Emergence of Life in an Inflationary Universe (2020)(nature.com)
nature.com
Emergence of Life in an Inflationary Universe (2020)
https://www.nature.com/articles/s41598-020-58060-0
58 comments
None of this probabilistic reasoning matters in the face of the anthropic principle. If there are infinite universes, we could easily be in the mostly stupidly improbable one possible, since we are not observing (and cannot observe) all possible universes, let alone an average one. This why a whole ton of speculation is completely meaningless, because we clearly live in a stupidly improbable universe that is already "fine tuned"--and that's not a problem. It doesn't mean there has to be God or anything. In fact, the settings of our universe imply nothing.
Indeed we might never be able to measure the global normalization of the likelihood function of life, but that doesn't mean we can't investigate it's local properties. In fact, I think we can learn a lot from doing just that.
This article's probabilistic reasoning seems interesting, because it suggests it is very unlikely we will find other random intelligent life within our observable universe. As opposed to another sense of the anthropic principle, where our universe is fine tuned to an extraordinary degree but the chances of finding other intelligent life nearby is higher.
> None of this probabilistic reasoning matters in the face of the anthropic principle... In fact, the settings of our universe imply nothing.
What a sad anthropic principle that would be!
In fact, you can use the fact that humans exist to put (loose) constraints on this universe's parameters. For example, clearly the average temperature must be below one billion Kelvin. Making that kind of argument tighter and more precise actually leads to interesting results: bounds on spacetime black hole formation rate, limits on densitiy of dark energy, etc.
The authors in OP's post take an interesting variant of this line of reasoning: If the universe is "really bad" at producing long strings of RNS, then humans must just be a fluke. In that case, maybe most life in the multiverse exists alone in its own observational bubble. They caculate with their model that self-replicating DNS is indeed hard to replicate. This also means that finding aliens would provide strong evidence against their model.
The weakest form of anthropic argument is the tautological aspect you mention, but I wouldn't cut it so short.
What a sad anthropic principle that would be!
In fact, you can use the fact that humans exist to put (loose) constraints on this universe's parameters. For example, clearly the average temperature must be below one billion Kelvin. Making that kind of argument tighter and more precise actually leads to interesting results: bounds on spacetime black hole formation rate, limits on densitiy of dark energy, etc.
The authors in OP's post take an interesting variant of this line of reasoning: If the universe is "really bad" at producing long strings of RNS, then humans must just be a fluke. In that case, maybe most life in the multiverse exists alone in its own observational bubble. They caculate with their model that self-replicating DNS is indeed hard to replicate. This also means that finding aliens would provide strong evidence against their model.
The weakest form of anthropic argument is the tautological aspect you mention, but I wouldn't cut it so short.
> to put (loose) constraints on this universe's parameters.
I was referring to the fundamental constants of physics. A lot of argumentation has happened around whether they are "fine-tuned". In the sense that a small change has a radical effect on matter and spacetime, to the point where chemistry would not work at all to make any kind of biological entities, YES, YES, absolutely, our universe is fine-tuned for human life. Or vice versa. Human life is fine-tuned for exactly this universe, planet, climate (!), and time period!
There are several traps that philosophers and cosmologists keep falling into, primarily around probability. Clearly we are not in an average universe, from the very get go. We have no idea how these constants get set, what set them, if there was a universe before that had different constants, if universes elsewhere have different constants. Even if we did know that other universes exist, we have no way to reason about the probability of our universe--we don't know the distribution. If we were to start positing that the constants are randomly chosen, then we're in a very special universe indeed. But somehow, when it comes to these constants, the "probabilistic thinking" just gets forgotten. Philosophers just blink and look away. These constants are special as hell.
The next issue is that there is a huge philosophical problem in assuming that probability is even a thing, because every rando weird thing that has happened has fed into the stupidly improbable fact of our existence. The assumption that we are drawn from some kind of distribution is just a philosophical axiom that goes unstated. Maybe we aren't drawn from some probability distribution but are instead linked in causal chains impossibly long and intricate that using probability has a tool becomes meaningless. To understand what I mean there, just recall that the dinosaurs ruled the Earth for over a hundred million years. They were wiped out by an asteroid with a stupidly improbable chance of impact. The mass extinction that followed was so brutal that literally every single thing that survived pretty much made it by the skin of their teeth--including mammals. So every Tom, Dick, and Harry rabbit that managed to eek out survival on the blasted plains, carrying their painstakingly tuned genetic code, mattered. To the extent that many whole genera of life today depend on literally just a few individuals having survived this cataclysm. The Earth didn't mint new kinds genomes from nothing, they grew and branched off what survived. And it wasn't luck...they were better adapted to the new hellscape. Or was it? Sliced as finely as single individuals, we might be here because a single proto mammal survived a harsh winter or leaped out of the jaws of a predator at just the right time. Put odds on that one.
