Mass Gap Revisited
Anyway, Carl has also been bugging me a bit about Hamiltonians. Honestly, I wish we could move beyond 19th century physics, but perhaps it is useful to think about what a Hamiltonian operator should be from a categorical viewpoint. To begin with, Vicary's paper is a must read, defining the harmonic oscillator entirely in categorical terms.
Let us say that a Hamiltonian is any operator sitting in an eigenvalue equation for states associated with mass-energy. Hmmmmm.