Thermodynamics of homogeneous Universes: de Sitter, Bonnor-Melvin and static Einstein
G. E. Volovik
Landau Institute for Theoretical Physics, 142432 Chernogolovka, Russia
Abstract
In the theories, in which dynamic gravitational field emerges from the
underlying matter fields, the gravitational field can be considered as a
part of matter. Using this approach, we construct the thermodynamics of
the homogeneous Universes - the de Sitter Universe, the Bonnor-Melvin-Λ
Universe and the static Einstein Universe. It is demonstrated
that although these three Universes have different types of matter fields
(ordinary matter, magnetic field, gravitational field and vacuum energy),
they have the same thermodynamic properties. Their energy densities obey
the same equation, which contains the corresponding matter densities and
the pairs of the thermodynamically conjugate variables. In Minkowski
vacuum, where the ordinary matter and magnetic and gravitational fields
are absent, this thermodynamic approach automatically leads to zero
cosmological constant.