I have a few theories on time travel:
1) If time travel is possible it cannot transport people. Otherwise there would be too many time travellers among us.
2) Paradoxes: A spacetime paradox (kill your grandfather etc.) is just a scar on the face of the universe. Just as you don't die if you scar yourself, the universe doesn't dissapear because it is scarred.

OK, the second theory is a bit far fetched, but if the first one is wrong then the second has to be right, as a person going back in time would make a very subtle change that would cause a paradox.

I am no longer a member of these boards.