On the Historical Development of the Indistinguishability Concept for Microparticles

Abstract

The kinetic theory of gases, founded in the 18th century by Daniel Bernoulli, was further developed during the 19th century by Clausius and Maxwell, and crowned by the achievements of Ludwig Boltzmann’s statistical mechanics. At the time Boltzmann was developing his method, the hypothesis of the discontinuous structure of matter, i.e., of the existence of atoms and molecules, was becoming increasingly a matter of certainty for physicists. Boltzmann’s colleague at the University of Vienna, Joseph Loschmidt, indicated in the year 1865 a method for determining the number of molecules in a mole (the so-called Avogadro’s number NA) and the order of magnitude of atomic sizes (1 Å = 10-8 cm). We know today that Avogadro’s number— determined by a dozen independent methods—has the numerical value NA = 6.025 × 1023, an enormously large number.