I can appreciate your critical eye for my perhaps wildly optimistic ideas. However, calling it a joke is a bit harsh.

    I still think the nanobot explorer is a viable option. These are extremely low-mass nanoscale probes. The article in google proposed some self-propulsion method called nanoFET yet to be developed. However, a low-mass object could easily be accelerated to near-light-speed by a space-based accelerator. So no rocket-formula problem. You wouldn’t send just one such probe to a particular destination but MILLIONS. So not just triple redundancy but million-fold redundancy. Ok some are taken out by cosmic rays, maybe even 90%, but some of them make it to their destination – it’s a probability game. Traveling at .995c means that they are exposed to the cosmic rays for only 1/10th the time as a larger slower probe. There is no principle of physics violated by this solution. Big engineering problems, yes, certainly. Nanobot technology is in its infancy. Ground based accelerators are expensive, putting one in space is some orders of magnitude more expensive. However, it certainly could be done by a more advanced civilization. So if we are asking where is everybody? Maybe we should be asking ourselves if we have looked in the right places. These things could be whizzing by us in outerspace, keeping surveillance on our solar system, and we would never know.

  197. Rob Grigjanis says

    Allen @202:

    Traveling at .995c means that they are exposed to the cosmic rays for only 1/10th the time as a larger slower probe.

    At that speed, interstellar gas, which is several orders of magnitude denser than cosmic rays, becomes hard radiation. I read somewhere (I can dig it up if necessary) that it would be comparable to being inside a nuclear reactor’s core.

  198. a_ray_in_dilbert_space says

    Rob, Indeed.

    Shall we do the math for Allen? At 0.995c, a low-energy atom will have a relativistic energy of 10x its rest mass–that’s roughly 9 GeV per nucleon. First the good news–at that energy, most particles will be minimum ionizing and will interact only weakly with matter as they pass through it. Let us give Allen the benefit of the doubt and assume he can launch a probe with a cross section of a square micron–though I cannot imagine how such a probe could do anything useful. The density of interstellar schmutz is about 1 atom per cubic cc. That’s a flux of nearly 300 particles per second through our probe. If we take 1000 years to reach our destination, that’s about 1E13 particles bombarding our intrepid little probe. If one in a million interact and produce secondary ions…well, our probe will be very unhappy. Multiple scattering along might bring your probe to a dead stop!

    Allen, I would recommend that you map out a mission for your probe. Just lay out what you want it to do. Do you want it to communicate with Earth? Do you want it to be able to maintain a trajectory. Do you want it to transport a message? What is its purpose? Now ask yourself how large it would have to be to achieve these goals. I think you’ll find that it will have to be a whole helluva lot larger than “nano”. Technology is amazing, but it isn’t magic.

  199. Nick Gotts says

    No idea what the time to evolve has to do with the probability of it happening elsewhere. – Alex SL@134

    Really? I would have thought it obvious: if it takes that long, it’s probably difficult, and probably involves unlikely events.

  200. Nick Gotts says

    If you go with 1% of light speed you need hundreds of years even to the next star, and there goes all your oxygen. And it is reasonable to assume that you need to travel much further than to the next star before you find a habitable planet. – Alex SL@134

    *sigh*

    It would be helpful if you actually paid some attention to what I’m saying. I’m not takking about sending organisms at all. No oxygen required. Nor cryonics.

  201. says

    @a_ray #204 – I am seriously doubting your credentials as a space expert or whatever you were calling yourself.

    For example, at .995c such a nanobot would only experience a transit time of about 4 months to Alpha Centauri due to Space Contraction – an effect of relativistic speeds that has been know for over a century. Perhaps you need to catch up to the 20th century????

  202. Nick Gotts says

    the alternative of us being unique seems like a very arrogant and implausible explanation. – Alex SL@147

    Why is it implausible? And even if it is “arrogant” (it isn’t), why would that have any bearing whatsoever on its feasibility?

  203. Nerd of Redhead, Dances OM Trolls says

    For example, at .995c such a nanobot would only experience a transit time of about 4 months to Alpha Centauri due to Space Contraction – an effect of relativistic speeds that has been know for over a century. Perhaps you need to catch up to the 20th century????

    And this has to do with how much time the nanobot spends in the harsh radiation of interstellar space, which is 4 years?

  204. Nick Gotts says

    Alex SL@155,

    I have no idea why anybody would ever have an incentive to send out replicators; what good does it do you?

    Expands the knowledge and resources available to your civilization, and increases long-term security against natural disaster. I have no idea why you were unable to come up with this answer yourself.

    Third, I have repeatedly seen the claim in this thread that the solar system has a lot of resources that we could mine. What are those resources? If we only had enough energy we would probably never need more metal or water than just what we find on earth because given enough energy we can clean and recycle everything. Energy is the main problem.

    So let’s start with energy: satellite solar power is one very obvious possibility: the sun shines all the time up there. Helium is another, as are various metals (current plans for asteroid mining, which admittedly are probably very premature, focus on gold and platinum). But if our civilization survives our current problems (a very big if), that of a few centuries may well consist mainly of intelligent machines, which don’t need to be built to require the same kind of complex habitat as human beings.

  205. Nick Gotts says

    But we will not find any additional oil, coal or gas on the other planets or moons. – Alex SL@155

    I missed this amusing gaffe, because I doubt the point is really all that relevant, but are you not aware that there are seas of hydrocarbons on Titan, and many asteroids are largely made of them?

  206. a_ray_in_dilbert_space says

    Allen Everhart,
    Sigh!

    OK, let me walk you through it.
    1) Alpha Centauri is NOT interesting from the point of view of space exploration as it has no planets.
    2)Time dilation does not affect the total fluence of particles through the “nanosat”. A 4 year voyage still exposes you to 4E10 or more particles–probably more since you will be spending more time near stars.
    3)You do realize, don’t you, that when folks are talking about nanosats, they are talking about objects that measure inches across? They are NOT nanometer scale.
    4)Do you understand how a particle accelerator works? Do you really think you could use one to accelerate a macroscopic object to near the speed of light?

    You seem very resistant to thinking this through systematically. Start with mission requirements. What are they? Where do you want to send your probes? What do you want them to do once they get there? En route? As to your snark, perhaps you can tell me precisely why time dilation is relevant? Granted, it would help you somewhat with wearout (which is time dependent)–but it has no bearing on the particle fluence you’d encounter. Again, technology is not magic. You may realize that if you bother to understand it.

  207. PaulBC says

    Allen Everhart #202

    You wouldn’t send just one such probe to a particular destination but MILLIONS. So not just triple redundancy but million-fold redundancy.

    Not all redundancies are created equal.

    Let’s start with useful redundancy. Say I want to send one bit of data across a transmission line so noisy that with 99% probability, the bit received is indistinguishable from random (it has a 50% chance of being 0 or 1, independent of how it was set before transmission). But with 1% probability, the bit is actually equal to its initial value. In that case, a single bit is too close to random to be very useful, but if you send enough of them, the presence of even 1% non-random bits will shift the distribution enough to determine the intended value with high probability (without doing the math, I think 100 bits won’t give you high confidence, but 1000 will).

    Now let’s say I want to drop a raw egg without any protection from a 10m tower onto a concrete slab and have it land intact. I am guessing that no amount of redundancy is going to help you here. Maybe there is some very low-probability event of being safely decelerated by several sparrows in flight on the way down, but simply saying “million-fold redundancy” doesn’t settle the matter. You need some statistical model for concluding that the redundancy helps.

    #207

    For example, at .995c such a nanobot

    I don’t believe relativity helps here. I’m inclined is to avoid speeds in this range when discussing self-replicating probes, since it makes the analysis harder, makes the energy requirements strain plausibility, and is not material to the Fermi’s question “Where are they?” assuming “they” had a head start of up to 100 million years.

    a_ray and Rob’s point is that any atom between you and your destination hits you like hard radiation at this speed. I don’t see a way around that. I don’t think time dilation will do more than slightly slow down the harmful effects. Moreover, to get a time dilation of 1000-fold, say, you need a mass increase by 1000-fold, and this mass is that of the additional energy. Sending a large, heavily shield probe at much more modest speed seems a lot more plausible to me.

    I also assume that while aliens much smarter than us cannot do magic, they might do something that looks like magic to our current limited understanding. The problem is that we can’t predict what that would be, and it’s useful to have some proof of concept that fits current understanding. I’m more convinced than ever that nanoprobes at relativistic speeds are a non-starter in this context, though I don’t see how this rules out the feasibility of covering the galaxy with self-replicating probes.

  208. PaulBC says

    I wrote:

    (without doing the math, I think 100 bits won’t give you high confidence, but 1000 will).

    Uh, maybe I should do the math. Given that only 10 of the bits are expected to be transmitted intact, it’s still not very reliable given that any series of 10 random bits has a 1/1024 chance (at least) of shifting the distribution in the wrong direction. However, you can eventually get a reliable signal with enough redundancy.

  209. says

    @a_ray: (212)

    OMG you are such a bully. Stop it.

    The point of what I was saying was not to suggest that humans take on such project right this instant with our underdeveloped nanotechnology but rather that given a civilization that is say, 1000 years(100?, 10^6?), further down the road of technology COULD THEY DO IT? If that is conceivable then perhaps we need to expand the question of “Why aren’t here?” That is to say the “here” part might anywhere in our solar system and the “they” part might be so small as to be, perhaps, undetectable with current Earth technology. And YES I am absolutely talking about an object that has a cross-section of a few tens of nanometers NOT MICROMETERS – THAT IS YOUR INTERPRATATION of what I meant. Nano means Nano not Micro.

    Furthermore, I didn’t say time dilation – reread the post with your glasses on. I said SPACE CONTRACTION (aka Lorentz Contraction) The effect that such nanoprobes would experience FROM THEIR REFERENCE FRAME is one of length contraction. And YES that does mean they will experience FAR LESS RADIATION EXPOSURE during transit.

    @nerd #209

    And this has to do with how much time the nanobot spends in the harsh radiation of interstellar space, which is 4 years?

    From an Earth-based point of reference it will take the probes 4 years to traverse almost 4 lightyears of space. However, from the nanobots perspective, traveling at .995c means they will experience about 1/10th of that time in transit AND THAT IS THE PERSPECTIVE THAT IS IMPORTANT when considering collisions and how many the nanobots might experience.

  210. David Marjanović says

    Your argument is not with me, but with physics, and when you argue with physics, you lose.

    The Minus-First Law of Thermodynamics.

    Traveling at .995c means that they are exposed to the cosmic rays for only 1/10th the time as a larger slower probe.

    Just to pile on: Traveling at 0.995 c means they slam into the exact same number of interstellar atoms than they’d encounter at any other speed. They just hit them in closer succession – and harder.

    I really recommend against slamming into a hydrogen atom at 0.995 c. Don’t try it at home.

  211. says

    @david #216

    Just to pile on: Traveling at 0.995 c means they slam into the exact same number of interstellar atoms than they’d encounter at any other speed. They just hit them in closer succession – and harder.

    Yeah ok, I’m picking up what you are putting down. Space contraction just increases the density of particles. I did miss that, my bad. However, consider this, ahead of the nanobot probes you launch of bunch of dumb atoms to run interference and clear the path – a kind of ablation shield. So if a dimwit like me could think of that could you conceive that a civilization with a million year headstart already has??

  212. says

    @PaulBC #213

    I don’t believe relativity helps here. I’m inclined is to avoid speeds in this range when discussing self-replicating probes, since it makes the analysis harder, makes the energy requirements strain plausibility, and is not material to the Fermi’s question “Where are they?” assuming “they” had a head start of up to 100 million years.

