Well I saw something interesting somewhere that one persons theory was that when you travel back in time your 'world line' begins to change, i.e different events occur in different ways. He says that it happens gradually, so If you traveled back twenty years maybe a few football games would have different scores and/or outcomes, whereas if you wanted to meet christ 2000 years ago you'd wind up in a dimension where he didn't exist (probably). I think the theory is interesting but kind've abstract, with no real reason why it occurs. By the way anyone who reads this should pick up the Beetle's White Album, damn these cd's are so kickass. I think something similar to the worldline idea, I wrote about it in my 'theory of interdimensional travel' under free thoughts. I think it's still on the first page.
