  It is generally believed that the dynamics of simple fluids can be considered
to be chaotic, at least to the extent that they can be modeled as classical
systems of particles interacting with short range, repulsive forces. Here we
give a brief introduction to those parts of chaos theory that are relevant for
understanding some features of non-equilibrium processes in fluids. We
introduce the notions of Lyapunov exponents, Kolmogorov-Sinai entropy and
related quantities using some simple low-dimensional systems as "toy" models of
the more complicated systems encountered in the study of fluids. We then show
how familiar methods used in the kinetic theory of gases can be employed for
explicit, analytical calculations of the largest Lyapunov exponent and KS
entropy for dilute gases composed of hard spheres in d dimensions. We conclude
with a brief discussion of interesting, open problems.
