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Friedmann–Lemaître–Robertson–Walker metric
About: Friedmann–Lemaître–Robertson–Walker metric is a research topic. Over the lifetime, 4113 publications have been published within this topic receiving 87752 citations. The topic is also known as: FLRW metric.
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TL;DR: In this article, it is shown that in the k = 0 FRW space, an impulse bulk viscosity ςinfl ~ 1060 g cm−1 s−1) acting at the phase transition at the end of the inflationary epoch corresponds to the correct entropy.
Abstract: 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,σ ~ 109, is so large. Using the 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 ofσ. 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 thek = 0 FRW space, an impulse bulk viscosity ςinfl ~ 1060 g cm−1 s−1) 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.
51 citations
TL;DR: In this article, the general expression for the entropy production in cosmologies with variable effective cosmological "constant" (Lambda ) is presented, by assuming that Lambda decays as Lambda = alpha R-m+ beta (R/R)2, where R(t) is the scale factor of the FRW models, the second law of thermodynamics and the Landau-Lifshitz theory for non-equilibrium fluctuations are used to establish constraints on the parameters alpha, beta and m.
Abstract: The general expression for the entropy production in cosmologies with variable effective cosmological 'constant' ( Lambda ) is presented. By assuming that Lambda decays as Lambda = alpha R-m+ beta (R/R)2, where R(t) is the scale factor of the FRW models, the second law of thermodynamics and the Landau-Lifshitz theory for non-equilibrium fluctuations are used to establish constraints on the parameters alpha , beta and m.
51 citations
TL;DR: In this paper, a cosmological model of the FRW universe with variable G and Λ was considered and the solutions have been obtained for flat model with particular form of cosmology constant.
Abstract: We have considered a cosmological model of the FRW universe with variable G and Λ. The solutions have been obtained for flat model with particular form of cosmological constant. The cosmological parameters have also been obtained for dust, radiation and stiff matter. The statefinder parameters are analyzed and have shown that these depends only on w and e. Further the lookback time, proper distance, luminosity distance and angular diameter distance have also been calculated for our model.
50 citations
TL;DR: In this article, the authors investigated the geometric consequences for dust universes of isotropies within the set of idealized galactic observations, including area distance, number counts, proper motions and image distortion.
Abstract: We investigate the geometric consequences for dust universes of isotropies within the set of idealized galactic observations---area distance, number counts, proper motions and image distortion. Anisotropy in the Hubble parameter is shown to indicate non-zero proper motions. If the proper motions and distortion are assumed to be zero (semi-isotropic observations), then the vorticity vanishes, the Hubble and deceleration parameters are isotropic, and Einstein's equations strongly constrain the area distance and the number counts. These constraints allow limited anisotropy, and in principle they provide indirect tests for the presence of proper motions and distortion. If, further, we assume isotropy of the area distance and number counts (isotropic observations), then we prove that Einstein's equations force the spacetime geometry to be isotropic. With the Copernican principle, this leads to an observational proof of the standard FLRW model.
50 citations
TL;DR: In this article, the power law, oscillatory and exponential behavior for the D-dimensional Einstein-Maxwell, N = 2, D = 10 and N = 1,D = 11 supergravity models were studied.
50 citations