> 1) It takes just ONE civilization not wiping itself out to colonize the galaxy; furthermore, colonizing the galaxy is a great insurance policy against extinction

Why? See my other post. You provide no evidence for this claim. We currently have no plans to colonize the galaxy so why would other "advanced" civilization get this crazy idea? Birth control was invented in the 60s already.

We have Musk wanting to colonize Mars, don't you think it will take just ONE eccentric trilionaire (after the solar system is colonized) to colonize the Milky Way?

Wanting to colonize mars and actually doing it are quite different things.

>colonizing the galaxy is a great insurance policy against extinction

I'm not so sure. The only difference between a colony ship and a kinetic world destroyer is that the colony ship slows down before it reaches its destination

The earth would easily handle the impact of any colony ship we could currently manage. Sure things are you approach the speed of light, but we can't.

1. If the chance for a huge colony to go extinct, raising the coefficient to galactic scale does not change the relative probability significantly unless you add constraints to the population dynamics. Basically you could get the same numbers for people in a colony and colonies in a galaxy. "only ONE" kinda obscures the fact that this one would be a mighty huge one.

2. On straight lines perhaps with ages long acceleration. Planning such a course might well take more than nuclear reactor, no?

I'm going to put on my sci fi glasses here and predict that the universe will suddenly blink out of existence once a scientist works on or develops something like warp speed.

Maybe, but I’d out my money on the universe blinking out of existence after someone begins a local escalation of privilege on the hardware simulating it.

... to be replaced by something even more unlikely...

We have not implemented space mining that would allow refilling those reactors in space though. Reusable landing is still very iffy.

Obviously we haven't done it yet, but that we know how is the point.

1% of the speed of light with nuclear reactors? I'm skeptical. It's 3000 km/s.

Project Orion was supposes to reach ~10% of the speed of light by using fission bombs and could theoretically be built using 1950's technology.

There are other proposed schemes to travel at ~light speeds - light sails, nuclear fragment rockets, but I'd bet on nuclear fusion in the not so distant future.

Faster than light travel may be off the table, but I see no reason why nuclear energy alone could not get us "close" to the speed of light in the next centuries or so.

Thanks, I didn't realize they were planning for so high delta vees. They were fusion bombs in the end.

Voyager 1 is already going about 17km/s. With no atmosphere or gravity to fight against you can keep accelerating as long as you have power.

No, you need a propellant even if you use a nuclear energy source.