Entropy: Mystery and Controversy. Plethora of Informational-Entropies and Unconventional Statistics

Abstract

Some general considerations on the notion of entropy in physics are presented. An attempt is made to clarify the question of the differentiation between physical entropy (the Clausius-Boltzmann one) and quantities called entropies associated to Information Theory, which are in fact generating functionals for the derivation of probability distributions and not thermodynamic functions of state. The role of them in the construction of the so-called Unconventional Statistical Mechanics, and the meaning and use of the latter, is discussed. Particular attention is given to the situation involving far-from-equilibrium systems.