[HN Gopher] SETI's hard steps and how to resolve them
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SETI's hard steps and how to resolve them
Author : JPLeRouzic
Score : 41 points
Date : 2025-02-22 07:33 UTC (3 days ago)
(HTM) web link (www.centauri-dreams.org)
(TXT) w3m dump (www.centauri-dreams.org)
| echelon wrote:
| Here's a parameter I don't think the Fermi Equation takes into
| account:
|
| I call it "Fragile Universe", based off of the notion of the
| "Fragile" or "Vulnerable World Hypothesis" [1].
|
| f_c is the parameter for the fraction of "civilizations that
| reach the technological level whereby detectable signals may be
| dispatched", so that handles the "Fragile World Hypothesis".
| Alien civilizations can wipe themselves out, exhaust resources,
| etc. before we get to see their detectable signals [2].
|
| What the equation doesn't take into consideration is the
| possibility that an advanced species can trigger the destruction
| or total reset of the entire universe, eg. by nucleating the
| vacuum collapse. The first advanced species to reach that point
| could kill every species in the universe and start the whole
| thing over from scratch.
|
| This is an extreme version of the anthropic principle [3]. We
| exist because the universe hasn't been reset yet. By us or
| otherwise. Presumably we might be the first to get there.
|
| Universe fragility could be the reason we don't see aliens. We
| could be the very first, and we could wind up hitting the reset
| button.
|
| [1] https://nickbostrom.com/papers/vulnerable.pdf ; tldr:
| advanced species can trivially wipe themselves out and will tend
| to do so. Not just nukes, but in the extreme, your average
| citizen can create grey goo at home with the press of a button
| that will turn the entire planet into paper clips.
|
| [2] It could be that the time frames in which advanced
| civilizations emit detectable signals are so geologically small
| as they shift into non-detectable modes (eg. dark forest,
| disinterest in expansion, shift into a higher plane of existence,
| etc.), but that's orthogonal to the discussion.
|
| [3] https://en.wikipedia.org/wiki/Anthropic_principle
| ziddoap wrote:
| > _eg. by nucleating the vacuum collapse. The first advanced
| species to reach that point could kill every species in the
| universe and start the whole thing over from scratch._
|
| How do you imagine the Universe resetting? Assuming the false
| vacuum decay occurs, I don't think any species (no matter how
| advanced) could reset the vacuum state back to a metastable
| state post-collapse.
|
| It does just appear to be the anthropic principle, but with
| some extra steps.
| echelon wrote:
| Maybe it doesn't? Maybe there are lots of other universes,
| and we just happen to be in one of the metastable ones that
| hasn't collapsed yet.
| jebarker wrote:
| Novice question here: What use is there in adding a term like
| that to the Drake equation? It seems like it's value would be
| completely uncertain (like other terms in the equation) and so
| you have overwhelming uncertainty in the output of the
| equation.
| andrewflnr wrote:
| Your instinct is largely correct. This is a silly idea.
| simne wrote:
| Right answer is - we don't know.
|
| Unfortunately, Drake equation now is just estimate, without
| any real data, as humanity just don't know example of any
| extraterrestrial life at all.
|
| And what even more sad, our empty knowledge is not because
| non-existence of life in Universe, but because our science is
| very young and we just don't have powerful enough instruments
| to detect et life.
|
| We could only be sure, life was not exist on Moon equatorial
| stripe on surface, but for example we cannot be sure about
| deep under-surface and about polar regions.
| bluGill wrote:
| The universe is 93 billion light years across. No alien can
| reset it within time spans that matter to our solar system
| which has maybe 8 billion years left before our sun dies)
| wat10000 wrote:
| I don't think that solves it. The Fermi paradox is that based
| on the probabilities we estimate, we should see lots of aliens,
| and we don't. Thus something in our estimates must be wrong,
| but we don't know what.
|
| This fragility idea just shifts it from "we should see lots of
| aliens and we don't" to "the universe should have been
| destroyed by now and it hasn't been."
| AnotherGoodName wrote:
| The steps don't have to be that hard for us to be unique.
|
| There are 10^22 to 10^24 stars in the Universe (a big range of
| uncertainty there but it doesn't matter for this point). That
| sounds like a lot but anyone with knowledge of combinatronics
| would immediately say holy shit that's a small number.
| Cryptography buffs are probably looking at that going "that can't
| be right, it's a tiny number", you divide it by 10 repeatedly, 24
| times in fact and you're down to nothing. 24 not-at-all 'hard'
| steps and we're probably alone.
