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The laws of physics as we know them today don't forbid time travel. In fact, they propose a fairly specific means of doing it via accelerating one side of a tra

The laws of physics as we know them today don't forbid time travel. In fact, they propose a fairly specific means of doing it via accelerating one side of a traversable wormhole to near the speed of light. The only reason this isn't actionable is it requires exotic matter that may not exist, and if it does, we certainly don't know where to find it or how to make it (and we don't currently know how to make a wormhole, but we know they're physically possible). Usually, when people rule out time travel as impossible, it's because it has the potential to introduce paradoxes that totally break any possible understandable notion of causality, i.e. the inventor of time travel going back and killing himself before he invents it. Thankfully, the known physically possible forms of time travel don't introduce that specific issue as they would not permit traveling back to any point before the wormhole was created, which also goes far to explaining why, if time travel is ever going to be invented in the future, we have never seen anyone come here from the future.

short_sells_poo 5y ago
> and we don't currently know how to make a wormhole, but we know they're physically possible I'm not aware of any actual observational evidence or even strong theoretical prediction that wormholes exist or that they are physically possible. Some parameterizations of our models don't rule out their existence, but it's all hypothetical. Including the question whether they are traversable.
nobody9999 5y ago
>The laws of physics as we know them today don't forbid time travel. In fact, they propose a fairly specific means of doing it via accelerating one side of a traversable wormhole to near the speed of light. That applies to time travel into the past. It's obvious, but it bears noting that the converse is a lot simpler. I say that because, IIUC (and that's a real question), quantum mechanics treats the time dimension as symmetrical, which contradicts observation, at least to this point. Is that because QM is wrong on that point? Which seems unlikely, since it's one of the most precisely confirmed (by observation) theories we have. Or is there something about the "macro" world that destroys that symmetry? I don't have the answer, but it's clear that in a particular reference frame, we move forward in time at a rate of 1 sec/second. Again, that's obvious, but based on my (limited) understanding, that seems to contradict QM.
- caf 5y ago
  I say that because, IIUC (and that's a real question), quantum mechanics treats the time dimension as symmetrical, which contradicts observation, at least to this point. As far as I'm aware, the weak force is known (and experimentally demonstrated) to break time-reversal symmetry. It's only combined Charge-Parity-Time symmetry that QM maintains. (This still does not explain how a macro arrow of time arises, though)
- GoblinSlayer 5y ago
  There's no contradiction there. Time symmetry is a mathematical property, so time reversal exists only in mathematics, this is perfectly expected behavior.

short_sells_poo 5y ago

> and we don't currently know how to make a wormhole, but we know they're physically possible I'm not aware of any actual observational evidence or even strong theoretical prediction that wormholes exist or that they are physically possible. Some parameterizations of our models don't rule out their existence, but it's all hypothetical. Including the question whether they are traversable.

nobody9999 5y ago

>The laws of physics as we know them today don't forbid time travel. In fact, they propose a fairly specific means of doing it via accelerating one side of a traversable wormhole to near the speed of light. That applies to time travel into the past. It's obvious, but it bears noting that the converse is a lot simpler. I say that because, IIUC (and that's a real question), quantum mechanics treats the time dimension as symmetrical, which contradicts observation, at least to this point. Is that because QM is wrong on that point? Which seems unlikely, since it's one of the most precisely confirmed (by observation) theories we have. Or is there something about the "macro" world that destroys that symmetry? I don't have the answer, but it's clear that in a particular reference frame, we move forward in time at a rate of 1 sec/second. Again, that's obvious, but based on my (limited) understanding, that seems to contradict QM.

caf 5y ago
I say that because, IIUC (and that's a real question), quantum mechanics treats the time dimension as symmetrical, which contradicts observation, at least to this point. As far as I'm aware, the weak force is known (and experimentally demonstrated) to break time-reversal symmetry. It's only combined Charge-Parity-Time symmetry that QM maintains. (This still does not explain how a macro arrow of time arises, though)
GoblinSlayer 5y ago
There's no contradiction there. Time symmetry is a mathematical property, so time reversal exists only in mathematics, this is perfectly expected behavior.