Random walks derived from billiards

We introduce a class of random dynamical systems derived from billiard maps, which we call random billiards, and study certain random walks on the real line obtained from them. The interplay between the billiard geometry and the stochastic properties of the random billiard is investigated. Our main results are concerned with the spectrum of the random billiard’s Markov operator. We also describe some basic properties of diffusion limits under appropriate scaling. Introduction This work is motivated by the following problem about gas kinetics. Suppose that a short pulse of inert gas at very low pressure is released from a point inside a long but finite cylindrical channel. The time at which gas molecules escape the channel through its open ends is then measured by some device such as a mass spectrometer. The inner surface of the cylinder is not perfectly flat due to its molecular structure, imagined as a periodic relief. It is not altogether unreasonable to think that the interaction between the fast moving (inert) gas molecules and the surface is essentially elastic, and that any thermal effects can be disregarded on first approximation. (See [ACM] for a more detailed physical justification of this assumption.) We thus think of the gas-surface interaction as billiard-like. (M. Knudsen, in his classical theoretical and experimental studies on the kinetic theory of gases begun around 1907, used a tennis ball metaphor [Kn, p. 26].) The assumption of low pressure simply means that the collisions among gas molecules are in sufficiently small numbers to be disregarded and only collisions between gas molecules and the channel inner surface are taken into account.