Causal Dynamical Triangulations and the Quest for Quantum Gravity

TL;DR

Causal Dynamical Triangulations offers a promising nonperturbative approach to quantum gravity, capable of generating a classical universe dynamically and enabling detailed analysis of spacetime at quantum scales.

Contribution

This paper reviews how Causal Dynamical Triangulations provides a nonperturbative, numerically accessible framework for quantum gravity, demonstrating the emergence of classical spacetime from quantum fluctuations.

Findings

Classical universe can be generated dynamically from quantum fluctuations.

The approach allows explicit evaluation of spacetime invariants.

Insights into which aspects of spacetime are fixed or emergent.

Abstract

Quantum Gravity by Causal Dynamical Triangulation has over the last few years emerged as a serious contender for a nonperturbative description of the theory. It is a nonperturbative implementation of the sum-over-histories, which relies on few ingredients and initial assumptions, has few free parameters and - crucially - is amenable to numerical simulations. It is the only approach to have demonstrated that a classical universe can be generated dynamically from Planckian quantum fluctuations. At the same time, it allows for the explicit evaluation of expectation values of invariants characterizing the highly nonclassical, short-distance behaviour of spacetime. As an added bonus, we have learned important lessons on which aspects of spacetime need to be fixed a priori as part of the background structure and which can be expected to emerge dynamically.