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Can light be deflected in an electric field

  1. Jan 14, 2006 #1
    Can light be deflected in an electric field, since light wave has an electric component and a magnetic component?
     
  2. jcsd
  3. Jan 14, 2006 #2
    light is the moving change of electro-magnetic field in space, constant electric field wont change its behaviour.

    its like rising the water level and expecting the waves on the surface to deflect.

    but changing the viscosity of the liquid at a certain interval will deflect the wave on the surface, just like changing the dialectric value in which the light travels (or magnetic permeability) deflects light.
     
  4. Jan 14, 2006 #3

    Doc Al

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    No. Electric fields would deflect the path of a charged particle, but not light, which carries no charge. (At extremely high intensities, there can be photon-photon interactions that do affect the path of the light, but I believe that the most direct answer to your question is still "no" for all practical purposes.)
     
  5. Jan 14, 2006 #4

    EL

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    According to the classical theory, that is Maxwell's equations, electromagnetic fields cannot interact with each other in vacuum. This follows directly from the fact that Maxwell´s equations in vacuum are linear in the electromagnetic fields.

    However, if we as Doc Al said, consider extremely intense fields, the classical theory does not hold anymore, but we have to use the quantum theory of electrodynamics, that is QED (Quantum ElectroDynamics).
    QED is a non-linear theory, and infact allows for this type of interactions thanks to so called virtual particles, although the cross-section for the interaction is very tiny. But the process you are asking about, so called Delbrück scattering, has indeed quite recently been detected in laboratory.

    I may add that another related process, photon-photon scattering, where light is scattered by light, has not yet been detected, but thanks to advances in high power laser technology, this will probably happen within a near future.
     
  6. Jan 14, 2006 #5
    photon-photon scattering as I understand is a fourth order effect, where you have two pair productions, the pairs interact then annihilate, and the emitted photons appear to be scattered from the original two. Is this correct?
     
  7. Jan 14, 2006 #6

    EL

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    Well, not exactly, but almost.
    The lowest order Feynman diagram for photon-photon scattering has four vertices and consists of two incoming photons, which annihilate into a virtual electron-positron pair, which then annihilates into two real photons again. However, note that the intermediate electron-positron pair is just virtual, so the incoming photons need not be energetic enough for real pair creation.
    So photon-photon scattering does not really happen through "two step", it's just that the lowest order Feynman diagram looks like that.
     
  8. Jan 14, 2006 #7
    How then would we prove that there is an electric component in light?
     
  9. Jan 15, 2006 #8
    If light waves pass in close proximity to our Sun, they "bend" slightly from the Sun's gravitional influence. Isn't gravity considered to be an electromagnetic phenomenon?
     
    Last edited: Jan 15, 2006
  10. Jan 15, 2006 #9

    Claude Bile

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    The fact that the observed speed of light precisely matches the calculated speed of an electromagentic wave is fairly solid evidence. In fact, all the (classical) observed properties of light are predicted by classical EM theory.

    Claude.
     
  11. Jan 20, 2006 #10
    No, gravity is quite distinct. Whether it's framed as gravitons or as curvature of space-time, there's no electromagnetic components to it.
     
  12. Jan 20, 2006 #11

    ZapperZ

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    You use the E-field component to accelerate charged particles. And VOILA! That's what we do in particle accelerators! RF cavities and LINAC use electromagnetic fields (I use standing wave cavity in TM mode) where by the E-field component of the EM field is the accelerating field.

    Zz.
     
  13. Jan 20, 2006 #12

    Meir Achuz

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    EM waves have an energy density.
    Gravitation acts on any kind energy. There is nothing EM about gravity.
     
  14. Jan 20, 2006 #13
    How does gravity bend light?
     
  15. Jan 21, 2006 #14

    Tide

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    Technically, it doesn't. Photons travel along geodesics (i.e. the shortest path from A to B like great circles on a globe) but the space through which they travel in the presence of a gravitating mass is curved and so to a distant observer the path of a photon appears to curve.
     
  16. Jan 21, 2006 #15
    In reality, observation is light. If it appears to bend, then it does bend. A strong magnetic field can also bend light- correct?
     
  17. Jan 21, 2006 #16

    ZapperZ

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    No, this is not the same thing. When you see something bends, you are seeing it bends IN SPACE, i.e. the FRAME that you are using to look at it does NOT alter. Try drawing a curved line on a cartesian grid. The grid doesn't curve. So you can see, based on the straight lines, that there is a bend in the curve.

    But a bend in space-time is where the "grid" itself is distorted. Your "frame" is the thing that is being bent. Even the use of the word "bend" isn't quite right becuase this is a rather naive view of a complex mathematical situation. If you're tracing the path of light in this frame, you do not notice where it "curves". You only detect that it has gone around an object only via a later detection.

    Be very careful in translating a mathematical description into "words". Never put more emphasis on the words than the mathematical formulation.

    Zz.
     
  18. Jan 21, 2006 #17
    "As far as the laws of mathematics refer to reality, they are not certain, as far as they are certain, they do not refer to reality."- Albert Einstein.
    Light can be bent, ie. its polarization can be altered by a magnetic field.
     
    Last edited: Jan 21, 2006
  19. Jan 21, 2006 #18

    Meir Achuz

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    A static magnetic field does not bend light. A rapidly oscillating field could.
    It would be a QFT effect that would not occur classically.
     
  20. Jan 21, 2006 #19

    ZapperZ

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    Before you think you can play "quote the scientist" with me, let me put a stop to that and tell you that I'm not impressed. I will challenge you if you even KNOW what exactly is meant by that quote. It is highly annoying when I put EFFORT into explaining the PHYSICS of what is going on, and all you can rebutt is a quote that you don't even understand!

    If all you can do, and if all you think physics is, is just a bunch of quotations taken out of context, then you have zero idea how physics is practiced.

    Show me EXACTLY where (i) theoretically this has been shown and (ii) experimentally this has been verified. And just in case you think you can simply show a quack website as a legitimate source, let me diffused that right now.

    Zz.
     
  21. Jan 21, 2006 #20

    Tide

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    I don't think so.

    Regarding light and gravity, read what Zapper said - carefully! He spelled it out very well. :)
     
    Last edited: Jan 21, 2006
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