Logical entropy – special issue

Entropy is a fundamental quantity in many areas of knowledge, from physics to information science to biology. Originally put forward in the nineteenth century for very practical purposes (to quantify the reversibility of thermodynamic cycles, hence of thermal engines), entropy was the key concept that allowed Ludwig Boltzmann to bridge the gap between the (time irreversible) macroscopic thermodynamics and the (reversible) microscopic Newtonian physics. As defined by Boltzmann, the entropy SB represents the number of microscopic states that are compatible with a given macroscopic realization: