Quantum Gravity, or The Art of Building Spacetime

TL;DR

This paper discusses how four-dimensional spacetime can emerge from a background-independent quantum gravity approach called Causal Dynamical Triangulations, supported by computer simulations showing universe-like behavior.

Contribution

It demonstrates that a macroscopic four-dimensional universe can arise dynamically from Causal Dynamical Triangulations without imposing the effective action by hand.

Findings

Emergence of a universe with scale factor dynamics similar to quantum cosmology models

Effective action for the scale factor derived from quantum theory, not assumed

Simulation results support the viability of the approach for quantum gravity

Abstract

The method of four-dimensional Causal Dynamical Triangulations provides a background-independent definition of the sum over geometries in quantum gravity, in the presence of a positive cosmological constant. We present the evidence accumulated to date that a macroscopic four-dimensional world can emerge from this theory dynamically. Using computer simulations we observe in the Euclidean sector a universe whose scale factor exhibits the same dynamics as that of the simplest mini-superspace models in quantum cosmology, with the distinction that in the case of causal dynamical triangulations the effective action for the scale factor is not put in by hand but obtained by integrating out {\it in the quantum theory} the full set of dynamical degrees of freedom except for the scale factor itself.