Semiclassical Universe from First Principles

TL;DR

This paper demonstrates that in four-dimensional Causal Dynamical Triangulations, the emergent macroscopic universe behaves as a semiclassical bounce, with a well-defined ground state wave function depending on the global scale factor.

Contribution

It provides a first-principles derivation of a semiclassical bouncing universe within nonperturbative quantum gravity using Causal Dynamical Triangulations.

Findings

Emergence of a four-dimensional bounce in CDT

Ground state wave function as a function of scale factor

Semiclassical equation satisfied by the macroscopic universe

Abstract

Causal Dynamical Triangulations in four dimensions provide a background-independent definition of the sum over space-time geometries in nonperturbative quantum gravity. We show that the macroscopic four-dimensional world which emerges in the Euclidean sector of this theory is a bounce which satisfies a semiclassical equation. After integrating out all degrees of freedom except for a global scale factor, we obtain the ground state wave function of the universe as a function of this scale factor.