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B What composes the E Field of the Electromagnetic Wave?

  1. Feb 10, 2017 #1
    What composes the E Field of the Electromagnetic Wave where "disturbances" for propagation occurs?

    If electromagnetic waves cause disturbances in the Electric Field… what “is” in this E Field which photons Interact with?

    I ask because in Vacuum, there are no electrons to excite. So what is “it” that's adding up in the E Field as a disturbance in wave propagation?
  2. jcsd
  3. Feb 10, 2017 #2


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    It's just the E field. That is as deep as the explanation goes. (*) Science is about discovering models that describe how things work. If those models predict measurable results and if experiments match the predictions then that is as good as it gets.

    The model you are using describes behavior of electromagnetism in terms of fields. The model can tell you what fields will be produced by a set of charges. It can tell you how charges will respond to a given field. It can tell you how an fields can evolve over time in the absence of charges. When you measure the motion of charges, they match the predictions of the model. So we consider it a good model and move on.

    The question of what the fields are made of does not arise. They could be made of little hooks and springs lubricated by fairy dust. The only part that matters to science are the quantitative testable predictions. Until we come up with a way to measure fairy dust, the underlying mechanism, if any, is irrelevant.

    (*) You could delve into Quantum Electrodynamics and get a somewhat more nuanced and mind-twisting model, but you still have a bottom level of "that's just the way it works".
  4. Feb 10, 2017 #3
    That's pretty much what I got from reading some sources on quantum ED. There is no explanation of what a field really is. Or infact, what drives the disturbance, which they say it is the Photon as a Propagator, but others describe the EM fields as the Photons themselves.

    Which drove me to asking a lot of questions, and this is just one of them.
    And it seems to me - We don't really know what are those fields nor what we called Photons.
    Except that Physics only Quantifies these observations.

    Thank you for your sincere well written answer.

    On another note - Where do I start reading on EM field interaction phenomena.... assuming other things than charges cause disturbances or different behaviours in Electric Fields/Magnetic Fields?
  5. Feb 10, 2017 #4

    m k

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    Actually, we know exactly what those fields are because we invented them.
    We also know exactly what those waves are because we invented them also.
    What we don't exactly know are those photons because those we are only observing.

    It's all just different sides of the same thing, energy.
  6. Feb 10, 2017 #5


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    Energy, photons, fields -- they are all elements of models. Experiment can only ever tell us whether a model makes accurate predictions. It cannot tell us whether the elements of the model are real. Whatever "real" means.

    For models that are well confirmed, we tend to take the existence of the elements of that model for granted. We think of fields, photons and energy as if they were real. As long as experiment does not contradict the correctness of the model, we can go on thinking that way without difficulty.

    In the same way we think of people, buildings and Buicks as being real. We each (seem to) have a well confirmed mental model of the world built through childhood which includes those entities and which works well enough to get us through life.

    [This response is getting perilously close to being philosophy. It will not break my heart if it is removed]
  7. Feb 10, 2017 #6


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    As has been explained already, we know exactly what a field is. A field in this context is a mathematical way of modeling something by having a value at each point in space and time, such as the values describing the electric force felt by a particle at a location. Whether or not this model is "real" or not is mostly a philosophical question. When done correctly, this type of model works accurately and it works beautifully. Therefore it is used extensively in physics and elsewhere (including weather reporting).

    Photons are a model of an observed phenomenon; the interaction between matter and the EM field is quantized. This quantized interaction transfers discrete amounts of energy and is called a photon. Again, whether photons "really" exist is a matter philosophy, not physics.

    I don't know what you mean here. As far as I know, electric charges are the only things that generate or cause changes in the EM field.
  8. Feb 10, 2017 #7

    Thank you for your answer. Yes, I did mean whether other things than electric charges generate or cause changes in the EM field.
  9. Feb 10, 2017 #8
    Aha, thank you, it makes more sense now.
  10. Feb 10, 2017 #9
    Yes, now I'm beginning to understand it from the concept of models, rather than 'thing'. A quantified model of observations and phenomena.
    Thank you.
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