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Your assumption that the odds of abiogenesis is given by `~1/2^n, where n is the complexity in bits' is utterly, completely false.

Statistical mechanical entropy and information theoretical entropy ('complexity in bits') are not the same quantities! But even if they were, your expression would still be incorrect because living system are definitionally not at equilibrium - so equilibrium statistical mechanics (whose predictions you are using to get that expression) does not apply.

No one is surprised when convection rolls spontaneously form as they boil a pot of water. But equilibrium statistical mechanics predicts that this should be extremely unlikely as convection roll states have very low entropy. That is, of all of the ways that the molecules in that pot of water could be oriented, vanishingly few of them correspond to convection roll states, where several Avogrado's numbers worth of particles conspire to all swirl around in a coordinated fashion to dissipate the heat of the burner faster than would occur just by diffusion.

The origin of life is very much analogous to the formation of convection rolls in the pot. And I believe is far more common than classical predictions imagine it to be - nearly everywhere there is an energy gradient in the universe, you will probably find life.

Citation: I have a degree in physics

How do you substantiate the analogy between origin of life and convection rolls formation?

I presume the idea is that of 'the other half' of evolution - that is, the spontaneous formation of order through simple physical processes coupled to symmetry breaking.

Of course it can be easy to over-do the analogies between things like convection rolls and the emergence of lipid bilayers (or whatever). However, the origin of life necessarily came about through purely physical processes and only once that bootstrap phase was over did evolution come into play as biological systems took over acting upon themselves.

As I understand it the idea is that a closed system that is driven far from equilibrium by a constant influx of energy can undergo 'symmetry breaking' where the symmetries of the system are changed. So the symmetric situation of the boiling pot is broken such that convection rolls are formed - which is new structure.

Similarly, a uniform soup of primitive chemical compounds could have been broken into less-uniform patches by some energy gradient (black or white smokers, for example). This diversity of chemical conditions then helped to form the initial replicators that could then further exploit various temperature, chemical, or proton gradients to create primitive life.

> Statistical mechanical entropy and information theoretical entropy ('complexity in bits') are not the same quantities!

This assertion (whether thermodynamic entropy and information theoretic entropy are equivalent) is an ongoing controversy open to debate - it shouldn't be stated as fact. See wikipedia for (a summary of) both sides of the story: https://en.wikipedia.org/wiki/Entropy_in_thermodynamics_and_... (specifically the #Theoretical_relationship and #Criticism sections)

I suspect that life is not uncommon in the universe, but my bet is that multicellular animal life is rare.

This has nothing to do with physics. He's saying if a first self replicator requires a very specific sequence (of something like RNA) to form by chance, then it can easily be incredibly unlikely to happen.

As an analogy, if I make a huge number of random files on my computer and execute them, the probability of getting a self replicating computer virus is really low. And one that successfully spreads itself to other computers over the internet should never happen.

If the first successful computer virus is 100 bits long, then probability of finding it in a single random search is 1/2^100. Which is just incredibly small and should never ever happen.

Purely hypothetical: where N is the fewest number of bits for a successful virus.

There could be 10 different ways to make a virus N bits long. There could be 1000 ways to do it in N+1 bits, and a billion ways in N+2.

The relationship between how many possible successful viruses exist to number of bits doesn't have to scale by any obvious pattern.

I don't see why adding more bits would make the program significantly more likely. Yes in theory that is possible, but I don't think it's relevant.

Knowing the size N of the smallest possible virus doesn't tell us much about the probability of a given random string being a virus (as long as it's longer than N)

There could be a magic threshold where if you're shorter than that you don't work.

For ex, maybe a valid file has to be at least 100 bytes, or the OS can't treat it as a file. Any random file 100bytes or longer could have a 10% chance of being a virus (the actual number depends on how the os works).

This would mean a really high chance of randomness creating a virus, even though N is 100.

The probability of vitality depends on the specifics of the operating system, and we can't infer it by looking at the size of the smallest possible virus.

