Galactic space-travel is within the galaxy. That’s already possible over long time scales. Intergalactic travel between galaxies is unlikely for those reasons.
It is problematic even within the Milky Way has a diameter of 100,000 light-years. We're in the middle-ish of one of the arms. It's not likely we ever leave the arm we're in.
Why would that be unlikely? Ignoring human problems like self-destruction. Given enough fuel, couldn't a spaceship easily pick up enough speed for significant time dilation, then GTFO of the galaxy?
No, it really isn't. Humans do not do well in low gravity for extended periods of time. We do not have a remotely practical way to artificially generate gravity.
Spinning the ship would require a gigantic diameter, which would require massive weight, which means moving it through space requires too much fuel (which requires even more fuel to move the fuel).
And we haven't even started touching on the problems we've run into trying to create sealed biosystems.
These may be addressable in the future, but we very much can not move people in generation ships now.
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u/ScratchLatch 4h ago
Galactic space-travel is within the galaxy. That’s already possible over long time scales. Intergalactic travel between galaxies is unlikely for those reasons.