Observables beyond scattering in quantum gravity

Determine whether quantum gravity admits gauge‑invariant observables beyond S‑matrix scattering amplitudes and, if so, explicitly construct relational observables that can be consistently defined without a fixed background.

Background

In the first panel, participants debated whether the quantum field theory framework is sufficient for quantum gravity and, crucially, what counts as an observable. While several panelists argued that scattering amplitudes may be the only well-defined observables, others emphasized relational observables as necessary in a background-independent context.

This led to the explicit recognition of a gap: the community lacks consensus and concrete constructions for observables beyond scattering amplitudes, especially in relational formulations compatible with diffeomorphism invariance.