ABSTRACT
In statistical mechanics the study of fluctuations is of great physical interest. The fluctuation-dissipation theorem relates the dissipative response of a system to an external perturbation with the microscopic dynamics of the system in a state of equilibrium. Energy fluctuations in thermal systems can be used to investigate the set of distinct, microscopic states that are accessible to a system maintained at a fixed temperature. Likewise, a study of density fluctuations in granular media may provide a framework for understanding the physical phenomenon of compaction, i.e., how a vibrated powder, that is not in a steady state, finally approaches a steady state.