For proteins, at least, there is a lower limit on sequence length below which it is less likely to form a folded structure. Most proteins are around 200-250 amino acids long (see http://www.umich.edu/~zhanglab/publications/1996-2001/Zhang_...).

There is a reasonable theory that I remember discussing/reading once that proteins may have started out as long sequences and were then selected for shorter more stable versions. Presumably the early proteins were partly disordered, and only optimised for having stable cores and domain structures later on.

In any case, it is not as simple as the number of bits in a program, as macromolecules are not 'just' software, but actual physical devices that have to (self)-assemble and carry out functions at various temperatures, pressures, pH, etc.

I think you're misunderstanding the grandparent comment. Your argument about convection rolls and nonequilibrium statistical mechanics is an excellent argument that the probability of abiogenesis is much, much higher than the probability of some organic molecules in solution spontaneously assembling themselves into a fully-functioning smallest-possible bacteria. However, that's not what the statement that "the odds of abiogenesis are ~1/2^n" is saying.

Saying that "the odds of abiogenesis are ~1/2^n" isn't an assertion of fact, it's merely defining n = -log2(probability of abiogenesis). (Of course, the probability of abiogenesis occurring in any particular body of water is not a constant, it depends on conditions; but all the oceans on Earth are only 80 binary orders of magnitude bigger than a single mL [1], so n for a lab experiment and n for the entire Earth can't be more than a couple decimal orders of magnitude different, so it's immaterial.)

In other words, your argument about convection rolls is an excellent argument that the n for abiogenesis is much, much lower than -log2(probability of organic molecules in solution spontaneously assembling themselves into bacteria), which grandparent claimed is ~1 million. I have no reason to believe ~1 million is accurate, but I don't care, because grandparent has convinced me that the upper bound is many orders of magnitude greater than 73. Your argument that n could be much less than that upper bound is convincing, but unless you're arguing it's so much lower that it isn't much greater than 73, grandparent's counter to the paper still holds.

[1]: http://www.wolframalpha.com/input/?i=log2((volume+of+ocean+i...)

One of my favorite explanations and counterpoints come from Neil deGrasse Tyson:

It took modern astrophysics to determine the origin of the chemical elements. We observe stars (and) we know what goes on in their center. They explode, laying bare their contents. And what we have discovered is that the elements of the periodic table -that which we are made of- derive from the actions of stars that have manufactured the elements, exploded (and) scattered their rich guts across the galaxy, contaminating or enriching gas clouds that then form a next generation of stars populated by planets and possibly life.

And so, when you look at the ingredients of the universe, the number one ingredient is hydrogen, next is helium, next is carbon- sorry- hydrogen, helium, oxygen, carbon, nitrogen. Those are the top ingredients in the universe. And you say well, okay, that’s kind of cool. Well, and you look at Earth- cause we like thinking of ourselves as special- we say Oh! we’re special! What are we made of?

Well what’s the number one molecule in the body? It’s water. But what’s water made of? H-2-O. Hydrogen and oxygen. Hm. Hydrogen and oxygen. In fact, if you rank the elements in the human body, with the exception of helium, which is chemically inert- useless to you for any reason other than just to inhale it and sound like Mickey Mouse. You can’t die from helium unless that’s all you breathe. So, number one in the human body is hydrogen. Matches the universe. Number two? Is oxygen. Matches the universe. Number 3? Carbon. Matches the universe. Number 4? Nitrogen. Matches the universe. And for each of us the fifth element- other- is the same in both places. Ok? Other.

So, we learned in the last 50 years that, of course, not only do we exist in this universe. It is the universe itself that exists within us. And had we been made of some rare isotope of bismuth, you’d argue and say hey, we’re something special.

From https://tiainkorea.wordpress.com/2012/04/22/a-fascinatingly-...

Also, this is the most interesting explanation to the Fermi paradox that I've seen: http://accelerating.org/articles/transcensionhypothesis.html

The only paradox in Fermi's paradox is the discarding of UFOs as possible ET manifestation

Most common elements in the universe [1]: Hydrogen, Helium, Oxygen, Carbon, Neon, Iron, Nitrogen

Most common elements in the human body [2]: Hydrogen, Oxygen, Carbon, Nitrogen

I agree that we can skip helium and neon since those are noble gases, but I do find the lack of iron interesting.

