Some conceptual issues in loop quantum cosmology

Understand

Loop quantum gravity is a mature theory.

• To proceed to explicit calculations in cosmology, it is necessary to make assumptions and simplifications based on the symmetries of the cosmological setting.
• Symmetry reduction is especially critical when dealing with cosmological perturbations.
• The present article reviews several approaches to the problem of building a consistent formalism that describes the dynamics of perturbations on a quantum spacetime and tries to address their respective strengths and weaknesses.