Fields a classical concept?

  • Thread starter Rockazella
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It’s my understanding that the field, whether it is electric, magnetic or EM field/wave is more of a classical concept. QM or QED completely replaces the field idea with subatomic particle interactions and reactions.
In classical field theory it’s said that perpendicular to the propagation of an EM wave there are electric and magnetic fields. In QM the propagation of an EM wave is represented by a photon.

My question is how does QM represent the electric and magnetic ‘fields’ that are perpendicular the direction of the moving photon?

If anything I’ve said prior to the question strikes you as incorrect feel free to correct me.
 

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  • #2
selfAdjoint
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Originally posted by Rockazella
It’s my understanding that the field, whether it is electric, magnetic or EM field/wave is more of a classical concept. QM or QED completely replaces the field idea with subatomic particle interactions and reactions.
In classical field theory it’s said that perpendicular to the propagation of an EM wave there are electric and magnetic fields. In QM the propagation of an EM wave is represented by a photon.

My question is how does QM represent the electric and magnetic ‘fields’ that are perpendicular the direction of the moving photon?

If anything I’ve said prior to the question strikes you as incorrect feel free to correct me.
Surprise! Quantum Field Theory has fields in it!

The fields are described in the Lagrangean, which is where all QFT starts. Indeed the Maxwell field is part of the QED Lagrangean. After they quantize they still have fields. The particles (bosons) are quanta of the fields, which doesn't mean they replace the fields but rather they add quantum behavior. There has been lately a move by some physicists to remove particles entirely and do quantum field theory with just the fields.
 
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Originally posted by Rockazella
electric and magnetic ‘fields’ that are perpendicular the direction of the moving photon?
As I said so many times before in these forums: I think this is a misconception.
Let me please state again my opinion:
- There is no such thing as a 'photon trajectory'.
- Thus, there is no 'direction of the moving photon'
- A single photon cannot be described by a field whatsoever.

Rockazella, I think what you're talking about is the Poynting vector, i.e. the vector of energy flow within an e.m. field - a purely classical concept.
 

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