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>If we can get to the point where we have the technology to colonize Mars, which will hopefully happen this century, then I would imagine it probably won't be long after that until we manage to have permanent space habitats that harvest materials from asteroids.

Bear in mind that we were certain colonizing Mars was just around the corner after landing on the Moon... about 60 years ago. In the interim, we lost the capability to land anything but probes beyond low earth orbit and are basically starting from scratch with private enterprise.

Not only is technological progress not always consistent, but it takes more time and effort to recover from regressions the further along the curve of advancement you happen to be. By which time, goals and priorities may have changed significantly to alter the trajectory of that progress.

So I would be wary of extrapolations that make it seem as if progress into space is like climbing a ladder. It seems more like building a Jenga tower as you climb it.

A few hundred years is nothing compared to the time the universe had habitable planets.

Civilizations don't operate on the scale of the universe, but on the scale of whatever constitutes the productive fraction of a single lifetime, and the influential span of a generation. Politics is more important to the rate of progress in this regard than physics.

If one civilization has existed over millions or billions of years it does.

A civilization can exist over millions or billions of years and still not maintain the same culture, or goals from one generation to the next. It's no different.

Yes, but it is impossible to prove that civilizations that remain the same over millennia dont exist.

Using hydrogen bombs you can get something like Project Orion to about 10% the speed of light, but not much faster. Project Daedalus is a more advanced design with the goal of accelerating an unmanned probe to 12% the speed of light [1]. The only somewhat practical ideas that seem to go beyond that involve antimatter fuel: not quite as easy to handle and well understood as nuclear bombs but certainly more attainable than giant black holes. There are a few designs that should allow travel at 60-80% the speed of light

1: https://en.wikipedia.org/wiki/Project_Daedalus

Isn't fusion power a promising technology to provide the energy needed to accelerate (and decelerate) for a long time?

Not my area but I think the fuel is the problem, not the power source. Even a fusion-powered drive needs to spit something out the back to accelerate (e.g. ions), so you need to carry many kg of ionizable fuel.

It's possible, yes, but even getting to the next system will take an enormous amount of time and resources; I want to believe colonizing the galaxy is possible, but it'll become a very long, slow and expensive process. I mean we're talking tens of thousands of years; by the time humanity has covered a decent portion of our local cluster, its evolution - both physical and cultural - will become really divergent. I'm sure a science fiction writer has thought about this.

It's interesting to consider that maybe life on earth is in fact a colonization effort from long ago. Sending probes with the base ingredients for life across the universe millions of years ago might've been a survival strategy. It feels meaningless without information to go along with it, but it's likely that information has either been lost, forgotten, or attributed to early humans instead of something Out There.

Accelerating to a fraction of c is no small feat. As per Tsiolkovsky rocket equation, growth in delta-v requires an exponenetial growth in fuel.

Not to mention all the fuel you'd need to decelerate so you can actually stop at your destination.

>>If we can get to the point where we have the technology to colonize Mars, which will hopefully happen this century, then I would imagine it probably won't be long after that until we manage to have permanent space habitats that harvest materials from asteroids.

We are already capable of that now. The issues are politics and economics and not science/engineering.

If I'm not wrong the USA spent like $1T on building a fighter plane, and something like double digits trillion dollars and ongoing on wars since the past 20 years alone.

You can mine asteroids for a part of that kind of budget already.

Going down gravity wells of planets makes no sense, space colonies are the way forward, and there is no shortage of resources in space for that.