Introduction

Summary

The idea that gases are disordered or amorphous states of matter is old. Actually, the word gas was created from the Greek word chaos by Joan-Baptista van Helmont (1577–1644). This Flemish physician and chemist born in Brussels was the first to distinguish different kinds of gases thanks to the experimental method and he also invented an air thermoscope which was the precursor of the modern thermometer. He was contemporary with Bacon (1561–1626), Galileo (1564–1642), Kepler (1571–1630), Descartes (1596–1650), Torricelli (1608–1647), as well as with the famous painter Rubens (1577–1640). His son published his work Ortus medicinae, id est initia phisicare inaudita at Amsterdam in 1648 (Farber 1961).

During the XlXth century, the spatial disorder of gases and of matter in general was quantitatively characterized with the concept of entropy per unit volume. However, the idea of dynamical chaos, i.e., of temporal disorder in physical systems like gases is more recent as it results from a long sequence of observations and works which extends throughout the XXth century with the development of statistical mechanics.

Today, we may say that statistical mechanics and kinetic theory are among the greatest successes of modern science. Since Maxwell and Boltzmann, macroscopic properties of matter can be explained in terms of the motion of atoms and molecules composing matter. In particular, transport properties like diffusion, viscosity, or heat conductivity can be predicted in terms of the parameters of the microscopic Hamiltonians, which are the masses of the atoms and molecules, and the coupling constants of their interaction (Maxwell 1890, Boltzmann 1896).