The thermodynamic description of the cosmological many-body problem

We investigate three fundamental aspects of the thermodynamic description of the cosmological many-body problem, which has been used extensively as a model of galaxy clustering. First we show explicitly how the thermodynamic description involves only the local fluctuating part of the gravitational field, even though gravity is a long-range force. Second we discuss the conditions for a quasi-equilibrium description to apply. Third, we derive the functional form of b((n) over bar, T), the ratio of gravitational correlation energy to twice the kinetic energy of peculiar velocities, which completes the equation of state. This functional form previously had to be postulated as an Ansatz. We also discuss how it is related to other physical properties of the system.