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I was watching a video on Youtube by Brian Greene, "the illusion of time."http://www.youtube.com/watch?v=j-u1aaltiq4

In that video, he introduces to me the idea of a "brane," or a slice of the universe at specific points in time. And then, he talks about an alien that is tens of billions of lightyears away from Earth. At that distance, he says that even the slowest movements can angle his brane, or slice of time, such that he is angling it towards the Earth's past (if the alien is moving away from us) or future (if the alien moves towards us).

So I got to wondering. What if you had a wormhole here on Earth, and walked through it to appear somewhere tens of billions of lightyears away from Earth. Depending on your speed of crossing through it, would you appear further into their past/future (depending on which direction you cross)?

And, if you had another wormhole there connecting back to the Earth, wouldn't you be able to travel back into Earth's past? Which would violate causality?

I know lots of people don't like the idea of wormholes, but it doesn't seem to have been scientifically ruled out. So, my question is, despite the fact that wormholes seem to possibly violate causality, why can't it be ruled out? Why is it still a theoretical possibility?

As a side question, if the past, present, and future exist at the same time -- what does that even mean?

(If anyone could edit my post, that would be great. My internet is giving me a horrible screen to work with. I have totally no ability to see my own tags -- look at this interface: https://dl.dropbox.com/u/106018191/phystackex.png)

(The image above is going to take a while to upload because of the slow internet, possibly a few hours at worst.)

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Possible duplicate: Tachyonic antitelephone vs messaging through a wormhole –  John Rennie Feb 26 '13 at 12:24

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