Is there proof that backreaction of inhomogeneities is irrelevant in cosmology?

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http://hdl.handle.net/10138/310154

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Buchert , T , Carfora , M , Ellis , G F R , Kolb , E W , MacCallum , M A H , Ostrowski , J J , Räsänen , S , Roukema , B F , Andersson , L , Coley , A A & Wiltshire , D L 2015 , ' Is there proof that backreaction of inhomogeneities is irrelevant in cosmology? ' , Classical and Quantum Gravity , vol. 32 , no. 21 , 215021 . https://doi.org/10.1088/0264-9381/32/21/215021

Title: Is there proof that backreaction of inhomogeneities is irrelevant in cosmology?
Author: Buchert, T.; Carfora, M.; Ellis, G. F. R.; Kolb, E. W.; MacCallum, M. A. H.; Ostrowski, J. J.; Räsänen, S.; Roukema, B. F.; Andersson, L.; Coley, A. A.; Wiltshire, D. L.
Contributor: University of Helsinki, Department of Physics
Date: 2015-11-05
Language: eng
Number of pages: 38
Belongs to series: Classical and Quantum Gravity
ISSN: 0264-9381
URI: http://hdl.handle.net/10138/310154
Abstract: No. In a number of papers, Green and Wald argue that the standard FLRW model approximates our Universe extremely well on all scales, except close to strong-field astrophysical objects. In particular, they argue that the effect of inhomogeneities on average properties of the Universe (backreaction) is irrelevant. We show that this latter claim is not valid. Specifically, we demonstrate, referring to their recent review paper, that (i) their two-dimensional example used to illustrate the fitting problem differs from the actual problem in important respects, and it assumes what is to be proven; (ii) the proof of the trace-free property of backreaction is unphysical and the theorem about it fails to be a mathematically general statement; (iii) the scheme that underlies the trace-free theorem does not involve averaging and therefore does not capture crucial non-local effects; (iv) their arguments are to a large extent coordinate-dependent, and (v) many of their criticisms of backreaction frameworks do not apply to the published definitions of these frameworks. It is therefore incorrect to infer that Green and Wald have proven a general result that addresses the essential physical questions of backreaction in cosmology.
Subject: relativistic cosmology
inhomogeneity effects
weak-limits
GENERAL-RELATIVITY
HIGH-FREQUENCY
GRAVITATIONAL-RADIATION
DARK ENERGY
AVERAGE PROPERTIES
DUST COSMOLOGIES
NEWTONIAN LIMIT
UNIVERSE
DYNAMICS
TENSOR
115 Astronomy, Space science
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