Guest post: Nearly all knowledge is provisional

Originally a comment by John Horstman on Knowing v accepting.

All knowledge is functionally Bayesian – it’s a matter of probability of being true, which we can sometimes even formally quantify, but it’s never 100%, with the exception of constructed abstractions (like mathematics or other formalized abstract systems, where things can have definite truth values because we construct them that way) and the existence of at least one ‘mind’ – some system capable of cognition such that I can even be here considering the questions.

This is due, as Ibis3 points out, to the solipsism problem, which can never be resolved – not even if there was a god (or some other outside observer of the universe) and you or I met it, because those experiences would still be subjective and questionable (indeed, many people HAVE met a god as far as they are concerned, and I doubt the veracity of those experiences categorically).

What’s ridiculous is the “therefore god [or other mystical claims]” leap Armstrong is implicitly defending – once you know that (nearly) all knowledge is provisional, you need some basis for whether you provisionally accept any proposition, and with what degree of certainty. Evidence that is validated by multiple subjectivities (assuming that other people exist, of course; and if they don’t, then really, none of this matters because I’m just arguing with myself, on the Internet, which is actually a delusion, so whatever) has been demonstrated over a long time to be our very best means of determining what is most likely to be true. Side note: this is why the scientific method has proved so useful, though that epistemic approach shows up everywhere we have groups of humans, as with cultural norms, shared historical or cultural narratives, etc. – we agree, so it is true (even when it isn’t). So what defenders of faith ignore is that lack of certainty does not mean that anything imaginable is thus equally certain – even without the possibility of perfect knowledge or actual independent verification (everyone verifying what I see could also be my own delusion), not all possibilities are equally likely.


  1. blbt5 says

    Bayesian theory has been really revolutionary in an epistemic sense, for example the work of Richard Carrier applied to disproving Christian mythology. But more importantly, it places a primary value on perspective, mechanism and consistency. This can have startling revelatory effect when applied to seemingly unresolvable problems that cannot be approached experimentally. For example, the origin of life in the universe- abiogenesis – involves complex geochemical mechanisms operating over deep time. Most biologists, with whom I’ve had a few heated exchanges recently, believe life originated here on Earth and I had agreed with that until recently. However, using a Bayesian approach, if one considers the very small timespan between cooling of the Earth and appearance of the first known life (rather complex cyanobacteria), the age of the Universe (roughly ten times that value), and known mechanisms of meteor impact transfer and interstellar diffusion, it now seems to me more likely, in a Bayesian sense, that life originated earlier in our galaxy, perhaps several billion years earlier than the origin of our solar system. This also fits expected interstellar diffusion kinetics, and is illustrated quite nicely in one of Neil Tyson’s (often overlooked) Cosmos episodes. This also more clearly reveals previous alternatives, such as “deep-sea vent” origins to be irrational and fundamentally disconnected with any mechanism of abiogenesis. Since a priori the conditions for abiogenesis are much more restricted and rarer than the conditons for the first microbes which quickly adapted to a multiplicity of autotrophic and chemoautotrophic modes, it is extremely unlikely that the historical conditions for both abiogenesis and evolution would be coincident on the same planet. Finally, a Bayesian perspective opens up the possible chemical mechanisms to geochemical configurations that may be peculiar and historical, which is closer to how real evolution works. For example, birds don’t evolve in the air and astronauts didn’t originate in space. It may be that the conditions for abiogenesis were not ideal for evolution, so that impact transfer may not have been fortuitous but necessary. All of these consequences from essentially a Bayesian analysis! The first test may be from probes sent to moons and planets such as Europa and Mars. Our planet has presumably been spraying the solar system with microbes for billions of years by impact transfer, so the life we find may not be native, but adapted from microbes evolved on Earth. And there are political implications: if it is true that we are in a sense all extraterrestrial, and this is not our native planet but an adopted one, another enervating solipsism will be eliminated – bio-chauvinism, if you will. And we may realize the fantastically diverse life on our planet is far too important and precious to waste. Religion has been rightly eviscerated by one of Christopher Hitchen’s favorite arguments, the absurdly coincidental appearance of religion hundreds of thousands of years after the appearance of humans. The coincidental appearance of life on Earth many billions of years after the development of the Universe, is, from a Bayesian standpoint, almost equally unlikely.

  2. says

    blbt5, I don’t understand your final point. (I’m sure there’s more I don’t understand, but your final point is what I’m asking about.) Life originated somewhere, right? Whether it was Earth, Qo’noS, Skaro or wherever, it happened somewhere, presumably at some point after the development of the Universe, right? Is your point that not-Earth is a more likely candidate than Earth, or are you saying something more than that?

