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Photon dimensions

  1. Feb 4, 2007 #1
    Does a photon have spatial dimensions.Also do two photons having different energy occupy the same volume?

  2. jcsd
  3. Feb 4, 2007 #2
    The motion (and location) of a photon is governed by its wavefunction, which contains all of the information about its "dimensions." To find the size of the region occupied by the photon, the uncertainty principle requires that you give up knowledge about its wavelength.

    Two photons with different energies will have different wavefunctions, and these can certainly overlap.
  4. Feb 4, 2007 #3
    i didn quite understand.Wats the anser about the volume question:yes or No?
  5. Feb 5, 2007 #4
    Yes, they can overlap in the same volume, but the fields add and you get just one combined wavefunction.
  6. Feb 5, 2007 #5
    so photons hav different energy density?(yes i suppose)er..
  7. Feb 5, 2007 #6
    You can't really define the energy density of a single photon. But you can calculate the number of photons per unit volume from the radiation intensity and the photon energy (E=h*freq).
  8. Feb 5, 2007 #7


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    The "size of a photon" has been discussed regularly here. You might like to review some previous threads:


    Tip: concentrate on links that do not contain "archive" in the URL. The archive versions of threads don't have information about quoting, which can make reading them confusing, because it's hard to figure out who wrote what.
    Last edited: Feb 5, 2007
  9. Feb 5, 2007 #8
    Very helpful. Thanks.
  10. Feb 5, 2007 #9

    I went thru a few of the topics u had suggested,but i fail to understand how a photon is a point particle.This is as energy occupies space and time so shudnt a photon:zzz:

    Also, duz a photon travel in a wave?
    Last edited: Feb 5, 2007
  11. Feb 5, 2007 #10


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    I quote marlon from one of the threads in the Quantum Forums as he explains the crux of the matter so eloquently;
  12. Feb 5, 2007 #11
    If you click on the "archive" links and then on the "View full version" link on the page that pops up, the threads are formatted properly.
  13. Feb 5, 2007 #12
    But still there must be some way of comparing the energy density of a photon wudnt there be eh...?
  14. Feb 5, 2007 #13
    You could measure the EM energy density before and after a photon is absorbed, and call the difference an equivalent energy density for the photon. But if the volume is different, you get a different answer. A photon really has no defined volume, so you are confusing classical and quantum concepts.
  15. Feb 5, 2007 #14
    Anantchowdhary, I think we should think how the properties of the macro world can be explained in terms of the sub-atomic world not how the sub-atomic world can be explained in terms of the macro world.
    Last edited: Feb 6, 2007
  16. Feb 6, 2007 #15
    But still..Energy occupies space isnt it.I am sorry and thank all of you for being patient.But does energy occupy space or not(I think so as it also curves space-time)
  17. Feb 6, 2007 #16


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    Does "pain" occupy space? What about the color indigo or the saltiness flavor? Do they occupy space?

    I'm not trying to be funny here, but it appears that this may be the only way to demonstrate to you why your assertion simply has no answer, unless you want to make one up.

    I also don't understand why, after a link to a previous thread on the identical question, that we're repeating everything all over again.

  18. Feb 6, 2007 #17
    Please be more polite .I am being straight-forward .Please be the same with me and please explain to me why a photon cannot have volume even though it occupies spacetime
  19. Feb 6, 2007 #18


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    Can you show me evidence that allows you to claim that "it occupies spacetime"? It appears that you used this several times, but you made no such support to how you would know such a thing.

  20. Feb 6, 2007 #19
    Sure.What i understand is tht if something curves spacetime then it occupies spacetime.Now please tell me whether that is correct or not
  21. Feb 6, 2007 #20


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    Er.. there is a problem with logical consistency here. You simply cannot make a connection like this in physics and expect to get away with it. Just because A does something to B doesn't mean that A=B. A photon can also cause the emission of an electron. Does that mean it is also an electron? Or "occupies the space of an electron"?

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