Cosmological Backreaction in Spherical and Plane Symmetric Dust-Filled Space-Times

Understand

We examine the implementation of Buchert's and Green & Wald's averaging formalisms in exact spherically symmetric and plane symmetric dust-filled cosmological models.

• We find that, given a cosmological space-time, Buchert's averaging scheme gives a faithful way of interpreting the large-scale expansion of space, and explicit terms that precisely quantify deviations from the behaviour expected from the Friedmann equations of homogeneous and isotropic cosmological models.
• The Green & Wald formalism, on the other hand, does not appear to yield any information about the large-scale properties of a given inhomogeneous space-time.
• Instead, this formalism is designed to calculate the back-reaction effects of short-wavelength fluctuations around a given "background" geometry.