There is a common topic among people who like to think about the future and space travel: the Fermi paradox. Simply put, if you take even tiny-seeming growth rates for any civilization in the galaxy, it should be everywhere in the galaxy within a billion or so years. And there have been 14 billion years, so where are they?
The wiki page suggests quite a lot of possible explanations, many of them nonsense, unfortunately. But it’s worth questioning the very basic assumptions of the argument, rather than resorting to making up extra things to explain the problem away.
The paradox rests on a few foundations:
- Civilizations are at least relatively common.
- Civilizations survive.
- Civilizations expand.
There are several other totally non-essential assumptions that are sometimes made. For example, the whole bit about radio broadcasts in the wiki isn’t really relevant because radio won’t be detectable from background noise at any real distance. But it doesn’t matter, because given a bit more time, you’d expect them to simply be everywhere.
There are already ways to question the first two assumptions. Most of them somewhat implausible. Dystopian sci-fi is all the rage these days (possibly partly fueled by inaction on climate change), so blathering about civilizations destroying themselves is a popular. But I’m not such a pessimist. The sticking point is that even if most civilizations die off, well… the rest ought to be enough.
The trick of the paradox is that even if the numbers are tiny (1 civilization per million stars! 1 in ten thousand survive!), you multiply by a big number (times 300 billion stars = 30 civilizations), and you basically only need to get 2 for the paradox to work. There’s us, and there’s someone else, then given enough time, we ought to be everywhere.
But… I don’t see people question the last assumption enough. Why expand? Usually this is hand-waved away (if the expansion rate is only 0.00000001% per year! Wow so little!) but that’s not good enough. The number really could be indistinguishable from zero.
Here’s the UN population projections to 2100. If anything, I think these are optimistic, and they suggest a leveling off around 11 billion humans. This isn’t due to any sort of resource constraint. It’s entirely due to the birth rate falling off a cliff (in fact, going below replacement and we expect population to decline!) as soon as a population reaches a certain level of economic security and education (particularly for women.)
So, here’s a thought, if we top out at 11 billion humans, just what are we going to fill those 300 billion stars with?
There are of course some counter arguments. For example, what about AI? Or curing aging? But I think these too are dead ends. I’m not worried about AI, but that’s a topic for another post. As for curing aging… I predict it will lead to an even more severe drop-off in the birth rate. (You know the “ticking biological clock?” Yeah, why rush? Without that deadline hanging around…)
One can also object that maybe other species won’t be like humans in this respect, but… why assume otherwise? We don’t really have any reason to. I don’t think this objection is sufficient when we’re calling the problem a paradox. You don’t get paradoxes from unfounded assumptions. Just don’t make that assumption, problem solved.
Ultimately, I don’t think civilizations will expand beyond maybe a handful of nearby stars, and that’s iffy. (Depends on whether there are any real unpredictable existential threats that can hit a whole star system at once.) And the long term expansion rate will be determined only by the rate that stars die (the sun should be useful for another 8 billion years, even if the Earth isn’t. Why move before then?) Which means the growth rate is indistinguishable enough from 0 that the paradox is no more.