  An analysis is given of the local phase space of gravity coupled to matter to
second order in perturbation theory. Working in local regions with boundaries
at finite distance, we identify matter, Coulomb, and additional boundary modes.
The boundary modes take the role of reference frames for both diffeomorphisms
and internal Lorentz rotations. Passing to the quantum level, we identify the
constraints that link the bulk and boundary modes. The constraints take the
form of a multi-fingered Schr\"odinger equation, which determines the
relational evolution of the quantum states in the bulk with respect to the
quantum reference fields at the boundary.
