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Is the universe a closed thermodynamic system, as defined in the laws of thermodynamics?

Some argue it is, or state it is, based on the fact that the universe is by definition everything there is, so it can't realy be in thermal contact with anything else as itself.

Can a closed thermodynamic system conserve it's entropy?

If we apply the second law, this would be a borderline, since the 2nd law states that the entropy can not decrease.

Can it be that the universe increases it's entropy indefinately?

I don't see how that can be true, unless for a finite subsystem of the universe of any size.

Because if it did, how to explain that the universe still has useuable energy left?

Some argue then that the universe had a begin, but such can not be conceived of. A universe can not pop into existence from nothing, and this would also break the first law.

Can an infinite system be a closed thermodynamic system?

Since the second law is applyable to finite systems only, we can not state that immediately.

The way we could conceive of the universe as a closed thermodynamic system is to start with a known finite and closed TD system, and add to that a surrounding part, which still match a closed TD system, and repeat that untill we cover all of the universe.

But since the universe is probably infinite, we could never conceive of it as a closed TD system.

Conclusion:

The universe in total conserves the amount of entropy (wether or not the universe is a closed TD system or not, and wether the term open or closed are applicable to the universe, or not)

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# Second law & universe

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