Can one observe quantum-gravitational effects in the cosmic microwave background?

TL;DR

This paper investigates potential quantum-gravitational effects on the cosmic microwave background anisotropy spectrum within canonical quantum gravity, providing bounds on inflation energy scale but finding effects too weak to observe.

Contribution

It calculates quantum-gravitational contributions to the CMB spectrum from a semiclassical Wheeler-DeWitt approach, offering new bounds on inflation energy scale.

Findings

Quantum-gravitational effects are too weak to detect in the CMB spectrum.

An upper bound on the inflation energy scale is established.

No observable modifications to the power spectrum at large scales.

Abstract

In order to find the correct theory of quantum gravity, one has to look for observational effects in any candidate theory. Here, we focus on canonical quantum gravity and calculate the quantum-gravitational contributions to the anisotropy spectrum of the cosmic microwave background that arise from a semiclassical approximation to the Wheeler-DeWitt equation. While the resulting modification of the power spectrum at large scales is too weak to be observable, we find an upper bound on the energy scale of inflation.