  We show that simple diffusive systems, such as the Lorentz gas and multibaker
maps are perfectly compatible with the laws of irreversible thermodynamics,
despite the fact that the moving particles, or their equivalents, in these
models do not interact with each other, and that the dynamics takes place in
low-dimensional phase spaces. The interaction of moving particles with
scatterers provides the dynamical mechanism responsible for an approach to
equilibrium, under appropriate conditions. This analysis provides a refutation
of the criticisms expressed recently by Cohen and Rondoni [Physica A 306 (2002)
117-128].
