An inhomogeneous universe with thick shells and without cosmological constant

TL;DR

This paper constructs an exact inhomogeneous universe model with thick shells and variable clock rates, demonstrating how it can mimic accelerated expansion without a cosmological constant, aligning with observational data.

Contribution

It introduces a novel inhomogeneous universe model with thick shells and non-uniform time flow, providing an alternative explanation for cosmic acceleration.

Findings

A non-uniform Hubble flow can produce a negative deceleration parameter.

The model fits WMAP data without requiring a cosmological constant.

Both uniform time and Hubble flow yield positive deceleration parameters.

Abstract

We build an exact inhomogeneous universe composed of a central flat Friedmann zone up to a small redshift $z_1$, a thick shell made of anisotropic matter, an hyperbolic Friedmann metric up to the scale where dimming galaxies are observed ($z\simeq 1.7$) that can be matched to a hyperbolic Lema\^{i}tre-Tolman-Bondi spacetime to best fit the WMAP data at early epochs. We construct a general framework which permits us to consider a non-uniform clock rate for the universe. As a result, both for a uniform time and a uniform Hubble flow, the deceleration parameter extrapolated by the central observer is always positive. Nevertheless, by taking a non-uniform Hubble flow, it is possible to obtain a negative central deceleration parameter, that, with certain parameter choices, can be made the one observed currently. Finally, it is conjectured a possible physical mechanism to justify a non-uniform time flow.