Testing loop quantum cosmology

TL;DR

Loop quantum cosmology suggests quantum gravity effects replace the big bang with a bounce and modify primordial perturbations, offering potential observational tests and raising open theoretical questions.

Contribution

This review summarizes key predictions of loop quantum cosmology, including the cosmic bounce and perturbation modifications, and discusses unresolved issues in the field.

Findings

Quantum bounce replaces big bang singularity.

Primordial perturbations are modified at large scales.

Potential observational signatures of loop quantum cosmology.

Abstract

Loop quantum cosmology predicts that quantum gravity effects resolve the big-bang singularity and replace it by a cosmic bounce. Furthermore, loop quantum cosmology can also modify the form of primordial cosmological perturbations, for example by reducing power at large scales in inflationary models or by suppressing the tensor-to-scalar ratio in the matter bounce scenario; these two effects are potential observational tests for loop quantum cosmology. In this article, I review these predictions and others, and also briefly discuss three open problems in loop quantum cosmology: its relation to loop quantum gravity, the trans-Planckian problem, and a possible transition from a Lorentzian to a Euclidean space-time around the bounce point.