But speaking of "luck", it wasn't "luck" that the asteroid hit at that moment. It hit because of orbital mechanics, a complex but completely predictable mathematical certainty of orbits and periods. Pretty much all the macro events that we observe as being to have led here to this moment with these funny barely space-faring apes yammering at each other through HN are deterministic, not stochastic events. And the next thought that pops into your head on how to reply won't be stochastic either.
Reasoning about our universe using some Drake-equation-esque probability floundering is a complete waste of time. We got here by history and this whole freaking show is one giant example of selection bias. Average universe, my ass!
I was referring to the fundamental constants of physics. A lot of argumentation has happened around whether they are "fine-tuned". In the sense that a small change has a radical effect on matter and spacetime, to the point where chemistry would not work at all to make any kind of biological entities, YES, YES, absolutely, our universe is fine-tuned for human life. Or vice versa. Human life is fine-tuned for exactly this universe, planet, climate (!), and time period!
There are several traps that philosophers and cosmologists keep falling into, primarily around probability. Clearly we are not in an average universe, from the very get go. We have no idea how these constants get set, what set them, if there was a universe before that had different constants, if universes elsewhere have different constants. Even if we did know that other universes exist, we have no way to reason about the probability of our universe--we don't know the distribution. If we were to start positing that the constants are randomly chosen, then we're in a very special universe indeed. But somehow, when it comes to these constants, the "probabilistic thinking" just gets forgotten. Philosophers just blink and look away. These constants are special as hell.
The next issue is that there is a huge philosophical problem in assuming that probability is even a thing, because every rando weird thing that has happened has fed into the stupidly improbable fact of our existence. The assumption that we are drawn from some kind of distribution is just a philosophical axiom that goes unstated. Maybe we aren't drawn from some probability distribution but are instead linked in causal chains impossibly long and intricate that using probability has a tool becomes meaningless. To understand what I mean there, just recall that the dinosaurs ruled the Earth for over a hundred million years. They were wiped out by an asteroid with a stupidly improbable chance of impact. The mass extinction that followed was so brutal that literally every single thing that survived pretty much made it by the skin of their teeth--including mammals. So every Tom, Dick, and Harry rabbit that managed to eek out survival on the blasted plains, carrying their painstakingly tuned genetic code, mattered. To the extent that many whole genera of life today depend on literally just a few individuals having survived this cataclysm. The Earth didn't mint new kinds genomes from nothing, they grew and branched off what survived. And it wasn't luck...they were better adapted to the new hellscape. Or was it? Sliced as finely as single individuals, we might be here because a single proto mammal survived a harsh winter or leaped out of the jaws of a predator at just the right time. Put odds on that one.
But speaking of "luck", it wasn't "luck" that the asteroid hit at that moment. It hit because of orbital mechanics, a complex but completely predictable mathematical certainty of orbits and periods. Pretty much all the macro events that we observe as being to have led here to this moment with these funny barely space-faring apes yammering at each other through HN are deterministic, not stochastic events. And the next thought that pops into your head on how to reply won't be stochastic either.
Reasoning about our universe using some Drake-equation-esque probability floundering is a complete waste of time. We got here by history and this whole freaking show is one giant example of selection bias. Average universe, my ass!
The probability for one asteroid hitting earth is low, but the probability that some asteroid will hit in a billion year time window is extremely high.
The specific asteroid that hit the Earth was not produced by a stochastic process, but a deterministic one. You are mistaking the tool (probability modeling) for reality. In reality, had that particular asteroid not hit at that time, yes, sure one would eventually have, but it might have been tens or hundreds of millions of years later....that a different asteroid hit, at which time the ecosystem of non-dominant species could have been completely different, and mammals would not have come out on top (and led to us). So when you actually look at reality and the casually-related events, you have to keep taking on massive amounts of zeroes to come up with probabilities for how things happened in exactly just the right way (this way)--we are talking thousands, maybe hundreds of thousands of zeroes, like 10^-1000000. That's exactly the problem with probability going wonky; so many things are not independent random variables. The whole analysis is wrong.
But that's just part of what I am saying. The odds are low, yes, but everything is distorted because of survivorship bias. Since the odds of our reality looking (exactly) like this are astronomically low, it is by definition not the case that we are in an average scenario, we're in a super rare scenario; but moreover, we are survivors in that scenario, and literally everything we look back at is hugely biased by the fact that we exist. So we are absolutely not in an average case, because the selection bias of surviving is inescapable.
Put another way, there could be a process that rolls a die every second and 99.99% of the time, destroys the universe. In the .01% of time, we survive and don't even notice. We keep perceiving those .01%, and multiplied together, the odds of surviving even a single minute are astronomically low. In the average universe in this scenario, everyone is dead! But we can't perceive universes in which we are dead; we wouldn't even be able to discover this process exists! So the whole business with universes randomly chosen from a distribution is just a bad model, as clearly our existence cannot be explained that way. Philosophers and cosmologists keep assuming that this is going on and that we must be in some average scenario. Uh, no.
