This sounds like a homework question, but I promise you it's not (I'm not even a student). To be honest, the question is simply for my own personal curiosity, to test a theory about a video game. My question is this: If an astronaut traveled for 15 years (their time) at twice the speed of light (supposing that were possible), how much time would have passed on earth? Based on my basic understanding of relativity, I am guessing I might get some responses that it can't be calculated (due to infinity possibly showing up somewhere). I'm not great at advanced math, but if no one wants to solve this, I'd settle for an equation or a rough idea.