Gravity, Geometry and the Quantum

TL;DR

This paper summarizes quantum Riemannian geometry in loop quantum gravity and demonstrates how it replaces the big bang with a quantum bounce, providing a deterministic evolution through the quantum bridge.

Contribution

It introduces the application of quantum geometry to cosmology, showing the replacement of the big bang singularity with a quantum bounce and a deterministic pre- and post-big-bang evolution.

Findings

Quantum geometry replaces the big bang with a big bounce.

Evolution is deterministic across the quantum bridge.

Pre-big-bang branch connects to current universe via quantum bridge.

Abstract

After a brief introduction, basic ideas of the quantum Riemannian geometry underlying loop quantum gravity are summarized. To illustrate physical ramifications of quantum geometry, the framework is then applied to homogeneous isotropic cosmology. Quantum geometry effects are shown to replace the big bang by a big bounce. Thus, quantum physics does not stop at the big-bang singularity. Rather there is a pre-big-bang branch joined to the current post-big-bang branch by a `quantum bridge'. Furthermore, thanks to the background independence of loop quantum gravity, evolution is deterministic across the bridge.