    My bad. I did get away from the topic self-replicating probes and moved on the simpler idea of nanoprobes that send back information without stopping to replicate. I was envisioning that perhaps our aliens would want a better idea of where they were going before committing huge resources to going there.

  213. PaulBC says

    Allen Everhart #215 to a_ray

    OMG you are such a bully. Stop it.

    I’m not going to make any assumptions about a_ray’s motivation, but I think the following is a reasonable summary of his argument against interstellar travel (in the most general sense, including probes).

    (1) Close to the speed of light, your probe will be hit by too much hard radiation to survive.
    (2) Much slower than the speed of light, the time scales are too long for your equipment to continue to function.

    I accept (1) as an argument from physical constraints. (2) still strikes me as an engineering limit. Some form of repair in transit may be necessary (though I’m not convinced that you cannot keep most systems well shielded and inert for 1000 years; some kind of fault tolerant bootstrap is also needed).

    My “rudimentary sketch” of how this works is that most of the mass of the probe is shielding and much of that can be used as initial construction material on arrival. The properties of this material are highly controlled at launch, unlike the matter available at the destination, so the initial replicator may be fairly fragile and specialized. It uses this matter to build the robust replicator, which can use locally available matter and energy. It may carry its information along with it or receive it as a transmission after it arrives, with significant differences in propagation time.

    There may be an argument (2a) but I haven’t had a clear answer, namely that speeds now attainable, such as 1/20000 c for Voyager probes are too slow for Fermi’s paradox, and accelerating a craft heavy enough to have sufficient shielding to even 1/1000 c is not feasible.

    I have mostly been stuck on (2a) because I don’t see an immediate resolution without invoking now non-existent propulsion technology. However, I really doubt it is a fundamental limitation.

  214. PaulBC says

    I wrote

    with significant differences in propagation time.

    WITHOUT significant differences

  215. Rob Grigjanis says

    Allen @218: You might like this paper, which discusses shielding issues at relativistic speeds.

    According to the paper, the local ionized component of interstellar gas is 0.1 cm^-3. At .995c, length contraction increases that to 1 cm^-3, at the front of the traveller. That’s 10^9 times as much as cosmic ray intensity at low speeds. And the cosmic ray flux at the bow would increase dramatically as well.

  216. unclefrogy says

    I think that you could drop eggs of a tower one at a time and eventually have one land intact in a large puddle/pile of broken eggs
    So if you sent nano probes off by the millions in some direction or other even with some thing sent ahead to clear the way I do not see how that would help.
    Everything is moving and it is not all moving in the same direction is it? It is not all as small as hydrogen either some small fraction is larger stuff isn’t it?
    What happens to the stuff that you send ahead of the probe when it collides with some of the intervening matter does not it just become more intervening matter? How close would the probes have to be to each other to avoid any new fresh matter moving into the path?
    Why would anyone upon encountering some self replicating probe coming into their area not view it as a hostile act or at least as a hostile organism that would need to be contained at the least if not destroyed at once.

    uncle frogy

  217. a_ray_in_dilbert_space says

    PaulBC: “(2) [parts remaining functional] still strikes me as an engineering limit.”

    Actually, no. Wearout mechanisms are pretty much unavoidable. You can slow them down, but you sacrifice performance to do so. And if you make one better, you often make others worse.

    Allen Everhart: “Nano means Nano not Micro.”

    Sorry. I gave you too much credit. Technically, nano tends to refer to things under 0.1 microns. I presumed that you would understand that a cubic nanometer would only contain a few thousand atoms. Now, dude, really, I ask you, what do you think you will be able to accomplish with a probe that size? You do realize that the smallest feature sizes in electronics are on the order of 20 nm now, right? And you do realize that even in their wildest dreams, electronics designers have not envisioned anything with feature sizes less than about 5 nm? I’m really curious, do you really think microelectronics fabs are just full of guys wearing robes and waving wands?

    OK, dude, let’s play your game. Let’s assume your probes are 1 cubic nm. You are still going to have on the order of 10000 nuclei slam into them, and in an elastic collision, you will impart about 6% of the incoming particle’s momentum to the struck nucleus. That is gonna make one helluva exit wound!

    Really, Allen, I am curious why you are so resistant to thinking through this systematically.

    As to the Fermi Paradox, I’ve already said that the difficulty of space travel doesn’t explain it, as any advanced species would surely have mastered radio and probably laser communications. As I said before, I think the most likely answer is
    1)They aren’t interested in us out here on the edge of the Galaxy. Much higher likelihood of establishing contact with planets near the center.
    2)They wipe themselves out when their technology becomes sufficiently advanced to screw things up on a planetary scale.

    Based on human experience, 2) seems the most likely.

  218. a_ray_in_dilbert_space says

    Rob Grigjanis,
    Electrons are stripped off pretty quickly once a particle collides with matter, so neutral atoms would also be ionizing.

  219. PaulBC says

    a_ray_in_dilbert_space #224

    As to the Fermi Paradox, I’ve already said that the difficulty of space travel doesn’t explain it, as any advanced species would surely have mastered radio and probably laser communications.

    Fermi’s question wasn’t why won’t we ever be able to detect them if we try, but why aren’t they here already (in 1950)? I agree that pointing a laser spotlight in every direction announcing our presence is easier than sending out a probe, and it’s reasonable to assume that someone in the galaxy might notice it if they were looking for such a signal. So that’s a different paradox (but I don’t think we’ve looked hard enough yet to make it paradoxical).

    However in 1950 when Fermi proposed the paradox, even a wildly active galactic internet would not have been detected on earth. So if there was a hard barrier to getting any functioning machinery between stars, that would indeed explain away the paradox.

  220. says

    To claim that life must be unique is an absurd proposition.
    To claim that life must exist elsewhere is equally absurd.

    Why?

    How many instances are there of observed solar systems with life?

    1.

    N = 1

    df = 0.

    Models and predictions are impossible when df = 0. Claims to the contrary are structurally fallacious.

  221. Jason Dick says

    It’s not quite that simple, Bryan Maloney.

    For one, life appears to have arisen on Earth pretty much immediately after the Earth cooled enough for life to survive. This would seem to indicate that life is very likely to arise whenever the right conditions are available.

    So the question then becomes: how frequently do the conditions for life occur? That is unknown, but we do know by now that planets are extremely common: most star systems have them. In a few years, we’ll probably have a good handle on how many star systems have rocky planets. In a decade or two, we’ll probably have a good handle on how many star systems have rocky planets in the habitable zone.

  222. Rolan le Gargéac says

    PaulBC @ 191

    We sell the ETs on how cool it would be to build their own copies of Sol technology, and maybe even clone real live biological humans.

    So, now we’re viruses ? Let’s hope we taste good.

  223. PaulBC says

    #228 Jason Dick

    For one, life appears to have arisen on Earth pretty much immediately after the Earth cooled enough for life to survive. This would seem to indicate that life is very likely to arise whenever the right conditions are available.

    It could also mean that life is only likely to arise when a planet is fairly new, so beyond a certain window of opportunity, the planet has a much lower probability of ever having life. I.e., maybe some other chemical reaction takes over than precludes the development of life.

    I’m not saying I believe this, but I think it’s a gap in your logic, essentially mistaking conditional probability for absolute probability.

  224. Jason Dick says

    While true strictly speaking, I don’t think that’s a possibility that is even remotely likely, as most anything that makes the formation of life impossible is also likely to exterminate existing life.

  225. Amphiox says

    1)They aren’t interested in us out here on the edge of the Galaxy. Much higher likelihood of establishing contact with planets near the center.
    2)They wipe themselves out when their technology becomes sufficiently advanced to screw things up on a planetary scale.

    Based on human experience, 2) seems the most likely.

    Human experience has not ever produced a single instance of 2). You cannot say that human experience makes “2 seem more likely”.

    Actual human experience actually suggests that the species as a whole is very resilient. Individual civilizations fall with regularity. New ones rise to take their place, equally and eventually surpassing their achievements. Technological achievements are often lost and forgotten, but they are not infrequently rediscovered, or a functional equivalent arises to replace them.

    The pattern for detectable civilizations over time really isn’t likely to be one of nothing (not technologically advanced enough to detect) to on to off (species goes extinct) as a single sequence. It is much more likely to be a flicker of on-off-on-off-on-off as the species experiences cycles of growth, decline, collapse, and recovery.

  226. PaulBC says

    Jason Dick #231
    Just to play devil’s advocate here, maybe the atmospheric changes caused by the development of self-replicating molecules prevent some kind of runaway greenhouse effect leading something closer to Venus-like conditions. It would be a kind of hysteresis. The reason this would not exterminate existing life is because the conditions would never arise in the first place.

    I’m not saying this is even remotely possible. I just don’t see how to rule it out. The other thing is life may only be likely in a very narrow range of conditions, and we just don’t how frequent this is. I would be reluctant to say that even a planet in an identical orbit with the same size and chemical makeup of earth would be likely to produce life. There may be other non-life equilibria that are more frequent.

    If we found any evidence of life past or present in the solar system or even much simpler self-replicating molecules, I’d revise my views on this.

  227. PaulBC says

    “If we found any evidence of life past or present in the solar system” (other than terrestrial life)

  228. Jason Dick says

    PaulBC #233
    Life on Earth didn’t significantly impact the makeup of the Earth’s atmosphere until the Great Oxygen Catastrophe, which was about 1.5 billion years after life began.

  229. a_ray_in_dilbert_space says

    Amphiox: “Actual human experience actually suggests that the species as a whole is very resilient. ”

    Compared to a colony of yeast in a bottle of beer, I would agree. But hominids have only been around for a couple of million years. Human civilization for only a few thousand. On a timescale that would be necessary for an intelligent critter to develop technology sufficient to traverse interstellar space, that is a blink of an eye. And our intelligence has been applied more toward lying to ourselves than anything else.

    Without question, the most critical technology for interstellar space travel is sustainability–and we haven’t even made the first steps toward that, nor do we seem capable of thinking in those terms. Intelligence may not be the evolutionary advantage we think it is. Ants have done better than us without even having a central nervous system to speak of.

  230. says

    a_ray: #224

    Now, dude, really

    I am not an 18year old. Condescension doesn’t help your argument.

    I’m really curious, do you really think microelectronics fabs are just full of guys wearing robes and waving wands?

    Sarcasm doesn’t help your argument which is why you see so little of it in journals.

    But yea, doubling the number of electronic components in an IC every two years for 50 years is almost magical. If you don’t think so then as Carl Sagan used to say, you must be made of wood. I don’t think they wear robes but the clean room suits they were in the Intel commercials are pretty cool, don’t you think?

    That was only 50 years. Imagine what our technology will be like in a million years if we don’t kill ourselves off with hot air.

  231. Menyambal says

    Well, life elsewhere in this solar system may not prove anything. We seem to be trading rocks back and forth between planets enough to be able to identify them.

    Spores that survive the impact, the time in space and the re-entry, are not impossible.

    Life that is wacked-out different, now, that may mean something.

  232. says

    a_ray #224:

    Really, Allen, I am curious why you are so resistant to thinking through this systematically.

    There is bit of arrogance in your manner of approach. You seem to take great liberties in prescribing what is not possible for an alien species with a million extra years of working the problem. All I’m saying is to look at the level of technology we have now and extrapolate a little. Maybe, just maybe, there are clever solutions to problems that even you or I can’t imagine. (Although, I do try.)

