It is often claimed that if we ever sent humans to colonize other stars, we would have to send them on generational ships. However, if the ship traveled at $99.9\cdots 9c$, wouldn't the passangers' time slow down, and make the travel time just, say, 1 year from their point of view?

  • $\begingroup$ I can't tell whether you're asking a purely theoretical question or a practical one. If the latter, how exactly do you intend to accelerate a ship massive enough to contain humans to $99.9999999c$ ? $\endgroup$
    – WillO
    Sep 16 '18 at 2:57
  • $\begingroup$ @WillO I'm thinking theoretically, I assume a practical question would be off-topic here; besides, I think there may be reasons why you would not travel that fast even if you could. For one, maybe you want to give yourself time to shoot any potential particles out of the way. What do you think? $\endgroup$
    – Ovi
    Sep 16 '18 at 3:41
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    $\begingroup$ I think you would enjoy the old Usenet Physics FAQ page on the Relativistic Rocket. $\endgroup$
    – PM 2Ring
    Sep 16 '18 at 6:56
  • $\begingroup$ Also see this answer, where I derive a simple formula for converting rest mass into kinetic energy with an ideal engine; I also derive the relativistic formula for constant acceleration. $\endgroup$
    – PM 2Ring
    Sep 16 '18 at 7:05

Yes, travelling close to the speed of light would allow a traveler to get to a distant star in his lifetime. This is clear from muon experiments. Muons have a lifetime that would tell us to expect them to decay within this time [x]. But when they are travelling very close to the speed of light they manage to travel far enough that they must have lived, in our frame, much more than [x].


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