|
| You've probably heard "there's soooo many stars in the universe
| there has to be other life out there". There really isn't that
| many in terms of probability.
| A_D_E_P_T wrote:
| This is too facile. The Copernican principle assumes that we
| are not in a spatially or temporally privileged position, and
| there are no _obvious_ hard steps -- to say nothing of 24. It
| 's frankly bizarre to go from there to "we are unique among
| 10^22 stars."
| AnotherGoodName wrote:
| Having thoughts around how many stars are in the observable
| universe is a very reasonable starting point. Even without a
| privileged position the observable universe is still well
| defined in an expanding universe - at some boundary other
| stars are moving away too fast to be observed. So we can
| absolutely state this.
| DennisP wrote:
| In this case the Copernican principle is at odds with the
| anthropic principle. If there were only one place in the
| universe with intelligent life, then necessarily that's where
| we would be.
|
| GP may be thinking of this paper, which uses a reasonable
| probability distribution for each parameter in the Drake
| equation, and finds a decent chance that there is no other
| technological civilization in the observable universe:
|
| https://arxiv.org/abs/1806.02404
| bluGill wrote:
| The speed of light is also a factor: most of those stars are so
| far away that they cannot detect our sun because to them it
| hasn't even lit up yet. (Our sun is about 4.6 billion years
| old, the universe is about 93 billion light years across).
| Stars like our sun are expected to last 10-12 billion years, so
| most stars that we think can support life in you 10^24 number
| have already died and we don't know it!. (stars need not be
| like our sun to support life, but I have to go with something
| to give numbers)
| RAM-bunctious wrote:
| Not that I'd call myself a buff, but I don't think my knowledge
| of larger numbers makes 10^24 a small number in any absolute
| sense. Cryptographic keyspaces are deliberately designed to be
| unfathomly large, whereas the number of stars in the universe
| is simply an observational fact. The number of stars really is
| huge in a human sense, as much as that's worth anything. There
| are more stars than there are grains of sand, etc.
|
| The fact that we exist to discuss these odds means that
| whatever the probability distribution, at least one instance of
| life has occurred. Not only that, but life arose and eventually
| led to intelligence at our level - something that appears to be
| rare even on our own planet, but achieved relatively quickly
| all things concerned (only a few hundred million years).
|
| While the anthropic principle guarantees that we observe
| intelligence as we're defining it (since we include ourselves),
| I agree that doesn't mean intelligence is inevitable or common.
| A more likely modelling in my opinion is that worlds of
| microbial life are abundant, worlds with complex multicellular
| life is rarer, and intelligent civilizations are rarer still.
| Given the distribution of intelligence levels on Earth, it
| seems unlikely that we simply passed every constraint while no
| other planet gets close. Also, if we observed a planet with
| humans as they were 100,000 years ago, would we even consider
| them intelligent life? Probably just as intelligent as modern-
| day humans if raised the same, but literally nowhere near our
| technological level.
|
| When scientists evaluate whether soil can support certaing
| thing, they don't treat each factor (like pH, moisture,
| nutrients, microbial conditions) as independent hurdles that
| must be overcome one by one. Instead, they see that multiple
| factors interact in complex ways. A deficiency in one area
| (e.g., nutrient content) can be mitigated by another factor
| (e.g., microbial activity enhancing nutrient cycling). If you
| extend this to conditions in which life might it arise, it
| suggests to me that planetary habitability may be more like a
| network of contributing conditions rather than a checklist --
| actually much more difficult to caclulate?
|
| Also, mostly as an aside, we also have the advantage of knowing
| that life and then intelligence arose relatively quickly once
| conditions stabilized - only a few hundred million years. n=1
| but I think this is a promising indication on where any
| variables might lie.
| d0odk wrote:
| Isn't that just the observable universe?
| AnotherGoodName wrote:
| Yes although that's all we observe from the point of view of
| the fermi paradox so is very relevant.
| d0odk wrote:
| Ah, that makes sense. Given your original comment, I was
| considering unevenly distributed life across an infinite
| universe. But you're right of course, that is irrelevant to
| the fermi paradox.
| A_D_E_P_T wrote:
| On timescales of billions of years, we don't know if any of those
| steps are "hard," "easy," or "inevitable." As the first commenter
| to that article notes at the link, we have only a single
| datapoint.
|
| It's certainly unclear that photosynthesis is an ironclad
| requirement for life, and, in any case, it evolved multiple times
| in parallel on Earth. (Anoxygenic photosynthesis in fact evolved,
| _de novo_ , more than once.)
