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The propagation of light through a vacuum.

  1. Jul 29, 2009 #1
    all i have under my belt is a high school physics class, so please bear with me. i have a pretty good understanding of light and waves, but this question still gets me. and nowhere can i find a decent answer, or rather, and answer i can comprehend. if EM waves dont require a medium, then what exactly are the electric and magnetic fields if they arent a disturbance of something besides the initial medium. are they a disturbance of spacetime? any help is Immensely appreciated.

  2. jcsd
  3. Jul 29, 2009 #2

    Oh :( I thought the underlined "immensely" was a link and was curious what it was. Anywho, the visualization of EM as oscillating magentic and electric field is actually a classical one. Quantum mechanically we often treat EM as the exchange of photons (i.e. particles of light) which might give you a visualization of what it is. The fact that there is no medium through which EM waves travel was established over a hundred years ago through what is called the "Michaelson-Morley Experiment" which is of great importance (wiki it). It was this understanding that light didn't propogate through any medium that made Einstein's theory of (special) relativity possible.
  4. Jul 29, 2009 #3
    Why does a vacuum ("empty" space) have a permeability μ0 and a permittivity ε0? Why does sqrt(μ00) = 377 ohms (the sqrt of E/H in a plane wave)? why does 1/sqrt((μ0 ε0) = the speed of light?

    α β γ δ ε ζ η θ ι κ λ μ ν ξ ο π ρ ς σ τ υ φ χ ψ ω
  5. Jul 29, 2009 #4
    i am familiar w/ the michaelson-morley experiment. the exchange of photons makes more sense for me.are your questions rhetorical, bob s?
  6. Jul 29, 2009 #5
    Because when we defined our unit of force (the Newton) we made no attempt to make it map onto our unit of charge via coloumbs law. Thus you need conversion factors. Look up GAUSSIAN UNITS for a more natural set of units for EM.
  7. Jul 29, 2009 #6


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    Definitions. μ0 has a defined value and is not a measured (or measurable) quantity. And ε0 is defined to be 1/(c2[/μ0) so, naturally, 1/sqrt((μ0 ε0) = the speed of light.
  8. Jul 29, 2009 #7
    Yes, I am familiar with all that, and the usefulness of permittivity and permeability in both physics and electrical engineering. The question I am asking what causes free space to have these properties? What is there in free space that leads to permittivity and permeability, in any system of units. Why isn't there a solution where free space is completely empty.
  9. Jul 29, 2009 #8


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  10. Jul 30, 2009 #9
    how do we know space is empty could it be the higgs field .
  11. Jul 30, 2009 #10

    Vanadium 50

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    A field is a set of numbers for all points in space. It has little to do with whether something is "empty" or not.
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