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I Why is the electromagnetic field not a 'charge field'

  1. Feb 17, 2016 #1
    This question is a continuation/topic-extrapolation of:
    https://www.physicsforums.com/threa...ng-to-special-relativity.856482/#post-5374651

    My question is 'how is the electromagnetic field different from some sort of mere electric-charge field?'
    The issue I have with the video posted in the thread is that, it kind of implies that the a magnetic field is just an electric field from different reference frames in special relativity, in which case the 'electromagnetic field' which permeates the universe would really just be a 'charge field' (positive and negative, like an electric field rather than electromagentic)....

    So electromagnets work according to special relativity but not quantum mechanics, and permanent magnets (residual magnetism) work according to quantum mechanics, but not special relativity?

    Thanks
     
  2. jcsd
  3. Feb 17, 2016 #2

    marcusl

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    There is no such thing as an "electric charge field" construct in modern physics. There are electric fields and magnetic fields. Magnetic fields can be explained as a manifestation of electric fields seen from reference frames in relative motion, but that doesn't mean we experience them any differently. The magnetic field still looks and feels the same--it arises from currents, follows the right-hand rule, produces the Lorentz force, etc.

    Your second statement is not quite accurate. At a far deeper level beyond relativity, electromagnetic forces arise from the exchange of virtual photons according to the theory of quantum electrodynamics (QED).
     
  4. Feb 18, 2016 #3
    when I said 'electric charge field' I mean that in the video had an electric field and it was just the electric charge that was causing the magnetic attraction and repulsion. As you said, via the reference frame. But what I'm saying is that under this interpretation you don't need to use the words 'magnetic' at all
    because it seems like a totally electric phenomena (RightHandRule -> special relativity).

    I get that if we have all these circulating virtual photons according to quantum electrodynamics that if a charged particle is moving through them, that a Lorentz force will be exerted on the particle, but that sounds like a totally different phenomena (Lorentz -> quantum).

    It's like electromagnets aren't part of the electromagnetic field at all (just electric). I get that Maxwell states how they're coupled as a single electromagnetic phenomenon, I'm just having trouble seeing the connection in the aforementioned special relativity example.

    cheers
     
  5. Feb 18, 2016 #4

    marcusl

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    This is correct. Speaking of magnetic fields is advisable in practice, of course--the average person won't know what you are talking about if you try to discuss the action of a motor, or of a solenoid in a washing machine or car door lock, in terms of Coulomb attraction and relativistic boost.

    No, the Lorentz force is classical. I was trying to address your confusion regarding quantum descriptions. Ultimately all electric and magnetic phenomena can be described quantum mechanically, but for practical situations we use classical descriptions.

    I'm still not understanding your confusion here. An electromagnet involves electricity (current, aka moving charges) and magnetism (field). Why is it confusing that electromagnetic theory describes it?
     
  6. Feb 19, 2016 #5
    Go read up on Maxwell's equations. You'll see that there are 4 important quantities: ##\mathbf{E}, \mathbf{B}, \rho, I##.
    ##\rho## is the charge density which you could call a field if you want, but it isn't enough information to solve everything.
    ##\mathbf{E}## and ##\mathbf{B}## depend on ##\rho## and ##I## but aren't fully determined by them. Indeed, you have wave solutions for ##\mathbf{E}## and ##\mathbf{B}## even when ##\rho## and ##I## are 0.
     
  7. Feb 19, 2016 #6

    ZapperZ

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    What EXACTLY does this mean?

    Zz.
     
  8. Feb 20, 2016 #7
    Hi, sorry but what do you mean by:
    like a classical wave = 0 ?
    I was just saying that special relativity produces a seen increased charge density 'electromagnet', which seems like a fake magnetism to me. And quantum mechanics (electron spin -> magnetic grain alignment) produces virtual photons (magnetic flux) which to me seem like a genuine magnetic side to electromagnetics. Whereas the special relativity charge density seems just to be an electric field which according the Right Hand Rule produces a magnetic flux, but in actual fact it's just electric repulsion or attraction in proximity of the wire.
    I'm trying to understand how special relativity via current in a wire can produce 'magnetism' without actual virtual photons, or does it actually somehow?
     
  9. Feb 20, 2016 #8

    Vanadium 50

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    I'm afraid that none of what you wrote is correct. It misuses both SR and QM ideas. It's not like there is an error in there - it's that none of it is right and the very statement of the problem is so riddled with errors and false assumptions that it is impossible to address. ("When did you stop beating your wife?") The earlier replies were good - but will require you rethink these assumptions.
     
  10. Feb 20, 2016 #9
    I'm happy to learn if AND how I'm wrong, however I'm yet to hear how anything I said is inconsistent with:

    and

    I also found your reply brash to the point of unhelpful.
     
  11. Feb 20, 2016 #10

    Vanadium 50

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    And I find what you wrote complete nonsense bordering on crackpottery. Fake magnetism? Magnetic flux equated to virtual photons? You're not asking questions any more - you're pushing your own model. And it's incorrect.

    You have a choice - you can give up this model and learn how the universe really works, or not. Up to you.
     
  12. Feb 20, 2016 #11

    ZapperZ

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    This is completely puzzling and utterly incomprehensible. It feels as if you learned this out of a pop-science book (at best) or some dubious website (at worst).

    It is difficult for me to try and "teach" you anything when I am not even sure what exactly it is that you are talking about. There's nothing here that resembles the physics that I know with regards to both SR and QM.

    Zz.
     
  13. Feb 20, 2016 #12
    I literally just said:
    so clearly I'm not interested in pushing falsities and I'm hardly on here to push a faux science cult.
    Why didn't you just point that out in the first place? I don't know much about virtual photons, hence why I'm here, I just go off what I can reasonably research or infer:
    https://www.physicsforums.com/threads/magnetic-field-is-made-of-photons.139760/
    I'm only just scratching the surface of virtual photons and I basically forgot about the concept.

    It's not my fault if my internal model has some flaws in it, not that you've done much to rectify that. I never said fake magnetism in a scientific context, I said it 'seems like' it doesn't seem to have the (moving charge) quantum mechanical mechanism which I had been basing my understanding from. So condescend me regarding my motives or integrity to learn, you volunteered a reply I didn't come to either of you asking to waste your time.

    Yeah fair comment about how well I am as a communicator, but it's just my raw inference from the video.
    which as far as I can tell still stands.
     
  14. Feb 20, 2016 #13
    You need to understand the basics before you can tackle more advanced topics. Classical electromagnetism explains what a field is without getting into photons, virtual particles, and the like.
     
  15. Feb 20, 2016 #14

    Dale

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    Closed pending moderation
     
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