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Entropy 2016, 18(6), 215; doi:10.3390/e18060215

General Bulk-Viscous Solutions and Estimates of Bulk Viscosity in the Cosmic Fluid

1,†
and
2,†,*
1
Department of Physics, Norwegian University of Science and Technology, Trondheim N-7491, Norway
2
Department of Energy and Process Engineering, Norwegian University of Science and Technology, Trondheim N-7491, Norway
These authors contributed equally to this work.
*
Author to whom correspondence should be addressed.
Academic Editor: Kevin H. Knuth
Received: 31 March 2016 / Revised: 25 May 2016 / Accepted: 26 May 2016 / Published: 2 June 2016
(This article belongs to the Section Astrophysics and Cosmology)
View Full-Text   |   Download PDF [346 KB, uploaded 2 June 2016]   |  

Abstract

We derive a general formalism for bulk viscous solutions of the energy-conservation equation for ρ ( a , ζ ) , both for a single-component and a multicomponent fluid in the Friedmann universe. For our purposes, these general solutions become valuable in estimating the order of magnitude of the phenomenological viscosity in the cosmic fluid at present. H ( z ) observations are found to put an upper limit on the magnitude of the modulus of the present-day bulk viscosity. It is found to be ζ 0 10 6 Pa·s, in agreement with previous works. We point out that this magnitude is acceptable from a hydrodynamic point of view. Finally, we bring new insight by using our estimates of ζ to analyze the fate of the future universe. Of special interest is the case ζ ρ for which the fluid, originally situated in the quintessence region, may slide through the phantom barrier and inevitably be driven into a big rip. Typical rip times are found to be a few hundred Gy. View Full-Text
Keywords: viscous cosmology; bulk viscosity; big rip; fate of the universe viscous cosmology; bulk viscosity; big rip; fate of the universe
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Normann, B.D.; Brevik, I. General Bulk-Viscous Solutions and Estimates of Bulk Viscosity in the Cosmic Fluid. Entropy 2016, 18, 215.

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