“…The metric η µν is defined only on spacelike sections t = const, because it enters the Schrödinger equation. The wave function ψ(t, x) is the section of the fiber bundle E R 4 , π E , C, U(1), P with the typical fiber being the complex plane C, which is associated with a certain principal fiber bundle P R 4 , π, U(1) . This principal fiber bundle is always trivial P ≈ R 4 × U(1), because its base is the four-dimensional Euclidean space.…”