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I just saw an exam question: Write down the antiparticle for the virtual photon.

The answer was "virtual photon".

Is the question even a meaningful one? If so please explain why?

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    $\begingroup$ No, the question is rubbish. $\endgroup$
    – ACuriousMind
    May 9, 2015 at 13:00
  • $\begingroup$ @ACuriousMind: Thanks. I find this frustrating because I put "the gamma photon isn't a particle" and it wouldn't have got me the points according to the mark scheme. Was my answer wrong? (is the gamma photon a particle?) $\endgroup$
    – user45220
    May 9, 2015 at 13:02
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    $\begingroup$ Photons are particles (and there's nothing special about a "gamma" photon, and the antiparticle of a photon is indeed the very same photon), the question is rubbish because "virtual particles" aren't proper particle states at all and so asking for their antiparticles doesn't make any sense. $\endgroup$
    – ACuriousMind
    May 9, 2015 at 13:04
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    $\begingroup$ Strictly speaking photons aren't particles, either. They are quanta, i.e. changes in the quantum numbers of a quantum field, but most people like to glaze over that by calling quanta particles. Virtual photons aren't even that. They are simply the uncertainty principle at work in case of quantum fields. $\endgroup$
    – CuriousOne
    May 9, 2015 at 13:55

1 Answer 1

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No, the virtual photon is not a particle, since a virtual particle is what one calls the internal lines in a Feynman diagram, and there are no asymptotic particle states associated to these lines, so a virtual particle is not a particle in the usual (or any other rigorous) sense.

Therefore, the question is non-sensical because it is not clear what an antiparticle of a virtual particle would be, since a virtual particle isn't a particle state to begin with.

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