Backreaction in Cosmological Models

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dc.creatorSicka, Christian
dc.creatorBuchert, Thomas
dc.creatorKerscher, Martin
dc.date1999-07-12
dc.date.accessioned2026-07-25T13:37:36Z
dc.descriptionMost cosmological models studied today are based on the assumption of homogeneity and isotropy. Observationally one can find evidence that supports these assumptions on very large scales, the strongest being the almost isotropy of the Cosmic Microwave Background radiation after assigning the whole dipole to our proper motion relative to this background. However, on small and on intermediate scales up to several hundreds of Mpcs, there are strong deviations from homogeneity and isotropy. Here the problem arises how to relate the observations with the homogeneous and isotropic models. The usual proposal for solving this problem is to assume that Friedmann-Lemaitre models describe the mean observables. Such mean values may be identified with spatial averages. For Newtonian fluid dynamics the averaging procedure has been discussed in detail in Buchert and Ehlers (1997), leading to an additional backreaction term in the Friedmann equation. We use the Eulerian linear approximation and the `Zel'dovich approximation' to estimate the effect of the backreaction term on the expansion. Our results indicate that even for domains matching the background density in the mean, the evolution of the scale factor strongly deviates from the Friedmann solution, critically depending on the velocity field inside.
dc.description4 pages LaTeX, 2 figures, a4wide.sty included
dc.identifierhttps://arxiv.org/abs/astro-ph/9907137
dc.identifierhttp://arxiv.org/abs/astro-ph/9907137
dc.identifierProc. of the Fifth SFB-375 Ringberg workshop, Ed. Daniel Thomas, Ringberg Castle, Tegernsee, Germany, 1999
dc.identifier.urihttps://dspace.dare.co.zw/handle/123456789/18875
dc.subjectAstrophysics
dc.subjectGeneral Relativity and Quantum Cosmology
dc.titleBackreaction in Cosmological Models
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