# Quasi-isotropic cycles and non-singular bounces in a Mixmaster cosmology

## TL;DR

This paper introduces mechanisms in a Mixmaster cosmology that produce non-singular, quasi-isotropic bounces, potentially allowing the universe to undergo endless cycles with some resembling standard cosmological models.

## Contribution

It presents novel methods using non-linear equations of state and negative anisotropic stresses to achieve non-singular, quasi-isotropic bounces in a Mixmaster universe, reducing chaos.

## Key findings

- Non-singular bounces achieved with a non-linear fluid equation of state.
- Negative anisotropic stresses isotropize the universe and suppress chaos.
- The universe can undergo infinite cycles with some being nearly isotropic.

## Abstract

A Bianchi IX Mixmaster spacetime is the most general spatially homogeneous solution of Einstein's equations and it can represent the space-averaged Universe. We introduce two novel mechanisms resulting in a Mixmaster Universe with non-singular bounces which are quasi-isotropic. A fluid with a non-linear equation of state allows non-singular bounces. Using negative anisotropic stresses successfully isotropises this Universe and mitigates the well known Mixmaster chaotic behaviour. Thus the Universe can be an eternal Mixmaster, going through an infinite series of different cycles separated by bounces, with a sizable fraction of cycles isotropic enough to be well approximated by a standard Friedmann-Lema\^itre-Robertson-Walker model from the radiation era onward.