The only really simple explanation is that life (abiogenesis) is somehow much harder than it looks, or there’s a hard step on the way to mice. Grey goo would not wipe out every single species in a crowded sky, some would be smarter and better-coordinated than that. The untouched sky burning away its negentropy is not what a good mind would do, nor an evil mind either, and the only simple story is that it is empty of life.
Though with all those planets, it might well be a complex story. I just haven’t heard any complex stories that sound obviously right or even really actually plausible.
How hard do you think abiogenesis looks? However much larger than our light-pocket the Universe is, counting many worlds, that’s the width of the range of difficulty it has to be in to account for the Fermi paradox. AIUI that’s a very wide, possibly infinite range, and it doesn’t seem at all implausible to me that it’s in that range. You have a model which would be slightly surprised by finding it that unlikely?
There doesn’t actually have to be one great filter. If there are 40 “little filters” between abiogenesis and “a space-faring intelligence spreading throughout the galaxy”, and at each stage life has a 50% chance of moving past the little filter, then the odds of any one potentially life-supporting planet getting through all 40 filters is only 1 in 2^40, or about one in a trillion, and we probably wouldn’t see any others in our galaxy. Perhaps half of all self-replicating RNA gets to the DNA stage, half of the time that gets up to the prokaryote stage, half of the time that gets to the eukaryote stage, and so on, all the way up through things like “intelligent life form comes up with the idea of science” or “intelligent life form passes through an industrial revolution”. None of the steps have to be all that improbable in an absolute sense, if there are enough of them.
The “little filters” wouldn’t necessarily have to be as devastating as we usually think of in terms of great filters; anything that could knock either evolution or a civilization back so that it had to repeat a couple of other “little filters” would usually be enough. For example, “a civilization getting through it’s first 50 years after the invention of the bomb without a nuclear war” could be a little filter, because even though it might not cause the extinction of the species, it might require a civilization to pass through some other little filters again to get back to that level of technology again, and some percentage might never do that. Same with asteroid strikes, drastic ice ages, ect; anything that sets the clock back on evolution for a while.
The only really simple explanation is that life (abiogenesis) is somehow much harder than it looks, or there’s a hard step on the way to mice. Grey goo would not wipe out every single species in a crowded sky, some would be smarter and better-coordinated than that. The untouched sky burning away its negentropy is not what a good mind would do, nor an evil mind either, and the only simple story is that it is empty of life.
Though with all those planets, it might well be a complex story. I just haven’t heard any complex stories that sound obviously right or even really actually plausible.
How hard do you think abiogenesis looks? However much larger than our light-pocket the Universe is, counting many worlds, that’s the width of the range of difficulty it has to be in to account for the Fermi paradox. AIUI that’s a very wide, possibly infinite range, and it doesn’t seem at all implausible to me that it’s in that range. You have a model which would be slightly surprised by finding it that unlikely?
There doesn’t actually have to be one great filter. If there are 40 “little filters” between abiogenesis and “a space-faring intelligence spreading throughout the galaxy”, and at each stage life has a 50% chance of moving past the little filter, then the odds of any one potentially life-supporting planet getting through all 40 filters is only 1 in 2^40, or about one in a trillion, and we probably wouldn’t see any others in our galaxy. Perhaps half of all self-replicating RNA gets to the DNA stage, half of the time that gets up to the prokaryote stage, half of the time that gets to the eukaryote stage, and so on, all the way up through things like “intelligent life form comes up with the idea of science” or “intelligent life form passes through an industrial revolution”. None of the steps have to be all that improbable in an absolute sense, if there are enough of them.
The “little filters” wouldn’t necessarily have to be as devastating as we usually think of in terms of great filters; anything that could knock either evolution or a civilization back so that it had to repeat a couple of other “little filters” would usually be enough. For example, “a civilization getting through it’s first 50 years after the invention of the bomb without a nuclear war” could be a little filter, because even though it might not cause the extinction of the species, it might require a civilization to pass through some other little filters again to get back to that level of technology again, and some percentage might never do that. Same with asteroid strikes, drastic ice ages, ect; anything that sets the clock back on evolution for a while.
If that was true, we’d expect to find microbial life on a nontrivial number of planets. That’ll be testable in a few years.