The Accelerated Expansion of the Universe Challenged by an Effect of the Inhomogeneities. A Review

TL;DR

This review discusses how inhomogeneities in the universe might explain the observed accelerated expansion, challenging the dark energy paradigm and questioning the cosmological principle's validity.

Contribution

It synthesizes alternative explanations to dark energy based on inhomogeneities, highlighting their potential to account for cosmological observations without new physics.

Findings

Inhomogeneities could mimic accelerated expansion effects.

Alternative models challenge the necessity of dark energy.

Future research directions are outlined.

Abstract

Since its decovery during the late 90's, the dimming of distant SN Ia apparent luminosity has been mostly ascribed to the influence of a mysterious dark energy component. Formulated in a Friedmannian cosmological modelling framework based upon the cosmological ``principle'' hypothesis, this interpretation has given rise to the ``concordance'' model. However, a caveat of such a reasoning is that the cosmological ``principle'' derives from a philosophical Copernican assumption and has never been tested. Furthermore, a weakness of its conclusion, i. e., the existence of a negative-pressure fluid or a cosmological constant, is that it would have profound implications for the current theories of physics. This is why we have proposed a more conservative explanation, ascribing the departure of the observed universe from an Einstein-de Sitter model to the influence of inhomogeneities. This idea has been independently developed by other authors and further enlarged to the reproduction of different cosmological data. We review here the main proposals which have been put forward to deal with this purpose and present some prospects for future developments.