J. Brian Pitts (Cambridge): Real Change Happens in Hamiltonian General Relativity

Speaker: J. Brian Pitts (Cambridge)

Time: 5:15pm – 6:45pm

Title: Real Change Happens in Hamiltonian General Relativity

Abstract: In General Relativity in Hamiltonian form; change has seemed to be missing; because the Hamiltonian is a sum of first-class constraints and thus supposedly generates gauge transformations. The gauge generator; a specially _tuned sum_ of first-class constraints; facilitates seeing that a solitary first-class constraint generates not a gauge transformation; but a bad physical change in electromagnetism or General Relativity; spoiling the constraints; Gauss’s law or the Gauss-Codazzi relations; in terms of the physically relevant velocities. Insistence on Hamiltonian-Lagrangian equivalence holds the key; including a reformed Bergmann-inspired notion of observables. Taking objective change to be ineliminable time dependence; there is change in GR without matter just in case there is no time-like Killing vector. The Hamiltonian formalism agrees.