[wallace_f]

It seems we have laws of physics covering everything from Newtonian mechanics, relativity and quantum mechanics... Is there any law stating time travel must go one direction? Has it ever been proposed?

[BlaXpirit]

Second law of thermodynamics https://en.wikipedia.org/wiki/Entropy_(arrow_of_time)

[matt_wulfeck]

>The Second Law of Thermodynamics states that the state of entropy of the entire universe, as an isolated system, will always increase over time

My understanding (which is very small) is that the multiverse theory takes care of not violating this law, since it’s not an isolated system.

[PhilWright]

And....there is no evidence at all that there is another Universe other than ours. Once you have proven the existence of a multiverse we can then take theories that require it seriously. Until then it is pure fantasy.