But that's just part of what I am saying. The odds are low, yes, but everything is distorted because of survivorship bias. Since the odds of our reality looking (exactly) like this are astronomically low, it is by definition not the case that we are in an average scenario, we're in a super rare scenario; but moreover, we are survivors in that scenario, and literally everything we look back at is hugely biased by the fact that we exist. So we are absolutely not in an average case, because the selection bias of surviving is inescapable.
Put another way, there could be a process that rolls a die every second and 99.99% of the time, destroys the universe. In the .01% of time, we survive and don't even notice. We keep perceiving those .01%, and multiplied together, the odds of surviving even a single minute are astronomically low. In the average universe in this scenario, everyone is dead! But we can't perceive universes in which we are dead; we wouldn't even be able to discover this process exists! So the whole business with universes randomly chosen from a distribution is just a bad model, as clearly our existence cannot be explained that way. Philosophers and cosmologists keep assuming that this is going on and that we must be in some average scenario. Uh, no.
Anthropic principle makes sense only for the past, not the future. We live in a universe with certain rules that make life possible, but there is no guarantee for the future. So why do the rules stay the same? The Bolzmann brain argument seems more probable.
what do you mean by guarantee for the future, why do you think that our universe have "guarantee for our future"?
Perhaps I should have phrased it differently to make it more clear:
If you make the assumption that our universe is drawn out of an infinite set of universes (saying we're here because of the anthropic principle), then the likelihood that life is possible in the future approaches zero, because the anthropic principle only says something about the past.
If you make the assumption that our universe is drawn out of an infinite set of universes (saying we're here because of the anthropic principle), then the likelihood that life is possible in the future approaches zero, because the anthropic principle only says something about the past.
> anthropic principle only says something about the past.
and it says nothing about the future, so I don't know why you think "likelihood that life is possible in the future approaches zero". If anything the possibility in the future correlates with it in the past.
Also we are not concerned with life that will start in the future, when we talk about extraterrestrial life, we're talking about now or in the past.
and it says nothing about the future, so I don't know why you think "likelihood that life is possible in the future approaches zero". If anything the possibility in the future correlates with it in the past.
Also we are not concerned with life that will start in the future, when we talk about extraterrestrial life, we're talking about now or in the past.
> and it says nothing about the future, so I don't know why you think "likelihood that life is possible in the future approaches zero".
Because usually the assumption in the context of the anthropic principle is that the likelihood of life is small, but the anthropic principle makes it appear as if it's 100%.
Because usually the assumption in the context of the anthropic principle is that the likelihood of life is small, but the anthropic principle makes it appear as if it's 100%.
There is no evidence that there are infinite universes and indeed the belief in such a concept absent any evidence beside "nothing says there can't be" by scientific people is a religious belief on the order of there being a god except with less elf honesty.
We have never detected an alternate universe and we don't even have math that makes it probable. It's just a concept. The same way "there's no reason entropy can't run backwards according to the physics" doesn't stop us not having any evidence for backwards running entropy or negative mass or a million other things that might conceivably exist but have no real evidence but sound cool.
We have never detected an alternate universe and we don't even have math that makes it probable. It's just a concept. The same way "there's no reason entropy can't run backwards according to the physics" doesn't stop us not having any evidence for backwards running entropy or negative mass or a million other things that might conceivably exist but have no real evidence but sound cool.
The most philosophically and mathematically consistent interpretation of Quantum Mechanics is that there are "many worlds". This is a very strong hint (but not proof, per-se) that there isn't a singular, unique Universe in the classical sense.
In other words, there is a continuum of possibilities where all scenarios consistent with the laws of physics are played out.
Note that this is not evidence (not even circumstantial) that there are other universes with different laws of physics. Just universes with different states or boundary conditions.
Still though, if MWI is true, then there are effectively infinite possibilities in which the chance of life occurring somewhere approaches certainty.
In other words, there is a continuum of possibilities where all scenarios consistent with the laws of physics are played out.
Note that this is not evidence (not even circumstantial) that there are other universes with different laws of physics. Just universes with different states or boundary conditions.
Still though, if MWI is true, then there are effectively infinite possibilities in which the chance of life occurring somewhere approaches certainty.
> The most philosophically and mathematically consistent interpretation of Quantum Mechanics is that there are "many worlds".
Why is "many worlds" the most mathematically consistent? (I won't bother asking for the philosophical bit; I'm sure it's too long for an HN post.)
Why is "many worlds" the most mathematically consistent? (I won't bother asking for the philosophical bit; I'm sure it's too long for an HN post.)
We have no evidence that we are randomly distributed over some population of universes, but that doesn't stop misguided philosophers from assuming that. I didn't assert infinite universes; rather the opposite. It's reasoning like this that is asserting other universes. One thing is certain; ours is super weird and has definitely produced self-aware apes in a long series of evolutionary accidents on a single planet.
What's more interesting is whether our universe can be described by finite information (closed formulae or not, even a stupidly huge but finite trace of all quantum events would suffice). If it's finite information then its description is encoded in every transcendental number in mathematics--which is an infinite number, including the number pi.
