Is Dark Energy Simulated by Structure Formation in the Universe ?

TL;DR

This paper explores how inhomogeneities and structure formation in the universe might account for dark energy phenomena through effective cosmological models derived from averaging Einstein's equations.

Contribution

It introduces a framework for understanding the impact of structure formation on cosmic acceleration without invoking dark energy, challenging standard homogeneous models.

Findings

Averaged Einstein's equations reveal scale-dependent effects of structure formation.

Cosmological backreaction can be modeled as an effective scalar field.

Inhomogeneities may explain dark energy phenomena without new physics.

Abstract

The standard model of cosmology assumes that the Universe can be described to hover around a homogeneous-isotropic solution of Einstein's general theory of relativity. This description needs (sometimes hidden) hypotheses that restrict the generality, and relaxing these restrictions is the headline of a new physical approach to cosmology that refurnishes the cosmological framework. Considering a homogeneous geometry as a template geometry for the in reality highly inhomogeneous Universe must be considered a strong idealization. Unveiling the limitations of the standard model opens the door to rich consequences of general relativity, giving rise to effective (i.e. spatially averaged) cosmological models that may even explain the longstanding problems of dark energy and dark matter. We explore in this talk the influence of structure formation on average properties of the Universe by discussing: (i) general thoughts on why considering average properties, on the key-issue of non-conserved curvature, and on the global gravitational instability of the standard model of cosmology; (ii) the general set of cosmological equations arising from averaging the scalar parts of Einstein's equations, the generic property of structure formation interacting with the average properties of the Universe in a scale-dependent way, and the description of cosmological backreaction in terms of an effective scalar field.