We’ve discussed humanity’s eventual expansion into the galaxy a few times before — see What Are We Learning from SETI?, where we said:
Assume we could travel at, say, around one-third of lightspeed, so that a large shipload of settlers could travel to a nearby star in about a dozen years. … Then assume that stars with habitable planets are, on average, not more than about 5 light years away from each other, so we can gradually expand our domain without encountering any impossible distance barriers. And then assume that each new settlement — if educated and well-equipped — could develop itself sufficiently so that in, say, about three generations (less than a century) it would be able to launch some of its own people to settle the next habitable system. Population growth will be the biggest constraint to such rapid expansion, but once a new world is settled more ships will arrive, so population shouldn’t be a problem.
If those assumptions are reasonable — and we’ll all be dead before anyone really knows — then the domain of human-occupied space can expand every century at a rate of roughly 5 light years in every direction. That’s a sphere which grows 10 light years in diameter every 100 years. In a thousand years the sphere of human-occupied space will be 100 light years across. That’s nice, but it’s no big deal. There could be several isolated pockets like that here and there in the galaxy, but they’re so far away that we’ve never noticed them. However, it doesn’t stop there.
Multiply our expansion time by 1,000, and conservatively assume no technological improvements over all that time. You get a sphere of human space that’s 100,000 light years across in only a million years. Think about that. The Milky Way galaxy is roughly 100,000 light years across.
In Evolution and the Conquest of the Galaxy we discussed the evolutionary consequences of humanity moving out in different directions, unable to breed with their distant cousins elsewhere in the galaxy. And in Humanity’s Next Adventure — Trek Three, we discussed humanity’s expansion out of Africa to all the habitable places on Earth, which undoubtedly protected us from extinction. By living everywhere they could, humans were immune from being wiped out by a local geological disaster.
Going to the stars is the same thing as migrating out of Africa, but on a bigger scale. Expansion throughout the galaxy is essential to assure our survival. When humans are living on several different planets orbiting other stars, we can’t be exterminated by a local planetary disaster like the dinosaurs were, or by the eventual death of the Sun.
In this essay we’re not going to adopt the argument of Stephen Hawking, that if we don’t go soon we’ll destroy ourselves. Instead, we’ll discuss the possibility that — despite the technological possibility of doing it — we won’t expand to the stars. Why wouldn’t we? Religion could be the reason, but this isn’t an argument for atheism.
If the dominant belief of Earth’s population is that science is evil and man is a sinful, unworthy creature, then: (1) we won’t think ourselves worthy of surviving beyond the time allotted to us on Earth; and (2) we won’t develop the technology to go to the stars. All of humanity’s efforts will be directed to seeking divine help and forgiveness.
That would be the ultimate disaster. If we remain a one-planet species, we’re doomed to extinction. If an asteroid collision doesn’t get us, maybe a bunch of supervolcano eruptions will, or another ice age, or a plague. Our planet has known mass extinctions before, and there’s no reason there won’t be more in the future. Even if there are none, the Sun’s lifespan is limited. It’s going to run out of fuel and die about 5 billion years from now, so our time on Earth is limited.
Then there’s the possibility of intelligent aliens out there. If we can dream of occupying all the the galaxy’s habitable planets in “only” a million years, so can they. Maybe some have already begun their expansion, but they’re still far enough away that we haven’t noticed them yet — but we will. What would it be like, being a one-planet species in someone else’s galaxy? It’s not the future your Curmudgeon hopes for, but it’s not very far from the way some religious sects think things are right now — and they accept it.
Will we go to the stars and occupy the galaxy, or will we cringe in fear here on Earth? Some might ask: “Are we worthy of being a galactic species?” What determines worthiness? If we do it, we’ll survive, and by definition we’ll be worthy. But if humanity is in the grip of a sect that teaches we are essentially unworthy, then we’re not going anywhere. In that case, you can add one more possible cause for our eventual extinction — death by religion. Humanity has some decisions to make.
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