I've always looked at it like this: Time travel is possible and we're doing it all the time, just at the standard rate. Mathematic models show that if you travel close to the speed of light that time slows down, effectively making you travel faster into the future. Once you hit light speed (which is theoretically impossible), time essentially stops. Past that (also theoretically impossible), I would imagine time reverses, though I haven't studied this stuff in years. Granted we'll probably never be able to travel that fast or backwards in time, but we're all traveling through time, just at 1second/second.