    As I said before, I think the most likely answer is
    1)They aren’t interested in us out here on the edge of the Galaxy. Much higher likelihood of establishing contact with planets near the center.
    2)They wipe themselves out when their technology becomes sufficiently advanced to screw things up on a planetary scale.

    I could add – they are interested in us but only as an entomologist is interested in a new species of insect. How often do you try to communicate with ants? But you might poke them with a stick. I don’t think your two likely answers are any more likely than any others. Not without some real information.

  233. says

    last response to a_ray #224:

    Now, dude, really, I ask you, what do you think you will be able to accomplish with a probe that size?

    Its probably not about what a single probe could accomplish but what a swarm of them might be able to do. My guess is that an objective would be to send back telemetry to the home world. Visuals, chemical analysis, temperature, planetary conditions. But you are probably going to tell me how that’s not possible for technology, even in a million years.

  234. says

    @Bryan M. #227

    How many instances are there of observed solar systems with life?

    One yes.But let’s not get too binary on this issue. If scientists were to find life on the Jovian moon Europa that would still be one star system with two life-bearing environments. There are reasons to think that exo-life might be more plentiful than can be observed with our limited abilities. Firstly, there are now many, many observed exoplanets, some of which may be in the goldilocks zone, some of which the astronomers are saying are likely to have liquid water. The speed with which life arose on Earth once liquid water was able to exist says something about the ease with which it arose. Since chemistry is universal that says once liquid water exists somewhere there is a good likelyhood that life is there. There are critters called extremaphiles that can exist in places where sunlight does not exist but because there is a source of energy such as a thermal vent they do. One such extremaphile called a tardigrade can even survive the vacuum of space (for up to 10 years), temperatures near absolute zero and above the boiling point of water. So it is not completely a matter of not enough data points. Scientists just haven’t seen too many other environments with liquid water close up. Europa, a moon of Jupiter, is thought to have liquid water underneath a thick crust of ice and that is probably where scientists think they can find exo-biology to study. But needless to say, that is an expensive project on the backburners at NASA.

  235. Amphiox says

    And our intelligence has been applied more toward lying to ourselves than anything else.

    Now this is simply not true in the grand scheme of things. If it were true, we would never have left the caves.

    But hominids have only been around for a couple of million years. Human civilization for only a few thousand. On a timescale that would be necessary for an intelligent critter to develop technology sufficient to traverse interstellar space, that is a blink of an eye.

    There is actually zero empirical evidence out there that says anything whatsoever about how long it takes to develop technology sufficient to traverse interstellar space. It might be a million years from our current level now, but it could be as little as a couple thousand more years, and that, compared to our entire history as a species, is hardly a rounding error.

    A “couple million years” is in fact well within the AVERAGE range of duration for a typical mammalian clade of the size and diversity of the hominids. There is nothing “only” about our existence at all. We are, in fact, quite typical relative to other lineages on this planet. We are NOT new kids on the block in this regard.

  236. Amphiox says

    There are JUST as many logical reasons to suppose that intelligence, as an evolutionary adaption, will tend to endure longer than average, and that intelligent species like humans will tend to endure longer than average, as there are to assume that intelligence predisposes to a self-destructive course.

    The species that endure the longest have typically been ones with a wide distribution, a generalist niche, with great variety in the behaviors and lifestyles of local populations, a large and widely distributed breeding pool. And on earth, among large animals, there really is no other species as widely distributed, or with such a multiplicity of varied ways of making a living, as humans.

    Indeed, if we are talking about SINGLE species, rather than separate species (and accepting the controversies that exist in actually identifying species), I do not think there is even a single species of bacteria that have as wide a distribution and as varied a set of lifestyles as we do.

  237. Amphiox says

    And indeed, NONE of the commonly thrown out mechanisms of self-destruction for an intelligent species, whether it is environmental collapse or nuclear war, is actually all that likely to result in EXTINCTION of the intelligent species.

    Destroy the current civilization, sure? But the likelihood that some few scattered bands of survivors, reverting to a hunter-gathering lifestyle, actually make it through, is really likely to be quite a bit higher than total species extinction. And if there are survivors, then given another 5000 years (which is still a blink of the eye in cosmic terms), and a SECOND technology civilization capable of reaching for the stars, may well arise.

    Never in the entirety of the history of human civilization has ANY environmental or other self-inflicted disaster resulted in the complete annihilation of the ENTIRE human population within even the local area. SOMEONE has always survived, and more often than not, that someone rebuilds.

  238. consciousness razor says

    Allen Everhart:

    However, consider this, ahead of the nanobot probes you launch of bunch of dumb atoms to run interference and clear the path – a kind of ablation shield. So if a dimwit like me could think of that could you conceive that a civilization with a million year headstart already has??

    Uhhh… because you’re acting pretty dimwitted, I can conceive that an advanced civilization would have imagined it too and would have rejected the idea. I don’t blame you for that — if it’s something you came up with in five minutes, it’s probably not going to work, and that doesn’t mean you’re really a dimwit, unless you’re going to insist it must be right anyway. (And never mind that bare conceivability or physical possibility still doesn’t tell us anything useful about what is likely or what should be expected…. something a lot of people seem to have trouble with here.)

    I’ll put it this way: if I had a choice, I would take my chances traveling (much slower) in the opposite direction of your “shield,” assuming you give me a nice head start. At best, what you’re doing here is putting more stuff/energy in the way of your probe, not less. You will not get “empty space” out of this, no matter what magical technology you believe would make it happen.

    You’re imagining this as if you could take a big cosmic broom and sweep all of the stuff out of the way. It is not that easy. For one thing, your “broom” isn’t very gentle. It causes explosions and shit, which tend to be the kinds of things you would want to avoid. It would mean some particles are reflected back in the direction of the source (the source of the probe as well). Action and reaction — you probably know how that goes. You’re firing lots and lots of bullets, over an extremely long period of time, to drill some holes into a very thick wall — but the wall’s still there, because it is itself made of tiny bullets and mostly empty space. So your bullets either miss or you have to account for being hit by the ones that actually do collide with the gas. So your “broom” (or “bullets”) just makes even more a giant mess than you already had, because that’s basically what things do: they get messier.

    To put it into a somewhat different perspective, consider a supernova or even the solar wind — those are reasonably good at “pushing” nearby gas away from some location. That is the sort of thing you’d have to do, over an even greater distance (meaning even more energy), which essentially means you’d need to blow yourself up as catastrophically as possible (somehow focused in one direction, requiring even more energy), in order to give your probe a somewhat clearer and less treacherous path. To the extent it would even “work” (creating less dense areas, not completely emptying them), it will also probably destroy anything that would’ve been interesting to your probe at its intended destination, because the path of destruction is not going to just stop in its tracks whenever that is most convenient to your argument. If you simply wanted to know what the targets looked like before you started shooting at them with this monstrous amount of energy, it’s too late for that.

    So that’s three for the price of one: you destroy the Earth, the probe isn’t actually shielded from anything, and you fuck up the place you wanted to “study” or “colonize” or whatever. Not worth it.

  239. consciousness razor says

    Oops, I meant to include my response to this too…

    Nick Gotts, #210:

    I have no idea why anybody would ever have an incentive to send out replicators; what good does it do you?

    Expands the knowledge and resources available to your civilization, and increases long-term security against natural disaster. I have no idea why you were unable to come up with this answer yourself.

    You can say it, but how would they do that? You send out replicators. They collect information and gather resources (at the very least for replicating themselves). They are not you, nor are they anywhere near you, so how do you get those resources? How does it offer you any kind of security against a natural disaster? What is there in interstellar space that poses any kind of a security threat, which you couldn’t see from a telescope in orbit somewhere in the solar system?

    Of course, I think it’s a great idea to, for example, send probes to study/deflect the orbits of comets in our solar system, since some will probably be on a collision course with Earth. But those would not be filling the galaxy or doing anything locally which would be noticeable to a distant observer. And those probes presumably wouldn’t need to be self-replicators anyway, so what exactly are self-replicators supposed to be good for?

  240. PaulBC says

    consciousness razor #246

    They collect information and gather resources (at the very least for replicating themselves). They are not you, nor are they anywhere near you, so how do you get those resources? How does it offer you any kind of security against a natural disaster?

    The purpose could be purely scientific. The probes could eventually send back information either directly or through a relay of probes. Since it could be thousands or millions of years before the information comes back, the definition of “you” needs to be extended to include the whole civilization (or lifespan needs to be extended).

    The advantage to doing this with replicators instead of manufacturing all the probes at the source star is that they each have a shorter interstellar trip to survive, and they don’t draw resources from the source star (which could become considerable after the first million destinations). Once you’ve built one of these replicators, the rest is free (well, unless you start getting bills–or worse–from the inhabitants of the places you visit).

    I agree that it’s not a given that every spacefaring civilization would think this was worth doing, but it only takes one, and if might require only a small share of their resources at their advanced level of technology. So send out a message in a bottle, only better. Why not?

    As for what it protects against… I agree that the replicated probes are not you, but neither are your kids either. Now reproduction is different because it’s a biological drive rather than a rational decision, but a civilization could express its collective pride by attempting to propagate something of itself through the galaxy.

    Actually, the most rational reason I could see for an advanced civilization to do this is if they concluded that they might be alone in the galaxy, in which case their destruction would leave the galaxy empty of intelligent life. So maybe what really happens is that intelligent life is common enough that something a bit more refined than SETI picks it up and long before being interstellar-capable, they cease to feel any need to expand. The galaxy is already pretty crowded, some of their potential rivals look scary, and their best survival strategy is to work things out at home.

  241. consciousness razor says

    The purpose could be purely scientific. The probes could eventually send back information either directly or through a relay of probes. Since it could be thousands or millions of years before the information comes back, the definition of “you” needs to be extended to include the whole civilization (or lifespan needs to be extended).

    Of course it does. That doesn’t change anything about the fact that the “civilization” stays put, or that they don’t make any additional resources available to it. You talk about information. Information about what? Nick seems to believe this could be useful in some way to the civilization at home, enough to justify the project (if not to somehow provide security from some unnamed “disaster”), not just information in the form of some trivial measurement of what exactly happens at some obscure location on the other side of the galaxy. I of course agree that it could travel at the speed of light (once the probe gets there), if you’re sending it with light, so that could makes it way back, assuming you can sort out the signal from the noise. But the question is still “what use is it?”

    I agree that it’s not a given that every spacefaring civilization would think this was worth doing, but it only takes one, and if might require only a small share of their resources at their advanced level of technology. So send out a message in a bottle, only better. Why not?

    A message to whom, about what?

    Actually, the most rational reason I could see for an advanced civilization to do this is if they concluded that they might be alone in the galaxy, in which case their destruction would leave the galaxy empty of intelligent life.

    But in the big scheme of things, the galaxy is insignificant. So what difference does it make whether this galaxy continues to have intelligent life for a while longer? (We’re also assuming here that these self-replicators are intelligent, but I don’t know why.) If you’re simply worried about “intelligence” or “sentience” existing, then by this logic, it does, somewhere. So you don’t need to worry about it or do anything.

    So maybe what really happens is that intelligent life is common enough that something a bit more refined than SETI picks it up and long before being interstellar-capable, they cease to feel any need to expand. The galaxy is already pretty crowded, some of their potential rivals look scary, and their best survival strategy is to work things out at home.

    Their only survival strategy is to work on their own survival “at home.” Making something else survive for a while (because that won’t be permanent either) is not doing anything about “your” survival or “your civilization’s” survival.

  242. PaulBC says

    consciousness razor #248

    Their only survival strategy is to work on their own survival “at home.” Making something else survive for a while (because that won’t be permanent either) is not doing anything about “your” survival or “your civilization’s” survival.

