The Emergence of Spacetime, or, Quantum Gravity on Your Desktop

TL;DR

This paper discusses Causal Dynamical Triangulations as a simple, geometric, nonperturbative approach to quantum gravity that produces emergent classical spacetime and evidence of fractal spacetime foam.

Contribution

It introduces a nonperturbative quantum gravity framework based on Causal Dynamical Triangulations that yields emergent classical spacetime and concrete numerical results.

Findings

Emergence of classical spacetime from quantum geometries

Evidence of fractal spacetime foam at Planck scales

A computational scheme for quantum gravity simulations

Abstract

Is there an approach to quantum gravity which is conceptually simple, relies on very few fundamental physical principles and ingredients, emphasizes geometric (as opposed to algebraic) properties, comes with a definite numerical approximation scheme, and produces robust results, which go beyond showing mere internal consistency of the formalism? The answer is a resounding yes: it is the attempt to construct a nonperturbative theory of quantum gravity, valid on all scales, with the technique of so-called Causal Dynamical Triangulations. Despite its conceptual simplicity, the results obtained up to now are far from trivial. Most remarkable at this stage is perhaps the fully dynamical emergence of a classical background (and solution to the Einstein equations) from a nonperturbative sum over geometries, without putting in any preferred geometric background at the outset. In addition, there is concrete evidence for the presence of a fractal spacetime foam on Planckian distance scales. The availability of a computational framework provides built-in reality checks of the approach, whose importance can hardly be overestimated.