Second law of thermodynamics in nonminimally coupled gravity. (arXiv:1908.02629v3 [gr-qc] UPDATED)

<a href="http://arxiv.org/find/gr-qc/1/au:+Azevedo_R/0/1/0/all/0/1">R.P.L. Azevedo</a>, <a href="http://arxiv.org/find/gr-qc/1/au:+Avelino_P/0/1/0/all/0/1">P.P. Avelino</a>

In the present work we show that the second law of thermodynamics does not

generally hold if the matter and gravitational fields are nonminimally coupled.

We demonstrate this result by explicitly computing the evolution of the entropy

of the matter fields in the case of a closed homogeneous and isotropic universe

filled with dust and radiation, showing that, in this case, the sign of the

entropy variation is determined by the evolution of the universe. The

preservation of the second law of thermodynamics in these modified theories

would require its generalization to account for a gravitational entropy

contribution.

In the present work we show that the second law of thermodynamics does not

generally hold if the matter and gravitational fields are nonminimally coupled.

We demonstrate this result by explicitly computing the evolution of the entropy

of the matter fields in the case of a closed homogeneous and isotropic universe

filled with dust and radiation, showing that, in this case, the sign of the

entropy variation is determined by the evolution of the universe. The

preservation of the second law of thermodynamics in these modified theories

would require its generalization to account for a gravitational entropy

contribution.

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