An Introduction to Loop Quantum Gravity Through Cosmology

TL;DR

This paper introduces loop quantum gravity through cosmological models, illustrating how quantum effects near singularities can be understood and how classical physics emerges at larger scales.

Contribution

It provides an accessible overview of loop quantum cosmology, demonstrating key features like emergent time and quantum geometry effects in a simplified setting.

Findings

Quantum geometry effects can resolve classical singularities.

Emergent time can be constructed in loop quantum cosmology.

Classical general relativity is recovered at low curvature regimes.

Abstract

This introductory review is addressed to beginning researchers. Some of the distinguishing features of loop quantum gravity are illustrated through loop quantum cosmology of FRW models. In particular, these examples illustrate: i) how `emergent time' can arise; ii) how the technical issue of solving the Hamiltonian constraint and constructing the \emph{physical} sector of the theory can be handled; iii) how questions central to the Planck scale physics can be answered using such a framework; and, iv) how quantum geometry effects can dramatically change physics near singularities and yet naturally turn themselves off and reproduce classical general relativity when space-time curvature is significantly weaker than the Planck scale.