Explicit Cosmological Coarse Graining via Spatial Averaging

Abstract

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.

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

References in corpus (32)

• Observational Evidence from Supernovae for an Accelerating Universe and a Cosmological Constant
• Measurements of Omega and Lambda from 42 High-Redshift Supernovae
• On average properties of inhomogeneous fluids in general relativity I: dust cosmologies
• Cosmic homogeneity demonstrated with luminous red galaxies
• On average properties of inhomogeneous fluids in general relativity II: perfect fluid cosmologies
• An inhomogeneous alternative to dark energy?
• On cosmic acceleration without dark energy
• Voids in the PSCz Survey and the Updated Zwicky Catalog
• Voids in the 2dF Galaxy Redshift Survey
• Can the Acceleration of Our Universe Be Explained by the Effects of Inhomogeneities?
• A Local Void and the Accelerating Universe
• The universe seen at different scales
• Large Scale Inhomogeneity Versus Source Evolution -- Can We Distinguish Them Observationally?
• Accelerated expansion from structure formation
• The effect of inhomogeneous expansion on the supernova observations
• Is dark energy the only solution to the apparent acceleration of the present universe?
• Cosmological Solutions in Macroscopic Gravity
• Mimicking Dark Energy with Lemaitre-Tolman-Bondi Models: Weak Central Singularities and Critical Points
• Cosmological parameters are dressed
• Correspondence between kinematical backreaction and scalar field cosmologies - the `morphon field'
• Minkowski Functionals of SDSS galaxies I : Analysis of Excursion Sets
• Regional averaging and scaling in relativistic cosmology
• Analyses of Type Ia Supernova Data in Cosmological Models with a Local Void
• Cosmic Microwave Background, Accelerating Universe and Inhomogeneous Cosmology
• Morphological fluctuations of large-scale structure: the PSCz survey
• The Possibility of Cosmic Acceleration via Spatial Averaging in Lemaitre-Tolman-Bondi Models
• Statistics of Voids in the 2dF Galaxy Redshift Survey
• Basic properties of galaxy clustering in the light of recent results from the Sloan Digital Sky Survey
• A Renormalization Group Approach to Relativistic Cosmology
• Inhomogeneous spacetimes as a dark energy model
• The Spatial Averaging Limit of Covariant Macroscopic Gravity - Scalar Corrections to the Cosmological Equations
• Gravitational Backreaction of Matter Inhomogeneities

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• On the curvature of the present-day Universe
• Toward physical cosmology: focus on inhomogeneous geometry and its non-perturbative effects
• The influence of structure formation on the cosmic expansion
• Is backreaction really small within concordance cosmology?
• Back-reaction and effective acceleration in generic LTB dust models
• Another look at redshift drift and the backreaction conjecture
• Description of our cosmological spacetime as a perturbed conformal Newtonian metric and implications for the backreaction proposal for the accelerating universe
• Observations in statistically homogeneous, locally inhomogeneous cosmological toy-models without FLRW backgrounds
• Virialisation-induced curvature as a physical explanation for dark energy
• Towards statistically homogeneous and isotropic perfect fluid universes with cosmic backreaction
• Can the cosmological constant be mimicked by smooth large-scale inhomogeneities for more than one observable?
• Weighed scalar averaging in LTB dust models, part I: statistical fluctuations and gravitational entropy
• Dynamical apparent horizons in inhomogeneous Brans-Dicke universes
• On the relationship between mean observations, spatial averages and the Dyer-Roeder approximation in Einstein-Straus models
• Observational tests of backreaction with recent data
• Effect of inhomogeneities on the propagation of gravitational waves from binaries of compact objects
• Averaging inhomogeneities in scalar-tensor cosmology
• Analytical solutions for two inhomogeneous cosmological models with energy flow and dynamical curvature
• Bayesian analysis of the backreaction models