Two approaches to nonstationary relativistic thermodynamics

Abstract

A nonstationary thermodynamic theory in general relativity is set up through a hidden variable approach. Such a theory, which is especially suited to the description of the behavior of heat conducting viscous fluids, considers evolution equations involving the gradient of the hidden variables too. The expression adopted for the second law differs from the usual Clausius–Duhem inequality because of the presence of an entropy extra-flux. Besides other results it is shown that, via a suitable choice of the free energy function, the theory so obtained reduces just to Müller–Israel’s one.