How Far Can One Travel From Earth?(en.wikipedia.org)
en.wikipedia.org
How Far Can One Travel From Earth?
http://en.wikipedia.org/wiki/Special_Relativity#How_far_can_one_travel_from_the_Earth.3F
1 comments
assuming that space traveler had the incredible amount of energy to accelerate long periods of time, interstellar medium would be the limiting factor. There would be upper limit (say 90-99% of the speed of the light) and after that particles, molecules and dust in the space would bee too energetic for the space ship to stay intact.