Talk:Quantization of the electromagnetic field

I read the article and have some questions.


 * 1) Why is the assumption made that the k-space waves are in a box? "a consequence of the boundary condition that A has the same value on opposite walls of the box".  I can see that the assumption allows stacking of the boxes.  Thus extending the analysis to all of space.  But it imposes a limit on the lowest value of k.
 * 2) Why are the k-space Fourier coefficients for the magnetic potential chosen to become operators?  Why weren't the E or B Fourier coefficients chosen?
 * 3) What motivated someone (Was it Dirac?) to quantize using this approach?  It's not at all obvious.  Was it a wild ass guess?  What was it guided by?  What was the insight?
 * 4) Under Quantization of EM field it shows commutation rules.  Why impose these rules? Does imposing these rules make a(t) a creation/annihilation operator?  If it does make them creation/annihilation operators, why do that?  — Preceding unsigned comment added by Chgenly (talk • contribs) 20:17, 17 November 2013 (UTC)

Thanks. chgenly — Preceding unsigned comment added by Chgenly (talk • contribs) 20:13, 17 November 2013 (UTC)

$$\vec{k}$$ runs over the "half space" only?
In the second section "Electromagnetic field and vectorpotential" it is stated in the expansion of the vectorpotential A into Fourier-components, that "[...] $$\vec{k}$$ runs over one side, positive or negative. (The component of Fourier basis $$ \exp(-i \vec{k} \vec{r}) $$ is complex conjugate of component of $$ \exp(i \vec{k} \vec{r}) $$ as $$ A(\vec{r}, \vec{t}) $$ is real.)"

In section 7 "Photon Momentum" however it is said that "The term $$ 1/2 $$ could be dropped, because when one sums over the allowed $$ \vec{k} $$, $$ \vec{k} $$ cancels with $$ -\vec{k} $$." If I see it correctly, one also needs "both sides" of $$ \vec{k} $$-space, in order to derive the second formula in this section from the first in this section.

So how do these two statements relate? Is it my misunderstanding? What is the error here?

After further thoughts and computations it seems to me, that the first quoted sentence is conceptually wrong here. Can you really talk about the "reality" of a quantum physical "field"? If I take the full $$ \vec{k} $$-space into the sum for my vector-potential, neglect the "$$ 2 $$" in the square roots in the conversion from the classic amplitudes to the operators and symmetrically quantize the absolute values in the expression for the energy-Hamiltonian, then I can obtain the same result, as stated in the original article. But also I can show the expression for the momentum [using $$ \hat{a}^{\dagger (\mu)} (\vec{k}) = - \hat{a}^{(\mu)} (- \vec{k}) $$; here the minus originates from the choice of the "phase" in front of the basis vectors for the circular polarization].

I didn't notice any mention that QED is still not mathematically well-defined! David edwards (talk) 12:00, 1 April 2018 (UTC)David edwards

Secondary spin quantum number of the photon is only +/- 1??
It's written in the opening the the z-component of the spin is either -1 or +1, but afaik it can also be 0.. is that a mistake? נועם ימיני (talk) 20:57, 3 May 2020 (UTC)

What is being quantized electromagnetic radiation or the electromagnetic field
Many seem to think the classical electromagnetic field and electromagnetic radiation are the same thing. This of course is completely false attraction per coulombs law is part of the classical electromagnetic field there is no need for photons for real attraction between moving charges to occur. Only electromagnetic radiation has been shown to be quantized. Bill field pulse (talk) 17:07, 18 January 2024 (UTC)


 * Early physicists may understandably have confused the two but a non quantized continuous single physical electromagnetic field exists between electrons and protons. Photons are only produce when energy leaves the atom. The electron remains held at any position in the atom without any photon. I trust we are all agreed on this point. The fields around the electron and the proton never leaves the atom right????. Bill field pulse (talk) 17:15, 18 January 2024 (UTC)
 * Photon and the photoelectric effect should not be here they are obviously electromagnetic radiation and nothing to do with EM field. This must be fixed. If there is any valid quantization being done to the EM field please stick to the field. Quantization of the field, if any, is far more more nuanced and subtle than the radiation and photons for example why do electrons hold to specific orbitals!!!! Something to do with protons not being fundamental charges maybe??? Bill field pulse (talk) 17:28, 18 January 2024 (UTC)
 * The definition must be changed to remove photons or it is just radiation being quantized and the article title is wrong. Bill field pulse (talk) 17:36, 18 January 2024 (UTC)
 * Note in Diracs" work the term Radiation is used. I doubt Einstein referred to the EM field as being packets perhaps it was a translation error. The photo electric effect only relates to radiation and not EM fields whatsoever. We certainly should take great care to use the terms correctly. Bill field pulse (talk) 22:05, 18 January 2024 (UTC)

Quondum ignores talk and edits contribution anyway
Quondum says "stick to the literature" and he does not see that there is a type of EM field when no radiation is present. He does not feel we have a role doing better than the literature. If ancient literature confused the two that is what we are stuck with. If a modern writer never learned the difference we are stuck with it. If we are trampled by dwarfs we do not see very far. Bill field pulse (talk) 20:46, 21 January 2024 (UTC)


 * Please read the Wikipedia policy on verifiability. Do you accept Wikipedia policies?  I said nothing that implied that the literature must be ancient.  —Quondum 22:53, 21 January 2024 (UTC)
 * I support the revert by @Quondum. The intro in this article is not correct, but the reverted edit did nothing to improve it. Johnjbarton (talk) 23:48, 21 January 2024 (UTC)
 * All EM fields result from the presence of fixed number of discrete whole particles. The quantized nature of the field is difficult to discern only when the numbers of particles is quite large. Therefore the EM field out of a stationary proton is not smooth at all but quantized by three discreet quarks moving at a high velocity within it. Bill field pulse (talk) 21:56, 22 January 2024 (UTC)

Near field and Far field
Since the near field has electric field peaks and magnetic field peaks which are out of phase they cannot be produced by any combination of photons which have the peaks in phase at all times. We need to clarify that only the far field is quantized in this way. Bill field pulse (talk) 19:50, 1 April 2024 (UTC)