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Noone really knows what an electric field is

  1. Jul 24, 2009 #1
    I think we know one when we detect one, understand many repeatable principles but no one really knows how a charge in xyz can say, repel another like charge a distance away without any mediating material in between them. If we knew that the electric field was an exchange of photons back and forth at the speed of light, that would be an acceptable explanation to me. But the what causes this exchange? And what's the cause of the cause?
    Any thoughts?
     
  2. jcsd
  3. Jul 24, 2009 #2

    ZapperZ

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    Have you looked into quantum electrodynamics before you posted this?

    Zz.
     
  4. Jul 24, 2009 #3
    Yes.
     
  5. Jul 24, 2009 #4

    Born2bwire

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    Look harder. The electric and magnetic fields are the basis of classical electrodynamics, but in QED, the basis are the vector and scalar potentials, propagated by photons.
     
  6. Jul 24, 2009 #5
    QED sounds interesting. do Aerospace engineers learn about it?
     
  7. Jul 24, 2009 #6

    ZapperZ

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    Then assuming that you've understood QED, your question is very puzzling.

    Zz.
     
  8. Jul 24, 2009 #7
    To save me some time, and to reiterate how clearly you all understand these concepts, quickly, what type of exchange of photons causes an electric field? Passing the ball back and forth at the speed of light???
     
  9. Jul 24, 2009 #8
    Most definetly not.
     
  10. Jul 24, 2009 #9
    wow thats bad news. i'll prob end up taking alot of extra physics classes while i'm working on my AE degree
     
  11. Jul 24, 2009 #10

    ZapperZ

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    What do you mean by "what type of exchange"? A photon exchange is a photon exchange. It makes use of a fundamental description of QFT. You can either visualize this via Feynman diagrams, or if you're a glutton for punishment, use the Tomonaga-Schwinger formulation.

    Maybe it's time that you clarify why you're having a problem with QED.

    Zz.
     
  12. Jul 24, 2009 #11
    I think almost entirely in analogy to understand complex concepts.
    Let's say you have a point charge at x1,y1,z1. If there were no other ojbects in the universe would it still have an electric field? And why? What is this field made of how does it develop to a steady state, are photons moving and in what direction, things like that?
     
  13. Jul 24, 2009 #12

    ZapperZ

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    This doesn't really answer my question to you.

    Based on your understanding of QED and QFT, where exactly is these two formulations that didn't quite answer your original question?

    Analogies can be highly inaccurate. These are to be avoided when we are not dealing with the general public. Dealing with the exact theory is always preferable.

    Zz.
     
  14. Jul 24, 2009 #13
    Exact theories don't give you a fundamental understanding of what's going on except in a mathematical sense. I can know the eq for F=ma and manipulate in problems etc but still not understand on a fundamental level.
     
  15. Jul 24, 2009 #14

    I assume what you mean is that you don't know anything about QED (i.e. the actual stuff, not like pop-sci stuff). Certainly nothing wrong with that but just be clear about it unless you want someone pulling out second quantization and path integrals on you.
     
  16. Jul 24, 2009 #15
    :( Unfortunately that won't get you to QFT of QED either. Normally the first QFT course one takes is only for people working in that area and would be during the first year of grad school. There wouldn't be an undergrad QFT course even for physics majors.
     
  17. Jul 24, 2009 #16
    That sucks! If only physicists got paid more i wud prob persue a PHD....
     
  18. Jul 24, 2009 #17

    ZapperZ

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    But what does that have anything to do with "analogies"?

    There's a difference between having a conceptual understanding and analogies. You are insisting that these are the same thing - they are not!

    So you are saying that you have a "mathematical understanding" of QED, but not a conceptual understanding?

    Zz.
     
  19. Jul 24, 2009 #18

    Dale

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    IMO you have it completely backwards. The mathematical sense is the fundamental one. The analogies and interpretations are just superficial stories that we use to cover up the fundamentals.
     
  20. Jul 24, 2009 #19
    I neither have an understanding of QED or otherwise. Walter Lewin uses 'stories' so why can't I?
     
  21. Jul 24, 2009 #20

    Dale

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    I never said the stories were not useful, just that the math is more fundamental.
     
  22. Jul 24, 2009 #21

    ZapperZ

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    So you really haven't "looked" into QED, have you, and your answer in Post #3 is really not true.

    Then don't you think it is rather arrogant to claim that "Noone really knows what an electric field is"? Because what is more accurate here is that YOU don't know what an electric field is. Your state of knowledge is not a reflection of the state of knowledge of the field.

    Would you like for me to edit the title of this thread to make a more accurate representation of the current situation here in this thread?

    Zz.
     
    Last edited: Jul 24, 2009
  23. Jul 24, 2009 #22
    The purpose of the 'stories' is to develop a more intuitive understanding of what the mathematics is saying. A professor such as Dr. Lewin uses them to help his students develop a better understanding of physical phenomena.

    By themselves, they don't really have much meaning. I always think back when I first heard about quantum tunneling: the 'stories' sounded so strange and mysterious! However, as soon as I took my first undergraduate QM class and saw the mathematics worked out for two square wells separated by a finite barrier, things became a lot clearer.
     
  24. Jul 24, 2009 #23

    Walter Lewin teaches first year undergrad courses. QED is like a second year graduate course. Things quickly become very mathematical (even in second year courses) and it very quickly becomes impossible to think entirely in pictures and one has to hunker down and learn the math. Way of the universe.
     
  25. Jul 24, 2009 #24
    But isn't QED a model that is offered as a plausible explanation, and not proven to be a set of facts? If so, I think "no one really knows" would be a true statement. Otherwise, how was the absolute certainty about the truth of the model obtained?

    It also sound to me like to me like an abstract model to say, as many people do say, that if I merely wiggle one charged particle a little bit, this act causes the entire universe to be bathed in individual photons that will relay the signal of my act to every point in all of space. What we do know is that the photon is the quantized nature observed when electromagnetic energy is transmitted or received, but not necessarily during the long journey across the light years. I think that's equivalent to saying that no one knows what the field itself is.
     
    Last edited: Jul 24, 2009
  26. Jul 24, 2009 #25

    jtbell

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    Which theories in physics have been "proven to be a set of facts?"
     
    Last edited: Jul 25, 2009
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