THERMODYNAMIC ENSEMBLES AND GRAVITATION

By including gravitation as described by general relativity as a part of a thermodynamic system, the authors have obtained formal path integral representations of partition functions for various ensembles including that appropriate to the microcanonical ensemble. This is possible because the boundary conditions for certain well posed Euclidean problems in general relativity exactly correspond to boundary conditions of certain well posed problems in thermodynamics. The different ensembles are obtained using the definition of variables conjugate both in the sense of the field theory of general relativity and in the sense of thermodynamics, the boundary data of which can be prescribed geometrically using gravity.