Let's just go through this. Do I think there's life - recognizably familiar, reproducing, information carrying arrangements of molecules - elsewhere in the universe? I think there's an awfully good chance. Do I think any of it's 'intelligent', like wot we are? Well, I think the odds are far worse, but given the size of the universe then sure, it just may be tucked away somewhere we'll never, ever, know about. So, on the face of it this kind of kills the notion of the mother-ship arriving over suburbia and hordes of iPhone wielding creatures texting us into submission. Except...well, except that there's another way to look at things.
I'll start by saying that I know this is not an original idea. Let's take the history of life on Earth. Intelligence - in the form of machine creating, modeling, mathematically fixated organisms - has not played a big role over the past 4 billion years. Dinosaurs were fabulously successful as a type of life, a hundred million years of romping (plus all the chickens running around today), extraordinary adaptations and variations...but not a wheel, differential equation, or moon shot in sight. Humans, by really all measures, are freakish - an extraordinary and wonderful oddity. This doesn't even begin to address the issue of the microbes, ancient and incredible terraformers and survivors, but no intelligence in the way we define it.
Given all of that, I think in-the-incredibly-unlikely-event that aliens show up on our doorstep they will be no smarter than your average jellyfish. They will not have built spaceships, at least not the way we think about spaceships, with flush toilets. They might have built some kind of structure to carry them through space, much in the same way that ants build a nest, or hermit crabs snag a nice shell, but they won't be doing this as an outcome of design review, they'll be doing it instinctively. These will be organisms that have evolved to treat space much like we treat the oceans. Sailing, drifting, or zooming, when they find a useful resource (if they need such things) they make planetfall and set to work, maybe like locusts, or maybe less destructively.
Is this crazy? Maybe, but less so than the other options. There are still significant physics problems. Assuming any such life originated on a planet, then climbing out of that gravity well is always going to be tough. Perhaps this filters out all but the tiniest organisms, lofted up to the exosphere, evaporated out into space. Or perhaps it filters out all but the oddities....
Obviously I should stop drinking the water.
Interesting post, Caleb.
ReplyDeleteOn the assumption that intelligent life did not require 4 billion years to develop, then the late appearance of machine-building life on Earth suggests that intelligent life is an unlikely outcome within 4 billion years. (Note, however, that if intelligent life had 3.5 billion years of prerequisites, then its nonappearance until recently is less damning for its overall probability, and it just means that we should target older stars in SETI searches.)
Anyway, interstellar spores seem possible. In fact, it's possible that dumber-than-jellyfish aliens have already shown up here, and maybe we are even their descendants. (I've been drinking that water too.)
I can't get away from thinking that with ~10^20 Earth-like planets in the observable universe, the likelihood of machine-building critters can't be so small that we're the only ones. Of course, even if only one in 10^20 Earth-like planets hosts life, still we would find ourselves on that very one.... But my answer to Fermi's paradox is similar to the answer to Olber's – they haven't shown up because they're too far away and the universe is too young. (At some point, every line of sight will land on an intelligent alien....)
Presumably to become spacefaring, a species would have to learn to build structures to maintain comfortable atmospheric pressure and temperature, not to mention whatever it is they breathe. Wouldn't that require the ability to mine metals and...you know...build things? I guess it's possible other species have some "natural" way of shielding themselves, perhaps by constructing metal shells on themselves, who knows....
ReplyDeleteI would say that a more likely way for "dumb" interstellar travelers to get around would be by total accident - supernovae shooting chunks of preserved creatures on asteroids from one planet to another over the course of billions of years.
C,
ReplyDeleteAsteroid/comet impacts can give ejecta escape velocity from a solar system and can therefore give rise to dumb spacefaring microbes.
Caleb,
ReplyDeleteThanks for your wonderful and informative blog, one of the best I have read.
Concerning your skepticism of extraterrestrial intelligence, I sense an inconsistency. Here is what I mean. You write, “Humans, by really all measures, are freakish - an extraordinary and wonderful oddity.”
That is to be expected if they are the result of contingent Darwinian processes. Humans (and human functional equivalents, to use Carl Sagan's terminology) would be an unexpected and extremely rare outcome.
But (as I understand it) the working assumption of origin of life researchers is that life emerged from biochemical reactions through Darwinian processes of natural selection. With that assumption, wouldn't carbon-based, information rich life also be a “freakish oddity?” If not, then the biochemical reactions would have a built-in bias toward the emergence of life; a sort of teleology.
It seems to me that the working assumption of astrobiologists tends toward the “bias for life” view, not the Darwinian view for the origin of life. If that were not the case, then your skepticism of ET should also apply to the occurrence of life itself.
I would be interested to hear your comments on this issue.
Thanks,
Otis Graf
Otis,
ReplyDeletethanks for the thoughtful - and provocative ! - comments. I think you do make an excellent point. You're certainly right that there is a tendency amongst astrobiologists to assume the bias-for-life in that early, origins, setting. I think I would argue though that there is a difference between the processes of selection in the biochemistry leading to life and the processes of selection at the level of complex life. This is really not a well formed argument on my part, but here goes.
At the molecular level - even if quite complex structures are involved - then I think things are much less forgiving of experimentation (mutation, variation etc). After all, in terms of pure combinations and permutations then while there may be vast numbers of ways to construct similarly shaped/functioning molecules consisting of a few hundred or thousand atoms - the ramifications of the 'wrong' atom here or there are significant and can lead to complete failure of that molecule for a particular chemical trait (that we might later call biochemical function). Now, that might simply tell us that getting to the stage of life is incredibly unlikely, but it also might suggest that the selection effects at that level are so severe that the system will necessarily converge quite rapidly onto viable 'solutions' - i.e. surviving rudimentary, self-propagating life.
By contrast I think I would argue that the nature of selection for later life (microbes and up) is even more complex, *but* that putting some pieces in the wrong place for an organism (i.e. non optimal
mutations, variations) are not as fatal as at a molecular level - where things tend to simply not work at all in that case. In that sense the evolution of organisms may follow a far more random path, especially as you get further up the complexity tree (i.e. to multicellular life in the case of the Earth).
So, in this picture humans are very unlikely, but at the base of the tree there are a limited number of routes in going from molecules to RNA/DNA, but those routes are quickly 'discovered' because the alternatives just don't go anywhere.
I'm sure I've dug myself into a colossal hole with this, but it's fun to discuss, and it's been a heck of a long day at my end - so consider this more of a stab at an answer rather than word written in stone!
Caleb,
ReplyDeleteThanks for your insightful response. I find this all very interesting. There are such fundamental issues involved.
Otis