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Q) If the Universe is infinite in all dimensions including time, can it be accurately described as being fully closed? Therefore, can entropy ever reach maximum disorder?

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- Thread starter berty
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Q) If the Universe is infinite in all dimensions including time, can it be accurately described as being fully closed? Therefore, can entropy ever reach maximum disorder?

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hellfire

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I am not sure whether one can consider the universe to be infinite when arguing about thermodynamics. Note that a universe in which space expansion accelerates contains cosmological event horizons, which make it impossible to speak about the content of the whole universe as an ensemble due to the missing causal contact.

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Phobos

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Phobos

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charlesa said:

The 2nd law of thermo states that the entropy in the final state of a closed/isolated system is never less than the original state (change greater than or equal to zero). If the change is zero, then the process is reversible. If the change is greater than zero, then the process is irreversible.

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Chronos

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Yes, everyone is confused. No one has successfully shown how the Schrodinger wave equation leads to the second law of thermodynamics. The Schrodinger equation predicts that the entropy change for a closed system is ALWAYS zero. People have speculated that Quantum mechanics may need to be modified to introduce a time asymmetric component.Phobos said:

The 2nd law of thermo states that the entropy in the final state of a closed/isolated system is never less than the original state (change greater than or equal to zero). If the change is zero, then the process is reversible. If the change is greater than zero, then the process is irreversible.

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Nereid

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There's also the small (?) problem that we know QM can't be all there is (as a description of the 'rules of the universe') - it's incompatible with GR. So we need a theory of quantum gravity (at least); in that theory (and the successor theories that will likely embed and replace it), who knows how thermodynamics will work (or even if it will be a meaningful concept)?charlesa said:Yes, everyone is confused. No one has successfully shown how the Schrodinger wave equation leads to the second law of thermodynamics. The Schrodinger equation predicts that the entropy change for a closed system is ALWAYS zero. People have speculated that Quantum mechanics may need to be modified to introduce a time asymmetric component.

Now thermodynamics works perfectly well for the tiny, tiny region of the universe (the parameter space of my statement includes things like energy density as well as space and time) that we have encountered so far.

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There's also the small (?) problem that we know QM can't be all there is (as a description of the 'rules of the universe') - it's incompatible with GR.

Right, but there is progress:

https://www.physicsforums.com/showthread.php?t=95958

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turbo

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Thank you for linking that thread. I firmly believe that Loll is taking the inquiry in the right direction.Andre said:Right, but there is progress:

https://www.physicsforums.com/showthread.php?t=95958

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