Gauge Gravity: a forward-looking introduction

TL;DR

This paper reviews gauge theory approaches to gravity, exploring their pedagogical foundations, new solutions, and implications for quantum tunneling and the Hartle-Hawking proposal.

Contribution

It introduces a gauge-theoretic perspective on gravity, highlighting new solutions and quantum phenomena inspired by symmetry breaking and topological structures.

Findings

Gravity can be viewed as a broken phase of an (A)dS gauge theory.

Infinite class of solutions as degenerate ground states.

Quantum tunneling between degenerate vacua relates to the no boundary proposal.

Abstract

This article is a review of modern approaches to gravity that treat the gravitational interaction as a type of gauge theory. The purpose of the article is twofold. First, it is written in a colloquial style and is intended to be a pedagogical introduction to the gauge approach to gravity. I begin with a review of the Einstein-Cartan formulation of gravity, move on to the Macdowell-Mansouri approach, then show how gravity can be viewed as the symmetry broken phase of an (A)dS-gauge theory. This covers roughly the first half of the article. Armed with these tools, the remainder of the article is geared toward new insights and new lines of research that can be gained by viewing gravity from this perspective. Drawing from familiar concepts from the symmetry broken gauge theories of the standard model, we show how the topological structure of the gauge group allows for an infinite class of new solutions to the Einstein-Cartan field equations that can be thought of as degenerate ground states of the theory. We argue that quantum mechanical tunneling allows for transitions between the degenerate vacua. Generalizing the tunneling process from a topological phase of the gauge theory to an arbitrary geometry leads to a modern reformulation of the Hartle-Hawking "no boundary" proposal.