[1] https://en.wikipedia.org/wiki/Abundance_of_the_chemical_elem...

[2] https://en.wikipedia.org/wiki/Composition_of_the_human_body#... (look for table, sort per atomic percent)

Indeed. Iron and other heavy elements sink into the core of planets as they're being formed. This leaves less iron on the surface for chemical reactions that might lead to life.

However, iron does play an important role in life as we know it, even today. Earth's molten and rotating iron and nickle core is what creates our magnetosphere that shields us--and presumably early life--from deadly solar radiation.

> However, iron does play an important role in life as we know it, even today

I would have thought the iron in mammal blood would come to mind first, but other aquatic life forms have copper-based blood, so it's not exactly required.

I think what will really help us to get at a better estimate is to answer the question whether there exists life in our solar system that evolved independently of that on Earth. If we should find traces of bacteria on Mars or another planet, that would immediately take the corresponding probability factor in the Drake equation to a number close to 1 (i.e. most solar systems with planets in the habitable zone produce simple organic life), which would then leave us only with the question of how likely it is that such bacterial life evolves into something more complex. That's an incredibly hard question to answer as well of course, but it's also something that we might be able to tackle within the next 50 years given a deeper understanding of how living cells work and how they came to be (and it seems we're making good progress there). So personally I'm quite confident that we will be able to get to a much better estimate of Drake's equation in the next 50 years.

    I think what will really help us to get at a better estimate
    is to answer the question whether there exists life in our
    solar system that evolved independently of that on Earth.

That's definitely the big question. But you left out the elephant in the room: is there life right here on Earth that's evolved independently? Abiogenesis doesn't simply halt after it's achieved its "goal". Perhaps we take the common-origin hypothesis for granted (that the "tree of life" has one root, and is in fact a tree), but it's actually nontrivial, strong evidence about the rate of abiogenesis, right under our noses. If it's true.

There's no hard reason why another, orthogonal family of life couldn't coexist with DNA/RNA life. We have 10^7 extant species of DNA/RNA life; that's an existence proof that hostile, competing "types" of life can coexist. Suppose we found terrestrial "XNA life" with a biochemistry totally unrelated to anything else, with no possible common origin or lateral gene transfer. Then we would know life on Earth developed independently N >= 2 times, instead of N >= 1. That would change a lot; we could update P(life | Earth-like planet) from the subjective probability range [10^-Graham's number, 1) to something more like [10^-4, 1).

What's really surprising is that this is completely untested! We genuinely don't know if there's "alien" life on Earth, because we don't know how to look for it. There's no black-box tool to approach unknown biochemistry:

    Some have postulated the existence of a 'shadow biosphere'
    on Earth, teeming with life that has gone undiscovered
    because scientists simply don't know where to look. It could
    contain life that relies on a fundamentally different
    biochemistry, using different forms of amino acids or even
    entirely novel ways of storing, replicating and executing
    inherited information that do not rely on DNA or
    proteins. [...] The trick is deciding what to look for and
    how to detect it. The usual way that researchers search for
    new organisms — by sequencing DNA or RNA — will not pick up
    life that does not depend on them.

http://www.nature.com/news/life-changing-experiments-the-bio...

    ...We could even be oblivious to unfamiliar forms of life
    right under our noses...

http://www.sciencemag.org/news/2015/02/shadow-biosphere-migh...

As soon as you get v1.0 life, it starts bioforming its environment.

v2.0 life would have to evolve in the changed environment - which would be considerably less hospitable, because the most useful chemical processes and energy sources will be colonised by v1.0 life.

v1.0 life will (more or less literally) get the low hanging fruit. v2.0 would have to evolve around the edges, which means the probability gradient is higher and therefore less likely.

