# Quantum gravity from general relativity

## TL;DR

This paper discusses the challenge of developing a quantum theory of gravity, exploring three approaches—semi-classical gravity, causal set theory, and loop quantum gravity—to understand how quantum effects could alter the nature of spacetime.

## Contribution

It provides an overview of the problem of spacetime in quantum gravity and analyzes three different approaches from the perspective of general relativity.

## Key findings

- Semi-classical gravity highlights limitations in merging quantum mechanics with general relativity.
- Causal set theory proposes a discrete structure of spacetime at the quantum level.
- Loop quantum gravity suggests a quantized structure of spacetime, potentially resolving singularities.

## Abstract

Although general relativity is a predictively successful theory, it treats matter as classical rather than as quantum. For this reason, it will have to be replaced by a more fundamental quantum theory of gravity. Attempts to formulate a quantum theory of gravity suggest that such a theory may have radical consequences for the nature, and indeed the fate, of spacetime. The present article articulates what this problem of spacetime is and traces it through three approaches to quantum gravity taking general relativity as their vantage point: semi-classical gravity, causal set theory, and loop quantum gravity.