When will the entropy of universe(an isolated system) stop increasing?

AI Thread Summary
The discussion centers on the concept of entropy in the universe as an isolated system, suggesting that entropy generally increases due to the second law of thermodynamics. It is proposed that if the universe continues to expand indefinitely, overall entropy will rise continuously. However, the possibility of the universe collapsing into a "crunch" raises questions about whether this could lead to a decrease in entropy, especially if it results in a new big bang. The debate includes the idea that while entropy may appear to increase universally, it could decrease locally during significant cosmic events. Ultimately, the relationship between entropy and the universe's lifecycle remains complex and unresolved.
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Consider the universe as an isolated system, its entropy always increase? when stop?

dS=>dq\T, as dq=o in universe an isolated system, dS always bigger than zero.


so increase nonstop?
 
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One answer should be that if it is isolated and keep expand forever, the overall entropy does increase nonstop.

But if the universe can reach a point in spacetime when it starts collapsing instead of expanding you could argue that the energy which has been spread out over vast distancies (cold objects, CMB) will now be doing work in this crunch and if the crunch results in a new universe (big bang) obviously at some time it must go against the second law and decrease.

I´m not sure how to decide when the internal entropy starts to decrease. But if the crunch actually spawns a new universe surely it must be a large drop in entropy during a big bang? A thought is that entropy doesn't really change on the universal scale, only locally.
 

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