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Carrier particles and E-Field Propagation

  1. Jan 23, 2015 #1

    BiGyElLoWhAt

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    A thought experiment that is a consequense of a question someone asked in my particle physics class:

    We place an isolated electron. We wait 10 years, and place a half ring of electrons (spaced far apart from each other, but uniform) 10 LY away from our central e. Will our charges move? If so, which ones?
    Next part, now imagine, shortly after adding the ring of electrons, we added in a ring of protons between, located 8 LY from our source. Will the outer ring of electrons accelerate outward for something to the effect of 2 LY (only feeling the field due to the central, initial charge) before realizing that there are a lot of protons, that are actually closer, and producing a stronger field that they can interact with?

    I would really like to see what people think would happen. I'm struggling how the carrier particle of an e field is a photon, but propagates to infinity in all directions, and somehow doesn't violate CoE. I know it's the exchange particle, but does it exist at a point where there's nothing to exchange with?

    More directly, is an electric field a physical thing, or just a math model?
     

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  3. Jan 23, 2015 #2

    Vanadium 50

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    What makes you think this has anything to do with virtual photons and can't be handled classically? And why is this in HENPP - again, isn't this classical? The test charge sees the electric field at that point, and it takes c for changes in the field to propagate.

    In science there is no distinction between "real physical thing" and "just a math model". Is an electron a real thing? What about wind? Or pressure?
     
  4. Jan 23, 2015 #3

    BiGyElLoWhAt

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    I'm not saying it can't be handled classically. You can Kq/r^2 and Kqq/r^2 all day. My concern is with the conservation of energy associated with the virtual photons as force carriers. That is why this is in HENPP and not classical.
     
  5. Jan 23, 2015 #4

    BiGyElLoWhAt

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    If there is spherical propagation of photons as force carriers, then these photons must have energy, otherwise, how would they transfer energy to the particle they interact with? Looking at this classically, the field from the central e exists where we add in the half rings, so they both feel the force of it's electric field, but not vice versa (unrealistic, I know). I'm not asking about that. I'm asking if the electric field actually has something that propagates outward, even if there's nothing there to exchange with. When you place a test charge, you are adding something to exchange with. The distances in this problem as well as the time frame are important to the concept I'm trying to get a hold on.

    When 2 charges (TWO) exchange particles, the net energy between them is conserved. This is not the case when there is only one charge, unless the field doesn't actually propagate, or it's "carriers" are energyless and massless.
     
  6. Jan 23, 2015 #5

    mfb

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    Virtual photons are a useful model in cases where the classical description does not work any more. It does not make sense to use them in a purely classical setup - it is possible, but don't expect intuitive answers from this model.
    Virtual particles are not real. It does not make sense to ask about their propagation.
     
  7. Jan 23, 2015 #6

    BiGyElLoWhAt

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    Does it make sense to talk about the propagation of an electric field? If it does, then what's actually propagating, if not these photons? If not, then why do we say an electric field propagates at c?
     
  8. Jan 23, 2015 #7

    mfb

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    Yes.
    The field.
    Even in quantum field theory, where the concept of virtual particles comes from, the fundamental thing are the fields.
     
  9. Jan 23, 2015 #8

    BiGyElLoWhAt

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    Hmmm... that's interesting. So let me ask a clarification question (I don't know a whole lot about quantum field theory): You have the higgs field, an excitation of which is the higgs boson. Are electrons, or other leptons for that matter, merely modeled as excitations of their respective fields? (perhaps other particles as well)
     
  10. Jan 23, 2015 #9

    Drakkith

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    Yes, they are. From here: http://en.wikipedia.org/wiki/Quantum_field_theory

    ...QFT treats particles as excited states of an underlying physical field, so these are called field quanta.

    For example, quantum electrodynamics (QED) has one electron field and one photon field; quantum chromodynamics (QCD) has one field for each type of quark; and, in condensed matter, there is an atomic displacement field that gives rise to phonon particles.Edward Witten describes QFT as "by far" the most difficult theory in modern physics.[1]
     
  11. Jan 24, 2015 #10

    BiGyElLoWhAt

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    That's pretty cool. Well at least I've got something to look into. Thanks.
     
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