Re: Time travel - Speed of light
Highly accelarated space vehicle acually mimicks Gravitational pull inside it, so at that speed, space travel will at least not cause that problem.
I think there is a difference between being (highly) accelarated and travelling at high speeds. In the former, indeed it will mimick gravity, - but in the latter no matter what your speed is (relative to some reference point) you will not experience any 'gravity' and therefore start loosing muscle and bone tissue.
as far as time travel goes, scientisits have calculated that the russian astronaut (i forgot the name) who has spent more than three years in orbit, due to his speed relative to us has travelled further in time by about 1/50th part of a second