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

Theoretical Limit on Frequency?

  1. Mar 15, 2007 #1
    Is there is theoretical limit on how large a frequency (or how small a wavelength) an EM wave can have?
  2. jcsd
  3. Mar 16, 2007 #2
    the frequency available is continuous and has no upper or lower bound, so there is no finite lower limit or upper limit on the possible energy of a photon. On the upper side, there are practical limits because you have limited mechanisms for creating really high energy photons. Low energy photons abound, but when you get below radio frequencies, the photon energies are so tiny compared to room temperature thermal energy that you really never see them as distinct quantized entities - they are swamped in the background.
  4. Mar 16, 2007 #3


    User Avatar
    Gold Member

    Last edited: Mar 16, 2007
  5. Mar 16, 2007 #4

    Meir Achuz

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

  6. Mar 16, 2007 #5


    User Avatar
    Homework Helper

    unfortunately, many of the physical theories we have are strictly valid at a relatively low energy... since freq is related to energy... so you may have problems when things go extremely large... but that doesn't mean there is definitely a limit..it is just a statement saying that we don't know ..yet
  7. Mar 17, 2007 #6
    If there is a limit then either the Doppler's shift is completely wrong for ultra high frequency or there is a bound (less than c) on how fast one can travel with respect to a source of a light.
  8. Mar 17, 2007 #7
    actually if you pump enough energy into a photon it will entually become a different kind of boson, I forgot the particulars however.
  9. Mar 17, 2007 #8
    How can you draw this conclusion?
  10. Mar 17, 2007 #9
    in Doppler's effect, the frequency goes to infinity as one approaches a light source close to the speed of light... so if there is a limit on how high frequency goes and Doppler's effect is correct, then there is limit (lower than c) on how fast one can travel toward a light source. similarly, if there is a lower bound on frequency, then there is a limit (lower than c) on how fast one can travel away from a light source.
  11. Mar 17, 2007 #10


    User Avatar
    Gold Member

    That is correct, invariance of the Planck energy scale could require at least a modification of special relativity so that blueshifting is only possible asymptotically up to Planck energy (or so that Planck length may not be Lorentz-contracted into a smaller length, etc). At worst, special relativity could break completely at this scale.
    Last edited: Mar 17, 2007
  12. Mar 17, 2007 #11
    So what happens in a photon-photon collision? There should be infinite frequencys involved?
  13. Mar 17, 2007 #12
    Infinities are very frequently :smile: serious problems in physics.
  14. Mar 17, 2007 #13
    This doesn't sound correct. No matter how great the energy of a photon is, there is always another frame, where the energy is arbitrarily small. If a photon could change into another particle, it should not depend on the chosen frame.
  15. Mar 18, 2007 #14
    Certainly. I didn't mean that tim_lou's conclusion have to be wrong, I know doppler effect equation and how it works. Mine was just a question.
    Of course I know that a reference frame where a photon is stationary doesn't exist, but what he said makes one think! it's an interesting consideration!

    (Nice the joke with "frequently"!)
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook