Comment by jawns | Hacker News Reader

Comment by jawns | Hacker News Reader

I don't have any philosophic objections to the existence of extraterrestrial life, but what does bug me is when people claim that simply because the universe is so big, that somehow makes it not only likely but practically certain that life has developed on other planets or in other solar systems or galaxies. That kind of thinking presumes some very important information that we just don't have. We are currently unable to enter any coherent value into the portion of the Drake Equation that pertains to how frequently life arises from non-life.

We have an admittedly very limited knowledge of events outside of our own planet, but so far as we know, abiogenesis has occurred only once, and from that one event, all life on Earth proceeded. (It's possible that abiogenesis occurred independently multiple times during the beginning of life on Earth, but I don't think we yet have a compelling argument that it must have happened more than once.)

My favorite analogy:

Suppose you see a number with this pattern:

0.1001000101001000101001000___

What would you say is the likelihood that a 1 is the next number in the sequence? Not that hard to compute a probability, is it?

But suppose you see a number with this pattern:

0.1000000000000000000000000___

What is the likelihood that a 1 is the next number in the sequence? You could say the odds are 1-in-25, but that doesn't takes into account the clear pattern we see in the sequence. Unless and until we start to see some more ones pop up, it's reasonable to assume that this is a sequence of infinite zeroes, or at the very least that it could perfectly well be a sequence of infinite zeroes. Suppose the sequence goes on for many trillions of numerals. No one's going to say, "Well, if there are trillions of 0s, it's highly unlikely that there won't be some 1s sprinkled in there somewhere."

The amazing thing about the Drake Equation is that it's a funneling pipeline where we're spitballing numbers with huge orders of magnitudes difference across different people's guesses. They're just random guesses, where one person says one particular odds are one in a million, the other guy says one in a billion, the other gal says one in a trillion. Yet in spite of a huge range, for each of the winnowing factors in this funnel, the odds of there being life are often significant.

Which is to say, two things are certainly true:

The universe is incredibly fantastically basically unimaginably vast. Practically countless (~10 million estimated) super-clusters of galaxies dot the heavens. There's just so many chances, so many opportunities, so much probability that, if you believe in life arising from a primordial soup, seem almost certain to be replicated.

Sometimes chaos, in it's fumbling teaming randomness, happens upon patterns. Patterns which sometimes stick, which sometimes reproduce, which sometimes grow. Entropy amid complex systems sometimes produces it's own enclaves of stability, sometimes.

The other true fact is that time is long and deep. Life on earth is not a flash in the pan, not an instant thing; it emerged slowly, over time, in differing waves, across time. The promise that life, once began, has a chance to ride these waves of time & to become significant, that it grows to fill rich biodiverse roles, grows to complete, that it thrives: if we believe in the soup of life, believe in the complex chemistries that powers cells, and believe in time, then a belief in other life seems not certain, but to me, highly highly probable.

If there are no more 1s, then we need to answer why our position in the universe is unique. That seems like a hard question to answer. It just seems like a _much_ better bet that we aren't the only 1.

This reasoning seems flawed, how is it that an answer that doesn't lead to difficult questions is more likely (rather than simply more convenient)?

There doesn't have to be an answer. We could just be "the first"[0] life to evolve - someone always has to be. Now, if we were to say that ours is the only life to exist in the entire past and future history of the universe, that would probably require a more specific explanation.

[0] to the extent that events across vast spans of space can be said to be ordered

If we're the first, that also requires just about as much explanation really. There are how many galaxies, and how many systems per galaxy, and how many planets per galaxy? If the chance of life per planet is anything more than on the order of 1/trillion, laws of big numbers suggest we just _can't_ be the first or only.

None of this is any kind of _hard_ proof of course, it's just attempting to reason through what we expect without having enough data to prove either way.

Again, some civilization will be the first, that is a certainty. Now, you may ask 'why did civilization only arise X billion years in the universe' s history' perhaps, but not 'why are we the first and not someone else' (assuming we were, which I have no opinion on).

Of course. But if we have reason to expect _many_, then betting that we're the first is a terrible bet.

If we conclude for some reason that we are the first, with enough evidence, sure, like you say someone has to be first.

But with so little data, the priors for "are we first or are we just missing the others" just have to be tilted heavily away from "we're first".

The "why" might be more of a philosophical question than a scientific question, but in terms of the science, I don't think it's hard to reason about.

Ultimately, the frequency at which abiogenesis occurs is 1/N.

It may be the case that N is small enough that the universe is positively teaming with life.

Or it may be the case that N is so unfathomably large that the odds are exceedingly small that abiogenesis occurs even once during the lifetime of the universe, and the universe just happened to get lucky.

But until we have some other confirmed, observed instance of abiogenesis, we can say nothing about N other than its lower bound is pretty large.

And I don't think we can pile probabilities on top of probabilities to say, "Well, we have no way of knowing how large N is, so I'm going to just bet that it's medium-sized."

