The power of Boltzmann's equation:
We do not solve the transport equation here.
But to illustrate the kind of processes it can describe, we
simulate a 2-dimensional system of hard discs in a rectangular box.
At the start all particles are in the left part of the container;
their velocities are randomly chosen (not from a Maxwell-Boltzmann
distribution). This nonequilibrium state is not stable, and in time
the particles will fill the entire box in a (statistically) homogeneous
way: approach to equilibrium.