For the sake of argument, we are going to assume that, like the reality we live in, there are alternate dimensions that account for every possible choice a person can make. Say for instance a person decides to drink orange juice with breakfast instead of grape juice, the realities split, and an alternate reality is created in which you choose grape juice instead. In the orange juice world, you accidentally spill your glass on your shirt, not a problem, you just change. In the grape juice world, you spill your glass on your shirt and that shirt is stained, any possible experiences you could have with that shirt are no longer part of the picture.
In the orange juice world, you wear the spilled on shirt on a date, it's complimented etc. In the grape juice world, you choose a different shirt on the same date, and it turns out that its not the most flattering of apparel. Thus two completely different realities are created... it's infinite. There would be a different reality for every choice of every person... infinite!
Okay, so my theory on time travel is that time travel is possible, but by participating in it, you would have to travel to a different dimension, and would never be able to return to your original reality because you have greatly affected the past of a different reality.