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Let's assume all processes are TPC symmetric. Be it the breaking of an egg (just reverse all momenta of all particles involved), the evolution or collapse of the wavefunction (a big if but let's assume), or the expansion of space.

This means we can't determine by looking at a movie that's played backwards that time is actually going backwards. All processes could actually be going forward with appropriate initial conditions. Though I'm not sure of the effect of dark energy. Could it be turned into contracting energy? But let's assume.

Which brings up the question what actually causes time to go forward when it could go backwards as well. Is it the asymmetry between the begin- and end-state of the universe as a whole? Is it just impossible for the begin conditions to lay at infinity? Are parity and/or charge involved?

Qmechanic
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Gerald
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    Possible duplicates: https://physics.stackexchange.com/q/19970/2451 , https://physics.stackexchange.com/q/669475/2451 and links therein. – Qmechanic Aug 04 '22 at 10:26
  • There is CP violation (considered a symmetry), that is T violation. This is one example of time-assymetry. – Nikos M. Aug 04 '22 at 10:30
  • There are many egg microstates that we refer to as broken and very few that we refer to as intact. This is all statistical arising from the highly ordered state of the early universe. – Connor Behan Aug 04 '22 at 12:48
  • @ConnorBehan But why doesn't it evolve backwards? It can do so. – Gerald Aug 04 '22 at 15:43
  • @NikosM. And can that be the reason why time doesn't run backwards? – Gerald Aug 04 '22 at 15:45
  • Because an extremely ordered state is rollnig a billion sided die where only one of the sides corresponds to a state even more ordered than the initial one. Yes, it could still land there. – Connor Behan Aug 04 '22 at 16:18
  • @ConnorBehan yes, but why doesn't time take off at infinity and starts evolving to the big bang? Which would be a big crunch. – Gerald Aug 04 '22 at 17:06
  • If it did, we wouldn't know because then our memories would unform instead of form. – Connor Behan Aug 04 '22 at 17:13
  • @ConnorBehan Yes but why do we know? Because it's running forward. I feel a circularity lurking. – Gerald Aug 04 '22 at 17:17
  • @Gerald CP symmetry violation means T is not a symmetry. If CPT is taken as a big symmetry, it cannot be verified as such. So yes it is one way to say that IMO – Nikos M. Aug 04 '22 at 17:55

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