Loops rescue the no-boundary proposal

TL;DR

This paper demonstrates that loop quantum cosmology's off-shell instantons induce a signature change that resolves issues in the semiclassical path integral, thereby rescuing the no-boundary proposal.

Contribution

It reveals how loop quantum cosmology naturally addresses problems in quantum gravity path integrals, specifically supporting the no-boundary proposal.

Findings

Signature change from off-shell instantons resolves path integral issues.

Loop quantum cosmology supports smooth initial conditions.

Rescue of the no-boundary proposal through quantum geometric effects.

Abstract

New and non-trivial properties of off-shell instantons in loop quantum cosmology show that dynamical signature change naturally cures recently observed problems in the semiclassical path integral of quantum gravity. If left unsolved, these problems would doom any theory of smooth initial conditions of the universe. The no-boundary proposal, as a specific example of such a theory, is rescued by loops, presenting a rare instance of a fruitful confluence of different approaches to quantum cosmology.