I agree things like the slit experiments are easily explained by classical waves, and thus seem to point to particles being waves; and I see no inherent reason to bring up probability distributions and such to answer that observation.
Where I'm struggling is that classical waves will always spread out spherically, and their energy must do so too. The issue here being that if a photon is a minimal quanta of energy, but is just a classical wave, what prevents it from spreading out and having sub-photon energy? Or if indeed it does, how does that sub-photon quantity get measured? -- if these experiments claim to be emitting a time-series of single photons, classical wave interference won't occur (again, being separated in time).
> The issue here being that if a photon is a minimal quanta of energy, but is just a classical wave, what prevents it from spreading out and having sub-photon energy? Or if indeed it does, how does that sub-photon quantity get measured? -- if these experiments claim to be emitting a time-series of single photons, classical wave interference won't occur (again, being separated in time).
Right, so that part is new and "spooky" - quantum phenomena are quantised (hence the name). The photon does spread out as a wave, there is in a sense half a photon heading towards the top half of the screen and half a photon heading towards the bottom half of the screen - but then when it hits the screen what we see is a single whole photon that hits either the top half or the bottom half (or, perhaps, half of an us sees a photon hit the top half and half of an us sees a photon hit the bottom half). This is the "wave-particle duality" and while it does fall out of the equations, it's definitely unfamiliar compared to classical physics.
If you want to fully understand, all I can suggest is "work your way through a QM textbook" - every popular explanation I've seen has messed it up one way or another. But it sounds like you're understanding correctly, and thinking for yourself as well - you've hit upon the actual essence of it, the kernel that really is hard.
I don't know how fringe this is, but Huygens Optics gives a possible answer here: https://www.youtube.com/watch?v=tMP5Pbx8I4s. TL;DW: if you assume certain non-linear properties of vacuum as a medium, it seems possible for light (EM waves) to self-contain spatially instead of spreading out, and such trapped energy seems, for all intents and purposes, to behave like particles.
Again, IANAPhysicist, so I don't know what to think of that video, but the channel seems legit, and the explanation is beautiful in its simplicity.
Where I'm struggling is that classical waves will always spread out spherically, and their energy must do so too. The issue here being that if a photon is a minimal quanta of energy, but is just a classical wave, what prevents it from spreading out and having sub-photon energy? Or if indeed it does, how does that sub-photon quantity get measured? -- if these experiments claim to be emitting a time-series of single photons, classical wave interference won't occur (again, being separated in time).