[Bring_Back_Shantz]

Originally Posted by HeartsOfFire

But at the same time, that 200 lbs is missing from the Future timeline. Balance achieved.

That's not achieving balance at all.

Let's say the normal mass of the univers is 10 billion tons.
Now when I leave the future the future timeline universe weighs 10 billion tons -200 lbs, and the past universe now weighs 10 billion tons + 200 lbs.
At some point those times are supposed to converge, and the universe can't weigh 10 billion +- 200 lbs at the same time now can it?

This is exactly the kind of thing Stephen Halking has talked about, and why he thinks real time travel isn't really possible. He figures that the universe would create enough feedback to sort of close any kind of "time portal" the way people think of it.