  The question is discussed whether the momentum of a photon has a quantum
uncertainty or whether it is a classical quantity. The latter assumption is the
main characteristic of reducible Quantum Electrodynamics (rQED). Recent
experiments in Quantum Optics may resolve the question. The non-classical
correlation of quantum noise in color-entangled beams cannot be explained by
rQED without modification of the standing explanation. On the other hand, rQED
explains uncertainty of the momentum of a single photon when it is entangled
with a quantum spin residing in its environment. The explanation of the
historical experiment with equally-polarized pairs of photons, showing
violation of the Bell inequalities, invokes the argument of collapse of the
wave function, also in rQED.
