Hi all, First post here. I have been debating with a collegue today about time dialation. I am certain that an astornaut in space will experience more time or age faster than people on earth due to time dialation of a massive object. He is saying that he will come back younger. Whos right? and why? Second. Speed also dictates time. So if i was in a 2 ton vehicle in space how fast would that vehicle need to travel in order to experience the same time lapse as on earth?