    Your reply may answer the original point, but I think there are much more compelling motives than “survival.” (and survival itself is ill-defined; we all die and pass on genes and some extrasomatic information, but the continuity of conscious is extinguished)

    I can’t really imagine that if I personally had the ability and resources to construct a self-replicating probe and send it off to another star that I wouldn’t be tempted to do it. It’s a finite investment with impact bounded only by the size of the galaxy. I might have a lot of second thoughts. Am I releasing something terrible and damaging? Am I drawing unwanted attention to myself that might have severe consequences? But the main reason to do it if possible is because it would be cool.

    That might sound like a stupid reason, but if you can imagine any advanced intelligence doing something for a stupid reason, this might be one of the things they’d do. How do you explain serial entrepreneurs? Why not cash out and spend the rest of your life relaxing in a hot tub drinking Dom Pérignon? Why does anyone do anything?

    It really comes down to numbers at some point. We don’t need to explain why something is a good idea, just consider the likelihood of it being carried out. And if this one was carried out anywhere in the galaxy 100 million years ago, we should know about it here.

    The more I think about this–and I’ve been aware of Fermi’s paradox for many years but haven’t thought about it much–I think Fermi was projecting his own motives on putative aliens with completely unknowable motives. Maybe the compulsion towards self-destruction is much more probable. Or maybe an idea that sounds possibly stupid to me sounds really stupid to any advanced intelligence capable of building an interstellar probe. There is really no inevitability at all.

    I’m also willing to consider that they are here, just not right here on earth. The outer solar system is still mostly unexplored. Earth is pretty far down in a gravity well and might not be a useful destination for a von Neumann probe.

  243. Menyambal says

    Yeah, really, what actual good information do you expect to gather from another solar system? What are you going to find out there that is worth a big pile of money and a few decade’s wait?

    I mean, yay for Mister Wizard and a jobs program, but what are you going to tell investors?

  244. PaulBC says

    Yeah, really, what actual good information do you expect to gather from another solar system?

    Observations about things that you can’t see in enough detail from far away, that aren’t similar enough to your own solar system to observe local equivalents, and that aren’t already predicted from theoretical considerations. In fact, you might just want confirmation of theoretical predictions. How else do you propose to get it?

    What are you going to find out there that is worth a big pile of money and a few decade’s wait?

    If you already have the technology to build self-replicating space hardware robust enough to operate in alien solar systems, then what exactly does money even mean? There might be some extended notion of an economy, but the conversion of some mass in your solar system to a spacecraft is not something you pay anyone for (i.e. matter and energy are abundant, and labor is free).

    And I’m thinking more like a few millennia wait time for the first results. This would definitely make it a poor “financial” investment, but it might be a compelling idea to rally around.

  245. Nick Gotts says

    consciousness razor@246,

    They are not you, nor are they anywhere near you, so how do you get those resources?

    You don’t – other than knowledge and other cultural products which can travel by radio, and which are also resources. But they (the intelligent beings travelling to or built at the destination) are part of your civilization.

    How does it offer you any kind of security against a natural disaster?

    You may have heard a proverb about not putting all your eggs in one basket.

    What is there in interstellar space that poses any kind of a security threat, which you couldn’t see from a telescope in orbit somewhere in the solar system?

    Supernovae, possibly “rogue planets”, brown dwarfs or black holes that could tangle the orbits of planets in our system, possibly dust clouds dense enough to cause problems, possibly hostile aliens. You might well be able to see any of these, without actually being able to do anything about them. Much more likely than any of these is a breakdown of civilization in the home system. You’ll no doubt say that we should focus on preventing that, and so we should, but it’s not obviously foolish to set up a branch elsewhere if you can. Moreover, and more important, even if it were foolish, it’s not at all obvious some civilizations won’t do it if it is technically possible. Remember that I’m arguing about explanations for the Fermi paradox, not advocating interstellar colonization.

  246. consciousness razor says

    PaulBC:

    Your reply may answer the original point, but I think there are much more compelling motives than “survival.” (and survival itself is ill-defined; we all die and pass on genes and some extrasomatic information, but the continuity of conscious is extinguished)

    Have you noticed how it just keeps shifting away from the things people are literally saying? Why so much backpedaling? And if it’s so terribly ill-defined, why did you bother using it in your argument? Whatever meaning it could possibly have to you, that’s the thing I’m talking about. So, given that, explain it to me and tell me what exactly the problem is with my argument.

    I can’t really imagine that if I personally had the ability and resources to construct a self-replicating probe and send it off to another star that I wouldn’t be tempted to do it. It’s a finite investment with impact bounded only by the size of the galaxy.

    You still have told me what “impact” it supposedly has. Just vagueness and backpedaling.

    But the main reason to do it if possible is because it would be cool.

    Still no usefulness or impactfulness. It’s just something “cool” that you would do. Do you have such a hard time seeing how that’s not very convincing?

    That might sound like a stupid reason, but if you can imagine any advanced intelligence doing something for a stupid reason, this might be one of the things they’d do.

    It might be, but as I keep saying, is it the case that stupidity and waste are what we ought to expect from an advanced civilization? If so, how is this sort of project ever going to get off the ground, considering this stupid wasteful civilization will probably blow itself up, fail to obtain adequate resources, or whatever else?

    It really comes down to numbers at some point. We don’t need to explain why something is a good idea, just consider the likelihood of it being carried out.

    Explaining why it’s supposedly good idea is exactly what you need to do, because it’s directly relevant to the likelihood of an intelligent species trying to do this thing. If I told you it’s “likely” that “most” intelligent species will fail to learn some form of mathematics and sciences, you’re going to give me arguments of the form “no, don’t be stupid; they’re intelligent, so that isn’t very likely.” That’s why I wouldn’t make such a claim in the first place, nor would I change the terms or tell you they’re undefined, while pretending as if I’m still defending the claim.

    Nick:

    They are not you, nor are they anywhere near you, so how do you get those resources?

    You don’t – other than knowledge and other cultural products which can travel by radio, and which are also resources.

    What’s the point of saying “knowledge and resources” when that only amounts to “knowledge and knowledge”?

    You may have heard a proverb about not putting all your eggs in one basket.

    All of our eggs are still in the basket. Nothing you’ve talked about would change that. That’s what I’ve been saying.

    Supernovae, possibly “rogue planets”, brown dwarfs or black holes that could tangle the orbits of planets in our system, possibly dust clouds dense enough to cause problems, possibly hostile aliens.

    I don’t see any reason why you couldn’t see all of that (ones that are close enough to worry about) with telescopes or probes that wouldn’t need to leave our own solar system.

    You might well be able to see any of these, without actually being able to do anything about them.

    So even if you could get better observations, but do nothing, what would be the point? Making sure everyone shits their pants well in advance?

    You’ll no doubt say that we should focus on preventing that, and so we should, but it’s not obviously foolish to set up a branch elsewhere if you can.

    A “branch” of us that consists of sentient self-replicating spaceships. I don’t consider that anything like an extension of humanity. I’m with you as far as cyborgs. Beyond that, I just do not understand the words you are typing.

  247. Amphiox says

    A “branch” of us that consists of sentient self-replicating spaceships. I don’t consider that anything like an extension of humanity.

    If they are sentient, then they are people.

    If we created them, then they are an extension of humanity.

  248. Nick Gotts says

    consciousness razor@253,

    What’s the point of saying “knowledge and resources” when that only amounts to “knowledge and knowledge”?

    I didn’t.

    So even if you could get better observations, but do nothing, what would be the point?

    You appear to be unable to read what I actually say. I didn’t claim that interstellar probes would provide better observations of such dangers – although they might.

    Making sure everyone shits their pants well in advance?

    Is the possibility that knowing about an approaching danger might allow mitigation measures to be taken really outside the scope of your imagination?

    A “branch” of us that consists of sentient self-replicating spaceships. I don’t consider that anything like an extension of humanity. I’m with you as far as cyborgs. Beyond that, I just do not understand the words you are typing.

    OK, that’s how you feel. But obviously, many people don’t, and you have not provided any serious argument that all technologically advanced civilizations would feel as you do.

  249. Amphiox says

    With respect to “nano” probes, in terms of total functional complexity, I can think of no exploratory or self-replicating space probe that would need to perform a wider range of activities than a typical bacterium (it just as perform different types of activities). So I see no fundamental law of physics that would prevent a probe being built on that scale. And as bacteria can form spores that, if sheltered within a chunk of rock, can survive in space, through all the radiation and impact debris, for millions of years, I see no fundamental law of physics that says that is definitely impossible to create a self-replicating probe of that size.

    You can then “inoculate” such probes into a carrier vehicle the size of a beachball or so (which need by no more complex than a rock), and then you launch it. And you could launch many of them.

    I suppose that would be “micro” probe rather than “nano” probe, if you want to nitpick.

  250. Nick Gotts says

    arids@various,

    You clearly have specialist knowledge of the difficulties of space travel, but I don’t find your claims convincing, and your certainty does not appear to be a consensus – but perhaps you can point me to something which shows the contrary. I’ve tried google scholar, and the most relevant article I can find is Semonyov’s Radiation Hazard of Relativistic Interstellar Flight, which someone else linked to above; but Semonyov appears to think that at non-relativistic speeds (by which he appears to mean below 0.3c):

    For velocities up to 0.3c, a titanium ‘windscreen’ of 1 – 2 cm can provide sufficient protection

    against interstellar gas. His estimates of radiation from cosmic rays look, to the non-expert eye, a problem to be taken seriously, but not obviously prohibitive. His article, like all those sceptical of interstellar flights I can find, focuses on human beings travelling, and on the supposed need to keep the duration of the flight below a (current) human lifetime, and hence for relativistic speeds; not on automated probes travelling at lower speeds, which is what is most relevant with regard to self-replicating probes. At a speed of 0.1c, well below Semonyov’s relativistic regime, flight times to nearby stars are measured in decades or a few centuries. You say (#142):

    And, yes, we can come up with unmanned probes (e.g. Voyagers I and II) that will last decades, albeit with very limited technological capability. There is no way most advanced electronics will last that long–we’re having trouble finding advanced parts that will last the 15 year life required of many GEO birds. There’s no way we have electronics lasting hundreds of years.

    Well of course we don’t, now. But this appears to assume that it’s technologically impossible that our descendants would ever do so. What is the basis for this claim?

  251. a_ray_in_dilbert_space says

    Allen Everhart: “My guess is that an objective would be to send back telemetry to the home world.”

    First, you only have a swarm if the satellites can communicate with each other. How does each know where the others are? Radar? Now you are talking macroscopic size, digital signal processing,…

    And communicating back to Earth requires not just the ability to send a signal, but to pinpoint not just Sol, but Earth from lightyears away. How do you plan to do that? It is not enough to simply assume that there will be a miraculous technological breakthrough. You have to start with our technology and posit a plausible path for how we’d reach that miraculous breakthrough. Otherwise you might as well rely on the invention of a magic wand.

  252. consciousness razor says

    What’s the point of saying “knowledge and resources” when that only amounts to “knowledge and knowledge”?

    I didn’t.

    You did, in #210.

    You appear to be unable to read what I actually say. I didn’t claim that interstellar probes would provide better observations of such dangers – although they might.

    I can read well enough. I’d like to know how self-replicators (or whatever expansionist program you come up with) are supposed to do something useful about any of the disasters you mentioned. That’s why I put it in the form of a question: to ask you, with some hope of getting an answer.

