I have a quick question: is the modern understanding that "the electromagnetic field itself quantized" OR is it just shorthand for "light emitted specifically by atomic electron orbitals changing is produced in discrete energy levels because the energy levels between orbitals are discrete"?
To me, it always felt like the latter, but I've never seen that written down explicitly, and everyone seems to talk like it's the former. I mean sure, 99.99% of the time experiments that emit or absorb photons are performed using atoms (and hence discrete electron orbitals) but that's certainly not the only way to create or or absorb photons. There's Cherenkov radiation, Bremsstrahlung, etc...
The EM field itself is quantized. You start with the classical electromagnetic field and you try to quantize it. The rules for this are not precise nor formal.
That means something a little different to "photons can only have specific energies" (that applies only to very specific atoms or atoms with certain structure; in many materials, electrons can exist in bands of continuous energy).
To me, it always felt like the latter, but I've never seen that written down explicitly, and everyone seems to talk like it's the former. I mean sure, 99.99% of the time experiments that emit or absorb photons are performed using atoms (and hence discrete electron orbitals) but that's certainly not the only way to create or or absorb photons. There's Cherenkov radiation, Bremsstrahlung, etc...