Dynamical frames in gravity: observables, locality and covariance

Abstract: The notion of locality seems a priori in conflict with the gauge symmetries of gravitational theories -- i.e. a group of diffeomorphisms --, which move spacetime points around. A means of addressing this issue is to invoke dynamical reference frames, which provide field-dependent coordinatizations of spacetime. In this talk, I will describe a completely general framework for constructing such dynamical frames and their associated relational observables in generally covariant theories. These observables describe the remaining degrees of freedom in a gauge-invariant manner relative to the frame and give rise to a relational notion of locality, based on the relationships between fields. Our framework unifies previous approaches and naturally comes with the notion of relational atlases and dynamical frame transformations that permit us to change between arbitrary relational frame perspectives. This can be viewed as establishing a genuinely relational -- and thus arguably more physical -- update of the usual notion of general covariance. I will then comment on how dynamical frames can be used to establish microcausality for gravitational observables and to define subsystems (i.e. subregions) in a gauge-invariant manner.