# Setting the physical scale of dimensional reduction in causal dynamical triangulations

## TL;DR

This paper investigates the physical scales at which spacetime dimension reduces in causal dynamical triangulations, finding that the spectral dimension drops from 4 to near 2 around 10 Planck lengths.

## Contribution

The authors develop a method to determine the physical scale of dimensional reduction in causal dynamical triangulations using Planck and de Sitter units.

## Key findings

- Dimensional reduction occurs around 10 Planck lengths.
- The spectral dimension decreases from 4 to near 2 at small scales.
- The method links the reduction scale to physical units.

## Abstract

Within the causal dynamical triangulations approach to the quantization of gravity, striking evidence has emerged for the dynamical reduction of spacetime dimension on sufficiently small scales. Specifically, the spectral dimension decreases from the topological value of 4 towards a value near 2 as the scale being probed decreases. The physical scales over which this dimensional reduction occurs have not previously been ascertained. We present and implement a method to determine these scales in units of either the Planck length or the quantum spacetime geometry's effective de Sitter length. We find that dynamical reduction of the spectral dimension occurs over physical scales of the order of 10 Planck lengths, which, for the numerical simulation considered below, corresponds to the order of 1/10 de Sitter lengths.