Gravitational Entropy and Inflation
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© 2013 by the authors; licensee m d p i, basel, switzerland. this article is an open access article distributed under the terms and conditions of the creative commons attribution license (http://creativecommons.org/licenses/by/3.0/).
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Original versionElgarøy, Ø., & Grøn, Ø. (2013). Gravitational Entropy and Inflation. Entropy, 15(9), 3620-3639. http://dx.doi.org/10.3390/e15093620
The main topic of this paper is a description of the generation of entropy atthe end of the inflationary era. As a generalization of the present standard model of theUniverse dominated by pressureless dust and a Lorentz invariant vacuum energy (LIVE), wefirst present a flat Friedmann universe model, where the dust is replaced with an ideal gas. Itis shown that the pressure of the gas is inversely proportional to the fifth power of the scalefactor and that the entropy in a comoving volume does not change during the expansion.We then review different measures of gravitational entropy related to the Weyl curvatureconjecture and calculate the time evolution of two proposed measures of gravitationalentropy in a LIVE-dominated Bianchi type I universe, and a Lemaitre-Bondi-Tolmanuniverse with LIVE. Finally, we elaborate upon a model of energy transition from vacuumenergy to radiation energy, that of Bonanno and Reuter, and calculate the time evolution ofthe entropies of vacuum energy and radiation energy. We also calculate the evolution of themaximal entropy according to some recipes and demonstrate how a gap between the maximalentropy and the actual entropy opens up at the end of the inflationary era.