    Is the possibility that knowing about an approaching danger might allow mitigation measures to be taken really outside the scope of your imagination?

    You think it’s going to detect a rogue planet or a brown dwarf somewhere far outside of our solar system (which for some reason we couldn’t otherwise see), and we’ll calculate that this planet is likely to collide with Earth (or cause instabilities in orbits of our planets/moons/comets/asteroids/etc.). Then, we do what? It’s the size of a planet or bigger. How the fuck do you “mitigate” that? Or it’s a nearby supernova, which we somehow didn’t already know about — that’s extra bad. Or it’s a black hole, which is really, really, really, super-extra bad. Or it’s a dust cloud, which seems less terrifying on the face of it, but I still don’t see what if anything we could do. Or they are “hostile aliens” (who knows how we detect hostility with this method), but what then? Shoot them with our space lasers?

    The idea that we should “do something” about it is fine, but it’s barely even a start. Do what? And how likely are any of these scenarios, given that they require something so far away (and hard to detect) that any detection equipment we come up with that’s in/near our solar system will be insufficient? How is this vanishingly small probability supposed to significantly raise the probability of seeing something like this from another advanced civilization?

    OK, that’s how you feel. But obviously, many people don’t, and you have not provided any serious argument that all technologically advanced civilizations would feel as you do.

    I have no intention of making such an argument, nor do I need to. I’ve already explained why, as clearly and explicitly, I would say. But I’ll try some more. If you make a probabilistic argument, you need to deal in probabilities, not simply other modalities like might, could, possibly, necessarily, conceivably, imaginably, etc. Does the probability need to be zero for my argument to be sound (or valid or even serious)? No, it does not — it needs to be low. If “some” civilizations “might” feel otherwise, or we don’t know what they might do (or it may otherwise not be that “all” feel as I do) that by itself tells us not a fucking thing about the probability. It’s not simply that you don’t know exactly what the probability is or that you aren’t doing the work of calculating it — you’re the one who’s not even seriously thinking about the way these arguments work. You can get all sorts of shit out of “possibility,” but not an empirical claim about reality. Maybe I’m misguided somehow and you could set me straight, but I have been working under the assumption that physical reality is what this is about, not possibility space.

  253. PaulBC says

    consciousness razor #253

    Have you noticed how it just keeps shifting away from the things people are literally saying? Why so much backpedaling? And if it’s so terribly ill-defined, why did you bother using it in your argument?

    Have you noticed I never made an argument based on survival? My first comment was #96, where I said, among other things:


    Properly managed, the resources of this solar system could support orders of magnitude more sentient beings than it now does.

    That alone doesn’t answer why at least one intelligent life form with the technological capability would not have expanded rapidly due to some compulsion rather than actual need for resources and eventually reached us.

    So my “argument” has consistently been that if self-replicating interstellar probes are possible and there is some possibility of intelligent life building one of them, then one of them ought be here by now. (Given certain numeric assumptions about the density of intelligent life in the galaxy and the speed of such probes.) If you can actually find an instance in which I’ve back-pedaled since #96, I’d be curious to see it. Maybe I did. I’ve been interested in this issue for years, but have given in more thought since posting to this thread. I don’t feel that my conclusions have changed substantially (though I am more pessimistic than ever about near lightpeed travel, which is immaterial to Fermi’s question).

    You still have told me what “impact” it supposedly has. Just vagueness and backpedaling.

    The impact (a word I used) consists of causing actions to happen throughout the entire galaxy, involving the manipulation of matter and energy many times what is present in your own solar system. I never made any claims about utility. It seems self-evident to me that I would find it interesting to do this, and might consider it if I could, so I consider that an advanced alien intelligence might (but again, might not, for reasons I may or may not be able to guess). Motives don’t matter, just the probability of it happening.

    So the simple fact of being able to manipulate resources directly that are a small fraction of those in your own solar system and by doing so cause the manipulation of resources bounded only by the size of the galaxy is the contrast I was drawing.

    I don’t really see your counterargument to the claim of “impact”. Your main point (taken) is that this impact may not be useful or even observable by the initiating solar system. The impact elsewhere in the galaxy is sufficiently great that (as one answer to Fermi goes) the reason we don’t see these probes is because once the impact is observable, other aliens go to effort to eliminate the probes.

  254. PaulBC says

    consciousness razor #253

    Still no usefulness or impactfulness. It’s just something “cool” that you would do. Do you have such a hard time seeing how that’s not very convincing?

    I guess I don’t have a hard time seeing why it doesn’t sound convincing at first, but I believe it is a sound argument and is based on the fewest assumptions about motives.

    My only claim is about probability. Why do I think others want to do something? Because I do, and I share many similarities in my thinking with others. To put it in perspective, look up “lawn chair balloonist”. At least two people have thought traveling in a lawn chair tied to a balloon cluster was an appealing enough idea to try out themselves. The more recent one may have been inspired by the first, but both did something dangerous with little clear utility. I would still say at some level I understand why they did it, though it’s not my thing. I would give some reasonable odds of another attempt in the next 20 years. (10/1 against maybe?)

    A self-replicating probe has the distinction that no matter how improbable, if it happens, it would advertise its presence across the entire galaxy in a “short” span of time (<100 million years).

    I don't claim everyone or even most people would want to. I'm also getting on very shaky ground making this kind of inference about alien intelligence, which might have entirely different thoughts. Again, one possible answer to Fermi's paradox is "It's not very likely because there is just a peculiarity in human thinking that makes this idea appealing to some percent of humans, but does not extend to aliens." (But again it comes down to numbers. I/we may be peculiar, but probably not unique.)

  255. PaulBC says

    consciousness razor #253 (sorry I keep adding replies, though this is a reply to a reply to Nick)

    A “branch” of us that consists of sentient self-replicating spaceships. I don’t consider that anything like an extension of humanity.

    I don’t consider my biological descendants an extension of myself, and I will not share in their consciousness and won’t even share their experience vicariously after I die. But I still take some interest in their potential existence.

    Granted (not backpedaling but repeating a disclaimer I made already in #247) reproduction is a biological drive, and not the same thing as a conscious decision to build a spacecraft, so the analogy should not be carried too far. The main point is that it is possible to care about future events that you caused even if it is impossible for you to feel the consequences directly.

  256. aziraphale says

    PaulBC #261

    I think we need to distinguish between 2 types of self-replicating probe, which I’ll call modest and extreme.

    An extreme probe replicates to the fullest extent of its ability. I agree that such a thing ought to be easily detectable.

    A modest probe is programmed to replicate only enough to fulfil its mission, and to use as material only asteroids or other objects unlikely ever to develop intelligent life. I imagine that our asteroid belt could house one of these, along with however many clones it needs to do its surveying task, without us yet having noticed it. Though of course we might trip over it quite soon.

    Now, when a civilisation is deciding on what sort of probe to send, which will they choose? I think the arguments against an extreme probe are strong. It might grab some raw materials belonging to a superior civilisation, which might then decide to remove the annoyance at source, as we do with a wasp’s nest. That’s the downside. I don’t see any counterbalancing advantage.

  257. PaulBC says

    consciousness razor #259

    But I’ll try some more. If you make a probabilistic argument, you need to deal in probabilities, not simply other modalities like might, could, possibly, necessarily, conceivably, imaginably, etc.

    Sure. And this is why a reasonable proposed answer to Fermi’s question “Where are they?” is:

    The actual probabilities (of intelligent life existing, being able to build such a probe, actually wanting to do it) do not bear out seeing it happen within this galaxy.

    I don’t think that makes it any less interesting as a thought experiment. It spurs consideration about how to fill in those numbers. The answers range from “We’re alone in the galaxy.” to “They are here, silly, just let me make a few more adjustments to this instrument and you’ll have your evidence.” It certainly occupies my time to think about it.

    Given resources to build such a probe, I would find it to be an interesting (though dangerous) actual experiment. I mean if your only claim is that it doesn’t make sense in terms of “survival” I can halfway grant that. I’ll concede that I consider robot progeny by replicator near a distant star to be a form of species survival, but reasonable people might disagree on this.

    For that matter, if you are making the strong claim that it is uninteresting as a thought experiment, it is a bit hard to see how to respond. I think it will remain interesting until the number of good answers is winnowed down to something very specific.

  258. says

    a_ray #258:

    You have to start with our technology and posit a plausible path for how we’d reach that miraculous breakthrough. Otherwise you might as well rely on the invention of a magic wand.

    Ah, so any advance you, a_ray, can’t personally envision all the steps of is something that an entire civilization can’t possibly accomplish with a million years of time!!!!?????????? You really must get over yourself.

  259. a_ray_in_dilbert_space says

    Nick Gotts,
    At 0.3c, your kinetic energy is just about 5% of your rest energy, so a proton has ~50 MeV, so, yes, a cm or so of titanium would stop the protons. However, you still have to worry about bremsstrahlung from the electrons, and single-event effects and dose from the galactic cosmic rays. Also, nearby stars aren’t all that interesting from the point of view of trying to find intelligent life. The nearest candidate is 42 lightyears away, so you are talking at least a century and a half at 0.3c (acceleration to 0.3c takes time, as does deceleration). That’s at the outside limits of reliability of electronics one might be able to attain, but you’d still get a fairly high radiation dose from GCR and bremsstrahlung. Then there’s the minor problem of how you power your satellite and how you accelerate and slow down.

    I’ll admit that I am a pessimist when it comes to space exploration. However, in opposition to my pessimism, I’ve never had anyone offer any coherent pathway towards solutions. They just assume technology will come up with an answer. The thing is that there are some things that are easy to solve with technology and some that aren’t–that’s why none of us has a flying car, but we all have cell phones that would have made Spock green with envy.

    Frankly, I blame Star Trek. People have started to just accept it as a blueprint for the future without asking themselves how they got past all these technological problems. People just assume that someone else will come up with a solution.

    Nick: “But this appears to assume that it’s technologically impossible that our descendants would ever do so. What is the basis for this claim?”

    The basis for the claim is that we need high-performance technology to have a hope in hell of getting a probe to any interesting star. The technology must last centuries. High tech relies on extremely tight management of material properties–to the near atomic level. Wearout mechanisms and radiation will obliterate this order on timescales of years to a few decades. You can’t repair such damage. You would need a semiconductor fab (and they are huge) to replace the parts, along with raw materials. You won’t find these in space, you you’d have to bring them with you. You have to accelerate the spacecraft to a not insignificant fraction of the speed of light and then decelerate it. You need an energy source that will last hundreds of years where there is no sunlight and starlight is exceedingly dim. None of these technologies exist, nor is there any coherent idea about how to develop them.

    All of this has led me to conclude that the probability of interstellar travel is infinitesimal on any timescale that is meaningful to humans living today. It’s not worth my time to think about it.

  260. a_ray_in_dilbert_space says

    Allen,
    I’m sorry. Do you have trouble reading English? Because the quote you give does not support your contention. I said posit a plausible path. That doesn’t sound to me as if I am asking for all the steps.

    Dude, why don’t you stick go gaming. This practical stuff really doesn’t seem to suit you. You’ll have more fun with your light saber.

  261. PaulBC says

    a_r_i_d_s #266

    All of this has led me to conclude that the probability of interstellar travel is infinitesimal on any timescale that is meaningful to humans living today. It’s not worth my time to think about it.

