1.f The program of the Eternal Universe

During the 80's, the group of Cosmology and Gravitation of CBPF developed a detailed analysis of some problematic issues in cosmology. It was assumed that GR describes correctly the gravitational interaction, and also that the current observations of our Universe are consistent with a dynamical geometry (of the Friedmann-Robertson-Walker type) that is spatially homogeneous and has isotropic nonsingular sections. We christened this program with the name Program of the Eternal Universe. The root of this program lies in the denial of the role of the Equivalence Principle as a source of physical laws (see M.Novello e J.M.Salim, Physical Review D 20, 377, 1979). As a consequence of this hypothesis, processes of direct interaction between matter fields and the curvature of space-time are enabled and must be accepted as possible ways of coupling gravity and matter. This program has been presented in several publications, in two books:

Cosmos et Contexte (Mário Novello, Ed. Masson, Paris, 1987),

The Program of the Eternal Universe (Mário Novello in Vth Brazilian School of Cosmology and Gravitation, World Scientific, Singapura, 1987),

and in the Proceedings of the Eighth Marcel Grossmann Meeting (Jerusalem, 1998). In a conformally flat universe (as seems to be the case of our Universe, according to observations), the type of interaction between the gravitational and electromagnetic fields that we examined (determined by the term RFF) can explain the observed redshift of radiation (as in the minimal coupling case) by examining the propagation of photons in null geodesics. The main novelty in this approach is associated to the question of thermodynamical equilibrium in a gas of fotons - in particular to the non-conservation of the total number of fotons in the universe (see, e.g., the paper M.Novello, L.A.R.Oliveira e J.M.Salim, Classical and Quantum Gravity 7, 51, 1990). In the examination of this question, we needed to have a closer look at the features of the cosmic background radiation. As a natural consequence of this work, we began an analysis of the effect of creation of fotons in an expanding universe in a non-singular cosmological model. The thermodynamical analysis of this phenomenon is one of the subjects of our investigations.

The description of the behaviour of the galactic fluid in regions with large gravitational fields led us, through the examination of their thermodynamical properties, to discover a new phenomenon: the possibility of a phase transition due to self-interaction processes in the gravitational field. These processes could constitute the basis for a model to explain the high spatial isotropy of our universe (see M.Novello e S.L.S.Duque, Physical Review D 47, 8, 3165, 1990), and should be examined carefully.