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There is no solid math or physics which supports time travel. There are a lot of cases where people claim to have found some loophole or another in the impossib
by cevi 5y ago
There is no solid math or physics which supports time travel. There are a lot of cases where people claim to have found some loophole or another in the impossibility proofs for time travel, sketching out a model that looks plausible at first glance, but they all end up postulating some blatantly non-physical entity somewhere along the way (i.e. cosmic strings, negative energy density, ... - I've gotten my hopes up quite a few times).
Speculating about parallel universes is a different story - even if they exist, we can't travel to them, so there is no sense in claiming that we can somehow harness their power. It's a philosophical question, not a physical one. In contrast, the rules of quantum mechanics (when phrased in terms of density matrices, at least) only describe things we can actually measure and observe, and people actually do test every single aspect of the predictions quantum mechanics makes.
- Crash0v3rid3 5y ago> There is no solid math or physics which supports time travel. This is false. Time travel to the future is possible and proven[0]. Perhaps you are referring to traveling to the past. [0] https://en.m.wikipedia.org/wiki/Experimental_testing_of_time_dilation#Twin_paradox_and_moving_clocks https://en.m.wikipedia.org/wiki/Experimental_testing_of_time...
- zachf 5y agoAs a nitpick, negative energy densities are indeed uncommon but they aren’t unphysical. In fact, every quantum field theory admits at least one state with negative energy density—its a theorem. But even in quantum field theory there isn’t enough negative energy density to actually form acausal (faster than light) shortcuts through the spacetime.
- cevi 5y agoOh, I didn't know about this! "Get past chapter four of any textbook on quantum field theory" has been on my to-do list for quite a while.