Gravity and the Quantum

TL;DR

This paper provides an accessible overview of quantum gravity, focusing on the conceptual development and status of loop quantum gravity as a major research program over the past two decades.

Contribution

It offers a non-technical, broad perspective on quantum gravity, emphasizing the ideas and progress in loop quantum gravity compared to other approaches.

Findings

Loop quantum gravity has made significant conceptual progress.

The paper clarifies foundational issues in quantum gravity.

It highlights the current status and challenges of the loop quantum gravity program.

Abstract

The goal of this article is to present a broad perspective on quantum gravity for \emph{non-experts}. After a historical introduction, key physical problems of quantum gravity are illustrated. While there are a number of interesting and insightful approaches to address these issues, over the past two decades sustained progress has primarily occurred in two programs: string theory and loop quantum gravity. The first program is described in Horowitz's contribution while my article will focus on the second. The emphasis is on underlying ideas, conceptual issues and overall status of the program rather than mathematical details and associated technical subtleties.