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What is free electromagnetic field?

  1. Nov 3, 2014 #1
    Maxwell's equations solutions in vacuum - is a free electromagnetics waves.
    Such solutions can be obtained even without knowing anything about the charges and currents. Does this mean that such waves is the essence , not related charges, e.g. free electromagnetic waves?

    Moreover, the Maxwell's equations with ##\delta##-shaped sources also give the solutions, that looks like free electromagnetic waves, but in a far (wave) zone. Sometimes it is said that it is a field that is off the charge , but its amplitude is uniquely determined by the motion of the sources .

    Is it possible to think that there are waves that are generated by charges , and others which exist independently?
     
  2. jcsd
  3. Nov 3, 2014 #2

    Jano L.

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    Yes, total field can be though of as sum of retarded fields of close-by particles and the background field. The background field can be thought of as having no sources, or as having very distant sources.
     
  4. Nov 3, 2014 #3
    Did I understand correctly, if we imagine the world with no charges, for example, the EM-waves will still exist?
     
  5. Nov 3, 2014 #4

    dextercioby

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    The classical e-m field is created by classical sources. The <free Maxwell fields> are a useful approximation, especially when going into quantum mechanics.
     
  6. Nov 3, 2014 #5
    Ok, thanks for all.
     
  7. Nov 3, 2014 #6
    There are two questions here. Do free-space solutions to Maxwell's equations exist? (Yes) Will they exist in a spacetime that has never contained any charges or currents? (No)
     
  8. Nov 3, 2014 #7
    But it does not follow from the Maxwell's equations.
    Therefore , the answer is "no" - a hypothetical.
     
  9. Nov 3, 2014 #8
    The answer rather "may be not, but it is possible"
     
  10. Nov 4, 2014 #9

    Jano L.

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    Mathematically, it is possible to have non-vanishing EM field without electric charge anywhere.
     
  11. Nov 4, 2014 #10
    Only if you have non-zero boundary conditions. Which then makes the problem, incomplete in a sense.
     
  12. Nov 4, 2014 #11
    Neutron-antineutron annihilation creates gamma rays. Can we conclude from this, the neutron is composed of charged subatomic particles ("quarks")
     
  13. Dec 27, 2014 #12
    *Bump*
    :)
     
  14. Dec 27, 2014 #13
    No, electron-positron annihilation also produces gamma-rays but there's no evidence that electrons and positrons have any substructure.
     
  15. Dec 27, 2014 #14
    You didn't understand the question
     
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