I've just started studying relativity and im having some slight problems. Say there are 2 persons, a and b. A is on earth and B is accelerating away from earth. While B gets faster and faster he will gain mass and his time will get slower from A's point of view. How does this look from B's point of view? I suppose he has normal mass, but how does he see the time relative to earth. Is the time on earth faster relative to his, and if so, why? (since moving away from earth is the same as the earth moving away from you, right?) And if not, then why is the time on earth so much later when B turns around and accelerates back to earth? Hope you understand my question.