Brett: We still have this problem of what DNA was doing for that approximately two and a half billion years—the overwhelming majority of the history of life on Earth. Why didn’t it evolve at all during that time? What’s going on?
There’s a book, Rare Earth, by Peter Ward and Donald Brownlee, and these guys talk about all the quirky things that happened in the evolutionary history of the Earth. I just picked on the fact that we universal explainers evolved seemingly fortuitously, seemingly once; but you can go back and realize that evolving from single-cell bacteria to a multicellular organism was weird and unusual and hasn’t been able to be repeated in a laboratory setting.
Then to go from the multicellular organism to something that’s like a plant and then something that’s like an animal—each of these things seems to have occurred for reasons that we don’t understand.
Naval: There could be a combination of things going on. Your argument can be statistical rather than absolute. We may not be alone in the universe, but becoming universal explainers might be so rare that when you start multiplying that by interstellar distances, which are quite vast, we might just be too far apart.
I think Fermi also had the unreasonable assumption that interstellar aliens would figure out how to get past the speed of light, when we have no hypothesis whatsoever as to how that might be possible. We have nothing even vaguely in the category of how to get past the speed of light.
So if you’re limited by the speed of light, and if the jump to universal explainers is rare, then we might just be too far apart. And it might just take a lot longer.
The universe is very big, but it’s also almost entirely empty, at least as far as planets and the stars are concerned. Given that, it’s still quite reasonable to say that humans and human-like explainers are quite rare; they’re still early in their formation across the universe; and they’re just spread out by such incredibly vast distances that we haven’t encountered each other.
If we did encounter each other, I think we’d know.
For example, by the time an alien spacecraft got here, their radio waves would have arrived long before. There’s a pretty long period in a civilization’s history when it invents the radio and starts to broadcast radio waves out, before it invents interstellar travel and it’s sending rockets and civilizations around the universe.