Then apart from time travel another one that interests me is the theory that when travelling at the speed of light (or faster) time slows down. Or speeds up. Or something...
I remember reading that if there were a pair of twins the same age, and one of them went out to space in a rocket at the speed of light and came back years later, one would now be older than the other even though technically the same period of time had gone by for both of them.
Huh?? How can that be?! !