An Extended Interpretation of the Concept of Entropy Opening a Link between Thermodynamics and Relativity

It is well known that thermodynamics raises conceptual difficulties. Far to be limited to students having to learn the subject, this impression is sometimes mentioned by specialists themselves who confess not being totally sure of the consistency of the thermodynamic theory, despite the fact that its practical usefulness is indisputable. The present paper deals with this interesting question and leads to the idea that there is an imperfect convergence between the way of using the thermodynamic tool and the way of understanding its significance. Illustrated by a very simple example, the discussion can be followed by every scientist having the fundamental basis in thermodynamics. The suggested hypothesis is that the Einstein mass-energy relation is closely associated to the concept of entropy, opening a link between thermodynamics and relativity.