Quantum Gravity in the Sky: Interplay between fundamental theory and observations

TL;DR

This paper explores how quantum gravity influences early universe conditions, proposing principles linking Planck-scale physics to observable cosmic microwave background features, notably a better fit to PLANCK data at large scales.

Contribution

It introduces two principles connecting quantum geometry and uncertainties at the Planck epoch with late-time cosmological observations, predicting specific large-scale power suppression.

Findings

Predicted temperature correlations match standard inflation at small scales.

Identifies a specific power suppression at large angular scales.

Provides a better fit to PLANCK data than standard inflation.

Abstract

Observational missions have provided us with a reliable model of the evolution of the universe starting from the last scattering surface all the way to future infinity. Furthermore given a specific model of inflation, using quantum field theory on curved space-times this history can be pushed \emph{back in time} to the epoch when space-time curvature was some $10^{62}$ times that at the horizon of a solar mass black hole! However, to extend the history further back to the Planck regime requires input from quantum gravity. An important aspect of this input is the choice of the background quantum geometry and of the Heisenberg state of cosmological perturbations thereon, motivated by Planck scale physics. This paper introduces first steps in that direction. Specifically we propose two principles that link quantum geometry and Heisenberg uncertainties in the Planck epoch with late time physics and explore in detail the observational consequences of the initial conditions they select. We find that the predicted temperature-temperature (T-T) correlations for scalar modes are indistinguishable from standard inflation at small angular scales even though the initial conditions are now set in the deep Planck regime. However, \emph{there is a specific power suppression at large angular scales}. As a result, the predicted spectrum provides a better fit to the PLANCK mission data than standard inflation, where the initial conditions are set in the general relativity regime. Thus, our proposal brings out a deep interplay between the ultraviolet and the infrared. Finally, the proposal also leads to specific predictions for power suppression at large angular scales also for the (T-E and E-E) correlations involving electric polarization. The PLANCK team is expected to release this data in the coming year.