Backreaction Issues in Relativistic Cosmology and the Dark Energy Debate

TL;DR

This paper reviews how inhomogeneities in the universe affect its overall evolution through backreaction, potentially impacting the understanding of dark energy, by reformulating cosmological equations with scalar fields and discussing observational implications.

Contribution

It introduces a framework for modeling backreaction effects in relativistic cosmology using scalar fields, revisiting standard equations and highlighting unresolved interpretational issues.

Findings

Backreaction can be modeled by a scalar field ('morphon field').

Reformulation of Friedmann equations includes backreaction terms.

Unresolved issues remain in connecting models to observations.

Abstract

The effective evolution of an inhomogeneous universe model in Einstein's theory of gravitation may be described in terms of spatially averaged scalar variables. This evolution can be modeled by solutions of a set of Friedmann equations for an effective scale factor, with matter and backreaction source terms, where the latter can be represented by a minimally coupled scalar field (`morphon field'). We review the basic steps of a description of backreaction effects in relativistic cosmology that lead to refurnishing the standard cosmological equations, but also lay down a number of unresolved issues in connection with their interpretation within observational cosmology.