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I know that thermodynamics 3rd law states that if a system in equilibrium is at zero temperature, its entropy is minimum.

Expansion of the universe made a transition from radiation dominated era (rde) to matter dominated era(mde). So the same question here occurred to me as well. But the answers did not satisfy me indeed. How is it possible that rde had lower entropy than today even if it was at higher temperature in the very early beginning of the universe? Isn't there any contradiction here?

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marked as duplicate by Jim, ACuriousMind, John Rennie, Kyle Kanos, JamalS Feb 27 '15 at 18:10

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

  • $\begingroup$ I cannot confidently answer the cosmological portion of your question, but I can help clarify entropy a bit here. High temperature and low entropy do not conflict--while it is true that many systems increase in entropy as they increase in temperature or energy, this results from the dynamics of a system such as if the kinetic theory of gases applies or not. Entropy is formally a statement of available states. Temperature is a statement of how entropy changes as the energy of the system changes. $\endgroup$ – Andrew S. Feb 27 '15 at 11:35
  • $\begingroup$ The answer not satisfying you does not preclude you from closure as a duplicate. If you find an answer insufficient, you can either offer a bounty or leave a comment with one of the answers. $\endgroup$ – Kyle Kanos Feb 27 '15 at 16:11
  • $\begingroup$ No problem. I am just looking for an answer. @KyleKanos $\endgroup$ – aQuestion Feb 27 '15 at 16:15