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So the problem starts with the way the question was phrased.

So, in QFT, there is a photon field but there is NOT any fundamental Electric field or Magnetic field.

So, we might imagine that an e-m wave is a collection of many photons or that an experiment involving one photon has been done many times and the e-m wave we observe is the combined average of all of these.

If you could fire just one photon through the usual double-slit experiment apparatus, then you probably won't get an interference pattern on the screen at the end. Instead we think you'll get just one spot to glow on the screen.

However, this demonstration gets close and claims to be using such a thin and dim stream of light that only "a few" photons per second will be produced.https://sciencedemonstrations.fas.harvard.edu/presentations/single-photon-interference

In our previous paper1 we pointed out that, strictly speak-ing, we are not detecting single photons of light but rathersingle photoelectrons liberated by the light impinging on thedetector; this is still true in the present experiment.Furthermore, the detection of a photoelectron does not neces-sarily imply that a single photon arrived.

many different versions of Quantum Mechanics.

Can quantum mechanics explain the generation, propagation, and reception of radio waves?

Quote from: hamdani yusuf on 07/09/2024 16:36:32Can quantum mechanics explain the generation, propagation, and reception of radio waves?It doesn't need to. Continuum physics does the job adequately below the terahertz region.

[ES said] So the problem starts with the way the question was phrased.[Hamdani replied] Can you suggest a better way?

How does it explain electrostatic and magnetostatic fields?

Concerning the double slit experiment with a single photon, Hamdani said: You seem to interpret one glowing spot on the screen as an event of a single photon being detected. Have you considered some alternative interpretations or explanations?

...By the name only,...

I didn't really understand what you meant here. QED , QCD, QFT and what I have tended to call simple QM differ by more than just their names. For example, Simple QM is based on the original Schrodinger Equation which is non-relativistic in nature. QFT is a relativistic quantum theory and was motivated by alternatives to the Schrodinger equation such as the Klein-Gordon and Dirac equations.

Maxwell's equations, which describe classical electromagnetism, are not directly derived from quantum mechanics. Instead, they emerge as a limit or approximation in the classical regime of quantum field theory, specifically quantum electrodynamics (QED).Here?s an overview of how the two are related:### 1. **Quantum Electrodynamics (QED) and Gauge Symmetry**: - In QED, the electromagnetic field is described by the photon, which is a quantum particle associated with the electromagnetic field. The interactions between charged particles, such as electrons, and photons are governed by the principles of QED. - QED is based on the principle of gauge symmetry, specifically U(1) gauge symmetry. This gauge symmetry is directly related to the structure of Maxwell's equations. Imposing U(1) gauge invariance leads to the field equations that resemble Maxwell's equations in the classical limit.### 2. **Classical Limit of Quantum Field Theory**: - When the quantum aspects (like particle-wave duality and uncertainty) of the electromagnetic field are ignored, or when considering the behavior of large numbers of photons, the quantum fields reduce to classical fields. In this classical limit, Maxwell's equations naturally emerge. - For example, the classical electric and magnetic fields are interpreted as the expectation values of the quantum field operators in certain states (such as coherent states).### 3. **Relation to Quantum Mechanics**: - Although Maxwell's equations arise from QED, they cannot be directly derived from non-relativistic quantum mechanics. In quantum mechanics, the interaction of charged particles with an electromagnetic field is incorporated via the minimal coupling of the electromagnetic potential A_\mu to the particle's wavefunction. However, this coupling is taken as a given, and the dynamics of the electromagnetic field itself is still described classically by Maxwell's equations. - The full quantum treatment of the electromagnetic field requires quantum field theory, not just quantum mechanics.In summary, while Maxwell's equations emerge from the more fundamental framework of quantum electrodynamics, they are not directly derivable from quantum mechanics itself. Instead, they correspond to the classical limit of the quantum field describing electromagnetism.

Have you considered that a single slit experiment, when the width of the slit is equal to the distance between the slits in double slit experiment, will also produce interference pattern on the screen with comparable size?

I don't know if we can ever be sure that we will detect a single photon in the sense of a small packet of light hitting only one spot.

Quote from: hamdani yusuf on 08/09/2024 07:51:22Have you considered that a single slit experiment, when the width of the slit is equal to the distance between the slits in double slit experiment, will also produce interference pattern on the screen with comparable size?Interpretation of the double slit experiment with dim light source and polarizers as a result of observer effect on which way detection has created more confusions than the explanation it had to offer. It lead to the introduction of quantum eraser, and subsequently, delayed choice quantum eraser paradox. https://en.m.wikipedia.org/wiki/Delayed-choice_quantum_eraserThey don't seem to have considered that a double slit apparatus has 4 edges, nor that a single slit experiment with comparable slit width as the distance between the double slits would produce a similar result of diffraction-interference pattern, although with different positions of bright and dark fringes.