What Happens When Your Spaceship Is Longer Than the Universe?

[Idunno]

So, as I understand special relativity, when you go close to the speed of light, observers see you "shrink" in the direction of motion, and you see objects as shorter than they were when you were in the same frame, according to L=Lo√1-v²/c².

So suppose I am nearby Earth (in the same reference frame) and my spaceship measures 1 km long, and Earth observers agree. Then I get to a terrific velocity, so that Earth observers see me as very contracted in the direction of motion, and I see Earth as being actually shorter than my 1 km long spaceship in the direction of motion.

Well then, I suppose I can get to an even higher velocity, so that I measure my ship to be even longer than the milky way in the direction of motion.

Then finally, what happens if I get to such a terrific velocity that I measure my ship to be longer than the observable universe? What happens then? Is this possible? I suppose it is impossible from a practical sense, but does it contradict something in physics? Is it allowed to happen?

 

[vanhees71]

Concerning the special-relativistic part, have a look at the socalled "barn-pole paradox":

https://en.wikipedia.org/wiki/Ladder_paradox

Concerning your question about the universe, you need general relativity. The short answer simply is that you cannot make your spaceship as big as to reach and extension larger than the observable universe, because there are horizons involved:

http://www.ita.uni-heidelberg.de/~dullemond/lectures/cosmology_2011/Chapter_4.pdf