|
| I'd add that it's also by no means a given that life, broadly
| defined, can only evolve around a sunlike star.
|
| Speculation around "hard steps" is pseud naval gazing until we
| gather more datapoints. It's not even valuable as speculation --
| except perhaps as an exercise in countering sloppy thinking.
| bluGill wrote:
| > I'd add that it's also by no means a given that life, broadly
| defined, can only evolve around a sunlike star.
|
| Not a given, but not unreasonable either. Larger stars die
| faster so they probably won't be around long enough for life.
| Smaller stars last longer, but they also emit less energy and
| so there is less likely to be higher life forms just because
| there isn't enough energy to support life.
|
| Of course life might not be like we know it, but carbon and
| water are very common in the universe compared to most of the
| other options and so they are more likely.
| jdhwosnhw wrote:
| > Smaller stars last longer, but they also emit less energy
| and so there is less likely to be higher life forms just
| because there isn't enough energy to support life.
|
| This isn't really true. The energy density at a planet's
| surface is a function of both the star's luminosity and the
| planet's distance. Most star's (at least in the Milky Way)
| are small, and most stars have planets in orbits closer than
| is Earth's. The so called "Goldilocks zone" is expected to
| have at least one planet in it for a very large number of
| stars (again, at least in our galaxy).
| sigmoid10 wrote:
| I guess the important bit that always gets left out is that
| these things revolve around life _as we know it_. Of course you
| could have a completely different biochemistry resemble the
| processes that we generally associate with life. But until we
| either replicate that in a lab or find signs of life on other
| planets (earth-like or otherwise), the best speculation we can
| do is based on what we see here. And we see that certain steps
| on the path towards complex multicellular life took very long
| compared to others.
| perihelions wrote:
| - _" The fact that it did happen here tells us nothing more than
| that, and until we dig out evidence of a 'second genesis,'
| perhaps here in our own Solar System inside an icy moon, or on
| Mars, we can form no firm conclusions."_
|
| I'm convinced the absence of evidence is, itself, valuable
| evidence. The (apparent) single origin of Earth life is a
| remarkable statistical observation hiding in plain sight.
| JohnMakin wrote:
| > I'm convinced the absence of evidence is, itself, valuable
| evidence.
|
| That isn't how science works. We have an astounding lack of
| evidence that there is a Flying Spaghetti Monster roaming
| around the deepest reaches of space, it doesn't indicate
| anything but the fact that there's a lack of evidence that
| there is a Flying Spaghetti Monster roaming around the deepest
| reaches of space. It may not indicate with absolute certainty
| whether there is or isn't one, but you cannot say its existence
| is more likely based on lack of evidence for it - that is
| superstition.
| aradox66 wrote:
| I think science does actually offer tools beyond pure
| falsifiability for evaluating truth claims
| jerf wrote:
| "Absence of evidence is not evidence of absence" is simply
| false, however much fun it may be to say. Let us suppose, for
| instance, that we had indeed scanned over the entire universe
| and found that there was no evidence for life. Would we then
| be justified in saying "the absence of evidence is not
| evidence of absence"?
|
| Of course not. What other evidence of absence do you expect
| to uncover, other than a lack of evidence for existence? Do
| you expect to go out into space and have some sort of space
| god hand you a genuine, bona-fide certificate of nonexistence
| of something?
|
| It is important not to overestimate the strength of the
| absence of evidence, but setting the strength to zero is just
| as wrong.
|
| If we look in many places where we expect to find life,
| because we have a theory that life is easy and essentially
| appears the cosmological instant it is possible, and we have
| a theory that the conditions for life are easy and abundant,
| yet we look out into the universe and see no evidence of
| this, yes, we are completely justified in adjusting our
| understanding of the probabilities involved. The more of the
| universe we see, and the more it lacks various sorts of life
| (all the way from the simplest, sparsest bacteria-type life
| up to galaxy-spanning intelligences, each to their own
| degree) the more we are justified in coming to conclusions
| about their probabilities.
|
| Another thing people have problems with in this debate is
| understanding the difference between _justified_ beliefs and
| _true_ beliefs. If we hypothetically examined all but one-
| trillionth of the observable universe and found it bereft of
| any other life, we would be _justified_ in the conclusion
| that the most likely scenario is that there isn 't any. We
| could end up being _wrong_ if that remaining one-trillionth
| just so happened to contain other life, but we would still be
| _justified_ , having collected extensive "absence of
| evidence". We can not claim that we have seen enough of the
| universe to know that it is _true_ that there is no other
| life, and we have not seen enough of it to be _justified_ in
| claiming there is no bacterial life, but I do feel at this
| point we are pretty _justified_ in claiming that at least
| this galaxy and the nearest ones do not have any galaxy-
| spanning, multi-million-year civilizations in them, for
| instance. _Maybe_ they 're there and they just don't do
| anything visible, but that's a pretty precise claim.
