Travelling in Time? Time is measured in relation to motion of one object to another. One object's "time" may appear to be altered, but only because of some outside forces acting on it (gravity). The only way for an object to start "travelling" back in time, would be if the laws of the universe were suddenly reversed, and every force acted opposite to what the do now. Gravity would repel, but pressure would attract. Our brains neurons would absorb instead of fire, etc. Everything would go backwards, not just a single object. Because if an object were to go backwards in time, by definition it would reach a time went it wasn't going back in time. Say you found a point "A" where you could go back in time in. You approach it at 12:01, enter into it at 12:02, and begin going back in time at 12:03. Time goes to 12:02 again. Well, guess what? That's when you were just entering point "A", so how can your mass be at the same time twice? It only exists once. (Unless that is it's the same mass, only the entire universe is travelling back in time; in which case you wouldn't notice anyways) and begin going back in time.