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Is the electromagnetic field real ?

  1. Jan 6, 2004 #1
    Is the electromagnetic field "real"?

    This is sort of a mix of classical and quantum so I put it here ...

    In our current view of the universe, is the electromagnetic field "real", or is it simply a manifestation of the true underlying causes behind the electromagnetic force?

    It seems to me to be the latter, since in quantum theory the photon is the carrier of the electromagnetic force. I guess my real question is: is light really electromagnetic waves, or is it photons acting according to a wave function? I don't want to get into the whole wave/particle debate. I'm really trying to figure out if the idea of electromagnetic field is just a holdover from times before quantum mechanics.
  2. jcsd
  3. Jan 6, 2004 #2
    If the em field is a holdover it is one that is going to stick around a long time. Just as no one would design an entire electric circuit starting from maxwell's equations, no one will design antennas and solve reception problems in real life from a photon model. Sometimes 'incorrect' models can be extremely useful and practical.
  4. Jan 7, 2004 #3
    Your question has to do with philosophy, not physics.
    Is the E-field real? Who knows. It's a good model in the macroscopic world, in QM you have the photons. Physics tries and constructs models, which hopefully work out in the real world. Them being real on a fundamental level (whatever that may be) is question that cannot be answered.
  5. Jan 7, 2004 #4
    Re: Is the electromagnetic field "real"?

    We understand the world through our mental models of it. Unfortunately no model is perfect. ALso unfortunately we can only see our mental models, never the real world. Is an apple really an apple, or is it "really" just a bunch of biomolecules, or is it "really" just a bunch of quarks and leptons?

    Electromagnetic fields are just as "real" as quantum mechanics. Both are models of the real world. Neither one is the real world itself. In some situations the "em field" concept is the right tool to use. In others, QED is the one you want. (And probably there are situations where QED fails, and something which combines gravity and quantum dynamics must be used instead.)

    The photon concept cannot replace the e-field concept any more than the "cloud of quarks" concept can replace the concept known as "apple." And no matter how advanced your screwdriver may be, it is still not a wrench. The right tool...
  6. Jan 7, 2004 #5
    Really? I'm a little confused now. It seems like you're saying that quantum mechanics is not sufficient to explain both wave and particle aspects of light. Is that true? I thought that QM stood on its own with respect to the electromagnetic force.
  7. Jan 7, 2004 #6
    Ah, I see how I may have miscommunicated. What I mean when I ask if something is real is like this:

    What is an apple really?
    At our present state of understanding, the apple is really a bunch of quarks.

    I want to know the lowest level. So is QM the lowest level in our understanding of electromagnetic force, and EM fields an "approximation" to it? Or is it really that QM is not sufficient?
  8. Jan 7, 2004 #7


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    No, what he's saying is that QM is not suitable for dealing with macroscopic phenomena or design tasks. On anything other than extreme scales, the increased cost in computation is not worth the increase in accuracy.
  9. Jan 7, 2004 #8
    I know that, of course. But in theory you could use QM to do it, and thus QM is a complete explanation of electromagnetism, correct?
  10. Jan 7, 2004 #9


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    Well, first off, it's unclear what you mean by 'compete explanation of electromagnetism', and I don't know enough about QM or EM to tell you whether QM actually implies all of Maxwell's equations.

    Even if we assume that the macroscopic notions of Electricity and Magnetism could be derived from QM, it may be superceeded by a newer more accurate theory, so it is not a 'compete explanation' in that sense either.

    In practice, Maxwell's equations are more usefull than the raw QM approach, so complete in the sense of utilty is also not really correct.
  11. Jan 7, 2004 #10
    Yes, I suppose that is what I'm really looking for. Thanks for helping anyway :smile:

    My quest here, really, is to understand how our world really works. For example, when we talk about friction, there's more to it than just "there's a force of friction." What's really happening is that there is some interaction between atoms on the surfaces. (which of course has deeper layers embedded in it ... how the interaction occurs, etc.) That's where I'm heading. And I know that eventually I'll meet a dead end, which is our present state of knowledge. Physics is still not unified. It's not alright to say, Sometimes it behaves like a wave, sometimes like a particle. There's something missing and we have to know what's really going on.
  12. Jan 7, 2004 #11
    No, an apple is a pattern *in* a bunch of quarks, so it isn't really a bunch of quarks. The same bunch of quarks could just as easily form an orange, and knowledge of quarks doesn't tell you which fruit you've got.

