Remarks on the viscosity concept in the early universe

Details Remarks on the viscosity concept in the early universe Remarks on the viscosity concept in the early universe

Sep 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994ap%26ss.219...99b&link_type=abstract

Astrophysics and Space Science (ISSN 0004-640X), vol. 219, no. 1, p. 99-115

Physics

Plasma Physics

28

Cosmology, Entropy, Ideal Fluids, Mathematical Models, Universe, Viscosity, Anisotropy, Kinetic Theory, Phase Transformations, Plasma Physics, Turbulent Flow

Scientific paper

Some aspects of viscous cosmological models, mainly of Bianchi type-I, are studied, in particular with the purpose of trying to obtain a natural explanation of why the entropy per baryon in the universe, sigma approximately 109, is so large. Using the Friedmann-Robertson-Walker (FRW) metric it is first shown, in agreement with previous workers, that the expressions for the bulk viscosity as derived from kinetic theory in the plasma era is incapable of explaining the large value of sigma. However it is possible to imagine the viscosity to be an 'impulse' viscosity operative in one or several phase transitions in the early universe. This is the main idea elaborated on in the present paper. It is shown that in the k = 0 FRW space, an impulse bulk viscosity (zetainfl approximately 1060 g per cm sec) acting at the phase transition at the end of the inflationary epoch corresponds to the correct entropy. If the space is anisotropic, it is natural to exploit the analogy with classical fluid dynamics to introduce the turbulent viscosity concept. This is finally discussed, in relation to an anisotropy introduced in the universe via the Kasner metric.

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