# On Extended Thermodynamics: From Classical to the Relativistic Regime

## TL;DR

This paper reviews recent advances in the thermodynamics of relativistic continuous media, emphasizing observational breakthroughs and their implications for the theory of relativistic dissipative fluids and irreversible thermodynamics.

## Contribution

It provides a comprehensive summary of the progress in non-equilibrium thermodynamics of relativistic media over recent decades.

## Key findings

- Relativistic dissipative fluids are crucial in astrophysics and subnuclear physics.
- Recent observational data motivate the development of relativistic thermodynamics.
- The paper connects classical thermodynamics with modern relativistic theories.

## Abstract

The recent monumental detection of gravitational waves by LIGO, the subsequent detection by the LIGO/VIRGO observatories of a binary neutron star merger seen in the gravitational wave signal $GW170817$,the first photo of the event horizon of the supermassive black hole at the center of the $M87$ galaxy released by the EHT telescope and the ongoing experiments on Relativistic Heavy Ion Collisions at the BNL and at the CERN, demonstrate that we are witnessing the second golden era of observational relativistic gravity. These new observational breakthroughs, although in the long run would influence our views regarding this Kosmos, in the short run, they suggest that relativistic dissipative fluids (or magnetofluids) and relativistic continuous media play an important role on astrophysical-and also subnuclear-scales. This realization brings into the frontiers of current research theories of irreversible thermodynamics of relativistic continuous media. Motivated by these considerations, in this paper, we summarize the progress that has been made in the last few decades in the field of non equilibrium thermodynamics of relativistic continuous media. For coherence and completeness purposes, we begin with a brief description of the balance laws for classical (Newtonian) continuous media and introduce the classical irreversible thermodynamics (CIT) and the role of the local-equilibrium postulate within this theory. Tangentially, we touch the program of rational thermodynamics (RT), the Clausius-Duhem inequality, the theory of constitutive relations and the emergence of the entropy principle and its role in the description of continuous media.