Coordinate time dependence in Quantum Gravity

TL;DR

This paper introduces a method to incorporate classical coordinate time into quantum gravity, enabling the study of semiclassical limits and showing good agreement between quantum and effective classical descriptions in loop cosmology.

Contribution

It develops a technique using group averaging to embed coordinate time into quantum gravity, facilitating the analysis of semiclassical emergence from quantum evolution.

Findings

Semiclassical effective equations align well with quantum results at small scales.

The method aids in understanding the transition from quantum to classical cosmology.

Implications for inflation and bounce scenarios are supported by the results.

Abstract

The intuitive classical space-time picture breaks down in quantum gravity, which makes a comparison and the development of semiclassical techniques quite complicated. Using ingredients of the group averaging method to solve constraints one can nevertheless introduce a classical coordinate time into the quantum theory, and use it to investigate the way a semiclassical continuous description emerges from discrete quantum evolution. Applying this technique to test effective classical equations of loop cosmology and their implications for inflation and bounces, we show that the effective semiclassical theory is in good agreement with the quantum description even at short scales.