Macroscopic Systems and Empirical Temperature

Abstract

The definitions of the macroscopic system and of empirical temperature are discussed. At the first step of the theory, a definition of the state of equilibrium must be given for isolated systems and the definition of mutual equilibrium between closed systems put in contact comes as a consequence. The property of being in mutual equilibrium is, by definition, denoted by saying that the two systems have the same temperature. Empirical observation shows that the property of having the same temperature, i.e., of being in mutual equilibrium, is transitive and this statement is assumed to be true in general. This is the content of the Zeroth Principle of Thermodynamics, and it is the necessary postulation which allows us to define the concept of empirical temperature as a physical quantity.