The Zedd
On the idea of different realities. I dont understand how they could exist. The theory has as much proof as god does. And for time travel, this is my prefered website. It explains that we may be able to travle back in time. But it would be impossible to change the course of the future.

http://en.wikipedia.org/wiki/Novikov_self-consistency_principle

The probability slope would keep those alternate realities from affecting the main line, since that is the top of the probability slope. Thus, if you time travel, just being in an area causes you to move downslope, and you have to compensate with more energy to be able to get back up it to travel forward or back.