After all, no matter even if life, and subsequently intelligent life, is statistically unlikely, its existence elsewhere is statistically certain. Further, since it is extremely unlikely that humans are the first intelligent life to emerge in our galaxy, then the seeming absence of intelligent life is a puzzle that needs explaining.
A decade later, Frank Drake formulated an equation supplying the terms that must be considered in contemplating how many extra terrestrial intelligences (ETI's) there might be.
In successive decomposition, it goes something like this: the number of stars, the fraction that have planets, the fraction of those that have habitable planets, the fraction of them that go on to develop life, the fraction of life bearing planets that yield intelligent life, the fraction that release detectable signals into space, and the duration those signals are emitted.
Of all those parameters, only the number of stars is approximately known, is large enough so that even the multiplicative combination of very low probabilities means the existence of ETI's is certain.
There are two potential resolutions to the Fermi paradox.
The first wasn't even remotely predictable in the 1950s and 1960s. At the time, radio and TV signals were often broadcast from 100,000 watt transmitters. What no one could predict then is a near certainty within a couple decades: our planet going dark. The combination of low power satellite transmitters, cellular networks and near-pervasive landline networks have rendered high power transmitters all but obsolete.
Now that alone doesn't eliminate the Fermi paradox, because even if other ETI's don't radiate enough energy to be detectable is of no real help. The likelihood that even one ETI has developed long before we did is a near certainty; therefore, such a civilization should long ago have pervaded the galaxy.
That, in turn, requires a more or less heroic assumption — that moving even anything more than trivial masses to other stars is possible.
Taken in combination, it is possible that the galaxy is littered with ETIs that will be forever confined to their stars, and undetectable from every other ETI.
But what if the certainty the Drake Equation predicts is? What if there has been widespread optimistic presumptions about some of its elements greatly overstating their likelihood?
The problem with the Drake equation is that it provides discrete estimates to each of the factors.
To quickly see the problems point estimates can cause, consider the following toy example. There are nine parameters (f1, f2, . . .) multiplied together to give the probability of ETI arising at each star.
Suppose that our true state of knowledge is that each parameter could lie anywhere in the interval [0, 0.2], with our uncertainty being uniform across this interval, and being uncorrelated between parameters.
In this example, the point estimate for each parameter is 0.1, so the product of point estimates is a probability of 1 in a billion. Given a galaxy of 100 billion stars, the expected number of life-bearing stars would be 100, and the probability of all 100 billion events failing to produce intelligent civilizations can be shown to be vanishingly small: 3.7 × 10−44. Thus in this toy model, the point estimate approach would produce a Fermi paradox: a conflict between the prior extremely low probability of a galaxy devoid of ETI and our failure to detect any signs of it.
Instead, the authors account for our uncertainty by applying a Monte Carlo simulation — randomly assigning a probability in the range [0, 0.2] for each factor, then combining the values for each of the factors.
The result?
More than 22% of the simulations produce a galaxy devoid of even one ETI.
But wait, there's more.
If, instead of assigning point probabilities to each factor, model each factor as itself a combination of factors. Take the existence of life as an example. Abiogenesis is a transition from non-life to life that "… occurs at some rate per unit time per unit volume of a suitable prebiotic substrate." Using informed guesses about rate, volume, protein folding, etc, yields a range of estimates for the existence of life on suitable planets spanning 20 orders of magnitude. (There is much more to this than I am presenting, btw.)
Applying uncertainty distributions reflecting current knowledge to each of the factors in the Drake Equation, what do you suppose the likelihood is that we are alone, not just in the galaxy, but in the entire observable universe?
Nearly 38%.
I sure didn't see that coming.
23 comments:
I read a lot in the dim dark past on this and related subjects and seem to remember that every tribe, civilization, etc. has some version of a god factor in their mythology.
What are the odds that we and what we think of as our universe is just a video game being played by adolescent boys in a real world beyond our ken.
Seriously, Skipper, nice work.
Double comment at work again. :-(
We've done this before, but...
If our brains our Turing machines and thus consciousness can be created through a computer program, it is not only possible we're living in a simulation but the most likely possibility.
Are, dammit. Are.
Spellcheck works in mysterious ways its miracles to perform.
Hi David, Hope all is well with you.
e
Hey, David, howyadoin?
Doing good. You?
All things considered, I really can't complain.
We've been living in Germany for the last three and a half years, another year to go. TOSWIPIAW is making sure that we see all the things before we leave.
And both sprogs are successfully adulting.
Like I said, can't complain.