But I think this actually happens with normal life as well: Individual species of bacteria try to conquer a biological niche by shifting conditions such that only they can survive. But by doing this they invariably create chemical by-products that can be harnessed by other life forms, thereby fueling their growth. It's an interesting question whether there are any biospheres on Earth that are colonized exclusively by a single species of life (I doubt it).

So although it's a very valid point I'm not sure if it's a sufficient argument against the hypothesis of having two independently evolved and fundamentally different types of life on a given planet.

Fascinating, thanks for pointing this out! Discovering a new kind of life on Earth that has coexisted with us without being noticed would be a huge event of course, and it would probably challenge what we regard as life in a general way.

This would be good stuff for a science fiction story as well.

It does make a good sci fi story: https://www.amazon.com/dp/B00M64A8EG/

Wow, thanks for the link :)

I think it's a winner take all task. If you are the first almost live form, you have plenty of time, and can evolved in an environment that has plenty of food. Something like the brown goo of Titan, with lots of hydrocarbons and other small molecules that you can pick up for free. And nobody is trying to eat you. So the reproduction process can be slow and unreliable, perhaps a few reproductions per day/week?/month??

The only way to die if a UV ray split you, or you fall into a volcano (there are no fire, because the atmosphere has very few oxygen), or a nasty oxygen molecule reacts with you, or ...

Well, there are many ways to die, but they are not targeting you, so perhaps you can hide from the sun under a rock. Or to be more clear, since you doesn't have any kind of senses or mobility, perhaps you are lucky and get beached under a rock. Perhaps the rock also makes a nice place to concentrate other molecules during the low tide.

Perhaps it's not a good idea to be near the surface and it's better to be lucky and get near a underwater sea vent with tasty hydrogen. I think the details of the first steps are not clear for anyone (in particular for me).

Once a stupid life for appears, the first thing it would do is eat all the free food. In particular, before the first life form the half of the amino acid were L and half D. We have used all the L amino acids (and created many more than the original supply), and we have also eaten all the original D amino acids. So there are very few of them floating around freely, it would be very hard to start an alternative D-tree.

A new life form will be targeted by the existing life form, like the free D amino acids. The competition will be extremely hard. So I think it's a winner take all task.

Moreover, then some moron decides to release a lot of oxygen to the atmosphere. Oxygen is extremely toxic for most life forms, and more toxic for isolated molecules that are barely alive ...

About the shadow biosphere: Perhaps we (humans) can't detect or identify them, but the bacteria and archaea can probably live there and eat them barely-alive. Our cousins can keep all the out-of-tree competition at bay.

    If you are the first almost live form, you have plenty of
    time, and can evolved in an environment that has plenty of
    food. Something like the brown goo of Titan, with lots of
    hydrocarbons and other small molecules that you can pick up
    for free.

But there's no food on Titan anywhere! There's no oxidizers for hydrocarbons to react with; hence no accessible chemical energy.

That's likely generic for pre-biotic environments. Planets don't naturally form redox gradients; if there's a large redox potential, that's reactive chemistry, which will react away to equilibrium over geologic time. It takes work to maintain such a gradient; for example, Earth's oxidizing atmosphere is actively maintained by life. Oxygen is geologically removed from atmospheres, reacting with exposed rock surfaces (oxygen weathering). It takes active expenditure of work (solar energy) to keep it existing.

There is some chemical energy in abiotic planets, but only small amounts, at very low power levels compared to Earth's aerobic biosphere (which eats something like 10^14 watts!). There's photochemistry caused by solar UV light, and there's atmospheric lightning (which is a major player in the Earth's N2 cycle). Most important is geochemical energy; i.e. primordial chemical gradients that aren't yet at equilibrium, because the two reactants are physically separated by rock layers. On Europa for example, a very slow process brings rocks into contact with the ocean, where slow serpentinization reactions can occur: oxidation of Fe++ to Fe+++ by water, with the production of H2. This would be the food source of Europa life, if it's there.

A very late reply.

