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

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SUMMARY

The discussion centers on the concept of entropy within the universe as an isolated system. It establishes that entropy, represented by the equation dS = dq/T, continuously increases as dq approaches zero. The conversation explores the implications of a potential universe collapse, suggesting that if the universe were to collapse and subsequently spawn a new universe (a big bang), there could be a significant decrease in entropy at that moment. However, the consensus indicates that while local entropy may fluctuate, the overall entropy of the universe remains on an upward trajectory.

PREREQUISITES
  • Understanding of thermodynamics, particularly the second law of thermodynamics.
  • Familiarity with the concept of entropy and its mathematical representation.
  • Knowledge of cosmology, specifically the expansion and potential collapse of the universe.
  • Basic grasp of the big bang theory and its implications for entropy changes.
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  • Research the implications of the second law of thermodynamics in cosmological contexts.
  • Explore the relationship between entropy and the big bang in more detail.
  • Investigate theories regarding the fate of the universe, including heat death and the big crunch.
  • Learn about local versus universal entropy changes in thermodynamic systems.
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Physicists, cosmologists, and students of thermodynamics interested in the fundamental principles governing entropy in the universe.

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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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