I’m not afraid to read a book (if I can handle it) but I feel you need to know something of a field, in order to know which books are definitive and represent a consensus.
That seems important to me, since today’s intellectual landscape is littered with people angling for their next TED talk, which unfortunately distorts the discussion toward “crowd pleasers” and “gee wow” theories, rather than stuff that’s less edge-science. So, I thought I’d throw out some things I have been wondering about, and trust The Commentariat(tm) to direct me toward reliable sources. Having been part of the atheism/skepticism scene for a while, now, I am familiar with the “author who appears to be a scientist but turns out to be a crank as soon as you challenge his assumptions of gender and cultural imperialism” such as Richard Dawkins. And then there was Christopher Hitchens. Suffice to say, I am no longer looking to learn from scientists who have pushed themselves into the cultural mainstream, because their motives are now permanently suspect, to me. [I certainly hope I do not fit that category, for some of you]
The questions I have are regarding black holes.
I’ll start with the big one and work my way down, and I’ll even number them in case anyone who is commenting wants to refer to them that way. For convenience’s sake I won’t pause every few words and as “is that right?” I don’t know this stuff and I am inviting you to jump in and hammer away wherever you see a dent.
1) Black Holes as a worm tunnel.
This appears largely as a sci-fi trope, a way of getting around Einsteinian space-time as a macguffin to hold up a cracking good story. Otherwise, the story would read: “intrepid explorers go to explore another star; it’s a 4,592 year-long trip with their highly optimized Optimism Drive(tm) and a Windows update fails 1,322 years into the trip and observatories notice a small spot of light.” So, we fly into a black hole and come out on the other side!
But wait, first question: isn’t that complete bullshit?
I understand that the gravity well near a singularity warps space and therefore time, and infalling stuff speeds up to closer and closer to light speed as the gravity is felt asymptotically, but there’s not a “hole” in space at the bottom, like a toilet, there’s a singularity which is a mathematically nasty region which contains the mass of many stars, compressed down into (?) blackholium? collapsium? badassium? ™ Neutron stars are neutrons packed together like ball bearings and have a hell of a gravity field, but black holes are worse, right? Nobody writes novels about flying through a neutron star.
But the fact that a singularity exists and has all that mass, and therefore a blackhole exists, makes me think that if we tried to fly our starship “through” a black hole, we wouldn’t “come out the other side” we’d be ripped apart in fascinating ways (next question!) and end up a small scum of collapsium on a much bigger ball of collapsium and remain there until the end of time.
2) Black Holes as Far Away
With regard to using a black hole as a worm tunnel, wouldn’t we have to get to it, first? It makes sense as a literary macguffin until you look at it closely: it’d take time getting there. Gaia 1B is the currently known nearest black hole to Earth (this is good, I like that distance!) it’s 1560 light years away. So even with an Optimism Drive(tm) it’s a long way to go to die. Besides, the natives of the Gaia system would be puzzled if their new neighbors travelled 1560+ years just to immolate themselves in the local black hole, “would you like to stay for trade and buy our hyperspace drive? oops. no.”
All of this leads me to believe that the whole idea of a black hole as a means of transportation is much more stupid than getting around in space on horseback would be – and that’s pretty stupid.
I understand that for people to write novels in which humans leave Earth and go out and start wars and stuff require some kind of literary trick for the transportation problem, but is that all we’re looking at? As an aside, I tried to study a bit about “Alcubierre drives” and kept noticing that everyone cheerfully talks about warping space like a carpet, etc, but nobody has anything to say about the energy budget for that process, and how that process would work in the first place. I’m forced to observe that rapid interstellar transport requires messing with space time, and “warping it” is one thing black holes do, so we’re just left with warpy-derpy because our authors are generally reluctant to just hypothesize that Gully Foyle learns how to D-jump and takes humanity along for the ride. [By the way, if you haven’t read The Stars My Destination, it’s good. I’m still amazed there is no netflix series based on it.]
OK, so the warpage is provided by black holes as a literary device, and space warps would require something similar, so I’m gonna guess that a space warp drive is gonna involve black holes and that’s all well and good is that the only place they take you is to where the collapsium grows until the end of time.
3) Up Close With a Black Hole
It seems to me that other than the relativistic effects, black holes are a kind of comprehensible thing. It’s a place where gravity’s pull goes up asymptotically to the point where everything gets fucked, even light.
