Time travel, while fun to think about, is logically impossible.
Think about it. If you want to go back, say, a year in time, you would end up where you were a year ahead in the future. And since the Earth would have moved, there would be nothing where you were except space.
Plus, there is no logical way for one to come up with any sort of device that would allow someone to go backwards in time, as there is only one way to move through time, and that is forwards, through the life you are living.