2006/09/30 by Aseem Paranjape, T. P. Singh · 35 citations
Physics and Astronomy · #COSMIC cancer database #Cosmology #Cosmology and Gravitation Theories #Deceleration parameter #Einstein field equations #Friedmann–Lemaître–Robertson–Walker metric #Galaxies: Formation, Evolution, Phenomena #Homogeneity (statistics) #Luminosity distance #Relativity and Gravitational Theory #Scale factor (cosmology) #Spacetime #astro-ph #gr-qc
paper · pdf · doi:10.1007/s10714-007-0523-2
published in General Relativity and Gravitation 40(1), 139-157 (Springer Science+Business Media) · 18 pages, 2 figures; (v2) added references, (v3) material and references added, (v4) material and references added, some clarifying remarks added, to appear in Gen. Rel. Grav
arxiv created 2007/09/10 · openalex publication_date 2007/10/04 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
The present matter density of the Universe, while highly inhomogeneous on small scales, displays approximate homogeneity on large scales. We propose that whereas it is justified to use the Friedmann-Lemaitre-Robertson-Walker (FLRW) line element (which describes an exactly homogeneous and isotropic universe) as a template to construct luminosity distances in order to compare observations with theory, the evolution of the scale factor in such a construction must be governed not by the standard Einstein equations for the FLRW metric, but by the modified Friedmann equations derived by Buchert [7, 8] in the context of spatial averaging in Cosmology. Furthermore, we argue that this scale factor, defined in the spatially averaged cosmology, will correspond to the effective FLRW metric provided the size of the averaging domain coincides with the scale at which cosmological homogeneity arises. This allows us, in principle, to compare predictions of a spatially averaged cosmology with observations, in the standard manner, for instance by computing the luminosity distance versus red-shift relation. The predictions of the spatially averaged cosmology would in general differ from standard FLRW cosmology, because the scale-factor now obeys the modified FLRW equations. This could help determine, by comparing with observations, whether or not cosmological inhomogeneities are an alternative explanation for the observed cosmic acceleration.