So, where does the light go after it gets sucked in? I know light is made of actual stuff that is both a particle and a wave but if it’s subject to getting sucked into a ball of collapsium by the gravity of a bigger ball of collapsium, then <gulp> that’s it right?
I was delighted a few years ago to learn that the singularities in some black holes appear to be spinning – not like a top, more like at close to the speed of light. I don’t quite understand how scientists were able to figure that out; it must have been a trick. Would a spinning blob of collapsium flatten out along its axis of spin, slightly, so it would look different from one angle or another, and could the rotational velocity be estimated by some estimates of how collapsium behaves in its own gravitation field?
The main question I have is heat. So, I always understood that the temperature of a thing or region has to do with the amount of brownian motion in the volume. More is hotter. Absolute zero (0K) is no motion at all. So far so good? So, if I have something biggish, let’s say an asteroid of rock, and it falls into a black hole, it must heat up considerably. Because there is still the same amount of brownian motion that used to be in an asteroid-sized space and now it’s getting smaller and smaller as it’s being pulled into the black hole. Eventually, it winds up “mighty tiny indeed” but would that not make it asymptotically hot? And how does a black hole shed its heat? Light can’t escape it, nothing can, so nothing can get energized (heated up) and kicked away to cool the whole thing down. Is there some maximum theoretical asymptotic temperature? So it’s not just a rapidly spinning oblate spheroid of collapsium, it’s also …? incredibly hot? I mean, something that swallows a star without blowing up, and does not somehow release the heat of the star, has got to be suffering the most amazing indigestion, ever.
That also has some implications for a traveler proposing to go through a black hole as a wormhole to somewhere else: they not only get ripped to bits by the tidal difference between gravity at their head, and gravity at their feet, they get heated up to something that would make a supernova cringe with envy?
Also, as things fall in and get compressed, would they undergo fusion? Is the collapsium or whatever it is at the bottom of a black hole a sort of peak product from fusion where everything has fused with everything and it’s quite warm?
Is this accurate-ish? Because it seems they are saying the singularity of TON416 is 400 billion kilometers wide. So that implies to me that a black hole is not just an asymptotic dot of mass, it’s got volume as well as mass, therefore it must have a mass/volume and we can say something intelligible about what a cubic foot of black hole weighs? Or does TON618 material weigh more than GAIA1B material?
4) What IS it made of?
That’s my final question. I’ve been calling it collapsium because I don’t have a name or know if it does have a name, but I’ve seen “gee wow” stuff like “the material in a black hole, if you had a spoonful, would weigh as much as Earth.” I assume that’s a wild-ass guess but I assume that’s based on being able to weigh black holes through gravitational lensing, then something something it weighs a bazillion trillion pounds and the singularity is this big, so we divide. Since we can’t see the singularity, we’re left weighing it by its effects, but how can we figure out its volume?
And what do you call the stuff at the bottom, the stuff the singularity is made of? Is it particle stew? Light, neutrons, electrons, etc, all jammed together under the pressure of being jammed together?
OK, that’s enough.
Any clues anyone cares to drop would be greatly appreciated. Mostly, “go read this book” would be best, especially if it’s an audiobook I can listen to over and over while I turn steel into dust. I watch Dr Becky Smethursts’ stuff on youtube and she knows more than I do, obviously, so I don’t have a good way of telling if she’s right or not. Is there someone out there who specializes in explaining black holes to people with liberal arts education?
How could a black hole be used as an energy source? I guess since “things go in but don’t come out” it would not be radioactive, itself, but the stuff falling into it is heating up, undergoing fusion, etc. A sci fi macguffin would be to put a portal in that compression/fusion zone and have a tiny bit of it blast into something that could handle turning it into useful form?
IANAS,MLAA, but one thing I heard proposed as a solution to the singularity problem is that there may actually be a surface to a black hole. There might be a way that the BH holds itself up against gravity. Though no known force can stand against that much gravity, the idea has something to do with physics getting super weird the closer you get to the singularity and **IF** you reach an actual singularity all physics come undone, so maybe if you get close enough physics come partially undone and it won’t let you collapse far enough to actually break the universe. We would be unable to see the surface of the BH b/c of the event horizon, but some smart people thought that it could be there.
