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Message: <blockquote data-quote="Umbran" data-source="post: 6038234" data-attributes="member: 177">Both of you are correct, and both incorrect.Relativity says a couple things on the subject of time travel:1) If you can travel faster than light (you can't, but if you could), then you can travel in time.  There's no "time machine" other than the FTL ship, and it can travel to times prior to its own creation.2) There are certain curvatures of spacetime (usually around "compact objects", things like black holes and neutron stars) that could allow you to fly what freyar mentioned - a "closed timelike curve".  You're never moving faster than light, but you end the route before you started it.  This kind of time travel does not allow you to move back before the curvature created by the compact object existed.  So, if you are flying a weird course around a black hole to travel in time, you cannot go to times before the star collapsed to create the black hole.  There are possibly some compact objects that can be used that have existed since the beginning of the universe, or the first inflationary period of the universe, such that how far back you could go using them is not an issue for human terms.  You would, of course, have to reach the objects in the first place, and none of them are anything like "nearby".When we get to wormholes, things get funky.  A wormhole is a shortcut through spacetime, and it is allowed by General relativity.  It is a shortcut through spacetime, so you can go to the place, and time, of either end of the wormhole.However, there's a catch - the wormholes of general relativity are not stable.  Flying a spaceship through one is likely enough of a disturbance to cause the thing to snap shut, destroying you and your ship in the process.  One can theoretically stabilize a wormhole with, get this, "negative energy".Now, general relativity doesn't tell you how to make negative energy.  Quantum mechanics does. But most of you probably know that quantum mechanics and general relativity as we know them don't get along very well.  They don't speak to each other.  So, can you use the combination to create a wormhole time machine that can go back to some arbitrary period in time?  Or would such a thing only be able to use its creation as the earliest end of the wormhole?  Nobody can say.  The math to describe how to do this doesn't exist yet.General relativity does not speak to the "many worlds" (or any other quantum mechanical) time travel.  In fact, "Many Worlds" time travel, in which you don't actually travel in time, but you travel to some other branch of the many-worlds tree, is as far as I understand it, a complete fabrication of science fiction.  It is a simple fictional crossing between the "many Worlds Hypothesis" and the idea of time travel, without any theoretical math supporting it, as far as I am aware.</blockquote>

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