The Nonperturbative Quantum de Sitter Universe

TL;DR

This paper demonstrates how a macroscopic de Sitter universe can emerge from quantum gravity using Causal Dynamical Triangulations, providing insights into the quantum origins of our universe and its effective dynamics.

Contribution

It shows the nonperturbative emergence of a de Sitter universe from quantum gravity without fine-tuning, using Monte Carlo simulations to reconstruct the effective action.

Findings

Emergence of a macroscopic de Sitter universe from quantum fluctuations.

Reconstruction of the effective gravitational action from Monte Carlo data.

Evidence for probing sub-Planckian regimes in quantum gravity.

Abstract

The dynamical generation of a four-dimensional classical universe from nothing but fundamental quantum excitations at the Planck scale is a long-standing challenge to theoretical physicists. A candidate theory of quantum gravity which achieves this goal without invoking exotic ingredients or excessive fine-tuning is based on the nonperturbative and background-independent technique of Causal Dynamical Triangulations. We demonstrate in detail how in this approach a macroscopic de Sitter universe, accompanied by small quantum fluctuations, emerges from the full gravitational path integral, and how the effective action determining its dynamics can be reconstructed uniquely from Monte Carlo data. We also provide evidence that it may be possible to penetrate to the sub-Planckian regime, where the Planck length is large compared to the lattice spacing of the underlying regularization of geometry.