I can’t find the original article/paper that I read years ago b/c so many people think that the event horizon is a solid surface that I can’t find discussion of potentially solid surfaces behind the impenetrable wall of articles debunking the wrong-headed idea of EHs as solid surfaces.
Regarding (1); You would eventually come out of a black hole… As Hawking radiation. :-/
(2) The Alcubierre drive requires a negative energy density. A relatively recent paper claims that it might be possible.
(3) A ring singularity (Kerr black hole) could theoretically work as a wormhole. Or that solution to the equations could just be a mathematical oddity. And then we have this interesting 2023 paper by R.P. Kerr (yes, that Kerr) which claims there are no singularities inside black holes.
John Varley wrote a short story about a sentient black hole.
It was evil, sort of.
check out this vid for good beginning info:
https://youtu.be/qZWPBKULkdQ?si=GC9Okti1WrbYxPjI
for a more physics, GR math-oriented take look at Sean Carroll’s course (probably at too high a level):
https://www.preposterousuniverse.com/activities/physics264/
you can also check out Sean’s Mindscape podcast. He has done a lot of podcasts with experts that tackle black holes.
The Black Hole war by Leonard Susskind has quite a bit of layman level information about black holes, string theory, and where all that energy goes. The driver is an argument between Susskind and Hawking about conservation of information.
Well, “singularity” just means “our theory has run out of steam and can no longer make any kind of statement about what happens next”.
In this case, having exceeded the ability of known forces that prevent a neutron star from collapsing further, we are no longer aware of anything that would prevent a continuing collapse to arbitrarily small size. Zero if you like. We really have no idea what is going on in there. But luckily none of our external observations require us to. Things like Hawking radiation, the behaviour of orbiting light or matter outside the event horizon, that all continues to behave in ways we have a basic handle on as long as whatever it is going on inside preserved mass, charge, and angular momentum. (And the fact that angular momentum is on the list suggests to me that “zero size point” is unlikely as a solution, so our theory is incomplete and something else is most likely going on there.)
But yes, eventually whatever is in there will kill you. Perhaps not for a while for a really big black hole where the gravity gradient at the event horizon isn’t so extreme, and assuming what is inside isn’t a huge mess of exotically fatal quantum radiation sat just inside the horizon.
I think a large part of it all assumes you can create pairs on demand, or preposition them the slow way to get faster travel later. Or that you do actually have some sort of basic FTL, and that gets to as far as a wormhole to a place so unimaginably further away that your STL ceases to be much help.
Or the writers just saw “hole” and ran with it and were hoping you wouldn’t ask such awkward questions.
Oh, I’m pretty sure I’ve seen serious discussions where that is answered “perhaps technically possible, but more than you can afford.”
That might depend on what exactly is inside, but the boring answer is that perhaps the vast majority of the volume inside the event horizon is just normal empty space. A region you cannot generate a velocity vector to get out of, but there is nothing stopping you from spending an *extremely* long time just looping around and around it.
Yes, I imagine that is true. Certainly infalling matter appears to get very hot indeed and that’s while we can still see it. Once on the inside? Probably hotter still. How does it shed the heat? Why would it? Heat is just energy, energy and matter are equivalent, and both are trapped forever on the inside. Apart from Hawking radiation, which gives the BH an “apparent temperature” based on the statistics of the outflowing radiation, which is based on the surface area, which is related to the amount of mass… But you seem to be troubled by the apparently unlimited temperature: we’re already in a regime where our best theories can say no more and certainly don’t appear to be able to set an upper limit on the amount of mass you can squeeze in there, why would temperature be different? (Hey, maybe the internal forces are so extreme that all loose forms of energy get condensed down to matter and so the inside is actually amazingly *cold*?)
A neutron star has already passed through the point where fusion is a concern, and a black hole has passed that by. So, err, maybe at some point bits of you might fuse? But you almost certainly ceased caring about that a long time ago, and if you didn’t you soon will.
Singularity or event horizon? The latter is sized by the mass. I don’t think we can say anything about the size of the former.
Roughly in order:
Wormholes are a mathematically possible solution to the equations of general relativity, and the required conditions are probably unlikely to occur in nature. It should be said that black holes were first discovered as a mathematical solution to the equations of general relativity, in fact the very first attempt at solving these equations (“let’s see what happens in a uniform universe where nothing is moving”) led directly to a black hole. That said, the conditions for black holes to exist are not at all onerous, which is probably why we observe them existing all over the place.
