Kinetic theory: Understanding nature through collisions

Abstract

The attempts to understand the macroscopic behavior of fluids, in particular their nonequilibrium properties, in terms of the dynamics of the many particles, out of which they consist, are sketched from Clausius, in the middle of the 19th century, to the present day. The fundamental role that collisions play for dilute as well as dense gaseous or liquid systems is emphasized. The main difficulty is to identify the relevant collision sequences in the myriads of collisions that go on in a macroscopic system. While for dilute gases uncorrelated binary collisions dominate, as was already known in the 19th century, relevant correlated collision sequences for dense gases and liquids have only been identified in the last 25 years, leading to vortex and cage diffusion. Applications to transport coefficients are discussed.