I'm having trouble understanding whether one dimensional time travel is conceptually possible or whether it involves contradictions instead.
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1What do you mean by "one dimensional time travel"? – Hypnosifl Jul 20 '20 at 4:44
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the answer is in the math. I suggest you post this on the physics stack exchange instead. – niels nielsen Jul 20 '20 at 5:00
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I am guessing "one-dimensional" means with a single timeline. Yes, it is theoretically possible in general relativity but uninteresting, self-consistent time travel can not alter the past. All actions of time travelers are already incorporated into the timeline as it is, see Novikov's self-consistency principle. – Conifold Jul 20 '20 at 5:15
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The conventional answer in the physics community is that all forms of time travel into the past will destroy causality. Depending on how you define them, "contradictions" will naturally result. Some physicists maintain that under certain sets of assumptions, time travel into the past will not destroy causality, but the assertion is untestable.
answered Jul 20 '20 at 5:06
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I do not see how consistency under a set of assumptions can be testable or untestable. The assumptions may be untestable, but whether they are consistent is no more subject to tests than consistency of Euclidean geometry. – Conifold Jul 20 '20 at 5:12
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what I mean is that until we achieve the ability to travel backwards in time, we cannot study the phenomenon and learn which model most accurately describes it. We cannot test, for example, whether or not causality is undone by it. – niels nielsen Jul 20 '20 at 6:03
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1I see. I read the question as asking whether it is "conceptually possible" on current theories to reconcile time travel (e.g. closed timelike curves) with causality, and the answer is yes regardless of any future tests. Yes, it may turn out to be physically impossible per some future theories but conceptual and physical possibilities are different things. – Conifold Jul 20 '20 at 6:13
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