centra

Abstract: The Weiss variational principle in mechanics and classical field theory is a variational principle which includes explicit displacements of the boundary. In this talk, I review the Weiss variation in mechanics, in classical field theory, and for the gravitational action. The Weiss variation is useful because it can be used to efficiently obtain expressions for the Hamiltonian and conjugate momenta for fields without performing an explicit 3+1 decomposition in the bulk spacetime. I demonstrate this explicitly for an action used to obtain the almost-Killing equation. I also briefly discuss how the Weiss variation can be used to formally derive the Wheeler-DeWitt equation from the functional integral for quantum GR.