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Entering at x does take you to the future. If this is not explicitly stated in Morris and Thorne 1988, Thorne does explicitly state this in his 1994 book Black Holes and Time Warps -- Einstein's Outrageous Legacy. You'll find the following sentences on page 504, "The wormhole has become a time machine. If I now (on 1 January 2010) climb into the ...

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This seems to be called the eternal-time-machine spacetime, and I believe the original paper was Morris 1988, which is available online and not paywalled. On p. 1447, they claim: ...at late times by traversing the wormhole from right mouth to left, one can travel backward in time (i.e., one can traverse a closed timelike curve)... The question says: ...

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There's nothing physically problematic with speeds, per se, that are faster than the speed of light. For example, if you quickly rotate an Earth-bound laser such that its beam crosses over the moon, the speed of the center of the beam as it travels across the moon's surface can easily be faster than $c$. There's no problem with a speed greater than $c$ in ...

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The twin paradox is generally considered to be an illustration of time dilation, not time travel. To answer your question, the difference between the twins is that Twin A was accelerated several times. Speed is relative; if an object is moving at a constant speed, whether the object is considered to be moving or not depends on which inertial frame of ...

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