    I find your conclusion convincing if by “meaningful” you mean “of practical significance”. However, Fermi’s question always assumed timescales in the millions of years, and I feel safe in saying that this is of no practical significance to me personally (hardcore transhumanists preparing to have their brain placed in cryonic storage may differ with me on this one, but other than that…)

    Whether it’s worth your time to think about it is a personal choice. You seem to think it’s worth your time to persuade people here of the infeasibility of interstellar travel. I’m not criticizing that either, but I think your specific objections shift the parameters of Fermi’s paradox rather than answering it. (Note that you’ve pointed out twice that you don’t think sending hardware to another star is even material to Fermi’s question, which I addressed in #266).

  262. a_ray_in_dilbert_space says

    Amphiox: “And as bacteria can form spores that, if sheltered within a chunk of rock, can survive in space, through all the radiation and impact debris, for millions of years,…”

    Citation fricking needed! Just how big a chunk of rock did you have in mind, and how did you plan to accelerate it to a substantial fraction of the speed of light, power it in flight, slow it down near its destination…

    And would you not want it to be able to take measurements and relay them back to Earth? If not, how would you know if you had succeeded? Have you considered how difficult it would be to point a laser at Earth from 10s to 100s of lightyears?

    And FWIW, I agree that the current difficulties we face (pollution, climate change, overpopulation, resource depletion…) are unlikely to result in our extinction. They likely will result in the collapse our our global, technological civilization and of our population. It is quite conceivable that our great-great grandchildren could be back to hunter-gatherer tribal groups. And with no easy energy source not requiring significant technological advancement to exploit, that is where they will likely remain.

  263. PaulBC says

    “you’ve pointed out twice that you don’t think sending hardware to another star is even material to Fermi’s question”

    I mean I addressed it in #226

    Fermi’s question wasn’t why won’t we ever be able to detect them if we try, but why aren’t they here already (in 1950)? I agree that pointing a laser spotlight in every direction announcing our presence is easier than sending out a probe, and it’s reasonable to assume that someone in the galaxy might notice it if they were looking for such a signal. So that’s a different paradox (but I don’t think we’ve looked hard enough yet to make it paradoxical).

  264. a_ray_in_dilbert_space says

    PaulBC, by meaningful to humans living today, I mean on consistent with what is likely to be the very brief excursion humans have made into advanced technology. The fact of the matter is that any technology we use in the future will have to be assembled out of atoms of the 92 stable or quasi-stable elements we know today. We are already controlling the devices we are assembling on the near atomic level. If you want matter than has properties inconsistent with those atoms, you are likely out of luck.

    Look, probably the most successful program for the development of new technology has been the International Technology Roadmap for Semiconductors. They have managed to keep Moore’s law going for nearly 2 decades after the collapse of CMOS scaling. They identify the problems faced by the industry and then allocate resources to solve the problems. It’s an excellent example of what can be accomplished when you bring the smartest people in a field together. One thing they cannot do is just assume someone will come up with a solution to a vexing problem. That would be suicide. Space exploration is still reading from Star Trek scripts and waiting for a Warp Drive. That won’t get you out of the solar system…at least not if you want to retain a degree of functionality. I just see a lot more fantasizing than I do serious thought. That tells me that the people involved don’t have a clue–and yes, that includes a lot of folks who ought to know better.

  265. Nick Gotts says

    consciousness razor@259,

    You did, in #210.

    OK, I should have said “knowledge and other resources” at that point. Since this is no way affects the argument, I’m somewhat at a loss as to why you brought it up.

    I’d like to know how self-replicators (or whatever expansionist program you come up with) are supposed to do something useful about any of the disasters you mentioned. That’s why I put it in the form of a question: to ask you, with some hope of getting an answer.

    I’ve already made this clear more than once: it would allow your civilization to continue even if a disaster wiped it out in the home system. OK, I get that you don’t feel this is worth anything, but I have answered, and for some reason you seem determined not to understand the answer.

    You think it’s going to detect a rogue planet or a brown dwarf somewhere far outside of our solar system (which for some reason we couldn’t otherwise see), and we’ll calculate that this planet is likely to collide with Earth (or cause instabilities in orbits of our planets/moons/comets/asteroids/etc.). Then, we do what? It’s the size of a planet or bigger. How the fuck do you “mitigate” that? Or it’s a nearby supernova, which we somehow didn’t already know about — that’s extra bad. Or it’s a black hole, which is really, really, really, super-extra bad. Or it’s a dust cloud, which seems less terrifying on the face of it, but I still don’t see what if anything we could do. Or they are “hostile aliens” (who knows how we detect hostility with this method), but what then? Shoot them with our space lasers?

    This is just bizarre. Surely it’s obvious that potential disasters come in all sizes, from “we can’t do anything at all” downwards; and that the more warning you have, the more likely you are to be able to do something about it? And that the more observers are looking out for potential disasters, especially if they are doing so from different viewpoints, the more warning there is likely to be. (Incidentally, a black hole isn’t necessarily super-duper dangerous: not more so, AFAIK, than anything else of the same mass.)

    If you make a probabilistic argument, you need to deal in probabilities, not simply other modalities like might, could, possibly, necessarily, conceivably, imaginably, etc. Does the probability need to be zero for my argument to be sound (or valid or even serious)? No, it does not — it needs to be low.

    How low it needs to be depends on how many technological civilizations capable of launching self-replicating probes there are or have been, within a range that would have enabled those probes to be apparent to us. Because it has to apply to all such civilizations that have actually existed, if it’s to be a sound explanation of the Fermi paradox. Drake’s original estimate was 50,000 civilizations in the galaxy currently capable of interstellar communication. Obviously, not all such civilizations would be capable of launching self-replicating probes, and if it can be shown that none would, then clearly (a) their absence does not indicate that technological civilizations are rare and (b) your claim that even if a civilization could launch such probes, it wouldn’t, is redundant. But if it’s actually feasible for civilizations technologically much more advanced than ours to launch such probes, then the question of whether they would is relevant; but the more such civilizations there have been, the more it stretches credibility that none of them would have done so, unless you can show that developing the capability to do so would imply not wanting to do so. But you’ve given no serious argument as to why the probability of civilizations capable of launching such probes actually doing so should even be low. Just because you wouldn’t think it worthwhile, when clearly a lot of other people would, isn’t a serious argument.

  266. PaulBC says

    a_ray_in_dilbert_space #271

    One thing they cannot do is just assume someone will come up with a solution to a vexing problem.

    But semiconductor developers have a completely different goal. So if the goal were to propose a roadmap for the development by humans of interstellar travel, then I agree wholeheartedly that a very poor strategy is to assume someone will solve the hard problems. I also think you might be right that “human civilization” isn’t too likely to get there, ever. Scare quotes because we remain a collection of non-cooperating nation states (often violently at odds) and have few shared goals or the means to achieve them.

    But for this discussion, the goal is to set the parameters of a thought experiment, and I think the burden of proof changes to having to rule out something happening based on clear constraints (e.g. speed of light, conversation of matter and energy).

    One take-away for me is that for Fermi’s paradox, it might be more useful to look at much slower speeds between stars. The “magic” part still seems to me to be the self-replicating hardware rather than getting a projectile to the nearest star in 1000 years or less. I do think that some form of self-replicating hardware could exist in the next 100 years, but the only suggestions that don’t strike me as pure vaporware are large-scale (robot mining equipment sending material by self-driving transport to factories that make robot mining equipment, construction equipment for transport systems, etc.) I’ll believe the nanotech route when I see some evidence. Getting self-replication going around an alien star certainly goes beyond any fleshed-out “proof of concept” I’m aware of, but for purposes of the thought experiment the question is whether it can really be ruled out, and I don’t think it can.

  267. PaulBC says

    D’oh. Make that conservation of matter and energy Sorry, I have been typing way too much to keep the typos under control.

  268. PaulBC says

    Mostly to a_ray_in_dilbert_space:

    I’m not sure if I’m being clear enough about what I will accept as an argument for infeasibility. I’m not even a big Star Trek fan (it’s more interesting as cultural commentary, character-driven drama, and entertainment in the broadest sense than as SF) so this is not my perspective.

    You make a strong (unassailable?) case that a small craft accelerated close to the speed of light would have no usable payload by the time it reached another star. I accept that as an argument for infeasibility of doing that particular thing, which clearly has some bearing on the question.

    But what got me going was #127 and maybe I took this out of context:

    Even storing the genetic information electronically likely would not work given the high radiation exposure.

    If you meant, narrowly, that information encoded in the radiation-damaged small craft sent at close to the speed of light was not likely to survive the trip under any circumstances, I agree with that too.

    What I thought you meant was that even sending genetic and other information needed by the probe was infeasible, and it caught my attention, because it’s the easiest problem to solve. Even if you cannot sufficiently protect some hard-media representation with enough redundancy to refresh it via error-correction on arrival, you can send the same information along later at the speed of light (admittedly using a lot more energy than today’s communication devices have).

    So the hard problem (and you say as much yourself) is getting the hardware between stars, not the information.

    The reason I point this out is that I think you might get less disagreement if you were more clear about the scope of what you are claiming as infeasible.

  269. Nick Gotts says

    arids@266,

    Also, nearby stars aren’t all that interesting from the point of view of trying to find intelligent life.

    That’s not what I’m talking about! The whole point of my argument has been that there may very well be none (other than a single marginal case) in the galaxy. From a scientific point of view, any nearby star system would be extremely interesting (even if you just do a flyby), and if you actually want to make use of a system’s material resources to set up a local industrial base (and populate it with AIs andor make new probes), what you need most is probably asteroids and comets.

    High tech relies on extremely tight management of material properties–to the near atomic level. Wearout mechanisms and radiation will obliterate this order on timescales of years to a few decades.

    Well that seems dubious given the performance of Pioneer and Voyager probes. Obviously there’s a tradeoff between performance and robustness, but it’s not obvious we are near the Pareto-optimal frontier of that tradeoff.

    You need an energy source that will last hundreds of years where there is no sunlight and starlight is exceedingly dim. None of these technologies exist, nor is there any coherent idea about how to develop them.

    I don’t have the expertise to assess it, but the current leading idea seems to be to leave the main power source at home, and accelerate the probe using a laser, or more probably a beam of neutral particles.

    All of this has led me to conclude that the probability of interstellar travel is infinitesimal on any timescale that is meaningful to humans living today. It’s not worth my time to think about it.

    Well if you mean “think about bringing it about within the next century or two”, I’m sure you’re right. But while the longer-term future may not be meaningful to you, you don’t get to say what’s meaningful to all humans living today, and evidently, quite a few of them do find the possibility – even in the far more distant future – meaningful.

  270. a_ray_in_dilbert_space says

    Nick Gotts: “…the current leading idea seems to be to leave the main power source at home, and accelerate the probe using a laser…”

    Even granting that you would be able to accelerate the probe for any significant amount of time by such a technique, how do you decelerate it when it nears its destination? How do you achieve pointing accuracy (do you realize how small an angle Earth subtends from 42 lightyears)? How do you power it to maintain a survivable temperature during flight?

    PaulBC’s idea of sending blueprints from Earth has the same problem. Communicating across lightyears is highly nontrivial.

  271. a_ray_in_dilbert_space says

    Nick mentioned Voyager–the mission has been going now for 36 years and 9 months. Reaching the nearest star with a hope of hosting life would take at least 5 times that long. Voyager used early 1970s technology, which was a lot less susceptible to radiation damage and a lot more robust to wearout. It is also much lower performance and so Voyager is both bulky and heavy. The fabs for making that technology don’t even exist anymore. What is more, technology has moved in a much different direction–toward performance and away from long-term reliability. So not only is there not a technological solution to building a satellite that would last >100 years, the technological infrastructure doesn’t even exist. It would take founding an entirely new industry whose only client would be builders of interstellar probes.