I don't think this is a very good analogy because we know far more about the nature of life, what is required to make it, and the abundance of those ingredients throughout the cosmos. Life isn't a lengthy, specific sequence of precise things. It's a phenomenon that occurs when certain kinds of things come together in certain kinds of ways -- many variations of these ingredients and permutations exist on Earth alone.

Your perspective reminds me of the anthropic principle: https://en.wikipedia.org/wiki/Anthropic_principle

The popular conception is the "puddle analogy." You can imagine a rain puddle becoming conscious, seeing the intricacies of its perfect fit with the pavement that surrounds it and concluding "wow, this hole fits me SO perfectly, it must have been made for me."

> many variations of these ingredients and permutations exist on Earth alone.

Apart from cells, what are you referring to here? Especially, is there anything that can be considered "somewhat living" that is not a by-product of regular life, which as far as we know has only ever appeared (or thrived) once Earth's history?

Let's take a different naturally-occurring type of object that has only ever been found on Earth: waterfalls. To get a waterfall, you need a set of ingredients and circumstances to occur in a particular way that a waterfall results. We've only ever seen this on Earth. They come in many forms: Niagara Falls, jungle waterfalls, small waterfalls, even frozen waterfalls and underground waterfalls. They even have different colors, chemical characteristics, and each one can be said to be very unique from all the others.

We know of no other planet that has waterfalls.

Yet, because we have seen enough waterfalls on Earth we have an evidence-based scientific belief that waterfalls cannot be Earth-specific because all that is required for one: water, erosion, gravity -- exists throughout the cosmos in very large amounts.

Life is the same. We have seen enough of it in enough variety to know that it can take on many forms, including exotic forms that are impossible on Earth but would be possible elsewhere. The abundance of the ingredients and time are all that's required.

I don't think that's a good analogy, all those waterfalls developed independent of each other.

As far as we know all life is related and has the same ancestor. Even on earth the emergence of life seems to be a freak accident.

Sigh. Analogies are hard.

I don't think this is just a limitation of the analogy, but it is the key point: for any structure where we know the process that forms it (like waterfalls or snow flakes), we can have some informed opinion about the chances of it happening elsewhere in the universe, even if we have only observed one instance of it happening.

However, for structures where we have no idea of the process by which they are formed (like cells), we can't have any opinion on how likely they are to happen elsewhere, unless we see more examples.

I think we know more about abiogenesis than you are giving us credit for.

We know a few things about the formation of organic compounds that life uses from inorganic compounds, and how some specific organic compounds crucial to life appeared, but not much more than that. Nothing even close to the formation of a simple self-replicating cell, for example.

> Life is the same. We have seen enough of it in enough variety to know that it can take on many forms, including exotic forms that are impossible on Earth but would be possible elsewhere.

What forms of life that are impossible on earth do we know about?

Silicon based for one.

That's a conjecture, not a known form of life that couldn't occur on Earth. There is no proof that silicon based life could exist, we barely know if silicon organic chemistry could actually exist.

https://en.wikipedia.org/wiki/Hypothetical_types_of_biochemi...

I understand the concept, but I don't think it applies to life specifically. Even the simplest cell is more complex than any other naturally occurring formation we have ever seen in the universe.

Furthermore, unlike waterfalls, we actually have no idea how life appeared and, despite trying for many years, have been entirely unable to produce life from non-living things, and we have never observed this process occurring naturally either.

Furthermore, every living thing we've ever looked at has been a relative of other living things - as far as we've been able to determine, all of the life on Earth has a single origin, a single original RNA/DNA code which must have been present in a single population of organisms, at a single location. This is a strong suggestion that the conditions that allowed life to appear on Earth may have been extraordinarily specific - otherwise, we would expect many unrelated beings sharing the planet (or at least it means that a particular for of life was overwhelmingly more adaptive and entirely wiped out all of the others).

Even worse, there is another phenomenon for which we only have evidence of one instance happening in the history of the Earth: all eukaryotic life has a single common ancestor, and there are no complex multicellular organisms which are not eukaryotes.

So, not only did life arise only once on the one planet we know it can thrive in, but complex life only arose once from simpler life.

So, while we can't say that it's plausible life will never again arise in the universe, we can say that for any particular moment of time, it is plausible that no new life is being formed anywhere else in the universe.

We have another datapoint though, the age of the Earth. Life started fairly early after the Earth cooled, about a billion years after initial formation. This implies that abiogensis could have happened several times since then and died out; created the same chemical system independently; was out-competed by regular DNA life; or they're around but we just haven't discovered alternative forms of life on earth.

But life capable of communicating across space didn't arrive until 4.5 billions years and after several mass extinctions. Even on a cosmic scale that's a very long time.

Question: is it possible that the universe is geared for DNA based life to emerge through abiogenesis? Just as the same crystals form under the same circumstances no matter where you are, perhaps DNA based life is the same, just a fundamental standard pattern you can find through abiogenesis at multiple points in time and location. Why do we presume that our form of life is so special?

I don't think it entails presumption that our form of life is special to say, "You can't determine frequency based on a single data point."

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