The CMB in a Causal Set Universe

TL;DR

This paper investigates how causal set theory impacts cosmic microwave background observations, providing new constraints on dark energy fluctuations and showing that the theory alone cannot explain late-time acceleration without major changes to General Relativity.

Contribution

It introduces a method to compute the power spectrum of causal set dark energy fluctuations using overlap volumes of past light cones and derives stronger observational constraints.

Findings

Constraints on the causal set dark energy parameter are improved.

Causal set theory cannot account for late-time acceleration without significant modifications to General Relativity.

The overlap volume method offers a new way to connect quantum gravity theories with cosmological data.

Abstract

We discuss Cosmic Microwave Background constraints on the causal set theory of quantum gravity, which has made testable predictions about the nature of dark energy. We flesh out previously discussed heuristic constraints by showing how the power spectrum of causal set dark energy fluctuations can be found from the overlap volumes of past light cones of points in the universe. Using a modified Boltzmann code we put constraints on the single parameter of the theory that are somewhat stronger than previous ones. We conclude that causal set theory cannot explain late-time acceleration without radical alterations to General Relativity.