# Nonsingular bouncing cosmology from general relativity

## TL;DR

This paper explores a classical nonsingular bouncing cosmology within general relativity by allowing degenerate metrics, proposing models with a spacetime defect replacing the big bang, and deriving observational implications and bounds.

## Contribution

It introduces a novel bouncing cosmology model based on degenerate metrics in general relativity, with observational predictions and bounds on the spacetime defect scale.

## Key findings

- Derived modified Hubble diagrams for luminosity and angular diameter distances.
- Presented a Gedankenexperiment to measure the defect length scale.
- Provided upper bounds on the spacetime defect size.

## Abstract

We investigate a particular type of classical nonsingular bouncing cosmology, which results from general relativity if we allow for degenerate metrics. The simplest model has a matter content with a constant equation-of-state parameter and we get the modified Hubble diagrams for both the luminosity distance and the angular diameter distance. Based on these results, we present a Gedankenexperiment to determine the length scale of the spacetime defect which has replaced the big bang singularity. A possibly more realistic model has an equation-of-state parameter which is different before and after the bounce. This last model also provides an upper bound on the defect length scale.