Wormholes as travel: obvious bollocks; going into one is as far as we can tell indistinguishable from going into a black hole for all practical purposes. Also, wormholes require negative energy density to remain stable, which makes about as much sense in a physics way as saying “for this dish, you need a negative number of chickens”.
Up close: every path in spacetime inside the event horizon points to the singularity. When the black hole is spinning, the singularity is not a point, but a circle (and also other things get complicated, look up “ergosphere” and “inner event horizon”). For black holes, it makes sense to talk about temperature, but only in the sense that the temperature of the event horizon is the blackbody radiation temperature of the Hawking radiation (or maybe it was the sum of temperature of everything that has fallen in? I don’t recall).
“The singularity of TON416 is … wide” no they mean the event horizon.
What is a black hole made of? The question does not make sense and should be un-asked; the only thing that is knowable is the event horizon. What’s inside? It’s unknowable; the “singularity” is only as real as the mathematics describing it, which everyone knows is incomplete. The singularity is a “divide by zero” kind of situation, mathematically; the physical meaning is “wait with that question until we have come up with something better”.
For an energy source: a possible, but shit one: build a Dyson sphere around the hole, and dump your trash into it, tied to a chain of dumpsters in such a way that the gravity pulls the (fully loaded) heavy side of the chain down while the (unloaded) light side goes up; tie it to a turbine and you have at least a few W.
CD @1: I’d recommend looking up stuff in the physics stackexchange for discussions and links.
As for the event horizon; it may not be a solid surface, but the question of whether you could cross it (in your own reference frame*) is, AFAIK, an open one.
https://physics.stackexchange.com/questions/79054/can-matter-really-fall-through-an-event-horizon
*Of course, from a distant observer’s POV, you’d never cross it.
Not a physicist, but I’ve absorbed way too much of the subject and I’m a computer scientist. Besides, I’m waiting for something to compile.
1. Some theories hold that the end of a wormhole can look like a black hole. Otherwise, you’re comparing apples and bananas. Actually creating a human-sized wormhole would take exotic and purely theoretical materials. The best hope for real-life wormholes comes from a cutting edge physics theory which contends quantum entanglement and wormholes are analogous. You’ll never be able to use these wormholes for travel or anything useful, alas.
2. Bending spacetime is easy, you’re standing on a ball of dirt that does it all the time. However, remember E = mc^2: the highest efficiency value I can find for a nuke is about 40%, and the heaviest they get is about a tonne. Mentally add up all the mass of the Earth, convert that to the energy of nuclear explosions, then hold out your arm. Congrats, the teeny bit of electrochemical energy you’re expending is enough to counter the spacetime warping of all that mass under your feet. Bending spacetime to do more than merely slow your aging down by a fraction of a second in a lifetime, and doing it in a controlled manner, is highly implausible and would take energy sources that we’d prefer to use on more useful things.
3. Our best guess is than nothing really falls in, per se; from the outside, it just moves slower and slower, and the light from it shifts ever more past infrared and into radio until it’s not really detectable at all. There’s no obvious heat generated, to us on the outside anyway. Some theories suggest a black hole does actually radiate a bit of energy, dubbed Hawking radiation, but for a reasonably-sized black hole that amount is so small you can’t really observe it. If any fusion occurs, it’s because matter circling the drain naturally orbits in a highly-compressed ring of former molecules, and its that ring and not the black hole itself that could be used as a power source.
4. One thing I don’t think is stressed enough: “singularity” is a code word for “the math breaks and gives us nonsense.” You can extend General Relativity and Quantum Mechanics a bit past the event horizon, but there’s always a point where all known physical theories just toss up their hands and walk away. There are no known forces that would stop matter from compacting ever-tighter, but “a spoonful of singularity has infinite mass” can’t be correct either. We don’t know what’s inside there, nobody’s come up with a credible and consistent theory for what could be in there, and the conditions are so extreme that no experiment can hope to come close to simulating it.
Dawkins was a good science writer, back when he was writing science. The Selfish Gene (1976) and The Extended Phenotype (1982) were both quite good. That was quite some time ago…
Answering as a former physicist who did not specialize in astrophysics… Other physicists correct me if I’m wrong.
