I’ve seen a bunch of people linking approvingly to this piece about the “Fermi paradox,” (the question of why we haven’t seen any evidence of other advanced civilizations) and I can’t quite understand why. The author expends a good deal of snark taking astronomers and physicists to task for constructing elaborate solutions to Fermi paradox on the basis of shoddy and unjustified assumptions. And then proceeds to offer a different solution for the Fermi paradox based on shoddy and unjustified assumptions. Whee!
I mean, there is an element of this that’s useful, namely the reminder that “We haven’t seen aliens because there are no aliens to be seen” is a perfectly valid solution and at least as likely as anything else anyone has come up with. But really, the entire business is so data-poor and bullshit-rich that I have a hard time taking it seriously.
The paradox comes down to a question of time scales, as the galaxy has existed for (in round numbers) ten billion years, while life on Earth took only four billion years to get from nothing to us. Surely, given the vast number of stars in our galaxy, some other species must’ve done the same before us, probably long enough before us to reach greater heights of technology, including interstellar travel. And as many people with half-assed network models will happily tell you via preprints on any number of web sites, if you can travel at 0.1c, you can colonize the entire galaxy in just a few tens of millions of years. So, there ought to be alien colonies all over the place.
But there’s all sorts of weird stuff behind those estimates, even leaving aside the “physicists don’t understand biology”/”biologists don’t understand math” sniping that goes on. The biggest neglected issues for me are the “why” questions. If you look at those estimates of time to cover the galaxy, a lot of them are talking about self-replicating robot probes. And while I’ll admit that it’s a lot more plausible to send a small robot off to another star at relativistic speed, I’ve never really understood what it is that the launching species is supposed to get out of that gigantic investment of energy resources. Some sort of abstract intellectual satisfaction, I guess. Even a single non-replicating probe to a neighboring system would be a huge undertaking, and require an astonishingly patient community of alien scientists willing to wait a few hundred years for pictures of the neighbors.
And even if robot probes were buzzing into the solar system, self-replicating, and leaving again, I’m not sure why anyone thinks that would be obvious. Space is vastly, mind-bogglingly huge, and that goes for space within the solar system. I mean, if some alien equivalent of Voyager or Cassini zipped past us snapping pictures, I’m not convinced we’d even notice. The only real hope is that whatever they use for a drive system is big and noisy and makes a lot of extra light at a time when we happen to be facing in the right direction.
Even the self-replicating part doesn’t need to leave obvious traces. There’s no reason at all why the self-replicating part of things would need to happen here, with our relatively dense atmosphere and strong gravity. There are huge numbers of floating space rocks and balls of ice out there in the Kuiper belt and Oort cloud that alien robots could mine to their heart’s content, and we’d never even notice.
And the problems are equally puzzling for anybody who could get here in person. Even at a peak speed of 0.1c, you’re talking decades to centuries to get from star to star. But if you have the resources and technology to maintain a livable environment in interstellar space over that span of time, I’m not sure why you’d need to visit Earth in the first place. Nostalgia? Some sort of alien-hipster retro affectation for the lifestyle of a dozen generations back? Again, you could park dozens of space arks in the asteroid belt and happily live there basically indefinitely without humans being any the wiser. If you need raw materials, it’s still easier to snag the occasional comet than to get on and off a rock ball like Earth.
The use case for alien visitation of Earth is ridiculously narrow– it’s basically limited to civilizations with some sort of hibernation technology that can preserve live specimens for decades or centuries, but only in some sort of suspended state that requires thawing out on a planet at the other end of the trip. And also some means of re-creating enough of their biosphere and technological base to make a viable colony there, but not enough of that technology to make habitats in space, or on asteroids or moons. So, assuming the aliens fall into that really narrow range of parameters, yeah, I guess we should’ve seen them by now.
Which comes around to the problem of communications, namely that we haven’t detected any signs of alien communications. But the electromagnetic spectrum is so huge, and our effort to find them has been so short and half-assed that it’s ludicrous to think we’ve actually ruled anything out.
So, I do agree with the Praxtime post in one very limited sense, namely that it’s ridiculously arrogant to think that the kind of calculation Enrico Fermi could dash off on a napkin says anything about the likelihood of alien civilizations. But at the same time, it’s equally ridiculous to think that the make claims in the opposite direction, based on the after-dinner napkins of biologists. We know so little about any of the parameters that go into any of this that it’s impossible to have a meaningful discussion about the idea.