The Dark Side of a Patchwork Universe

TL;DR

This paper explores how loop quantum gravity's discrete space structure could provide a quantum explanation for dark energy, potentially solving the cosmological constant problem and guiding future observational tests.

Contribution

It investigates the potential role of loop quantum gravity in explaining dark energy through its quantum geometry effects and proposes tests to validate this hypothesis.

Findings

Loop quantum gravity may produce effects consistent with dark energy.

Discrete space structure influences matter Hamiltonians relevant to cosmology.

Proposes observational tests for quantum gravity effects on dark energy.

Abstract

While observational cosmology has recently progressed fast, it revealed a serious dilemma called dark energy: an unknown source of exotic energy with negative pressure driving a current accelerating phase of the universe. All attempts so far to find a convincing theoretical explanation have failed, so that one of the last hopes is the yet to be developed quantum theory of gravity. In this article, loop quantum gravity is considered as a candidate, with an emphasis on properties which might play a role for the dark energy problem. Its basic feature is the discrete structure of space, often associated with quantum theories of gravity on general grounds. This gives rise to well-defined matter Hamiltonian operators and thus sheds light on conceptual questions related to the cosmological constant problem. It also implies typical quantum geometry effects which, from a more phenomenological point of view, may result in dark energy. In particular the latter scenario allows several non-trivial tests which can be made more precise by detailed observations in combination with a quantitative study of numerical quantum gravity. If the speculative possibility of a loop quantum gravitational origin of dark energy turns out to be realized, a program as outlined here will help to hammer out our ideas for a quantum theory of gravity, and at the same time allow predictions for the distant future of our universe.