Criticality and Averaging in Cosmology

Criticality and Averaging in Cosmology

We propose comparing cosmological solutions in terms of their total spatial volumes V (τ ) as functions of proper time τ , assuming synchronous gauge, and with this intention evaluate the variations of V (τ ) about the Friedmann-Lemâıtre-Robertson-Walker (FLRW) solutions for dust. This can be done successfully in a simple manner without solving perturbation equations. In particular, we find tha...

Averaging in spherically symmetric cosmology

The averaging problem in cosmology is of fundamental importance. When applied to study cosmological evolution, the theory of macroscopic gravity (MG) can be regarded as a long-distance modification of general relativity. In the MG approach to the averaging problem in cosmology, the Einstein field equations on cosmological scales are modified by appropriate gravitational correlation terms. We st...

Regional Averaging and Scaling in Relativistic Cosmology

Averaged inhomogeneous cosmologies lie at the forefront of interest, since cosmological parameters such as the rate of expansion or the mass density are to be considered as volume–averaged quantities and only these can be compared with observations. For this reason the relevant parameters are intrinsically scale–dependent and one wishes to control this dependence without restricting the cosmolo...

Averaging Problem in Cosmology and Macroscopic Gravity

Averaging inhomogeneities in scalar-tensor cosmology

The backreaction of inhomogeneities on the cosmic dynamics is studied in the context of scalar-tensor gravity. Due to terms of indefinite sign in the non-canonical effective energy tensor of the Brans–Dicke-like scalar field, extra contributions to the cosmic acceleration can arise. Brans–Dicke and metric f(R) gravity are presented as specific examples. Certain representation problems of the fo...