Maybe it's just me, but the thought we might well be alone in this galaxy (which is as near as makes no difference the same as being alone in the universe) is far more sobering than what I think most people had long taken for granted: there are others out there, just beyond reach.
One thing this paper didn't note is that stars outside roughly 2/3 of the galactic radius are in a region where stellar density isn't sufficient for there to be enough heavy elements for planet formation. For those within about 1/3 radius, the stellar density is sufficiently high that violent stellar events will wipe out any chance of nascent life developing any further.
So, roughly half the stars in the galaxy shouldn't even be counted.
Making the odds even longer.
Since my "creation myth" is radically different than everyone else's, none of your numbers really have meaning.
I believe that the universe extends forever beyond the observable universe, time had no beginning and that panspermia is a near certainty.
Modern scientific lore has it that the 19th century was shaken by scientific advances, especially Darwinism, and that a "crisis" of faith ensued with people resisting provable empirical truths and clinging desperately to their comforting scriptures. I think a lot of that is overblown--they were much further down the materialist path than we realize--but there was probably a fair bit of it. What's fascinating about Fermi and some other cutting-edged speculative science is how we can see the same syndrome in reverse among scientists themselves today and the lengths they will go to avoid anything that could even hint at the dreaded t-word-teleology--even when it's still light years away from anything that could be described as religion. Not a shred of evidence in well over a hundred years (actually since time immemorial) but still we spend millions searching for them and put some of our best and brightest on the case to spend their careers in the quest, reminding themselves the day long that absence of evidence is not evidence of absence. Why? Because we just KNOW THEY HAVE TO BE OUT THERE! That we might be alone is just too disturbing to contemplate. Does not compute!
It's similar with things like the multiverse, which many physicists apparently see as a flight into fantasy born not of evidence or even reasonable conjecture but of a reaction to the fact that randomness in the creation of the universe has become harder and harder to defend due to fantastically massive statistical improbabilities. Same with the creation of life. Now that we know the mind-boggling complexity of cell structures, the old freak chemical reaction in a warm pond of primal goop just won't cut in anymore. Enter Bret's panspermia. I think it's pretty wild, but who am I to question another man's faith.
[Bret:] Since my "creation myth" is radically different than everyone else's, none of your numbers really have meaning.
But this isn't anything like a creation myth, since it takes creation as given. Rather, taking that as given, how likely is it that there is one additional instance of intelligent life in the galaxy/universe?
Now, of course these numbers have no strict meaning, since they can't be quantified. However, to the extent they reasonably model the combinatorial problems required for intelligent life to exist, then they do have meaning: given some presumed number of ETI's, X, then presuming the cloak of distance could be instantly removed, how surprised should we be to find the actual number of ETI's reasonably close to the presumed number.
Previously, with a naive -- and, judging from the literature, widely shared -- notion of the everything involved in the Drake equation, I would have expected X to be in the dozens. Yet, even being fairly liberal on some estimates, it appears very likely that the actual number of ETI's is far, far smaller than anyone would have guessed.
I believe that the universe extends forever beyond the observable universe, time had no beginning and that panspermia is a near certainty.
But you are making an assumption absent evidence. Confining ourselves to the visible universe, beyond which we can say nothing, then the rate of ETI's coming into existence is so low that there could well be none in addition to us. That is very counterintuitive.
Why are we here? was a very interesting read -- trying to comprehend probabilities with a limit approaching zero with an infinite number of chances is very difficult to come to terms with. However, that isn't an issue here. All the quantities involved are well short of infinity.
[Peter:] What's fascinating about Fermi and some other cutting-edged speculative science is how we can see the same syndrome in reverse among scientists themselves today and the lengths they will go to avoid anything that could even hint at the dreaded t-word-teleology--even when it's still light years away from anything that could be described as religion.
Recently, I was invited to join a FB group dedicated to debunking theology in total, including disproving the existence of any god.
Regrettably, I accepted the invitation.
After taking a shellacking for suggesting that it is perfectly reasonable and possible to include several simple postulates, and, bingo, God!
So having taken abuse for presuming something for which there is no evidence exists (which requires a very tendentious notion of what constitutes evidence and existence) I countered with this: by your own lights, there is no life anywhere else in the universe.
For which I also took a shellacking. Apparently, proof can be whatever you want, so long as it proves what you want.
What that did prove, though, is that atheists are as dogmatic, and immune to the implications of their own arguments, as the most ardent religious fundamentalist. Maybe even more so.
