A little off topic. Not just time travel, but space travel too.
A while back on artbell there was a guy(can't remember his name) had a theory.
Each solarsystem(or universe, can't remember) is one of many bubbles. Around the bubbles is just space. Now, these bubbles are actually travelling VERY fast in all different directions. So if we had a spacecraft of somekind that could take us outside our "bubble", it would be very difficult to come home, because our "bubble" won't be where it was when we left it. Another thing with time is that the farther you go out there, the faster time speeds up on "earth" in your eyes. So, if you could travel to the edges of our "bubble", then come back to earth, it would be millions of years later(even if it only took you a few weeks to travel).
RMF