  272. Amphiox says

    Just how big a chunk of rock did you have in mind, and how did you plan to accelerate it to a substantial fraction of the speed of light, power it in flight, slow it down near its destination…

    We have recovered bacterial spores on earth entombed in rocks that have survived intact for 250 million plus years, and there is no indication that they could not do the same in the heart of a meteoroid.

    The rock chunk need only be big enough so that it can survive reentry through a planetary atmosphere while maintaining survivable temperatures in its interior. That way I don’t actually have to slow it down near its destination. I let the gravity of the star I am aiming at capture it, and let the thing impact on a planet. Of course one would need to KNOW the orbits of the planets in the target star system (and the motion of the star relative to the sun) with high precision, but that’s just a matter of building bigger telescopes and Newtonian, rather than Einsteinian, physics.

    I do NOT in fact need to accelerate it to a “substantial fraction” of the speed of light to make this work, since I am content with a slow approach.

    If you make a probabilistic argument, you need to deal in probabilities, not simply other modalities like might, could, possibly, necessarily, conceivably, imaginably, etc. Does the probability need to be zero for my argument to be sound (or valid or even serious)? No, it does not — it needs to be low.

    To say that the probability needs to be low is NO DIFFERENT from saying modalities like “might not, could not, possibly not, not necessarily, hardly conceivably, unimaginably” etc.

    You are doing the same kind of thing in the opposite direction to what you are criticizing.

  273. Amphiox says

    Reaching the nearest star with a hope of hosting life would take at least 5 times that long. Voyager used early 1970s technology, which was a lot less susceptible to radiation damage and a lot more robust to wearout. It is also much lower performance and so Voyager is both bulky and heavy. The fabs for making that technology don’t even exist anymore. What is more, technology has moved in a much different direction–toward performance and away from long-term reliability. So not only is there not a technological solution to building a satellite that would last >100 years, the technological infrastructure doesn’t even exist. It would take founding an entirely new industry whose only client would be builders of interstellar probes.

    Now you’re just nitpicking. We aren’t talking about sending an interstellar probe TOMORROW, after all. We are talking about whether or not such a thing is POSSIBLE, and if possible, how likely it be achievable.

    That fact tat 1970s technology is less susceptible to radiation damage than 2010s technology is irrelevant. The important point of that example is that such technology EXISTS. There is no reason why someone couldn’t engineer future technology back in the direction towards less susceptibility.

    That fact that technology happens to have moved in a direction towards greater performance and away from long-term reliability is also irrelevant. Nothing prevents it from being moved back in the other direction.

    The fact that it would take founding an entirely new industry is also irrelevant, since nothing actually prevents the makers of such probes from founding such a new industry, if sufficiently motivated to do so.

    One would not expect a civilization to leap immediately from planetbound status, like we are today, straight to interstellar probe making anyways. A civilization is much more likely to be sending interstellar probes only after it has already colonized much of its own home solar system. Much of the foundational technological infrastructure would be developed initially for the purpose of interplanetary space activity, and then later for outer-star-system-Oort-Cloud-region space activity, first.

    (I think Clarke’s 3001 is not that inaccurate a projection. One thousand years in the future and still no serious attempt at interstellar missions, but widespread activity within the solar system itself. THAT would be the kind of civilization that could be seriously thinking about attempting a first interstellar mission.)

  274. Amphiox says

    And there’s no reason to think that the information-processing technology that runs an interstellar probe need by electronics of the same sort as the electronics currently used on earth.

  275. Amphiox says

    All of this has led me to conclude that the probability of interstellar travel is infinitesimal on any timescale that is meaningful to humans living today. It’s not worth my time to think about it.

    Then you don’t have to participate in this discussion. Go spend your time on something you think more worthwhile then. Its your time and your mental energy, and you are a free agent.

    Some of us LIKE to think about far future timescales from time to time. Someone earlier talked about the mind being boggled. Well some of us ENJOY the feel of a good mind boggling, and it is MEANINGFUL to us. Don’t presume to think yourself entitled to exclude us from your category of “humans living today”.

  276. aziraphale says

    If I understand you correctly, you aim this thing at where you think a planet will be when it arrives, and that’s it. No mid-course corrections. To do that, you need to know not just the orbits but the mass of everything whose gravity might affect its path along the way – dust clouds, Kuiper belt and Oort cloud objects belonging to the target star, all the planets of the target star. The slower it is, the more all those things will affect its course. And, of course, the timing has to be exactly right. Crossing the Earth’s path 4 minutes late would convert a bullseye into a miss.

  277. PaulBC says

    a_ray_in_dilbert_space #279

    The fabs for making that technology don’t even exist anymore.

    I think I need some ground rules on what non-existent technology I’m allowed to assume. Are you saying that I can’t assume the use of 70s-era high-reliability electronics until someone actually reinvents the capability? My working assumption is that equivalent or better technology could be produced in the same or less time given sufficient economic incentives. (Likewise, we could return to the moon pretty fast if there was enough money and political will behind it.)

    I’m also not saying Voyager technology is the secret to interstellar travel, just noting that many of your statements are immaterial, and you would make a stronger case by sticking to actual physical limitations. You do have me convinced that travel at relativistic speeds is a non-starter given our best current understanding of physics.

  278. Rob Grigjanis says

    a_ray @278:

    how do you decelerate it when it nears its destination?

    This is addressed in the paper Nick linked to;

    An additional advantage of using a magnetic sail for interstellar propulsion is that the same sail can be used for both propulsion and also to slow the probe at the destination by drag against the interstellar medium and the stellar wind of the target star.

  279. PaulBC says

    In fact, my infatuation with relativistic travel was short-lived and long ago, lasting from seeing Carl Sagan explain the idea of a Bussard ram jet on the original Cosmos, and succumbing to sticker shock after considering that to get 100-fold time dilation, you will need 99 times your rest mass in energy. I was never bothered by the idea of going on a jaunt to the next star and coming home hundreds of years in the future. That part sounded cool. But marshaling orders of magnitude more energy that it would take to move a good-sized planet at merely classical speeds just doesn’t seem cost-effective.

    That said, I wonder what it it would look like from far away if there were large masses of any kind traveling through interstellar space at 0.9 c or higher. Given all that’s been said about the intervening particles turning into hard radiation, shouldn’t any sizeable starship leave a detectable wake along the line of sight between stars? I mean, this radiation will probably scatter in every direction and there should be a lot of it. Is anyone actively looking for this?

  280. a_ray_in_dilbert_space says

    PaulBC: “I think I need some ground rules on what non-existent technology I’m allowed to assume. ”

    The point is that current technology is going in a very different direction–high performance and lower reliability. Space hardware builders are already having difficulty finding vendors for some critical components. Right now, no one is even looking at trying to achieve product lifetimes greater than about 5 years.

    And unless you decelerate fairly rapidly, your average velocity will suffer a great deal using this technology. That’s the problem I have with these efforts–no on is looking at the problem systematically. They concentrate on finding a quasi-plausible solution to one problem but ignore that it will play havoc with other parts of the mission and design.

  281. a_ray_in_dilbert_space says

    Amphiox, what you are engaging in is fantasy. Did said bacterium survive for 250 million years in a high radiation environment?
    Why do you abandon your skepticism when it comes to Star Trek?

    My objection to this sort of exercise is two-fold. First, I’ve noticed a direct anti-correlation between the ease one attributes to leaving this planet and the level of effort one is willing to expend to keep it habitable by humans. Second, these sorts of exercises always devolve into criticism of NASA, ESA and other such organizations as “conservative” and “hidebound”. Inevitably, this is because those making the accusations have no appreciation of what is involved in making something that will function autonomously for a period of years in a hostile environment. (Yeah, I mean you, Elon Musk)

    If you were really serious about this, you would start with a straw-man mission, identify the tall poles and red brick walls in your way and work at it systematically. Anything less than this is just fantasy.

  282. PaulBC says

    a_ray_in_dilbert_space #288

    That’s the problem I have with these efforts–no on is looking at the problem systematically. They concentrate on finding a quasi-plausible solution to one problem but ignore that it will play havoc with other parts of the mission and design.

    I think you’re conflating some things here. I agree that proposing a vaporwave stardrive, concluding that we’ll all just leave earth when we have to, declaring job well done, and driving off into the sunset in your Hummer is not a great indication of either clear thinking or basic human decency. (In my class, you don’t even get partial credit if you drive off in a Tesla.)

    But this discussion was originally about something else entirely. When Fermi asked his question, the state of the art rocket was a few years in advance of a V2. He was a great scientist, but he hadn’t worked out the details either, and was in no position even to begin. But “this sort of exercise” was specifically about the limits of the possible over timescales we’re not accustomed to considering. Perhaps humans suffer from fundamental social tendencies that preclude the development of interstellar travel, but does that mean nobody will? The loss of industrial capacity is also relevant to the development of technology on 20th-21st century earth. That doesn’t make it some kind of universal.

    While your points about radiation make sense, the other points don’t really seem relevant. Today components are trending away from reliability. Who’s to say what will happen in another 40 years?

    We’ve seen command economies in action, such as in WWII. They have their own problems, but they definitely can happen on large scale, so it’s not totally crazy to wonder if somewhere out there it could occur on such a scale to produce a self-replicating interstellar probe. Or even to imagine that at some level of technology and industrialization (well beyond anything we know) the resources needed would not even require a command economy to assemble.

    I think this is a fine “sort of exercise” when put in perspective. I agree that if it is used as an excuse to stop funding practical space research it’s bad. It’s also bad if it is used to develop a panglossian view of the ultimate future of humanity and stop caring about the environment, war, and every other threat to people and other living things.

    But Fermi’s paradox as a thought experiment isn’t about those things. Personally, I think it’s very intriguing puzzle without any obvious answer. You don’t have to think that, but I’m certainly not alone in the view.

  283. Amphiox says

    Amphiox, what you are engaging in is fantasy. Did said bacterium survive for 250 million years in a high radiation environment?

    My speculation puts a functional equivalent to that bacterium in an environment which by your own numbers would have it shielded from radiation. In other words I am NOT proposing a high radiation environment at all.

    It is your assertion that all conceivable environments in which a space probe must travel have to be high radiation ones that is fantasy, as we ALREADY KNOW that there exists in interstellar space low radiation environments, in the centers of meteroids, asteroids, and other such debris.

    This entire discussion IS fantasy. That was established from the very beginning. That is the parameter upon which the discussion was begun. If you do not like it that way, you are free to stop participating in it at any time.

    First, I’ve noticed a direct anti-correlation between the ease one attributes to leaving this planet and the level of effort one is willing to expend to keep it habitable by humans.

    That is an asinine and frankly offensive assertion, and pertaining to the participants of this particular thread, on this thread, there is no evidence of it whatsoever.

    Second, these sorts of exercises always devolve into criticism of NASA, ESA and other such organizations as “conservative” and “hidebound”.

    Yet another asinine and frankly offensive assertion, which, pertaining to this thread, there is no evidence for whatsoever.

    On THIS thread, most of what I’ve seen doesn’t even mention those organizations at all, since we are talking about technologies far in advance of anything they would have access to.

  284. Amphiox says

    It is quite frankly intellectually dishonest of you, ARIDS, to glibly toss at me accusations of insufficient skepticism, and then throw out slanderous accusations like the above two with zero evidence whatsoever to support them.

    At least MY speculations do not involve casting aspersions on the motives and intents of real, actual people living on this planet today, which yours do.

  285. says

    Come to think of it, they can’t get here from there.

