A 2D model of Causal Set Quantum Gravity: The emergence of the continuum

TL;DR

This paper demonstrates that a 2D causal set quantum gravity model naturally favors configurations resembling 2D Minkowski space at large scales, addressing the entropy problem and supporting the emergence of classical spacetime geometry.

Contribution

It introduces a 2D causal set quantum gravity model showing the dominance of physically reasonable spacetimes in the continuum limit, overcoming the entropy problem.

Findings

Partition function dominated by causal sets approximating 2D Minkowski space

Model overcomes the entropy problem in quantum gravity

Predicts emergence of classical geometry from quantum causal sets

Abstract

Non-perturbative theories of quantum gravity inevitably include configurations that fail to resemble physically reasonable spacetimes at large scales. Often, these configurations are entropically dominant and pose an obstacle to obtaining the desired classical limit. We examine this "entropy problem" in a model of causal set quantum gravity corresponding to a discretisation of 2D spacetimes. Using results from the theory of partial orders we show that, in the large volume or continuum limit, its partition function is dominated by causal sets which approximate to a region of 2D Minkowski space. This model of causal set quantum gravity thus overcomes the entropy problem and predicts the emergence of a physically reasonable geometry.