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Comment by rsynnott | Hacker News Reader

> A species that colonizes will fill the galaxy in a few million years unless it just decides to stop.

I think this may be making some weird assumptions about motivation. Let’s say, for the sake of argument, that travel at 5% of the speed of light is practical. Would you be signing up to go colonise a planet around Alpha Centauri? What would be the motivation opportunity such colonisation? Who would pay for it?

If interstellar travel turns out to be permanently slow, difficult, and expensive, then that may cast doubt on the idea that anyone who theoretically can spread out all over the place given a hundred million years actually will.

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It’s interesting to me that in these conversations, some people think it’s inevitable that intelligent life will want to colonize other systems (or die trying) while others think it’s impractical.

But I think both of these opinions come from human-centric reasoning. A species that could hibernate may be able to control hibernation through technology, so a ten year journey wouldn’t be as complicated for them. Other species on earth simply don’t have the curiosity to explore the way humans do.

Speculation about alien intelligence is interesting to me, but I imagine it’s a lot weirder than we think. Especially around topics adjacent to intelligence, like curiosity, motivation, and cultural values.

Whether they want to or not is irrelevant. I'm only concerned with whether or not they do. My point is that for a civilization to have an unlimited lifespan it either has to exist in multiple star systems or progress beyond the need for a star system at all. A single planet is just too vulnerable. Nuclear war, biological war, grey goo, supervolcano, gamma ray burst, ecological collapse. To exist for billions of years on one planet requires that a species be dynamic enough to create hyper-advanced science but so peaceful it doesn't kill itself with it while being so incredibly culturally stable that doesn't change for eons. I don't buy it. Living on one planet is a death sentence in probably much less than a billion years.

Multiple is not the same as all. Once a civilization colonizes a handful of solar systems, it is essentially impervious to any disaster. Further expansion produces diminishing returns. There is no resource which can justify the cost of interstellar travel, and any civilization capable of making technology on that scale will have to be social enough that a latency of years to centuries in communication with the civilization's core would be a major disincentive. Even if there were a brief exploration phase when everything was new and uncharted, there would be no reason to maintain all those colonies indefinitely. A civilization inhabiting a dozen star systems all within a few lightyears of eachother would not be significantly more detectable than a single planet civilization.

That's a lot of assumptions you're making. For example, some undiscovered resource could be that valuable. Perhaps the species has a slow enough physical metabolism and mental process that interstellar travel times are only mildly inconvenient.

It is easier to synthesize any substance from scratch than it is to transport it between even the nearest star systems. The only way such a resource could exist is if our entire understanding of physics is way off.

Earth gives us a wide range of organisms with different lifespans and metabolic rates. There are not that many species that live longer than us, and extremely few that live significantly longer than us. Even if something lived 100 times longer than us, only a very small portion of the galaxy would be traversible within a lifetime, and there is still no reason to go more than a few lightyears.

I think it was implied that the motivation would be a lack of resources here. Space and water to start with probably.

I suspect solving those problems within a solar system will almost always be easier than traveling to other systems. Then again maybe travel to neighboring systems is easier in a denser neighborhood.

If you have the energy technology to build enough starships to put a dent in your population, you probably don’t have to worry too much about space or water unless you have runaway population growth.

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