Though what he really said is open to doubt, the nuclear physicist Enrico Fermi gave his name to a short and possibly final argument against the existence of intelligent life on other planets. There are 200 billion stars in our galaxy alone. 20 billion of these are like our own sun. Let us assume that one in five of these has planets – and we find new exoplanets every year – and let us assume that one in a hundred of these one in five has one planet with liquid water: that gives us 40 million Earth-like planets. I will not carry on with the assumptions, but it seems reasonable that there should be around a hundred thousand other advanced civilisations in our galaxy alone.
This being so, the “Fermi Paradox” asks, where are they? So many other civilisations – so many of them presumably older and more advanced than our own – and they have not visited us. Nor, after generations of scanning with radio telescopes, have we detected any unambiguous signals from them. Either intelligent life on other planets does not exist, or it is so rare and so far apart in time or distance or both, that we shall never find it.
Writing in 2008, Nick Bostrom of Oxford University takes the argument to conclusions that are either depressing or exhilarating. He proposes a set of Great Filters, each of which limits the emergence of intelligent and technologically-advanced life. The most obvious filters are in the past. We shall soon be able to estimate how many planets in our galaxy have liquid water. We still have do not know how life begins. Obviously, it began here. But we have never been able to create a self-replicating organic process in our laboratories. It may be very unusual. It may also be very unusual, once begun, for this process to evolve beyond the very simple. Then it may be very unusual for larger and more complex living structures to evolve, and hardest of all for anything to emerge with the right combination of mind and appendages to enable the birth of a technological civilisation.
Or the Great Filter may be in the future. It may be that civilisations like our own are reasonably common – but that they invariably blow themselves up shortly after finding how to split the atom.
Bostrop’s conclusion is to hope that, when we get there, we shall find that Mars is, and always has been, a sterile rock. Independent life of any kind on a neighbouring planet would suggest a universe teeming with life, and some probability of civilisations like our own. This being so, the lack of contact would put his Great Filter in the future, and would suggest that we are, on the balance of probabilities, heading for self-extinction. No life at all on Mars, now or in the past, would let him keep hoping that the Great Filter is in the past, and that we may have a splendid progress before us.
Sean Gabb, “Do Flying Saucers Exist?”, Sean Gabb, 2020-11-15.
August 1, 2022
QotD: Fermi’s Paradox and the Great Filter(s)
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I’ve always found speculation on intelligent alien life–which we have no evidence for or against–to be little more than navel-gazing. We’ve had the capacity to look for alien life for a few decades, and have dedicated pitifully few resources to the search. And yet we’re attempting to establish the psychology of life-forms we haven’t found, based on the fact that an incredibly brief search (where we don’t actually know what we’re looking for) has failed to find evidence of them.
We also aren’t seriously looking for alien life. We are looking for Earth-like life on other planets–a very different quest. This is decided stupid, because we know life can exist in other conditions. A paper published about the time a NASA probe arrived at Titan demonstrated that life can use liquid methane as its basis, for example. I understand that we must start the search somewhere, but we cannot rationally use a failure to find evidence as evidence of a lack when we are still in the preliminary stages of investigation.
Further, we have found evidence of life on other planets/moons. When that NASA probe reached Titan they found the dramatic drop in hydrogen concentration at the surface that was predicted by the paper I mentioned. The only other explanation is an as-yet unidentified geological process, which isn’t an explanation at all. On Mars we’ve also found fossil stromatolites–a type of trace fossil formed by primitive organisms (cyanobacteria on our planet) common in the early days of our planet. There are other explanations, yes, but again, evidence for the alternate explanations is lacking. As the paper on Martian stromatolites put it, the only reason why these fossils are not acknowledged as such is that they’re on Mars; the author went to great pains to demonstrate that exactly the same structures are universally accepted as fossils when found on our planet, in formations of the same age as those stromatolite fossils on Mars.
This brings up a second issue with our investigation: Our standards of evidence are unreasonably high. We absolutely must have high standards for evidence, but the current standard for identifying extraterrestrial life is so high that there are places on our planet that wouldn’t meet the criteria. You can’t use a lack of evidence as evidence of a lack when the reason you lack evidence is that you’re dismissing it.
Comment by Dinwar — August 1, 2022 @ 09:08
I remember being quite disturbed as a young teen the first time I encountered Fermi’s Paradox and — as a thought experiment — it’s a useful thing to wrestle with or to have as a late-night bull session topic.
I can’t have been the only person who got pranked by office mates when I was running the SETI@home screensaver! Surely that counts! 😉
I imagine getting the US or other governments to fund searches like this pretty much have to emphasize the “military” threat aspect to get much money … modern day Curtis LeMays are not going to put any of their funding in that effort unless there’s some belief that aliens could be a threat and that they can survive on Earth (that is, they’d have some credible reason to want to “invade”).
Comment by Nicholas — August 1, 2022 @ 12:27