Johanna Borissova: Suppression of spacetime singularities in quantum gravity

Spacetime singularities as predicted by general relativity signal the breakdown of our classical description of gravity and are expected to be absent in a fundamental theory of quantum gravity. On this basis, we investigate the requirement of suppressing spacetime geometries with a curvature singularity via destructive interference in the Lorentzian gravitational path integral as a constraint on the microscopic action for gravity. Based on simple examples of static spherically symmetric spacetimes, we demonstrate that complete singularity suppression in the path integral stipulates that the action for gravity be of infinite order in the curvature, as for example in asymptotically safe gravity. Accordingly, an effective-field theory perspective on gravity combined with the viewpoint of fundamentally Lorentzian quantum amplitudes may provide a resolution to the problem of spacetime singularities encountered at the classical level.