Departures from the FLRW Cosmological Model in an Inhomogeneous Universe: A Numerical Examination

TL;DR

This paper presents the first fully relativistic, non-linear numerical study of an inhomogeneous universe's expansion, revealing deviations from the standard FLRW model due to local inhomogeneities.

Contribution

It introduces a novel numerical relativity approach to cosmology that captures non-linear inhomogeneities without symmetry assumptions.

Findings

Universe exhibits average FLRW behavior

Locally inhomogeneous expansion exceeds linear perturbation predictions

Demonstrates importance of non-linear effects in cosmological modeling

Abstract

While the use of numerical general relativity for modeling astrophysical phenomena and compact objects is commonplace, the application to cosmological scenarios is only just beginning. Here, we examine the expansion of a spacetime using the Baumgarte-Shapiro-Shibata-Nakamura (BSSN) formalism of numerical relativity in synchronous gauge. This work represents the first numerical cosmological study that is fully relativistic, non-linear and without symmetry. The universe that emerges exhibits an average Friedmann-Lema\"itre-Robertston-Walker (FLRW) behavior, however this universe also exhibits locally inhomogeneous expansion beyond that expected in linear perturbation theory around a FLRW background.