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Volume 12: Pages 115-124, 1999

A Simple Procedure to Assess the Time Dependence of Cosmological Parameters

Guibert U. Crevecoeur

Institut Scientifique du Verre, 10 Boulevard Defontaine, B 6000 Charleroi, Belgium

A classical computation of the variation of the cosmological parameters (pressure, density, deceleration parameter, Hubble constant) during the expansion of a flat universe in a hot big bang cosmology leads to step‐like transitions between epochs. The values of the parameters at transitions are computed separately according to the chosen physical models. The present paper starts from an analogy between the time variation of the Hubble constant as it results from different classical models and the aging kinetics of systems. It seems therefore interesting to investigate if this sheds new light on the assessment of the expansion of the universe by considering it as a system still governed by Einstein's field equations, but where the equations of state are not postulated choosing any physical model (which would give the classical results), but rather deduced from an equation of systems aging. It is shown that this gives a simple procedure to evolve the cosmological parameters smoothly up to the present without separate computation. An example is given combining an inflationary stage with a radiation‐dominated era followed by a matter‐dominated era. Except for the transitions, where a complex behavior is expected, the classical equations of state are found to hold throughout the three epochs considered. During the transitions, the procedure allows one to get a rough estimate of the evolution of the parameters. The computations also put into evidence the possible need for the Hubble constant to involve a time‐constant term if the actual pressure/density ratio is not strictly zero at the end of the radiation‐dominated era.

Keywords: universe as a system, aging of the universe, simple computational procedure, cosmological parameters, time variation of the Hubble constant

Received: July 24, 1998; Published online: December 15, 2008