    (apologies to Marshall Dodge and Bob Bryan)

    Seems to be the best explanation for the Fermi Paradox based on all the talk here.

  286. a_ray_in_dilbert_space says

    Amphiox, it appears you have more capacity for outrage than critical thinking. Fine, have a nice life.

    I did not accuse you of holding the views I decried. I said correlation (or anti-correlation). You have simply ignored every obstacle I’ve brought up. That is fine, but it won’t get us anywhere as far as exploring the cosmos. Realistic consideration of the risks and obstacles is what is required–not fantasy.

  287. says

    Another counter argument starts from the observation that the life on the early Earth might have already had several billion years of evolution, e.g. on previously existing planets around other stars. If so, it might be that we need to look at the time elapsed since the Big Bang rather than the time elapsed since the formation of the Earth.

    If that is so, then it might be that evolution has only just reached the stage where intelligent life in our galaxy is probable. Evidence in favour of this idea comes from the work of the geneticists and who have applied the evolutionarily equivalent of Moore’s law in reverse and come up with a probable date for the origin of life around 10 billion years ago. See Rare Earth – enough time elapsed since the big bang for evolution to occur

  288. says

    Maybe this is a little OT but it has to do with how long a technological civilization might exist:

    The growth of Earth-based civilization is nearing an end due to thermodynamic constraints. At current growth of human energy consumption from any source, green or otherwise, the temperature of the Earth will reach the boiling point of water in under 500 years, according to:

    http://physics.ucsd.edu/do-the-math/2011/07/galactic-scale-energy/

    I find this a bit alarming because I was mislead to believe the global warming problem was purely a matter of greenhouse gas emission. Even with a super-fantastic-yet-to-be-achieved energy source such as fusion, the limit to growth is nigh.

  289. aziraphale says

    Don’t worry about it, Allen #299. The current growth in energy use comes mostly from population growth (which has to level off soon, or we will be in deep trouble) and third world countries catching up with first world consumption. Our household machines, our cars and our aircraft are steadily becoming more efficient. There’s no way we would need to consume energy on the scale projected here. If we tried it, our houses would catch fire long before the ocean boiled.

  290. Anton Mates says

    @PaulBC,

    A self-replicating probe has the distinction that no matter how improbable, if it happens, it would advertise its presence across the entire galaxy in a “short” span of time (<100 million years).

    I wonder if this is actually true. It seems to me that there’s a problem with employing a self-replicating machine to perform a particular task for thousands or millions of years: replicators evolve. The mutation rate for a probe (especially a small one) would probably be quite high, due to radiation damage. And natural selection would not tend to restore a probe lineage to its original factory settings.

    I see two main issues here:

    1. The designer needs their probe to replicate a zillion times when it arrives at a new system, to make sure its descendants can beat the odds on their next search. But natural selection will favor traits that give probes a competitive advantage over their relatives in the short term, not traits that maximize the growth rate of the entire population. (See Fisher’s principle, for instance.) If a probe can ensure that its descendants make up a larger fraction of the population by sabotaging/destroying/consuming other probes, then the population is likely to evolve that behavior.

    2. The designer needs their probe to leave the system and head off through interstellar space once it’s done replicating. But the programming instructions for that goal have no particular survival value during the replication phase, so there’s nothing to keep them from mutating into incoherence. And the ultimate goal itself is, for an individual probe, reproductively suicidal–in the short term, it’s far more advantageous to stay in your current system and compete for a share of its resources. (Think about how bird species colonize new islands and then become flightless.) Yes, there’s a huge payoff if you happen to be the one probe that makes it to a new system, but that happens incredibly infrequently relative to an individual probe’s generation time, so it won’t provide a strong selection pressure. Evolution doesn’t plan ahead.

    So it seems possible to me that, even if self-replicating probes are technologically feasible, within a couple million years of launch they will evolve into an ecosystem of competing lineages, preying on one another and losing their capacity to colonize further systems. Maybe.

  291. says

    @anton #301

    yes! you bring up a brilliant point. thanks for that contribution.

    But the programming instructions for that goal have no particular survival value during the replication phase, so there’s nothing to keep them from mutating into incoherence.

    this got me thinking again about an extremaphile critter called the tardigrade which for some reason has retained the ability to withstand exposure to space environments (vacuum, cosmic rays, uv and the like.) presumably, these traits had survival value when the Earth was being bombarded by comets and asteroids, but other than flying in science experiments launched by humans they don’t experience that environment all that often wrt to their life span (70 years without dormancy.) so one would think that these traits would have little survival value in our era of low bombardment, yet are retained. what do you think?

  292. PaulBC says

    Allen Everhart #302
    I was planning not to add anything else to this thread, but it’s an interesting topic.

    My main problem with the mutation idea is that much better error-correction could be built into these probes than we see in DNA copying. So if the originating aliens didn’t want any significant evolution, they could at least hold it at bay for millions of years.

    Even if it was not always possible to convey the signal intact through radiation hazards, it would be possible to identify corruption with a checksum. So mutation might be ruled out completely (with very high probability. The probe could be designed to self-destruct if the replication instructions changed at all.

    That doesn’t make it a given that the probe could propagate over the entire galaxy easily, because there would be issues of competition. However, my gut feeling is that collections of competing self-replicating probes would be at least as easy to detect as one non-competing variety of probe.

  293. Amphiox says

    The probe could be designed to self-destruct if the replication instructions changed at all.

    Well, that’s basically what many tumor suppressor genes actually do. They trigger apoptosis if mutations in the DNA are detected.

    But cancer still occurs, and DNA still evolves.

    Evolution being what it is, any mutation of the replication instructions that eliminates that self-destruct instruction would be highly favored.

  294. says

    Evolution being what it is, any mutation of the replication instructions that eliminates that self-destruct instruction would be highly favored.

    Indeed. Any line without this self-destruct mechanism would, by definition, be replicating faster than those with the mechanism. Even if you make a perfect self-destruct system, you run into a more basic problem:

    Zero tolerance for error means your system either has to be pretty close to perfect, or your new probes will constantly self-destruct. The less tolerant your system is to error, the greater a portion of your new generation will be destroyed and some base level of replication is necessary just to keep the population from falling.

    Besides, how are the errors supposed to be discovered? Surely, if errors can occur in replication they can occur in error-checking. Even multiple check-passes wont fix the problem, since that only increases the risk that a correct instruction will be mistakenly read as mutated.

    You can reduce mutation rates, but I don’t see any realistic way to eliminate mutations completely without utterly crippling the probe’s ability to reproduce at all.

  295. Anton Mates says

    @Allen Everhart,

    but other than flying in science experiments launched by humans they don’t experience that environment all that often wrt to their life span (70 years without dormancy.) so one would think that these traits would have little survival value in our era of low bombardment, yet are retained. what do you think?

    Well, I think those traits actually have a lot of survival value in the modern era. Tardigrades live in really crappy places–under ice sheets, in hot springs, on exposed lichens, etc. Desiccation, temperature extremes, low oxygen levels and mutagen exposure are all threats they regularly face in their life cycle. Even their radiation resistance is probably a side effect of having really good DNA repair mechanisms, which are necessary if they’re going to spend long periods in stasis, even environments with low background radiation.

    So I doubt that these traits have been retained without the help of natural selection. Plus, hibernating tardigrades can only survive about 10 years in an earth-like environment, and 10 days in space; that’s an eyeblink compared to the time an interstellar trip would take. And they can only survive for that long while in stasis. If they had to do things in space–navigate, propel themselves, repair damage, replicate–they would necessarily have a much tougher time of it. (Embryonic tardigrades can’t survive in space, for instance.) So tardigrades are awesome, yeah, but I think it’s telling that they’d need to be about ten million times more awesome in order to survive the trip to another solar system. Creating a living probe that could do that, plus actually propel itself, plus replicate once it arrived, would be a hellishly hard task.

    As additional evidence for the suckiness of space as a habitat for life, consider that our biosphere basically stops a few miles above ground level. You get the occasional bird up there, and windblown bacteria get even higher up, but there doesn’t seem to be much of anything actually living up there…despite the fact that it’s not terribly hard to get to, physics-wise. In other words, although Earth life has adapted to colonize some pretty freaky niches over the last few billion years, it hasn’t adapted to colonize our upper atmosphere, let alone space. Apparently organisms would rather evolve to hang out in pressurized, superheated acid than in a space-like environment. So even if you can build an organism that can survive in deep space, natural selection may basically drive it to get the hell out of there as soon as possible and never go back.

    @PaulBC,

    My main problem with the mutation idea is that much better error-correction could be built into these probes than we see in DNA copying. So if the originating aliens didn’t want any significant evolution, they could at least hold it at bay for millions of years.

    I wonder if that’s true. If your probe is going to do everything that natural life does–feed, replicate, heal from damage, and do these things well enough to require no maintenance for millennia–then who’s to say that it can simultaneously maintain its genome/program with far greater fidelity than any known life form or machine?

    After all, Earth organisms have 3-4 billion years of practice resisting and repairing genetic damage, yet mutations still occur in every replication cycle.

    Even if it was not always possible to convey the signal intact through radiation hazards, it would be possible to identify corruption with a checksum.

    Other posters have suggested reasons why error-checking might be both ineffective and evolutionarily unstable; I’d also note that frequent error-checking is very costly, even without the “commit suicide if you find anything wrong” bit. It requires time and energy, and it requires your data storage medium to be “unpacked” in some sense, which usually leaves it more vulnerable to further damage and corruption.

    Does that mean that it’s practically impossible to construct a living probe that can do this successfully for thousands or millions of years? I have no idea, really. I just wanted to raise the point that evolutionary instability is yet another obstacle you’d need to overcome, in addition to the question of mere probe survival.

    However, my gut feeling is that collections of competing self-replicating probes would be at least as easy to detect as one non-competing variety of probe.

    Depends what form the competition takes, I think. If the probes are spending most of their energy and resources on eliminating competitors, and surviving competitors’ attempts to eliminate them–which is pretty much how natural organisms spend their time–then an ecosystem of competing probe species might be much more sparsely populated than a monoculture would be.

  296. Rob Bos says

    “It’s silly to expect that the successful, thriving interstellar life forms will be bipeds adapted to life on a planetary surface, living in large metal shells as autonomous agents crewing a spaceship.”

    Yes, but it’s not silly to expect that interstellar life forms won’t need some protection. In much the same way that, say, mammals are genetically “simpler” (in the sense of having to cover fewer contingency cases during development) because you can guarantee a gestation environment, a lot of things are simplified if you can guarantee a living environment.

    A machine is simpler if it doesn’t have to account for temperature variations, vacuum, radiation, self-repair, and whatnot. The combination of a protective shell with a living environment that can be discarded as needed, and an organism (be it “organic” or silicate or something else) is probably still a pretty optimal model.

    Don’t think spaceship – think coral reef.

  297. says

    A self-replicating probe

    Wouldn’t anything self-replicating that faced different outcomes based on circumstance, that didn’t replicate itself exactly begin to, you know, … evolve?

  298. says

    Seriously? Because we can’t save everyone, we shouldn’t save anyone? Unless everybody makes it, we shouldn’t even try to save the ones we can? Please tell me I’ve misunderstood you.

    No, I not quite. I was questioning whether it’s possible to save anyone, and whether – after being saved – they’d be human, anyway, Would humans pining for long-lost Earth be relevant (what are those feet, fot but to walk on Earth?) maybe it would make more sense to transfer our hopes to robotic children that would carry on after us, then die as a species giving them our blessings and programming them not to superceed our flaws. Isn’t that what good parents do?