Don't trifle with infinity. I wasn't.
What's more interesting is whether our universe can be described by finite information (closed formulae or not, even a stupidly huge but finite trace of all quantum events would suffice). If it's finite information then its description is encoded in every transcendental number in mathematics--which is an infinite number, including the number pi.
Don't trifle with infinity. I wasn't.
Having any belief at all, none, one, many, infinite, all falls into the same category. We don't know.
To me it seems like the additional universes in this context serve a purpose similar to (my understanding of) additional dimensions in math/physics. It allows you to navigate around singularities.
To me it seems like the additional universes in this context serve a purpose similar to (my understanding of) additional dimensions in math/physics. It allows you to navigate around singularities.
> Having any belief at all, none, one, many, infinite, all falls into the same category. We don't know.
If you have no evidence for it, your belief in a multiverse is religious not agnostic.
>To me it seems like the additional universes in this context serve a purpose similar to (my understanding of) additional dimensions in math/physics. It allows you to navigate around singularities.
This is additional dimensions in physics, and we just don't have any actual evidence that a multiverse exists. We have a some suppositions that say 'well there's nothing to say it couldn't exist' but no evidence that it could.
You could view that as 'useful' but you can't judge its truthfulness or whether reality reflects such a 'purpose'. Either something exists or it doesn't, and a multiverse is a strictly religious belief at this point.
If you have no evidence for it, your belief in a multiverse is religious not agnostic.
>To me it seems like the additional universes in this context serve a purpose similar to (my understanding of) additional dimensions in math/physics. It allows you to navigate around singularities.
This is additional dimensions in physics, and we just don't have any actual evidence that a multiverse exists. We have a some suppositions that say 'well there's nothing to say it couldn't exist' but no evidence that it could.
You could view that as 'useful' but you can't judge its truthfulness or whether reality reflects such a 'purpose'. Either something exists or it doesn't, and a multiverse is a strictly religious belief at this point.
I can see two ways around the low probability problem, for RNA abiogenesis:
1) The crystal gene hypothesis of A. G. Cairns-Smith. As a clay crystal grows and splits, the info in the crystal's defect structure is replicating with impressive fidelity, and those defects also interact with the surroundings. So you get the Darwinian game bootstrapped pretty much for free. Later on, the crystals start using organic polymers; later still, the polymer technology is developed well enough to take over from the clay. So this might make abiogenesis reasonably probable on one planet.
2) An observable universe is just any epsilon size patch, on an inflationary universe. The space-time curvature of our whole observable universe is too small to measure, hence the radius of our inflationary universe is a large multiple of the 13 G-lightyear radius we can observe. So abiogenesis could be highly improbable in any observable universe, answering Fermi's paradox, yet be probable within the much greater volume of an inflationary universe (maybe this is what TFA said? TLDR [Edit: yeah, it says that right in the abstract]). And there could even be a large number of inflationary universes, for all we know.
1) The crystal gene hypothesis of A. G. Cairns-Smith. As a clay crystal grows and splits, the info in the crystal's defect structure is replicating with impressive fidelity, and those defects also interact with the surroundings. So you get the Darwinian game bootstrapped pretty much for free. Later on, the crystals start using organic polymers; later still, the polymer technology is developed well enough to take over from the clay. So this might make abiogenesis reasonably probable on one planet.
2) An observable universe is just any epsilon size patch, on an inflationary universe. The space-time curvature of our whole observable universe is too small to measure, hence the radius of our inflationary universe is a large multiple of the 13 G-lightyear radius we can observe. So abiogenesis could be highly improbable in any observable universe, answering Fermi's paradox, yet be probable within the much greater volume of an inflationary universe (maybe this is what TFA said? TLDR [Edit: yeah, it says that right in the abstract]). And there could even be a large number of inflationary universes, for all we know.
One nice thing about 1) is that it is more falsifiable than 2). 2) basically gives us the ability to explain any almost arbitrarily unlikely event (at least unless we figured out a lower bound on the space time curvature of the observable universe). You might as well say that life is vanishingly unlikely but a series of vanishingly unlikely many-worlds quantum coincidences happened to result in the particular universe we see.
There is a sort of philosophical upper bound on the total size of the Universe in an eternal-inflation scenario. This is the Boltzmann brain paradox. The argument goes that if there are infinitely many universes it is infinitely more likely for you to be a brain randomly fluctuating into existence in the vacuum, rather than being an actual human being evolved through evolution.
This conclusion is obviously absurd, so the argument goes that there can't be infinitely many places in which random things can happen in the Universe. Note that the size of the Universe required to produce a Boltzman brain is much larger than that discussed in the article. It's still nice to think that there might be an upper bound for us to avoid some of the more daunting implications of the anthropic principle.
This conclusion is obviously absurd, so the argument goes that there can't be infinitely many places in which random things can happen in the Universe. Note that the size of the Universe required to produce a Boltzman brain is much larger than that discussed in the article. It's still nice to think that there might be an upper bound for us to avoid some of the more daunting implications of the anthropic principle.
