Equilibrium time correlation functions and the dynamics of fluctuations

Equilibrium time correlation functions are of great importance because they probe the equilibrium dynamical response to external perturbations. We dis cuss the properties of time correlation functions for several systems that are simple enough to illustrate the calculational steps involved. The discu ssion underscores the need for avoiding language which misleadingly suggest s that thermal equilibrium is associated with a quiescent or moribund state of the system. (C) 1999 American Association of Physics Teachers.