I'm not sure if this is for or against your comment, but I hope you find this interesting:

"A cave in Romania that was sealed for 5.5M years" http://www.bbc.com/earth/story/20150904-the-bizarre-beasts-l... HN discussion: https://news.ycombinator.com/item?id=11682816 (889 points, 38 days ago, 163 comments)

what if life didn't evolve here but arrive on other space debris? Has that theory been ruled out?

The term you're looking for is panspermia. Nothing can necessarily be ruled out but it seems both 1) highly unlikely from a mechanistic perspective and 2) unnecessary to the explanation of life origin.

That's called panspermia, and no, it hasn't been ruled out. Main problem with it though is that it doesn't explain how life as we know it came into existence, it simply shifts its origin from Earth to somewhere else

> Specifically, the odds of abiogenesis are ~1/2^n, where n is the complexity in bits of the smallest self-replicator. n is bounded below by ~100 or so (or it would have happened in a lab somewhere), and is bounded above by ~1 million (the smallest existing bacteria), so we know it's somewhere in there.

If the odds of abiogenesis are 1/2^128, and if that is the source of life, then we're the only life in the Universe. As the article indicates, there are only 2^73 stars.

OP's argument here is slightly wrong I think, as it does not take into account the amount of time: Abiogenesis probably hasn't happened in a lab yet because the corresponding experiments have been running for a couple of years or decades at most, whereas nature's "experiments" have been continuously running at planetary scale for billions of years. If we count the number of attempts to invent life in the sense of putting together some anorganic and organic chemicals, supplying some energy and waiting for e.g. one year, then Nature has probably run 10^18 times more experiments than we have (10^9 years of experiments, each one running on a 1 m² surface [not taking into account depth]). And, fossil evidence points to life having started 4.1 billion years ago, or roughly 500 million years after the formation of the planet, which is a rather short amount of time (it's very likely that first lifeforms existed even earlier than that). So my naive guess would be that n < 100, though without further evidence (e.g. finding life on other planets) this is hardly more than a belief.

In the Observable Universe

An alternative is if you believe in the principle of terrestrial mediocrity, that we are on a fairly average planet in a fairly average bit of the universe where fairly average things happen, the fact that life popped up on our planet in less than a billion years implies it probably has done so in loads of other places.

Quote Martin Amis's The Information:

“The history of astronomy is the history of increasing humiliation. First the geocentric universe, then the heliocentric universe. Then the eccentric universe – the one we’re living in. Every century we get smaller. Kant figured it all out, sitting in his armchair. What’s the phrase? The principle of terrestrial mediocrity.”

The actual time taken to randomly clear a hurdle actually tells you very little about how unlikely it was to clear, so long as there are several hurdles and you condition on them all occurring (i.e., that you exist). In particular, the expected time to clear a hurdle asymptotes at a constant value even as the difficulty becomes arbitrarily hard. This is a very unintuitive but very important result for thinking about this topic.

http://mason.gmu.edu/~rhanson/greatfilter.html

"One in 10 billion trillion" sounds like a very large number, and it's put in italics for emphasis,"

And the author even asserts it's "irrational" to think real-world probabilities are this small!

It's easy to construct "unreasonably" small probabilities: take a few small ones and multiply them. If you path-sum all the evolutionary state transitions summing to P(intelligent life|planet), is it a shallow graph with many alternatives (additive probabilities), or a deep graph dominated by long, conjunctive sequences (probabilities multiply)?

I had a similar intuition reading the article. I don't think we understand much at all about the probabilities of life forming even under the ideal circumstances. The events that took place on earth could still be one in a billion, or they could be one in an incomprehensibly high number.

Nevertheless the progress on the other factors in the Drake equation is very interesting and impressive.

> . The events that took place on earth could still be one in a billion, or they could be one in an incomprehensibly high number.

I disagree with this.

It seems that, from what happened to other planets on the solar system, that nothing happened on Earth too much out of the ordinary. Mars had a similar story (except for the whole Moon coming out of a giant collision), and had water. But maybe it was too small to keep warm for enough time

Earth had 5 mass-extinctions, that "reset the game" before we got to humans. Doesn't seem too far fetched to me

I really don't buy that Earth is one in a billion unless Mars is one in a billion as well. Maybe one in 1000? One in 100000?

