There's a theory that the direction of time arises from entropy and the correlations (interactions) between bodies. However, I don't see how this would incorporate the effects of General Relativity, in which time is a dimension which can be warped and dilated. I'm not too sure about what the theory said exactly, but could it be correct?

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    $\begingroup$ Note that GR doesn't care which dimensions that are "time" - it is all about spacetime manifold shape, not the activity going on inside them. The arrow of time issue is more like why a general direction on the manifold gets singled out as "forward in time". $\endgroup$ Commented May 14 at 9:41
  • $\begingroup$ Eggs being more likely to crack than uncrack agrees with GR, yes. $\endgroup$ Commented May 14 at 12:37
  • $\begingroup$ What is time, does it flow, and if so what defines its direction? $\endgroup$
    – mmesser314
    Commented May 14 at 15:31

1 Answer 1


General relativity doesn't tell you, in principle, what is the direction of time. This is something you add in by hand. In fact, some spacetimes don't even admit a choice of time-orientation.

When a choice of time-orientation is possible, you still have two possibilities to call future. Hence, it is not absurd to use an external criterion to choose which of them is correct.

Understanding time completely is definitely a hard subject, and an open question. But it is not incompatible with GR to say that the direction of time (not time itself, but the choice of what is past and what is future) is determined by thermodynamics.


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