Quantum gravity, information theory and the CMB

TL;DR

This paper explores the deep connections between quantum field fluctuations, spacetime geometry, and the cosmic microwave background, highlighting how information theory and spectral data could reveal fundamental aspects of quantum gravity.

Contribution

It introduces the idea that spacetime metrics can be derived from quantum fluctuation correlators and discusses the potential observational signatures in the CMB related to quantum gravity effects.

Findings

Spacetime metric can be expressed via quantum field correlators.

Spectra of quantum fluctuations may determine spacetime geometry.

Ultraviolet cutoff effects could be observable in the CMB.

Abstract

We review connections between the metric of spacetime and the quantum fluctuations of fields. In particular, we discuss the finding that the spacetime metric can be expressed entirely in terms of the 2-point correlators of the fluctuations of quantum fields. We also discuss the open question whether the knowledge of only the spectra of the quantum fluctuations of fields suffices to determine the spacetime metric. This question is of interest because spectra are geometric invariants and their quantization would, therefore, have the benefit of not requiring the modding out of the diffeomorphism group. Further, we discuss the fact that spacetime at the Planck scale need not necessarily be either discrete or continuous. Instead, results from information theory show that spacetime may be simultaneously discrete and continuous in the same way that information can. Finally, we review the finding that a covariant natural ultraviolet cutoff at the Planck scale implies a signature in the cosmic microwave background (CMB) that may become observable.