Snowmass 2021 White Paper: Observational Signatures of Quantum Gravity

TL;DR

This paper reviews recent theoretical insights into how quantum gravity effects at the Planck scale could manifest at large scales, suggesting potential experimental detection methods using interferometry.

Contribution

It introduces a simple physical model, based on random walk intuition, connecting ultraviolet quantum gravity effects to observable infrared phenomena, supported by various formal approaches.

Findings

Quantum gravity effects may accumulate at large scales as L^2 pprox _p L/4a0pi

Random walk intuition aligns with calculations from AdS/CFT and shockwave models

Experimental detection prospects with interferometers are discussed

Abstract

This short review is intended as a colloquium-level summary, for the Snowmass 2021 process, on recent theoretical results on infrared observables in quantum gravity. We rely on simple physical arguments, most notably a random walk intuition, to show how effects of quantum gravity in the ultraviolet (at the Planck length $\ell_p \approx 10^{-35} \mbox{ m}$) may integrate into the infrared when the large measurement length scale $L$ enters into the observable. A quantum uncertainty at lightsheet horizons would give rise to an accumulated effect of size $\delta L^2 \simeq \ell_p L/4 \pi$. We discuss how the random walk intuition falls out from more formal calculations, such as from AdS/CFT, from the dimensional reduction of the Einstein-Hilbert action to dilaton gravity, from multiple gravitational shockwaves generated by vacuum energy fluctuations, as well as from an effective description of gravity as a fluid. We overview experimental prospects for measuring this effect with a simple Michelson interferometer utilizing many of the tools developed for gravitational wave observatories.