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Is there such thing as an anti-photon?

  1. Sep 12, 2011 #1
    Is there such a thing as an anti-photon? and if it did exist what would happen if it collided with a normal photon?
     
  2. jcsd
  3. Sep 12, 2011 #2

    tom.stoer

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    Photon and anti-photon are identical.
     
  4. Sep 12, 2011 #3

    Drakkith

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    A photon is it's own antiparticle.
     
  5. Sep 13, 2011 #4
    there is no anti photon ..... some how if there is an anti photon and if they collide they end up in an explosion
     
  6. Sep 13, 2011 #5

    DrChinese

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    Welcome to PhysicsForums, space girl!

    You may be thinking of the proton and the anti-proton, which release a lot of energy when they meet. Photons are different particles altogether, and do not act the same.

    I might suggest reading up on what is called the "Standard Model of Physics" to gain a bit more understanding on the subject.
     
  7. Sep 13, 2011 #6
    When two photons cross each other (for example when shining two beams of light across each other) is there a noticeable difference between annihilation-creation and just passing through each other?

    EDIT: Hm, on second thought this might be off-topic of me? I'm not sure? Please tell me if it is, didn't intend it
     
  8. Sep 13, 2011 #7
    No I was not confusing photons with protons. Because I know that when a particle and an anti-particle collide (such as a proton and anti-proton) the immediately turn into energy such as photons and gamma radiation. And if photons are created during the collision then what would happen if they had a anti-particle collision.

    Thank you for your responses. :)
     
  9. Sep 13, 2011 #8

    cmb

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    That would have been my stock answer.. but, hang on a minute...

    At the quantum level, if we have two photons in anti-phase, each still has hv worth of energy. One cannot have '-hv' of energy!

    So if the two are actually anti-particles, then where does the 2hv of energy go?
     
  10. Sep 13, 2011 #9

    DrChinese

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    Photons do not annihilate in the same manner, as you say they are in fact a byproduct of other interactions. Photons (and "anti-photons") obey Bose-Einstein statistics, and can occupy the same region of space without issue.
     
  11. Sep 13, 2011 #10

    tom.stoer

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    Antiparticles do not have negative energy.

    This perception is perhaps based on some formal arguments introduced by Dirac regarding the "negative-energy-solutions" of his famous equation. Look at positrons (antiparticles of electrons) in bubble chambers: they have positive mass, energy and momentum.
     
  12. Sep 13, 2011 #11

    cmb

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    Exactly, but what happens to the energy of two photons, if they act as each others anti-particles and 'annihilate'?
     
  13. Sep 13, 2011 #12

    tom.stoer

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    Two photons don't annihilate "to energy" b/c they carry energy which is conserved.

    When two photons collide to lowest order NOTHING happens; they don't interact at all. In next-to-leading order they scatter elastically, i.e. two new photons are created. In addition there are processes (starting at a certain threshold) where other particles like electrons can be created.
     
  14. Sep 13, 2011 #13

    PAllen

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    Two photons in, two photons out. It is called photon scattering, a rare process that needs to be mediated by virtual charged particles (e.g. charged vector boson or quark).
     
  15. Sep 13, 2011 #14

    cmb

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    So, what happens to the energy of the photons during destructive electromagnetic interference?
     
  16. Sep 13, 2011 #15
    From my understanding is that nothing will happen.
     
  17. Sep 13, 2011 #16

    jtbell

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    The photons are not destroyed. They're simply distributed differently than they would have been in the absence of interference.
     
  18. Sep 13, 2011 #17

    tom.stoer

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    Destructive interference does not mean that the photons will vanish completely, it does only mean that it's not allowed for the two photons to be detected at a certain location (they can of course be detected elsewhere).
     
  19. Sep 14, 2011 #18

    cmb

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    OK, so back to my question on 'does that mean negative energy'; if we go to a location where we measure destructive interference of the two photons in that location, then what energies do we measure there?
     
  20. Sep 14, 2011 #19

    tom.stoer

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    Zero energy.

    A detector which "sees" destructive interference in a certain place sees nothing and cannot distinguish this "nothing due to destructive interference" from "no photon at all".
     
  21. Sep 14, 2011 #20

    cmb

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    So is there no energy there, or is it just this type of detector that cannot detect it.

    And if not, then what sort of theoretical detector could detect the energy of the two anti-phase photons at the moment of their intersection? I mean, if we had an infinitesimal electromagnetic detector, then it'd be registering 'no energy' there, right?, but we're saying there is actually 2hv there, because they head off after their encounter?

    So if an EM type detector could not detect the extant energy of two anti-phase photons at the moment of their intersection, then what sort of detector can?
     
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