Soft modes and boundary degrees of freedom are closely linked in gauge theory and quantum gravity, with implications for infrared structure, holography, and black hole information. I will present a relational framework in which these features are described using dynamical (quantum) reference frames, illustrated in Maxwell theory.
In this setting, subregional edge modes can be viewed as U(1) reference frames built from the dynamical fields. Certain choices yield a universal extension of the subregional phase space by a gauge-invariant corner Goldstone symplectic pair. The resulting phase space carries physical symmetries localized at the corner, corresponding to frame reorientations, with distinct relational interpretations in terms of cross-boundary data, from the addition of hard or soft radiation to asymptotic large gauge transformations.
In gravity, quantum reference frames provide a natural ultraviolet regularization of entropy, while in gauge theory they yield a well-defined, distillable notion of entanglement. Together, these results offer a unified perspective on questions at the heart of quantum information, quantum geometry, and infrared physics.