1) Black holes as wormholes is fiction, for sure. However, I think the idea comes from the fact that trajectories just end at the singularity. You can think of a black hole like a cone, and objects follow lines along the surface of the cone. What happens to objects that reach the point of the cone? There’s nowhere for the line to go.
The real solution probably involves something something quantum.
2) Space travel in general is just way harder than sci-fi imagines it to be.
3) Under classical physics, there’s the “no-hair theorem”, which states that black holes only have three meaningful properties: mass, angular momentum, and electric charge. Note that temperature is not among these. Black holes don’t have heat. Your question of where the heat goes is really just a restatement of the black hole information paradox–where does the information go?
But under quantum physics, we have Hawking radiation, which many physicists believe resolves the information paradox. Hawking radiation implies a non-zero temperature. The information (and heat) is in the radiation.
Also note that when anything falls into a Black hole, it emits a lot of (non-Hawking) radiation before it even reaches the event horizon, so that’s going to account for a lot of the heat.
That happens before a star collapses into a black hole. A neutron star is essentially a star with such strong gravity that it fuses all the protons, neutrons, and electrons together into a massive pile of neutrons. Neutron stars are basically held up by the Pauli exclusion principle. Black holes form when gravity overcomes even that.
I didn’t watch the video and am not familiar with TON416, but surely they’re referring to the size of the event horizon.
4) I don’t know what black hole singularities are made of. Most of the space inside a black hole’s event horizon is empty though. The event horizon doesn’t represent any sort of physical material, it’s just a threshold at which gravity exceeds a certain strength.
1) Do wormholes actually exist?
Well, they have never been observed.
2) Black holes are far way.
Except for that time in 2012 when scientists fired up the LHC for the first time and created a black hole which ended our reality. It explains a lot doesn’t it?
link
It’s over 20 years old, but still worth a listen: https://www.bbc.co.uk/programmes/p00547f4
The blurb:
Melvyn Bragg and guests discuss Black Holes. They are the dead collapsed ghosts of massive stars and they have an irresistible pull: their dark swirling, whirling, ever-hungry mass has fascinated thinkers as diverse as Edgar Allen Poe, Stephen Hawking and countless science fiction writers. When their ominous existence was first predicted by the Reverend John Mitchell in a paper to the Royal Society in 1783, nobody really knew what to make of the idea – they couldn’t be seen by any telescope. Although they were suggested by the eighteenth century Marquis de Laplace and their existence was proved on paper by the equations of Einstein’s General Theory of Relativity, it was not until 1970 that Cygnus X 1, the first black hole, was put on the astral map. What causes Black Holes? Do they play a role in the formation of galaxies and what have we learnt of their nature since we have found out where they are?With the Astronomer Royal – 2001 Sir Martin Rees, Professor of Physics and Astronomy at Cambridge University; Jocelyn Bell Burnell, Professor of Physics at The Open University; Professor Martin Ward, director of the X-Ray Astronomy Group at the University of Leicester.”
Bragg did have Dawkins on a few times in the early days of the show (late 90s) but not lately. These three here, however, are very much not the “angling for a TED talk” type. JBB *discovered pulsars* ffs.
Explaining why a black hole produces light when ripping apart a star
I have a new theory that the information that gets lost into black holes comes out the other end as output from generative AI. But the information gets scrambled along the way, which explains the extra digits.
Regarding the “a teaspoon of black hole would weigh as much as Mt. Everest” bit, I never heard that about black holes but I have read that regarding neutron stars that have yet to collapse into a BH. I had always assumed it was because the space between the particles had been compressed out. Most of what we think of as solid is really just space. In my intro electricity course we would talk about the structure of an atom. I would pull out my “golf ball of science” and say something like “If an electron was this big, the proton of a hydrogen atom would be on average somewhere near Parkway Pizza” (which was way past the other side of campus). Now think of the volume encompassed by a sphere with that radius. It’s mostly nothing. A bit oversimplified for sure, but it gets the idea across to the freshmen.
sonofrojblake @13:
Laplace did more than suggest; he did a detailed (classical) calculation in an essay, a translation of which is reproduced as Appendix A in Hawking and Ellis’ The large scale structure of space-time.
@12, Reginald:
https://www.hasthelargehadroncolliderdestroyedtheworldyet.com/
Siggy @11:
Dunno about “anything”. Accretion disks around compact massive bodies (not necessarily black holes) can get pretty hot, but there’s nothing AFAIK which says any body falling in will emit radiation. At some point (maybe outside the event horizon) it might get torn apart by tidal forces, but that’s another matter, so to speak.
