Reconstructing the Universe

TL;DR

This paper demonstrates that nonperturbative quantum gravity via causal triangulations can produce a four-dimensional universe with semiclassical dynamics, revealing nonclassical features like dimensional reduction and fractal structures at small scales.

Contribution

It provides evidence that causal dynamical triangulations can reconstruct a four-dimensional universe with realistic large-scale behavior from quantum principles.

Findings

Spacetime dimension is four at large scales.

Universe volume dynamics are semiclassical.

Spacetime reduces to two dimensions at short scales.

Abstract

We provide detailed evidence for the claim that nonperturbative quantum gravity, defined through state sums of causal triangulated geometries, possesses a large-scale limit in which the dimension of spacetime is four and the dynamics of the volume of the universe behaves semiclassically. This is a first step in reconstructing the universe from a dynamical principle at the Planck scale, and at the same time provides a nontrivial consistency check of the method of causal dynamical triangulations. A closer look at the quantum geometry reveals a number of highly nonclassical aspects, including a dynamical reduction of spacetime to two dimensions on short scales and a fractal structure of slices of constant time.