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Mechanics of Electromagnetic Waves

  1. Nov 8, 2008 #1
    How do electromagnetic waves travel in space? I understand these types of waves are different than sound waves where matter acts as a medium. But how do these waves travel in space where there appears to be no medium? Is the space time continuum actually a physical substance although far different from matter, making it a medium for light? And why does light oscillate up and down anyway. Is it possible electromagnetic waves actually spiraled like it was falling kind of like water in a sink. At a side view it would look just like a regular wave if that was the case. I'm obviously no professional so don't laugh at this but I'm just throwing some thoughts I had out there.
     
  2. jcsd
  3. Nov 8, 2008 #2

    atyy

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    Well, a particle exists in space without needing a medium, so why should a wave need a medium? A particle has a particular position, whereas a wave (or more generally a "field") is spread out in space. Just like particles can have properties like mass or charge, an electromagnetic field has properties which we call the electric field and the magnetic field. Because the field is not localized, the electric and magnetic fields vary from point to point in space. When a particle moves, the charge it carries also moves, and the particle has momentum. An electromagnetic wave is type of movement of the electromagnetic field that carries momentum.
     
  4. Nov 9, 2008 #3
    Oh alright, I appreciate the answer.
     
  5. Nov 9, 2008 #4
    A wave of light, like all waves, does not "oscillate up-and-down" although some text books
    may give that impression. The oscillation takes place at the generating source and
    the instant state of the source at every moment is propagated as a fixed not oscillating
    EM-field at phase velocity = C for EM-waves that light also is. So if you could "follow"
    a wave at its own phase velocity, it is "static" not oscillating, although may be attenuated
    due to for instance distance. But of course an observer at rest (or at velocity differing from this phase velocity) perceives the wave as "oscillating" as it is passing - regard it as a moving "sinusoidal profile" at velocity C, where every point on the profile represents the state of the
    oscillating source at a corresponding (distance/C earlier) instant.
     
    Last edited: Nov 9, 2008
  6. Nov 9, 2008 #5
    I would tend to agree with you M but that is not what science says is it?
    Didn't Einstein envisage himself riding a light wave and still seeing it oscillating?
    I must admit being confused by that. If you accelerate away from a light source the colour shifts redwards or in other words the light has less energy to you.
    The faster you go away the more the energy of the light approaches towards zero energy.
    If you could travel with a light wave I would imagine that it would have zero energy relative to you; as you say it is static and not oscillating.
    But I thought current science agreed with Einstein's early vision that it would oscillate even if you could move with it?
     
  7. Nov 10, 2008 #6
    Thanks for comments "gonegahgah" ! What Einstein perceived riding on a wave must be hypothetical - and I think that was what he imagined very early in his career. My point of
    view was regarding waves in general, that I thought also yelded EM-waves including light.
    If Einstein meant as you say, he must have changed his mind later after creating his special theory of relativity (STR), because that implies time stands still at velocity C why no oscillating may be perceived on the wave at that velocity. Maybe this time standing still at velocity C is linked to wave front not oscillating?
     
  8. Nov 10, 2008 #7
    Fair enough. Thanks M.
     
  9. Nov 10, 2008 #8

    rbj

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    E&M waves travel in space for the more fundamental reason that like-signed charges repel and unlike-signed charges attract. there is no medium for this force and for that reason, plus that the laws of nature must be the same for every inertial observer, then everyone measures the speed of propagation of this force to be the same, which is c.
     
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