In addition to Ketil Tveiten’s #7, from Chandra:
Q: “Are worm holes traversable?”
A: … “So, in order to hold a wormhole open long enough for space travel, an incredible amount of negative energy would be required. For example, it has been estimated that to create a wormhole with a diameter one millionth the size of a proton, wormhole engineers would need negative energy equivalent in magnitude to the energy generated by ten billion suns in one year. As you can see, this would be a very expensive way to travel!
Further reading:
Much of the information presented here was adapted from:
L. Ford and T. Roman, “Negative Energy, Wormholes and Warp Drive” Sci. Am. Jan. 2000, p.46.
An excellent introduction to black holes and wormholes is:
K. Thorne, “Black Holes And Time Warps: Einstein’s Outrageous Legacy” W.W. Norton, 1994.”
Cranky Old Bastard (me) take: All the sci-fi-adjacent stuff (wormholes, etc) is bollocks until it isn’t, which will probably be never. Doesn’t mean people shouldn’t work on that stuff. It’s just given far too much importance in pop media. There’s so much cool stuff going on within our theories’ domains of validity, I don’t really get the layperson’s fascination with the speculative stuff.
“So, in order to hold a wormhole open long enough for space travel, an incredible amount of negative energy would be required.
My ex-girlfriend would never allow that!
[That’s actually inaccurate in many ways but I could NOT pass up a chance like that.]
I could name some people who emit copious amounts of negative energy.
Rob Grigjanis@#20:
All the sci-fi-adjacent stuff (wormholes, etc) is bollocks until it isn’t, which will probably be never. Doesn’t mean people shouldn’t work on that stuff. It’s just given far too much importance in pop media. There’s so much cool stuff going on within our theories’ domains of validity, I don’t really get the layperson’s fascination with the speculative stuff.
That sounds like a very good summary, thank you.
I have often thought that such speculation is perhaps actively harmful. It encourages people to believe that some great big macguffin may come along and neatly allow humans to side-step important problems we’d rather ignore. Population out of control? No problem: some old guy in a home lab will invent a warp drive and then we’ll have all the space (and hot alien chicks in colored paint with latex prostheses to mess with) that we could possibly need. No need to try to bring things into sustainability, we just wait ’till the macguffin comes along. And we wait and we wait and we wait. “Science Fiction considered dangerous” film at 11.
jimf@#15:
Regarding the “a teaspoon of black hole would weigh as much as Mt. Everest” bit, I never heard that about black holes but I have read that regarding neutron stars that have yet to collapse into a BH. I had always assumed it was because the space between the particles had been compressed out.
You’re right. I misspoke. Neutronium is not the same as collapsium(tm) which may not even be “matter”, apparently.
Most of what we think of as solid is really just space. In my intro electricity course we would talk about the structure of an atom. I would pull out my “golf ball of science” and say something like “If an electron was this big, the proton of a hydrogen atom would be on average somewhere near Parkway Pizza” (which was way past the other side of campus). Now think of the volume encompassed by a sphere with that radius. It’s mostly nothing. A bit oversimplified for sure, but it gets the idea across to the freshmen.
I’ve seen similar illustrations and have always found them to be mind-blowing.
Isn’t the problem something like that our models of how atoms work is that the models don’t work when the atoms get collapsed into something else, and how that might happen? Obviously, an absurdly powerful gravitational field might make things collapse, but is there a theory for that? Is energy released or consumed, etc?
Reginald Selkirk@#14:
I have a new theory that the information that gets lost into black holes comes out the other end as output from generative AI. But the information gets scrambled along the way, which explains the extra digits.
I just handed that off to midjourney and the results were not particularly compelling, even when I changed “digits” to “fingers”
sonofrojblake@#13:
It’s over 20 years old, but still worth a listen: https://www.bbc.co.uk/programmes/p00547f4
The blurb:
Melvyn Bragg and guests discuss Black Holes.
Ah, yes, I need to re-listen to that because obviously it did not stick.
That is a great show. It’s delightful the way Bragg gets real experts in their field to loosen stays and talk. And there are thousands of episodes.
It’s a tragedy that we in the US have Joe Rogan and the brits have Melvyn Bragg.
