HI, Is space time influencing by the speed or the acceleration ? Here the following problem : Marc and lisa are on earth. Marc takes his super space ship and (from the lisa's point of view) almost reaches the speed of light. Then marc remain still for a few minutes. He doesn't accelerate neither slow down. This is the moment which interests me now. afterwards, he returns to earth and have a romantic drink with lisa :!!) Well, when marc accelerated, lisa could see (with her super telescope) marc's rolex slowing down. After that, Marc remained for a moment at the same speed before to come back on earth. At this very moment, what difference did it make wether it is lisa or marc who was moving away from each other. As time is relative, there's no absolute time so why would marc's time would be spending slower than lisa's ? We could say that they are together moving from each other. So is space time "bending" only when acceleration occures or just whenever the speed from one thing to another is different ? In that case, why would it be marc's time which slows down and not lisa's. I hope that makes sence :S I'm very new to interest about physic, I really found what I was looking for in that forum. Thanks to all !