| feoren wrote:
| Science is ultimately rooted in logic, and I'm not sure why
| so many people forget this. We seem to pretend that we can
| evaluate every possible claim in a complete vacuum, and that
| it's somehow pure to ignore any sort of logic or prior
| knowledge when we do so. But this has never been "how science
| works", nor how humans work. Science operates on top of the
| logic and knowledge that we already have about the universe.
|
| So if I claim that there is a Flying Spaghetti Monster
| roaming around our solar system, and it is 1000x larger than
| our sun, emitting a divine brightness so intense that it
| would burn the eyes of all who gaze upon it, you're 100%
| justified to say "no there isn't. We would have seen it."
|
| "Aha!" I say, "but absence of evidence is not evidence of
| absence! Therefore you can't say _anything at all_ about
| whether there 's a supermassive superluminal Giant Spaghetti
| Monster!". That is absolute nonsense.
|
| > you cannot say its existence is more likely based on lack
| of evidence for it
|
| If its existence would imply evidence, then you absolutely
| can judge its likelihood based on whether that evidence
| exists or not. And you can also judge its likelihood based on
| a reasonable extrapolation from prior knowledge, by the way.
| Yes, it is more likely that there is a 10 kg rock orbiting
| Neptune than a 10^20 kg Spaghetti Monster, even though we
| have not directly observed either one. We understand the
| mechanisms by which a small rock comes to orbit a planet. We
| see that kind of thing all the time. It may be difficult to
| formalize some of these priors, but that's a failure of our
| formalisms, not a mandate that we must not use that knowledge
| when doing science.
| JohnMakin wrote:
| > "Aha!" I say, "but absence of evidence is not evidence of
| absence! Therefore you can't say anything at all about
| whether there's a supermassive superluminal Giant Spaghetti
| Monster!". That is absolute nonsense.
|
| Note that the comment you are replying to said nor implied
| anything of the sort.
| close04 wrote:
| If I read 98% of your comment I might draw a pretty accurate
| conclusion based on the absence of something in it. But if I
| read just 2% any conclusion I draw is whatever I want to read
| in the tea leaves.
|
| Do you think we investigated closer to 98% or to 2% for
| possible evidence?
| bluGill wrote:
| Not in this case. the amount of the universe we can really
| observe is tiny. Sure we can see a lot of stars, but that is
| about it. We cannot directly see any planets outside our solar
| system (this might not be completely true, I'm not sure what
| the limits are), except by how they change the light of the
| star. Basically we can't even detect earth sized planets around
| most stars, as they are too small. If we cannot detect planet
| sized objects that means there is no hope of seeing lifeforms
| on the planet.
|
| The limits are not just our technology levels. Many of the
| signs you want to life for of life are things that we know by
| laws of physics could not possibly reach us no matter how good
| the detection equipment is.
|
| That is why SETI looks for radio waves - they are one of the
| few signals we can detect that could signal life. However we
| would never detect earth technology levels of just 120 years
| ago (there is some debate about what we could first detect).
| There are not many stars within 100 lightyears of earth, so the
| vast majority of our galaxy (must less the universe) still has
| no idea we are here. Even radio signals degrade with distance,
| so there is a limit to how far we can detect them or they can
| detect us.
|
| In short, while there is absence of evidence, there is reason
| believe that we don't have enough evidence to declare anything.
| If we find life that will be conclusive, but the we don't
| before our sun dies there still won't be enough evidence to
| state there is none.
| happosai wrote:
| > We cannot directly see any planets outside our solar system
| (this might not be completely true, I'm not sure what the
| limits are)
|
| Glad you expressed uncertainity. Indeed We can see some
| exoplanets directly. I also only learned this very recently.
|
| https://en.wikipedia.org/wiki/List_of_directly_imaged_exopla.
| ..
| gxd wrote:
| This topic is near and dear to me. It is so important that I'm
| working full-time on a game about how a first contact with an
| extraterrestrial could look like. If you are interested, I just
| released a free demo with ~2 hours of content:
| https://store.steampowered.com/app/3040110/Outsider/
| jonhohle wrote:
| I know you're being serious, but I was really hoping this was a
| link to the shareware version of Doom.
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