I believe I read on the internet that quantum mechanics predicts that the fundamental laws are time invertible. The web page probably really meant one theory predicts that. Does that theory combined with the big bang theory or some other beginning of time theory really predict an arrow of time at the macroscopic level? If so, how is it possible that it predicts that?
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Possible duplicate of What is time, does it flow, and if so what defines its direction? – John Rennie Oct 04 '19 at 03:55
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Very short answer is that the Schrodinger equation is symmetric in time but wave function collapse may not be (depending on your interpretation of choice). For an overview of the arrow of time in QM see https://en.wikipedia.org/wiki/Arrow_of_time#Quantum_arrow_of_time – gandalf61 Oct 04 '19 at 11:18
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I don't know the answer so I will make a guess. I believe it is not correct to explain it using entropy. I believe that 3 immiscible liquids all in contact with one another for real will not form a thermal and solubility equilibrium with one another and so there will be a continuous preferential direction to flow of heat and flow of particles by diffusion. However, I think it can be explained using another method. I will use a very complicated to describe definition of randomness that I won't bother to explain. Starting at the beginning of time, it's fully random what state the universe will get into a short time later so it's not fully random which state it got into that state from. However, the state it will get into a bit later from it is random because there's no reason for it not to be so it's not fully random which state it got to that state from. Again, it's fully random what state it will get to at a tiny bit later time from it so it's not fully random what state it got to that state from. This definition of randomness does not mean you can't have a perpetual motion machine of the second type. It is however possible that the arrow of time allows for a perpetual motion machine of the second type but doesn't allow for that kind of perpetual motion machine to run backwards. It's also possible that the arrow of time might allow for a substance whose tendency is to exponentially approach a non time-invertible state with the atoms synchronizing their actions giving it zero vapour pressure above absolute zero but doesn't allow that substance to exist in the time inverse of that state.
Timothy
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