[neutralino]

Originally Posted by Profpat

If you were traveling at the speed of light it wouldn't take YOU any time at all yo circumnavigate the universe. Time stops at light speed.

Just to point out a few things that you probably know, but other readers may not. Of course a massive body cannot travel at the speed of light, and in fact any body travelling at the speed of light must always travel at the speed of light, by definition. It's also not so much that time stops at the speed of light, but rather that proper time (the time measured on the moving body's clock) is not defined for bodies travelling at the speed of light. This is because, as I said above a body moving at the speed of light cannot have a rest frame attached to it, and so there is no frame in which one can measure proper time.