Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Does light speed apply to all waves traveling in vacuum?

  1. Apr 23, 2008 #1
    Seriosly, waves have different frequencies, and light is somewhere in the middle of the EM spectrum, then maybe the right or left side could travel faster than c
     
  2. jcsd
  3. Apr 23, 2008 #2
    Light is generally the term used to refer to electromagnetc waves in the visual spectrum (but its really the same as other E&M waves, just at different energies).
    They all behave generally the same, i.e. all E&M waves travel at the speed of light.
     
  4. Apr 23, 2008 #3
    All massless waves (and all massless particles) travel at the speed of light.
     
  5. Apr 23, 2008 #4

    Danger

    User Avatar
    Gold Member

    That includes gravity, by the way.
    I think that in one regard, you can say that not all waves travel at c in vacuum, but I'm not sure if my reasoning applies. It seems to me that the matter waves associated with a particle can't do so, since the particle itself can't.
     
  6. Apr 24, 2008 #5
    CT, all EM waves travel at the same speed in a vacuum. As far as I am aware this is not the case when dealing with a medium in which the waves are travelling slower.

    If by speed of light you mean around [itex]3\times10^8[/itex] then I can't see how that is correct.
     
  7. Apr 24, 2008 #6
    The phase velocity of a wave is a product of the frequency and wavelength:

    L*f=v

    The electromagnetic wave equation has solutions with different frequences, but the wavelength must be inversely proportional to the frequency, so the product is always the same:

    L*f=c
     
  8. Apr 24, 2008 #7

    Has it been experimentally proven that gravity waves travel at the speed of light.
     
  9. Apr 24, 2008 #8
    The original question was about waves in a vacuum.
     
  10. Apr 24, 2008 #9
    That doesn't make what you said correct.
     
  11. Apr 24, 2008 #10
    You can think what you want. I won't engage in a pointless argument over semantics.
     
  12. Apr 24, 2008 #11
    Well, how about traveling slower than the speed of light? If you are in a car that's goin at 100mph and you light a flashlight backwards, does the light travel at c-(100mph)?
     
  13. Apr 24, 2008 #12

    ZapperZ

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor
    Insights Author

    Please refer to the basics on relativistic velocity addition.

    http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/einvel.html

    The speed of light is constant in all inertial frames, no matter the speed of the source.

    Zz.
     
  14. Apr 24, 2008 #13

    rbj

    User Avatar

    only to within 20%, IIRC.
     
  15. Apr 24, 2008 #14
    Excellent question, CT, and the answer is very important (ZapperZ already mentioned it). Make sure to keep reading every text you can get your hands on, because we've all asked this question at one time or another; if you can accept the true answer it will blow your mind.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?