And that's limiting intelligent life to what we know. Yes, maybe the ideal speed of chemical reactions (for intelligent life) happen around 273K, or maybe there's another way

It's not about how probable are these conditions but given these conditions how probable is that life will appear.

It seems that the probability of life appearing (in some form), given the ideal conditions, is higher than that of obtainiing the ideal conditions.

Phantom downvotes. Awesome. Don't really care about "karma", but thought this was a place for discussion.

Anyway, what reason do we have to believe that Earth is special 2X? That we happened to have the right conditions plus some randomness occurred against all odds that gave rise to life? Why is that a rational proposition?

We know the chemical elements and processes that give rise to life, and we know why Earth is a suitable place. I suggest that, given the right (e.g. Earth-like) conditions, formation of life is not only more likely than the existence of the conditions, but the formation of life may even be likely overall. Hawking has expressed this possibility. [0]

There is fossil evidence suggesting that some forms of life existed on Earth as few as 500 million short years after it was formed. So, what are the odds that one astronomically improbable event (creation of a hospitable environment) was followed in such a short period by another alleged astronomically improbable event (abiogenesis)?

[0] http://www.hawking.org.uk/life-in-the-universe.html

I suspect that given the right conditions, some kind of proto-life appears easily.

But it takes a lot of time to get to "life" as we know it.

(Now the right conditions are probably not what you have on Earth today except in a couple of places)

Life on Earth is at least 4Bi y.o. http://newsroom.ucla.edu/releases/life-on-earth-likely-start...

What does it even mean? Why would it not appear when the necessary conditions arise?

I don't know enough to know if the range you specify is right, but I agree that it is silly to say 10^-22 is a ridiculously small number. For one thing, when talking about the size of probabilities, we should talk about the size of the exponent. -22 is not a ridiculously small number.

People base the idea that there should be other life in the universe on the fact that life developed at least once, which is here on earth. The odds are it would happen either 0 times or many times, but not exactly once.

This argument is reasonable if there is one universe. Another scenario is that there is some god awful large number of universes (for round numbers let's say 10^1000 raised to the 10^10000 power, which would be a huge underestimate), and that most of these universes contain no life, because the odds of life developing are also very, very small. We ARE special in that we are viewing one of the small fraction of universes that has life, because if it didn't we wouldn't be viewing it. This allows for life to exist exactly once in our universe. There could also be universe where life developed independently more than once, but the odds of us being in that universe are very small relative to the odds of being in a universe with one life.

But how would there be many universes? Here is one possibility that is surely controversial. In quantum mechanics, things happen in parallel. Is that electron spin up or spin down? It is both, but the electron in one state is not influenced by the electron in the other state. Each exists wholly on its own. This is true whether you believe the Stockholm or the Many Worlds interpretation of quantum mechanics. These two cases only differ when some special life form makes an observation, in which cases something very dramatic happens in the Stockholm interpretation (which is observationally indistinguishable from the "nothing different" that happens in the Many Worlds interpretation). If we think about the simplest form of life that can not make observations rather than looking for human-like life, the distinction between Stockholm and Many Worlds is mute. These parallel states of the system form our many universes, some that contain life and some that do not.

AIUI the term "observation" in quantum physics has absolutely nothing to do with life.

In some interpretations of quantum mechanics, it actually has:

https://en.wikipedia.org/wiki/Von_Neumann%E2%80%93Wigner_int...

https://en.wikipedia.org/wiki/Many-minds_interpretation

More precisely, these interpretations require consciousness, but we can take that consciousness requires life.

Yes, my discussion of it was my attempt to say it was not a factor in my point, as I didn't want some people to get caught up in it.

73 bits is massive. Considering the variability of conditions on each planet, you will get into ridiculously contrieved scenarios of what could be needed to start life way before you come even close to that number.