**Mainly OT**
It's been a good while since focusing on Schroedinger, but I'll try to address what I see as the source of our significantly differing "perspectives".
<...If the photon is spread over space, what is spread? Momentum? Or what we must say is the spread is composed of spacetime points. It begs the question. If that which is spread over space has angular momentum which is not spin,intrinsic angular momentum, that which is spread must be undergoing angular momentum...>
When QM says a particle is spread out, it's understood to mean that at any given time, there is a non-zero probability of detecting that particle at many places. Now clearly, if we set up many detectors, only one of them will indicate the presence of the particle. As you know, introductory QM 'explains' this as being a "collapse of the wave function".
You extracted and addressed my statement "represented by a pure momentum state, which implies that the photon is uniformly spread over space" from a paragraph which is explicitly from a QED context. Questioning whether 'it' is *momentum* which is spread out - implies to me a misunderstanding of QED. In QED, the angular momentum of a pure momentum state is explicitly *undefined*, where the photon's spin in this state is 1. The spreading or smearing is not a *relativistic* effect - it's *already* evident in Schroedinger. To then wonder whether a photon is particulate or not is the realm of *philosophy*, not the realm of quantum mechanics.
Of course this wondering *might* well yield some interesting "alternate" physics, but QM has already resolved the particle/wave duality, which renders these questions in the context of QED to be irrelevant. The photon in QED is identified with an one particle state of the quantum field which *simultaneously* has BOTH wave and particle properties (remember Flatland?).
Of course you are welcome to disagree with accepted principles of QM, but where does that leave the discussion? No doubt you can confirm this in any basic QM text (check out, for instance, Liboff or Anderson)
But for now, I'll have to beg off and make the SI query "is there a quantum field theorist in the house who can weigh in?"
[BTW, I do appreciate everyone's thorough consideration of the SR technology, to which the above is tangential at best.] |
