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Averaging Inhomogeneous Universes: Volume, Angle, Line of Sight

Eric V. Linder
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Abstract

Cosmologies that match in a volume averaged sense need not generally have the same light propagation behaviors. In particular a universe with inhomogeneity may not demonstrate the Friedmann-Robertson-Walker distance-redshift relation even after volume averaging to FRW spacetime. Even the Dyer-Roeder prescription for incorporating inhomogeneity within a universe equivalent to FRW in an angle averaged sense does not guarantee FRW behavior in general. To legitimately use the FRW distance-redshift relation to interpret observations, the physical conditions must match in a line of sight sense (defined herein: most observations do), since light probes the mass distribution or geometry on all length scales.

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Eric V. Linder. 1998-01-14. Averaging Inhomogeneous Universes: Volume, Angle, Line of Sight. https://arxiv.org/abs/astro-ph/9801122

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