# Time reversal symmetry in cosmology and the creation of a universe-antiuniverse pair

## TL;DR

This paper explores how time reversal symmetry in cosmological models could lead to the creation of universe-antiuniverse pairs, potentially explaining the universe's time asymmetry and matter-antimatter imbalance.

## Contribution

It proposes a scenario where symmetric solutions under time reversal can produce universe-antiuniverse pairs, offering a new perspective on cosmological asymmetries.

## Key findings

- Time reversal symmetry can produce symmetric universe-antiuniverse pairs.
- Such pairs could explain matter-antimatter asymmetry.
- The model aligns with a realistic cosmological scenario.

## Abstract

The classical evolution of the universe can be seen as a parametrised worldline of the minisuperspace, with the time variable $t$ the parameter that parametrises the worldline. The time reversal symmetry of the field equations implies that for any positive oriented solution there can be a symmetric negative oriented one that, in terms of the same time variable, represent an expanding and a contracting universe, respectively. However, the choice of the time variable induced by the correct value of the Schr\"odinger equation in the two universes makes that their physical time variables could be reversely related. In that case, the two universes would be both expanding universes from the point of view of their internal inhabitants, who identify matter with the particles that move in their spacetimes and antimatter with the particles that move in the time reversely symmetric universe. If the assumptions considered are consistent with a realistic scenario of our universe, the creation of a universe-antiuniverse pair might explain two main and related problems in cosmology: the time asymmetry and the primordial matter-antimatter asymmetry of our universe.