Gravitational thermodynamics

The gravitational N -body problem, for N > 2, is the oldest unsolved problem in mathematical physics. Some of the most ideal examples that can be found in nature are globular star clusters, with N ∼ 10. In this overview, I discuss six types of fundamental sources of unpredictability, each of which poses a different challenge to attempts to determine the long-term behavior of these systems, governed by a peculiar type of thermodynamics. Gravitational Thermodynamics 3 April 1997