Comment about quasi-isotropic solution of Einstein equations near cosmological singularity

TL;DR

This paper extends the quasi-isotropic solution of Einstein's equations near cosmological singularity to include arbitrary hydrodynamical matter, showing that such solutions always exist with more complex term dependencies.

Contribution

It generalizes the Lifshitz-Khalatnikov solution to arbitrary matter content, broadening understanding of cosmological singularities.

Findings

Quasi-isotropic solutions exist for arbitrary hydrodynamical matter.

The dependence of expansion terms becomes more complex.

The solution's existence is confirmed beyond radiation-dominated cases.

Abstract

We generalize for the case of arbitrary hydrodynamical matter the quasi-isotropic solution of Einstein equations near cosmological singularity, found by Lifshitz and Khalatnikov in 1960 for the case of radiation-dominated universe. It is shown that this solution always exists, but dependence of terms in the quasi-isotropic expansion acquires a more complicated form.