Planckian Birth of the Quantum de Sitter Universe

TL;DR

This paper demonstrates that a quantum universe modeled via causal dynamical triangulations closely resembles a four-dimensional de Sitter spacetime, with quantum fluctuations remaining semiclassical at Planckian scales.

Contribution

It provides numerical evidence that nonperturbative quantum gravity can produce a universe with de Sitter geometry emerging from Lorentzian sum-over-geometries.

Findings

Quantum universes are approximately de Sitter in four dimensions.

The size of these universes is between 17 and 28 Planck lengths.

Quantum fluctuations are well-described semiclassically.

Abstract

We show that the quantum universe emerging from a nonperturbative, Lorentzian sum-over-geometries can be described with high accuracy by a four-dimensional de Sitter spacetime. By a scaling analysis involving Newton's constant, we establish that the linear size of the quantum universes under study is in between 17 and 28 Planck lengths. Somewhat surprisingly, the measured quantum fluctuations around the de Sitter universe in this regime are to good approximation still describable semiclassically. The numerical evidence presented comes from a regularization of quantum gravity in terms of causal dynamical triangulations.