Violations of the strong energy condition for interacting systems of particles

This paper generalizes the analysis of Parker and Wang regarding violations of the strong energy condition, demonstrating that they remain applicable even without the assumption that the system of interest is in thermal equilibrium. It does indeed seem possible to violate the strong energy condition even for "normal" matter described by a "reasonable" distribution function or density matrix. As a tool in deriving this result, a special relativistic analogue of Clausius's virial theorem is derived for particles interacting via instantaneous two-body central forces, either in flat space or in a Friedmann universe.