Your second point is probably the most critical for this article; all we can conclude (eventually) is an upper bound on the probability of abiogenesis for a certain volume, total mass, age, or number of stars. There is literally no lower bound; there may be uncountably many other inflationary universes without life.
Yeah I think the idea that the first self-replication was RNA-based to be really really dubious.
Going straight to working RNA is a huge assumption in the analysis, but it's thought provoking to set some sort of lower bound and see how big the cosmos would need to be.
Still, somehow we may find a process like natural selection at a cosmic level that makes life way more likely than a purely random starting sequence.
Still, somehow we may find a process like natural selection at a cosmic level that makes life way more likely than a purely random starting sequence.
Atheists: "We have faith natural selection at a cosmic level makes life way more likely."
Christians: "We have faith supernatural selection at a cosmic level makes afterlife way more likely."
Christians: "We have faith supernatural selection at a cosmic level makes afterlife way more likely."
It seems much more likely to me that life started as an 'autocatalytic set' of molescules, each of which contribute to catalysing reproduction of the whole set, rather than a single strand of active RNA that can reproduce itself.
If we look at life now, DNA does not reproduce itself directly, there is an entire ecosystem of chemicals that reproduces itself collectively, using RNA/DNA as a blueprint.
The question then is how a set of molecules encoded itself in RNA, but I see that as much more envisionable (eg some RNA, and a host set of catalysts) than a self-reproducing strand of RNA appearing all at once.
If we look at life now, DNA does not reproduce itself directly, there is an entire ecosystem of chemicals that reproduces itself collectively, using RNA/DNA as a blueprint.
The question then is how a set of molecules encoded itself in RNA, but I see that as much more envisionable (eg some RNA, and a host set of catalysts) than a self-reproducing strand of RNA appearing all at once.
Is a single strand of rna with all the right nucleotides to self reproduce the only starting point for life? I feel like there must be alternatives- perhaps a whole network of simpler organisms that each could do a small piece of a complete replication. I’m not a biologist so I can’t say- but notably, neither is the author (he’s an astronomer). I’d like to hear the point of view of a biologist on this.
One somewhat incremental approach, is called a hypercycle: several simple self replicators "form an alliance" wherein they promote each other's self replication.
Not specific to RNA.
And I'm not a biologist.
Not specific to RNA.
And I'm not a biologist.
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To my simple mind, unless we find another case of life in this universe, there is no way to determine/estimate/calculate the frequency/probability of origin of life. Unless someone can convince me, in a simple way, that it is possible to determine.
I took a course from the Complexity Explorer on the origins of life. It made the point that although understanding life is hard, life is actually seemingly easy when considered in terms of it showing up or starting. It pointed to evidence that life began basically as soon as Earth formed, basically as soon as the oceans arrived.
The Solar System itself has plenty of examples of water. For example, Enceladus is surmised to be completely covered in an ocean below its icy crust. As far as I know, there's not much evidence that points to life as being special. Earth is certainly special in the time window that we are experiencing it in given its balances of energy, heat, water, etc.
Utilizing models to predict what's out there doesn't seem all that controversial when evidence points to life not being all that hard cosmically. We just don't have strong enough binoculars yet.
The Solar System itself has plenty of examples of water. For example, Enceladus is surmised to be completely covered in an ocean below its icy crust. As far as I know, there's not much evidence that points to life as being special. Earth is certainly special in the time window that we are experiencing it in given its balances of energy, heat, water, etc.
Utilizing models to predict what's out there doesn't seem all that controversial when evidence points to life not being all that hard cosmically. We just don't have strong enough binoculars yet.
We might never know with complete certainty, but then what can we know? Exploring the limits of the theories we pose is the only way to gain knowledge. The physical world is after all fairly predictable. Even if we will never know anything with certainty.
Well this article/study talks about the likelihood by looking at the likelihood that an RNA sequence randomly forms long enough enough number of times until a self replicating sequence exists. Such a probabilistic approach indicates that life, while not necessarily rare in the universe, might be rare enough that it is unlikely for it to occur twice in a volume that is observable from one occurrence, or that there is some unknown mechanism that makes it more likely.
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> Unless someone can convince me, in a simple way
Seems like you're happy with your own theories.
Seems like you're happy with your own theories.
I have the same take. The probability of emergence is 1 because the universe continues forever. Yet there is no evidence of it outside this planet. Until we find evidence of another instance, it is foolish to state anything with certainty.
Curious where the estimate of 10^100 stars came from. I've seen the estimate of 10^80 particles in the observable universe thrown around several times. No idea how either is calculated or what assumptions are made.
I'm still skeptical, because even with a statistically improbable RNA forming event, what are the chances actual life will emerge from it? Have we thrown pure RNA into a bucket of water and observed life emerging?
I’m curious what the actual estimates of the likelihood of a self-replicating RNA stand coming together randomly are. There’s a lot of volume and time on earth where these random reactions could’ve happened.
Well, the article is literally doing that math.
