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Question about nature of light

  1. Jul 30, 2013 #1
    Hello everyone! This is my first post as a member to this forum and as such will start out with a question that hopefully more brilliant minds than mine can help me with. I am an amateur physicist and simply enjoy pondering theories in regards to many topics in the field. Today I was thinking about light and ran into a question that even the great Google couldn't answer for me, so here I am!
    With respect to "Light" or the whole em spectrum, is it possible for different wavelengths to travel at different velocities?? Also, do we know the entire spectrum of light from end to end or are there still gaps in our current knowledge?

    Any help is appreciated. Thanks!!
  2. jcsd
  3. Jul 30, 2013 #2
    All electro magnetic waves have the same speed in vacuum....the speed of light.
    In different media the speed does depend on wavelength, the effect is called dispersion.
    This is how a spectrum is produced when light travels through glass, water etc.
  4. Jul 30, 2013 #3


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    All wavelengths of light travel at same speed because EM waves have a "linear dispersion relation". There's no theoretical limit for how short or long wavelength EM waves could have, so the spectrum does not have 'ends'. If I remember correctly, the highest energy photon ever measured (from cosmic rays) had an energy of about one joule in a single photon!
  5. Jul 30, 2013 #4


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    Light travels at c in a vacuum. Frequency is irrelevant. For example, light from distant galaxies is red-shifted, but still arrives here moving at c.

    Not sure what you mean by "gaps". The spectrum is a range of frequencies. What "gap" did you have in mind?
  6. Jul 30, 2013 #5
    Thanks for the answer...so for EM waves to slow down at all, it depends solely on the medium it passes through? Thanks again for your help.
  7. Jul 30, 2013 #6
    By "gap" I meant in our current knowledge of the entire EM spectrum, but I think that has been answered in a previous post. Thanks!
  8. Jul 30, 2013 #7
    Thanks for the resposes so far everyone.... just to let everyone understand where my current line of thinking is going, I wss wondering if we might be wrongly going at the question of "faster than light" travel by assuming that there is something "other" than light that is faster. My thought was maybe there is a spectrum of light itself that IS faster....just a thought. :)
  9. Jul 30, 2013 #8
    In any medium other than vacuum you could say...." There is a spectrum of light that is slower!"
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