Same with the creation of life. Now that we know the mind-boggling complexity of cell structures, the old freak chemical reaction in a warm pond of primal goop just won't cut in anymore.
Even knowing we exist, there is no explaining it.
Skipper:
I think I posted this here quite a while ago, but it's one of my all-time favourites and maybe it's a good time for a repeat. It's a quote from the self-declared agnostic, brilliant polymath and scourge of scientific pretensions, David Berlinski:
"We seem to live our lives in perfect indifference to the Standard Model of particle physics, the world we inhabit nor only remote from the world it describes but different in detail, thank God."
"Over there, fields are pregnant with latent energy, particles flicker into existence and disappear, things are entangled, and no one can quite tell what is possible and what is actual, what is here and what is there, what is now and what was then. Nothing is stable. Great impassive symmetries are in control, as vacant and unchanging as the eye of Vishnu. Where they come from, no one knows. Time and space contract into some sort of agitated quantum foam. Nothing is continuous. Nothing stays the same for long except the electrons, and they are identical, like porcelain Chinese soldiers. A pointless frenzy prevails throughout."
"Over here, space and time are stable and continuous. Matter is what it is and energy does what it does. There are solid and enduring shapes and forms. There are no controlling symmetries. The sun is largely the same sun now that it was four thousand years ago when it baked the Egyptian deserts. Changes appear slowly, but even when rapid, they appear in stable patterns. There is dazzling variety throughout. The great river of time flows forward. We anticipate the future, but we remember the past. We begin knowing we will end."
"The God of the Gaps may now be invited to comment--strictly as an outside observor, of course. He is addressing us. And this is what He has to say: You have no idea whatsoever how the ordered physical, moral, mental, aesthetic and social world in which you live could ever have arisen from the seething anarchy of the elementary particles."
"It is like imagining sea foam resolving itself into the Parthenon."
Peter:
That is a very appropriate passage.
However, that reminds me of way back in the quaint day when we cared about the theory of evolution -- Berlinski being fairly hostile to the idea.
Unfortunately, what plagued him then, making assumptions about what must be true that later turn out to be ill-assumed, faces a similar objection here.
Indeed we have no idea how our ordered world could have ever arisen from elementary particles.
Yet, despite our cluelessness, it seems to have done so, nonetheless.
Back in my day, there was a theory that given time immemorial, a passel of monkeys tapping on typewriters would reproduce all of Shakespeare's sonnets? As Skipper above says, we seemed to have accomplished an even more marvelous trick by creating ourselves and an ordered world from elementary particles -- whatever they are and wherever they came from.
Kudos to us.
Thanks for bringing this one up, Skipper.
I took a fast look when this paper went out, but didn't pay proper attention. I don't think their conclusions are strong though: averaging out over orders of magnitude of ignorance does not lend all that credence to your conclusions either. It ends up being fancy math to restate what you already didn't know to begin with.
The most interesting thing about this subject, in my opinion, is not so much what it says about aliens, but what it says about us. Sometimes I like to tease believers with the question "How your Faith would be impacted if we just discover alien life like us over there?".
You end up giving me the other side of this coin: what is the reaction of non-believers to the question "What if we are truly the only intelligent race of the whole Universe?"
Paul Dirac, an avowed atheist and undoubtly one of the greatest geniuses to ever live on this planet, by the end of his life shared the following thought (he rarely shared his thoughts, by the way, so this is gold):
"It could be that it is extremely difficult to start life. It might be that it is so difficult to start life that it has happened only once among all the planets... Let us consider, just as a conjecture, that the chance life starting when we have got suitable physical conditions is 10 −100 . I don't have any logical reason for proposing this figure, I just want you to consider it as a possibility. Under those conditions ... it is almost certain that life would not have started. And I feel that under those conditions it will be necessary to assume the existence of a god to start off life. I would like, therefore, to set up this connexion between the existence of a god and the physical laws: if physical laws are such that to start off life involves an excessively small chance, so that it will not be reasonable to suppose that life would have started just by blind chance, then there must be a god, and such a god would probably be showing his influence in the quantum jumps which are taking place later on. On the other hand, if life can start very easily and does not need any divine influence, then I will say that there is no god."
Well, your "sobering thought", Skipper, ocurred to other minds, so you are not alone after all.
Skipper: The quote should be savoured for its literary and metaphorical punch, not its scientific rigour. But I think you were wrong about Berlinski. I've read a lot of his stuff and he's very much in the "dunnoist" camp. He just has a bee in his bonnet about the pretensions of modern religion-bashing scientists.