> There’s a lot of volume and time on earth where these random reactions could’ve happened.
Life began basically as soon as the Earth did. So, in terms of biological or geological time, it took almost no time.
Life began basically as soon as the Earth did. So, in terms of biological or geological time, it took almost no time.
>Life began basically as soon as the Earth did.
Note that this doesn't tell us as much as you might think about the likelihood of abiogenesis happening: we find ourselves relatively near the end of Earth's habitability before the expansion of the Sun will make it uninhabitable in a few hundred million years. If abiogenesis happened much later on Earth, then there would not have been enough time for intelligent life to evolve. Planets where intelligent life manages to evolve within the planet's time of habitability will be the weird rare ones where abiogenesis luckily happened ridiculously fast, no matter how unlikely it is for abiogenesis to happen.
Note that this doesn't tell us as much as you might think about the likelihood of abiogenesis happening: we find ourselves relatively near the end of Earth's habitability before the expansion of the Sun will make it uninhabitable in a few hundred million years. If abiogenesis happened much later on Earth, then there would not have been enough time for intelligent life to evolve. Planets where intelligent life manages to evolve within the planet's time of habitability will be the weird rare ones where abiogenesis luckily happened ridiculously fast, no matter how unlikely it is for abiogenesis to happen.
I also wonder why life with a different chirality (if it ever existed) was outcompeted by known life, and could not co-exist with it.
"Random" isn't really a relevant concept when it comes to chemicals. Get out some vinegar and some baking soda. Mix them. Wow! A chemical reaction that shouldn't have happened according to the laws of probability!
Can you elaborate on this further? Why don't the laws of probability apply to chemistry?
They definitely do apply, but it's like laws of probability apply to gas dynamics: sure there's a very small, but not non-existent chance that all the air in your room will end up confined to the half you're not in. There's a very tiny probability that acetic acid in vinegar and sodium bicarbonate in baking soda won't combine. I suppose some extremely tiny fraction of the acid and baking soda I've mixed together in my life didn't react. But the probability is so tiny, it just doesn't matter: all my cookies and soda bread rose.
Same with self replicating organic molecules - if you mix amino acids together, you're going to get some long strands virtually every time you try it because the probability of amino acids not reacting is very tiny. The probability of getting self-replicating strands approaches 1 after only a few trials. That is, your solution of amino acids would end up with some goop in it, some polymerized amino acid strands that had replicated themselves.
This "what's the probability!?!?" category of anti-evolutionary arguments is just false. "If you put all the pieces of a car in a box and shook it, the probability of getting a car is zero!" True, but an inapplicable analogy to organic chemistry reactions. Intuition about probability leads you astray. Nuts have an extremely low probability of getting agitated into screwing themselves on a bolt. The chemicals relevant to life have an extremely high probability of reacting to form larger molecules.
Same with self replicating organic molecules - if you mix amino acids together, you're going to get some long strands virtually every time you try it because the probability of amino acids not reacting is very tiny. The probability of getting self-replicating strands approaches 1 after only a few trials. That is, your solution of amino acids would end up with some goop in it, some polymerized amino acid strands that had replicated themselves.
This "what's the probability!?!?" category of anti-evolutionary arguments is just false. "If you put all the pieces of a car in a box and shook it, the probability of getting a car is zero!" True, but an inapplicable analogy to organic chemistry reactions. Intuition about probability leads you astray. Nuts have an extremely low probability of getting agitated into screwing themselves on a bolt. The chemicals relevant to life have an extremely high probability of reacting to form larger molecules.
That's an interesting point, thanks. Please pardon some ignorant questioning.
How far down does this apply? E.g., do amino acids come basically for free in the same way? If not, what's the bootstrapping process like, and how random is it? How many steps do you have to take from self replication to functional cells? That chemical reactions are quite deterministic makes sense to me, but I don't quite understand how one gets from chemistry to biology.
How far down does this apply? E.g., do amino acids come basically for free in the same way? If not, what's the bootstrapping process like, and how random is it? How many steps do you have to take from self replication to functional cells? That chemical reactions are quite deterministic makes sense to me, but I don't quite understand how one gets from chemistry to biology.
I'm not an expert - I just follow this as an amateur, and I don't know those answers.
Amino acids seem to form fairly often - they find (spectroscopic) evidence of them in deep space: https://www.newscientist.com/article/dn2558-amino-acid-found... and in the clouds of Venus: https://www.sciencealert.com/astronomers-report-they-ve-dete...
There's also the famed Mill-Urey experiments.
There's quite a bit of thought and argument about that "bootstrapping". Little cell-sized bags of lipids form pretty readily, but the problem is how to get the information (DNA) and metabolism into the cell-sized bags. You can google for "metabolism first hypothesis" and "rna world" for 2 different ideas about how that might have happened.
