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Comment by SketchySeaBeast | Hacker News Reader

If we assume that most stars are in a sort of orbit around the core, wouldn't the stars stay in relatively the same place? And regardless, wouldn't they still require the ability and timing to take advantage of those moments the solar system's get close to each-other? That still requires a monstrous amount of technology and energy, doesn't it?

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An lower orbit is faster than a higher orbit (orbits trade speed for height a bit like pendulums). So on long enough timescales your neighbors change as every solar system is on a slightly different orbit.

> That still requires a monstrous amount of technology and energy, doesn't it?

If we wanted we could spend ~10 years R&D on a practical nuclear pulse drive and send a probe at 10% the speed of light to the nearest solar system. That makes 40 years travel time for the probe and 4 years communication delay. Add some time for acceleration , deceleration and exploration and we might be able to send a colony ship 60 years after the probe left. Another 40 years travel time and we have a colony on another solar system 110 years from now, at a price point attainable for a large corporation or a medium sized country (after all most of the cost is research spread over half a century)

Now imagine what a more advanced civilization with more incentives for colonisation could do.

We could be mining asteroids today for materials that are scarce on earth, yet we don't. There isn't enough incentive to drive anyone to do that yet. What makes us so sure advanced civilizations recognize a worthwhile incentive to colonize other worlds around other stars?

Yeah, even in 2019 here on Planet Earth, some of our limitations on space exploration are self-imposed. If we were more willing to use nuclear power in our rockets, we would probably be much further along with having stuff in space.

Presumably all those aliens that aren't getting to space because of their nuclear wars are that much more likely to be willing to use nuclear power for space travel, too, in which you'd think at least one of them would have threaded the needle between nuking their home planet, but getting to self-sustaining in space, first.

Have you considered the acceleration that such a nuclear pulse drive creates? I am totally with you on the topic, not just with living organisms. If it were only electronics that need to be transported the force by acceleration wouldn't be such a huge issue. But any living organism that is to be transported is such a way needs to be able to adapt to pretty extreme acceleration/deceleration forces.

Maybe parent is a bit optimistic, both in terms of costs and travel time, but the orders of magnitude are approximately correct. Project Orion did come up with theoretical designs that were feasible for human travel (1 g acceleration).

https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propuls...

Huh, interesting... I always thought this kind of propulsion would be an almost instantaneous transmission of energy, thus enormous acceleration in a small timeframe. Thanks for the link...

In this scenario who is "we" that invests that time and energy?

I think The Expanse had the right idea with a powerful religious organisation like the Mormons. I could also imagine a totalitarian regime doing it to unite their people under a common goal (similar to the space race being a source of national pride especially for the Soviets). Or maybe a billionaire chooses to dedicate his money to such an endeavour (a Bill Gates who loves space as much as Elon Musk).

I agree it's unlikely that our civilization does it now. But given some time and a handful of civilizations and it seems like it should happen all the time (even more so if overpopulation or collapsing ecosystems were serious problems for some civilisations)

Stars closer to the core move faster, so it's more like a whirlpool than a rotating disk.

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