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I Moving charge magnetism explanation

  1. Feb 28, 2016 #1
    I'm from a country in Africa where I didn't have the privilege of learning the Standard Model, so I'll try and rephrase my question here:

    In a way where my ignorance doesn't outrage and offend.

    A couple of years ago I read (and from memory understood) Fundamentals of applied electromagnetics by Ualby.

    Attempting to push through being told there are some boundaries of comprehension due to my background which forbid me from discussing the "advanced topics" in a youtube video.

    As far as I can tell, in the video:

    is as SR explanation of magnetism due to increased particle electric charge density of the reference frame outside the wire. Which (as far as I can see) has nothing to do with quantum mechanics. Despite there being quantum mechanical equations for electromagnetism (I think, I've seen...years ago).
    I basically know nothing about virtual photons, I've read conflicting explanations about if a magnetic field / magnetic flux is made of virtual photons or not. I pretty much just want to know how the explanation of magnetism is consistent with the 'electromagnetic field' model, and electron spin and virtual photons...and QM in general...
  2. jcsd
  3. Feb 28, 2016 #2


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    If you have a question, ask the question. But make it specific enough that it can be answered.
  4. Feb 28, 2016 #3
    Is magnetic flux made of virtual photons?
    As far as I know electromagnetism is described by QM,
    Is there a source that elaborates how the (SR?) explanation in this video....I don't know how to say it....'works with the electromagnetic field in the standard model and / or virtual photons and QM'?
    because as far as I can understand from that video, the attraction and repulsion outside the wire created by the internal moving charge (purely electric charge).
  5. Feb 28, 2016 #4


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    All interactions that occur via the EM force, whether they are electric or magnetic, can be modeled as occurring because of the exchange of force carrier particles, virtual photons in this case.

    Well, I know that Quantum Electrodynamics already incorporates SR into it, so there may not be any difference except the "extra" description given by QED.
  6. Mar 1, 2016 #5
    Hi and thanks for the reply.

    See this has attempt as understanding for me has seemed like an overly complicated multi-faceted disconnected irritation. And in my experience it usually means it's actually simple, but I'm just not fitting the pieces in together but when they fall into place the questions will become answers for other questions.

    So, running the risk of making great oversimplifications...I assume a virtual force particle is a disturbance in the electromagnetic field(?)

    So would it be like as the electrons are travelling through the wire. The reference frame of the electromagnetic field has more disturbance from the electrons because they seem to be more tightly travelling, and so there are more virtual photons circulating around the electrons (normal to the direction of travel)? And what, the disturbance in the electromagnetic field can travel through an Iron core better? The permeability of Iron means that the virtual photons can permeate through the electromagnetic field better?

    I take it that there is no way to have electrons drift through a piece of wire at different speeds?
    Is electron drift velocity independent of conductivity and the amount of potential difference?
    What I'm wondering is, I assume that the electrons drift around all over the place when there is no potential difference, at room temperature, so there is no net magnetic flux around the wire, but when they're lined up, there is. But I'm wondering if just being lined up (that is, oriented in the wire, as I imagine happens when a potential is applied over the path) is enough, or if you need some sort of relativistic compression of the space between the moving electrons.

    I just found this page:


    which I am going to read very soon.

    These Feynman diagrams, is the virtual particle / photon oscillating back and forth in time as it travels through space?


    (Feel free to 'shoot me down')

    P.S: so is magnetic flux quantised like a light photon?
    Sorry about the long reply.
    Last edited: Mar 1, 2016
  7. Mar 1, 2016 #6


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    Nope. Even in a static situation the force is modeled as being the result of the exchange of virtual particles.

    There is no orientation of the electrons during current flow. The average velocity of all these electrons bouncing all around in the conductor is zero when there is no voltage applied and non-zero when voltage is applied. When in motion, the electric field of the electrons is compressed in the direction of travel, but the space between them is not compressed. Space is not an object. It cannot be compressed.

    Good lord, no! That's just something odd Feynman observed in the way the math and everything works I believe. It was never meant to be taken seriously as far as I understand.

    I don't think so. An EM wave is quantized, but the rest of the EM field is not. Unfortunately some of this is a little beyond my knowledge so I'm semi-guessing here.
  8. Mar 2, 2016 #7
    Thanks for the reply Drakkith.
    So is it virtual photons that comprise a virtual force particle? If so is it virtual photons that are a disturbance in the EM field? What separates a virtual photon from a real photon?
    If the magnetic field around a wire isn't due to orientation of the electrons during current flow, than what causes it? This is what I was confused about before, otherwise doesn't it just seem like electric attraction or repulsion from charge density are the cause? (I.e. than where does the magnetic flux come into the picture?)
    Sorry, I didn't mean that space was compressed, I meant it 'seems compressed' from the outside reference frame. (I sort of understand that space is not an object, but I'm still struggling with that cosmologically.)

    Thanks heaps
  9. Mar 2, 2016 #8


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    In QFT, virtual photons mediate the electromagnetic force, while the other forces have their own force carriers.

    I don't know enough about this to explain it. But there are plenty of threads here on PF on this subject if you do a search. You can always make a thread in the quantum physics forum too.

    I believe that the charge density is all there is in this case. But this is a bit beyond my expertise, so I could be wrong.
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