PBS Eons has a video about the "Last Universal Common Ancestor" that might be of help: https://www.youtube.com/watch?v=pk213XSSktQ&t=0s
Amino acids seem to form fairly often - they find (spectroscopic) evidence of them in deep space: https://www.newscientist.com/article/dn2558-amino-acid-found... and in the clouds of Venus: https://www.sciencealert.com/astronomers-report-they-ve-dete...
There's also the famed Mill-Urey experiments.
There's quite a bit of thought and argument about that "bootstrapping". Little cell-sized bags of lipids form pretty readily, but the problem is how to get the information (DNA) and metabolism into the cell-sized bags. You can google for "metabolism first hypothesis" and "rna world" for 2 different ideas about how that might have happened.
PBS Eons has a video about the "Last Universal Common Ancestor" that might be of help: https://www.youtube.com/watch?v=pk213XSSktQ&t=0s
Good question, I wonder the same.
If I may add, how far does this apply when getting from biology to consciousness, i.e from functional cells to general intelligence, as seen in living organisms and humans?
If I may add, how far does this apply when getting from biology to consciousness, i.e from functional cells to general intelligence, as seen in living organisms and humans?
I'm not the parent commenter, but I studied biochemistry and find abiogenesis to be a particularly fascinating topic, so I'll take a crack at answering your questions:
> How far down does this apply? E.g., do amino acids come basically for free in the same way?
Broadly, I think it is fair to say that many molecules that we associate with biological processes (e.g. amino acids, nucleotides, simple alcohols, etc.) do come "for free" in the sense that there are known pathways for these molecules to be produced in the absence of living organisms. The Miller-Urey experiment is probably the most well-known proof of concept of this idea, though it's debated how well the experimental conditions correspond with "the real world."
> ... [W]hat's the bootstrapping process like, and how random is it?
If I understand you correctly, here you're asking "what does it take to get from prebiotic organic molecules to living organisms?" And that is a fascinating question that has, to my mind, several possible answers, though ultimately I think the answer is "we don't know."
One very suggestive paper I read describes the bootstrapping process as a "surface metabolism" [1] that succeeds through several epochs before eventually producing free-floating lipid-membrane-enclosed micelles containing complex organic molecules and a rudimentary metabolism - i.e. protocells.
However, the IIRC paper falls short of explaining how these protocells can then start to independently reproduce. One hypothesis I recall from David Deamer is that hydration/dehydration cycles in shallow pools promote complex organization of simpler protomolecules into structures we typically associate with living organisms [2]; in other words, given the protobiomolecules mentioned above, certain environmental conditions encourage [proto]cell formation.
So, to answer your question (I think), there are many good candidates for the "bootstrapping process" and while there is randomness involved, it turns out that certain environmental conditions that were present on the early Earth (as well as currently!) tended to promote complex molecular formation.
> How many steps do you have to take from self replication to functional cells?
Not many; I would say that if you have something that looks like a cell and reproduces itself, it's a "functional cell." Personally, I think from that point we are at an, if not the, "origin of life," and understand in broad strokes "what happens next" - ever-more-refined single-celled organisms, multi-cell aggregates becoming "true" multi-celled organisms, and so on.
Let me know if you're curious about any other aspect of this topic and I'll try to provide more info!
[1] https://www.ncbi.nlm.nih.gov/labs/pmc/articles/PMC373159/
[2] https://www.liebertpub.com/doi/10.1089/ast.2019.2045
> How far down does this apply? E.g., do amino acids come basically for free in the same way?
Broadly, I think it is fair to say that many molecules that we associate with biological processes (e.g. amino acids, nucleotides, simple alcohols, etc.) do come "for free" in the sense that there are known pathways for these molecules to be produced in the absence of living organisms. The Miller-Urey experiment is probably the most well-known proof of concept of this idea, though it's debated how well the experimental conditions correspond with "the real world."
> ... [W]hat's the bootstrapping process like, and how random is it?
If I understand you correctly, here you're asking "what does it take to get from prebiotic organic molecules to living organisms?" And that is a fascinating question that has, to my mind, several possible answers, though ultimately I think the answer is "we don't know."
One very suggestive paper I read describes the bootstrapping process as a "surface metabolism" [1] that succeeds through several epochs before eventually producing free-floating lipid-membrane-enclosed micelles containing complex organic molecules and a rudimentary metabolism - i.e. protocells.
However, the IIRC paper falls short of explaining how these protocells can then start to independently reproduce. One hypothesis I recall from David Deamer is that hydration/dehydration cycles in shallow pools promote complex organization of simpler protomolecules into structures we typically associate with living organisms [2]; in other words, given the protobiomolecules mentioned above, certain environmental conditions encourage [proto]cell formation.
So, to answer your question (I think), there are many good candidates for the "bootstrapping process" and while there is randomness involved, it turns out that certain environmental conditions that were present on the early Earth (as well as currently!) tended to promote complex molecular formation.
> How many steps do you have to take from self replication to functional cells?
Not many; I would say that if you have something that looks like a cell and reproduces itself, it's a "functional cell." Personally, I think from that point we are at an, if not the, "origin of life," and understand in broad strokes "what happens next" - ever-more-refined single-celled organisms, multi-cell aggregates becoming "true" multi-celled organisms, and so on.