    Or look at it this way: a video game is just a bunch of flipflop states, so if you wanted to become an expert in game software, should you study flipflops? To understand the software even better, should you study NAND gates or silicon atoms? Obviously not, since "video game" is a high level pattern which cannot be seen if you disassemble it and then look at the microscopic parts. The video game is REAL, even though it's "just a pattern." The same video game could even be made up of NOR gate flipflop states running in a gallium arsenide computer, so knowledge of NAND flipflops and silicon atoms doesn't help. Knowledge of silicon atoms cannot teach you Windows application programming. Knowledge of silicon atoms is not somehow "better" than programming knowledge.

    In an analogous way, knowledge of quantum mechanics is worthless if you're asking questions about radio equipment where the answers involve discussions of EM fields. Quantum mechanics knowledge will never replace concepts like "e-field," any more than knowledge of NAND gates will replace computer programming skills.
  13. Jan 7, 2004 #12
    After spending decades in science pursuits, I'd have to say that one of the most useful topics I studied was Complexity science, "pattern physics" such as Chaos concepts, artificial life, cellular automata, emergent properties, etc. In many many cases the Complexity concepts give understanding, when delving into the micro level does not.

    Friction is a good example. If many bonds form, the objects stick together completely, and if many bonds do not form, friction is zero, so how can we understand sliding friction? Knowing how patterns behave in things like "Conway's Life," I could speculate that small patches of bonds could form between moving objects, and when they stretch and break, they send out surface waves on the object which have a huge effect on other spots. The sliding surface would suffer an "outbreak" of a pattern of bonded and unbonded surfaces which perhaps looks like a complicated pattern of ripples. This gives me hints about doing friction research. Perhaps there's a way to make bonded and unbonded surfaces appear in different colors or flourescence, so it might be possible to videotape the patterns with a high speed microscope. I could work on computer simulations of the surface rules at the same time, and try to massage my software until it reproduces the same sorts of things I see in the microscope.

    If instead I chose to study chemistry (or even quantum mechanics), I'd miss exploring this whole new field of "frictional chaos-plexity" science.
  14. Jan 7, 2004 #13
    (This is a reply to wbeaty's 2nd last post)

    Ok ... thank you guys so much for drilling that into my head over and over again. But seriously, I understand it. I get it. I've thought about that stuff many times. I know it's meaningless to say whether forces, space curvature, etc. is "real" or is it just a description, a theory that merely explains phenomena ... I would just like my question answered about whether Maxwell's equations can be derived from QM. And if someone could point me to some resources, that would be great also.

    BTW, I agree that the thing we call "apple" is really a bunch of quarks arranged in a pattern. But you know what I mean - I'm looking for the lowest level description.

    If you really want to understand my questions, think of it this way: Imagine I wanted to create a simulation of the universe. I want to find the complete rules that will allow me to do this. (Yes, yes ... I know about Heisenberg )

    Also, where you say QM will never replace E-field - of course I agree with that. It's just like saying Einstein's relativity will never replace Newtonian dynamics - but Einstein's relativity IS more correct, and Newton is an approximation (a very useful one!) to Einstein. Let's not get into a big debate about this however.

    You see, what I'm really trying to find out is if the Newton-Einstein relationship is analogous to the E-field:QM relationship.
  15. Jan 7, 2004 #14
    That's true. I think of it this way. Once we have discovered the ultimate laws of physics, there will be only one thing left to science: applying it. And this part of science involves approximations, such as E-field and Newtonian Dynamics, and also the CA (cellular automata) stuff you're talking about. Anyway, let's get back to my question since that's what the thread is about. There's no doubt that this sphere of science is very interesting, but we're trying to get at the roots of things.
  16. Jan 7, 2004 #15
    I may have found something:

    this is from another forum

    He says:

    This relates to the fact that (I do not remember who did it, Feynman?
    Jackiw?) it is possible to "derive" Maxwell equations (dF=0) from Jacobi
    identity in quantum mechanics. And these Maxwell equations need to hold
    only "almost everywhere".

    Does anyone understand this?
  17. Jan 7, 2004 #16
    i believe i understand it.

    basically, if you had a continuous magnetic monopole density, maxwells equations would have to be modified to include a source term for the magnetic monopole. then the electromagnetic field could no longer be viewed as the curvature of a gauge bundle.

    but you can keep maxwells equations intact if you have only isolated monopoles.

    incidentally, while electromagnetism doesn t permit this, i think certain non-Abelian Yang-Mills fields do allow magnetic monopoles, if their gauge group satisfies certain topological conditions.
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