# Distortions of Robertson-Walker metric in perturbative cosmology and interpretation as dark matter and cosmological constant

## TL;DR

This paper explores how relativistic distortions in the universe's metric, caused by matter inhomogeneities, can influence interpretations of dark matter and dark energy, suggesting the actual dark matter content may be overestimated.

## Contribution

It introduces a novel perspective on cosmological distortions, proposing that inhomogeneities can account for effects attributed to dark matter and dark energy.

## Key findings

- Distortions depend on past matter distribution, not current.
- Expansion rate perturbations are significant despite small inhomogeneities.
- Dark matter estimates may be overestimated due to relativistic effects.

## Abstract

In the last years, we saw more and more attempts to explain dark matter as a general relativistic effect, at least for some fraction. Following this philosophy, we considered the gravitational distortions due to the inhomogeneous distribution of matter in the universe, which we know from general relativity to be retarded distortions. This provides a magnification effect, since the distortions we feel now depend not on the present matter density, but on the past one, which is greater. The expansion rate of the universe is perturbed as well, in a not negligible way, despite matter inhomogeneities are small, because of the same magnification effect. The deceleration parameter, which is a way to evaluate the quantity of dark matter in the universe, is perturbed in turn, so that the real amount of dark matter is less than what is usually believed.