  3. monad says

    I would argue that in a certain philosophical way, even things like mathematics are provisional. I certainly don’t expect logic to be inconsistent, but that’s not because there’s any way to prove it, it’s because all our experiences with it indicate that it’s not.

    The rules we use are based on that experience. We tell people (P implies Q) means (not Q implies not P), but it doesn’t mean (Q implies P). When people ask why not, we usually give them examples showing it doesn’t work in practice. It might not be meaningful to talk about the probability of logic being correct, but it’s still something we’ve established inductively.

    That’s my thought, anyway, I hope it’s not too off-topic.

  4. says

    @1 blbt5:

    Does your bayesian analysis take into account the likelihood of life surviving the incredibly dangerous journey of interstellar space? Unless life evolved in the solar system and was seeded to Earth from there, I think it’s -INCREDIBLY- unlikely that single-celled organisms from another solar system happened to survive being blasted off their planet, ride out the interstellar hazards of radiation, supernovas, collisions with other asteroids/space debris etc, probably for millions (if not billions) of years and then landed on Earth, which it happened to find so pleasantly structured that it could take root and thrive into the ecosystem that we see today.

    I think there’s life outside of Earth. But in the same way I don’t think we’ll manage to seed another solar system in the future, I highly highly doubt that Earth was seeded with life from outside the solar system.

  5. blbt5 says

    1. Drewvoge, yes, that’s all I’m saying. In all Bayesian likelihood, not-Earth.
    2. Drewzilla: yes it does. Yes, all of the independent elements you cite are definitely salient and necessary but are known to occur already. Perhaps the newest area of research in astrophysics is interstellar diffusion, not well understood, but to address your points: Even in the apparently densest areas of interstellar particles ranging from asteroids to dust, nearly all the space is emptier than the most powerful laboratory vacuum. In this months’s issue of Science for example, the dust clouds of stellar nurseries are reported to have a density of about one molecule per cubic meter. So collisions of diffusing particles ranging from a few micrograms to a few kilograms are extremely unlikely to encounter collisions over ranges of many hundreds of light-years travel, unless drawn in by gravitational attraction. As to the whole possible mechanism of impact transfer as a plausible seeding mechanism, perhaps the most important point is that most of the biomass of the planet happens to reside in the Earth’s crustal microbial flora, approaching a density of many billions/ml of organisms in many places, and often containing communities largely encased in rock. It is now known, for example that the reports of “T. Rex tissue” a decade ago were really just inclusions of reddish filamentous bacteria. We also now know, since the past 20 years, not only that meteorites from Mars are found on Earth, but that these are not uncommon, accounting for about 0.1% of all known meteorites, and that water inclusions are commonly found. This proves not only that impact transfer occurs on a significant scale in our own solar system, but that the interior environment of meteorites can survive unscathed. It has been known for decades that bacteria survive in space, can tolerate high loads of ionizing radiation, and can survive frozen for at least tens of millions of years. Importantly, the microbial geoflora of the Earth occupy and are adapted to a geothermal zone common not just to Earth, but to most condensate planetary bodies with a molten core and thus a source of geothermal energy. It is therefore likely that primal abiogenetic organisms were similarly adapted or rapidly proliferated into the geothermal crustal zone extending perhaps tens to hundreds of miles below the surface, and thus are both ideally positioned and adapted both to be ejected by meteor impact and survive ejection, travel, gravitational capture and reentry to another planet. Finally it’s important to consider spacetime expansion, which has been proceeding up to now in the slow asymptote (hence roughly linearly) of an acceleration, so that in the first couple of billion years, the Universe was only a fraction of its present size and diffusion was also thus fractionally smaller, but hence exponentially shorter to travel in cubic space, so seeding was easier. Trillions of years from now the Universe will dramatically and nonlinearly ramp in size and virtually eliminate interstellar diffusion. I agree that it is unlikely we will ever see extrasolar seeding since the population of planets even within a hundred light-years is very small, even if a significant fraction could support even microbial life. On the other hand, if microbial seeding by impact transfer is operative, the Earth has already seeded a significant fraction (0.1 – 10%) of our galactic space since the 3.5 billion years since microbial life started to proliferate on Earth.

  6. says

    You’re using the vastness of space to point out that the ejecta from a planet won’t have any collisions with interstellar material (presumably before it hits Earth). The very same vastness of space disproportionately reduces the chances of matter foreign to the solar system from coming in contact with the Earth. Using rocks from Mars as examples of the ability for rocks to travel through space relatively unharmed is laughable when you compare it to the distances between Earth and Mars and the distance between our solar system and the very next closest one.

    Just because we have some ejecta from the local solar system that trades between planets doesn’t really give us any data whatsoever on life and it’s ability to travel between solar systems.

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