BTW, Frederik Pohl’s Gateway (1977) had a pretty big footprint on my imagination. Although I never quite understood why the hero reacted the way he did.
Marcus: Nobody writes novels about flying through a neutron star.
But they do write novels about living on the surface of one. Dragon’s Egg and its sequel, Starquake, by Robert L Forward. I warmly recommend them (I can’t offer the same book recommendation guarantee as Marcus does, though).
@28 Marcus:
Because he was the ultimate product of completely unrestrained capitalism?
Dragon’s Egg is a corker. Didn’t know there was a sequel.
@mjr, 27:
If you’re going to play that game, it’s a tragedy that in the UK we have Andrew Tate and the Yanks have Joe Rogan. I mean, at least Rogan is on some level funny and not AFAIK an actual rapist and people trafficker. Low bar, I know, but…
There are in fact just over one thousand episodes of In Our Time – I think the thousandth was in September. It’s pretty cool how the BBC have curated it to podcasting such that on the Android app of my choice (Castbox) I can choose to subscribe to (and thus download any episode of) just the general show feed, and/or have a feed of just the science ones, just the history ones, just the philosophy ones and so on. I don’t think I’ve ever made it to the end of the one on phenomenology awake, but please don’t think that’s not a recommendation. Then again, there’s an early episode on consciousness that I just can’t listen to, because it’s an early one with just the two guests, and one of them is a complete arse. For instance, when asked to define consciousness, his response was “it is, in a way, for a world, to exist”. Which clearly makes no fucking sense at all, but he repeated it. It was infuriating. Give it a try!
As a lay person here, I’ve always thought of the event horizon as the point where you say “fuck it, that’s above my pay grade” and wander off. I kinda get the vibe that is what our mathematical theories do too
Siggy @11
“2) Space travel in general is just way harder than sci-fi imagines it to be.”
The physics is way harder than sci-fi imagines it, the distances are just mind boggling and the environment messes complex things up. When you start considering the biology it gets even worse. there’s a reason humans haven’t left low earth orbit in the last 50 years
The way I think of a black hole is that the singularity is a point of zero volume, thus having infinite density with variable mass, angular momentum, and charge, each of which change with all that falls through the event horizon and the evaporation loss from Hawking radiation. I also think that once past the event horizon all things must travel faster than C to get to that infinitely dense singularity. One thing not mentioned often is the linear momentum imparted to the black hole by infalling mass. All those stellar masses that fell into Sagittarius A* have kept it moving along with the rest of our galaxy in its journey with our local group.
Alan @33:
No, the local speed limit anywhere outside the singularity is always c. In the simplest case of an uncharged, non-rotating black hole; If you were carrying a stopwatch as you fell in from the event horizon (and ignoring little details like being torn apart by tidal forces ;-)), the time it measured to get to the singularity would be τ = πGM/c³, where M is the black hole’s mass.
Depending on the mass of the black hole, that could vary from microseconds to days.
OT: Life imitates art
Dog with six legs has operation to remove extra limbs
The rumor that the dog’s name is ‘Midjourney’ is entirely unfounded.
Rob Grigjanis @8
“As for the event horizon; it may not be a solid surface, but the question of whether you could cross it (in your own reference frame*) is, AFAIK, an open one.
https://physics.stackexchange.com/questions/79054/can-matter-really-fall-through-an-event-horizon
*Of course, from a distant observer’s POV, you’d never cross it.”
Sean Carroll made a comment in one of his talks at the RI that a distant observer would see objects disappear behind the event horizon. The EH would react to the mass of an object and expand to engulf it.
The Royal Institution YouTube channel has a recent lecture by Carlo Rovelli on White Holes.
captainjack: Was Carroll talking about quantum mechanics in a curved spacetime (firewalls, Hawking radiation, etc)? That’s been his thing for a while. Classically (general relativity without quantum mechanics) you would never see a body reach the event horizon.
As for Rovelli: smart guy, but I find it hard to read or watch him, since he’s a signatory to this piece of shit.
https://internationalpeaceconference.info/it/pagina-iniziale/?__cf_chl_tk=6FZLsIpUbpuDZw023Wp5Yshy26WxQbiYleeADArTeBI-1705451482-0-gaNycGzNDOU
I don’t remember the lecture well. I think it was fairly recent.