Let me know if you're curious about any other aspect of this topic and I'll try to provide more info!
[1] https://www.ncbi.nlm.nih.gov/labs/pmc/articles/PMC373159/
[2] https://www.liebertpub.com/doi/10.1089/ast.2019.2045
These are good comments and resources; thanks! I'm a bit out of my depth in the papers, but reading through them gradually and trying to absorb them. Again, please bear with me--this is not an area in which I have much experience.
A couple quick follow-ups on your thoughts, though:
> Broadly, I think it is fair to say that many molecules that we associate with biological processes (e.g. amino acids, nucleotides, simple alcohols, etc.) do come "for free" in the sense that there are known pathways for these molecules to be produced in the absence of living organisms.
How likely are the conditions for such pathways to obtain? At a minimum it seems like you need the constituent elements to be collocated and for appropriate environmental conditions to occur.
In order- or structure-sensitive reactions, is it true that further conditions need to be met? (Unless the argument advanced is that these challenges are addressed by a (somewhat?) deterministic process that results in appropriate chirality of molecules?)
Is there a substrate or solvent in which these reactions are postulated to have occurred? The challenges with the primordial soup hypothesis, as described in the first paper, are fairly well known to me...but the reactions have to take place in some kind of an environment. The obvious solvent is water, or you could imagine some other viscous substrate (like clay?); are there other candidates? Or are these questions just terribly ignorant?
> > How many steps do you have to take from self replication to functional cells?
> Not many; I would say that if you have something that looks like a cell and reproduces itself, it's a "functional cell."
How would we measure what "looks like" means? Through functional analysis (like metabolic action?) or constituent parts (e.g., we differentiate eukaryotes and prokaryotes but consider both cells--is there something distinct from prokaryotes that we would also consider a cell?)?
> Let me know if you're curious about any other aspect of this topic and I'll try to provide more info!
I'm super interested. Do you have a set of base references that are your go-to sources for reacquainting yourself with these things? I'd love to keep reading.
A couple quick follow-ups on your thoughts, though:
> Broadly, I think it is fair to say that many molecules that we associate with biological processes (e.g. amino acids, nucleotides, simple alcohols, etc.) do come "for free" in the sense that there are known pathways for these molecules to be produced in the absence of living organisms.
How likely are the conditions for such pathways to obtain? At a minimum it seems like you need the constituent elements to be collocated and for appropriate environmental conditions to occur.
In order- or structure-sensitive reactions, is it true that further conditions need to be met? (Unless the argument advanced is that these challenges are addressed by a (somewhat?) deterministic process that results in appropriate chirality of molecules?)
Is there a substrate or solvent in which these reactions are postulated to have occurred? The challenges with the primordial soup hypothesis, as described in the first paper, are fairly well known to me...but the reactions have to take place in some kind of an environment. The obvious solvent is water, or you could imagine some other viscous substrate (like clay?); are there other candidates? Or are these questions just terribly ignorant?
> > How many steps do you have to take from self replication to functional cells?
> Not many; I would say that if you have something that looks like a cell and reproduces itself, it's a "functional cell."
How would we measure what "looks like" means? Through functional analysis (like metabolic action?) or constituent parts (e.g., we differentiate eukaryotes and prokaryotes but consider both cells--is there something distinct from prokaryotes that we would also consider a cell?)?
> Let me know if you're curious about any other aspect of this topic and I'll try to provide more info!
I'm super interested. Do you have a set of base references that are your go-to sources for reacquainting yourself with these things? I'd love to keep reading.
I read a paper somewhere along the line that claimed that DNA itself shows evidence of having evolved - the 3-pair codons that have some error-correcting capacity evolved from single-pair codons. When I write that down it seems wrong, but that's what I remember. Can't recover the paper, however so you don't need to believe me.
> I read a paper somewhere along the line that claimed that DNA itself shows evidence of having evolved - the 3-pair codons that have some error-correcting capacity evolved from single-pair codons. When I write that down it seems wrong, but that's what I remember. Can't recover the paper, however so you don't need to believe me.
Thinking about this a little bit, what are likely traces that we could even identify in the evolution of these building blocks? If, hypothetically, single-codon DNA went "extinct," is it possible we could even find evidence of it?
Thinking about this a little bit, what are likely traces that we could even identify in the evolution of these building blocks? If, hypothetically, single-codon DNA went "extinct," is it possible we could even find evidence of it?
what if life exists everywhere we are just incapable of detecting it? All we know for sure that there is none on the moon, and soon we will make that claim for Mars, after turning a couple of rocks.
If there is life with the same technologies to us sending some beacon signal, what's the odd that we get it?
If there is life with the same technologies to us sending some beacon signal, what's the odd that we get it?
no, there is not 10^100 stars in universe, only 10^80 atoms. why such a mistake ?
All our calculations are fucked by having a sample size of one.
The article is an argument against that argument.