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I gave you a reference to a book which discussed this in the other thread, Bob: "Black Holes, Wormholes, and Time Machines". Theoretically, if you have a spinning cyclinder of hyper-dense matter (the fact that it's spinning is important!), by orbiting it you can travel through time - (forwards only, I'm afaid!). Of course, the engineering problems are ... considerable, but if our understanding of General Relativity is correct, it should work.
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