Clovis:
The most interesting thing about this subject, in my opinion, is not so much what it says about aliens, but what it says about us.
I've always found it amusing that when we humans try to imagine contact with aliens they seem to be one of two types. Either they are wise, rational Mr. Spock types who will teach us how to cooperate, abolish war, etc. and save ourselves or they are terrifying brutes that will enslave or eat us. I have this fantasy of a spaceship arriving finally and disgorging a horde of nerd-like aliens in thick glasses who follow everybody around asking repeatedly "Can I be your friend?"
That's a great quote, but despite my sympathies with religious impulses, I think using the word god in this context causes more problems than it clarifies. Most humans are pretty limited in their conceptions of what that word means. But I do like this quote from Freeman Dyson: As we look out into the Universe and identify the many accidents of physics and astronomy that have worked together to our benefit, it almost seems as if the Universe must in some sense have known that we were coming.
[Clovis:] The most interesting thing about this subject, in my opinion, is not so much what it says about aliens, but what it says about us. Sometimes I like to tease believers with the question "How your Faith would be impacted if we just discover alien life like us over there?".
Exactly like I gave non-believers the opportunity to gore their own ox.
Speaking personally, I have always taken as given there are other intelligent life forms in our galaxy, never mind the universe. Finding proof would be a very memorable moment, but would have no real impact on me, because it would only demonstrate what I already assumed as true.
Outside the startle factor for those who don't give this sort of thing much thought, I don't expect Christianity, or Hinduism, for that matter, to be much affected. Nothing in the former insists on Earthly exclusivity, and for what little I know of the latter, it would probably be taken as a further affirmation of their beliefs.
Islam, however, would take a real hit. The Quran is the literal word of Allah, and contains within it all then knowledge humans need.
Forgetting about other intelligent life would seem a pretty serious omission.
It ends up being fancy math to restate what you already didn't know to begin with.
Which makes it really nothing more than a, perhaps, more statistically informed way to resolve the Fermi paradox.
I'm somewhat surprised at why no one seems to mention what we already have many good reasons to strongly suspect: Fermi's paradox doesn't exist if you can't get here from there.
[Dirac:] …if physical laws are such that to start off life involves an excessively small chance, so that it will not be reasonable to suppose that life would have started just by blind chance, then there must be a god, and such a god would probably be showing his influence in the quantum jumps which are taking place later on.
That physical constants are so perfectly and finely tuned to an absolutely fare-thee-well would seem to settle the argument in favor of there must be a god.
By his line of reasoning.
By mine, that is a perfectly astonishing fact, but can't get us anywhere in either the direction of a god, or not.
Skipper,
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Finding proof would be a very memorable moment, but would have no real impact on me, because it would only demonstrate what I already assumed as true.
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That's a pretty big statement. Boy, it would definitely have a huge impact on me.
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That physical constants are so perfectly and finely tuned to an absolutely fare-thee-well would seem to settle the argument in favor of there must be a god.
By his line of reasoning.
By mine, that is a perfectly astonishing fact, but can't get us anywhere in either the direction of a god, or not.
---
Heh, I chuckled with your "By his line of reasoning".
Dirac's line or reasoning were often very different from anyone's else. He for example played with the idea that physical constants aren't constants at all, from his large number hypothesis, sparking controversies and new theories still in discussion to this day. In this scenario the fine tune now observed would be just a passing phase.
Peter,
Thanks for the image of ETs as needy nerds, that's a pretty good addition to my mental universe.
I suppose that, after watching us from afar for some time, they would most probably land in Canada, just to maximize their chances of finding some decent humans.
Clovis: I must confess I cringed a bit when you linked my fantasy of extraterrestrials as nice needy nerds to Canada, but given what is going on in the rest of the world, I"m learning to savour our reputation for boring needy niceness. :-)
How are you doing?
I don't know if Canadians ask that question in earnest, Peter. Brazilians and Americans don't, while Germans usually mean it. Anyway, I am doing terribly due to personal matters, though they touch the difficulty of living in a land of pirates. But I won't bother the blogosphere with it right now.
You probably ask due to politics. So far, our elected President looks to be delivering less of a bomb than I expected. He is even nominating normal people to some important positions. There are chances we end up really emulating the US, with his worst impulses being modulated by reality and whatever institutional weights we still have.
At this moment, I really need to believe that, least I run in panic to join that caravan crossing Mexico, though I would aim at Canada! I long for a very, very quiet and boring place these days. I feel like one of those aliens too.
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