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Wave-particle duality and my non-physicist friend

  1. Jan 21, 2015 #1
    Hi, I'm a vet with an amateur interest in physics. In discussion with a friend about the usefulness of physics he stated that physicists had not even decided whether light was a wave or a particle. I said the following:

    'The question of whether light is a wave or particle is not one which really troubles modern physicists. A photon is not something we can describe in terms of things we humans can see with our eyes. If you do an experminent to see if light is a wave, it is; if you do the same for particles, it is too. Quantum physics tells us that photons are quanta of electromagnetic waves, so if you were to twist my arm I'd say it is a particle which has emergent wavelike properties. Photons are described by wavefunctions and governed by quantum amplitudes; these are complex numbers and as such have a magnitude and also a phase. This phase rotates as time goes on and gives rise to an illusion of wavelike behaviour.'

    Was I taking crap?
  2. jcsd
  3. Jan 21, 2015 #2


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    A photon is a particle only in the quantum field theoretical sense. This is not what you would tend to call a particle in classical mechanics. A photon is also not a wave.

    However, what we call particles in QFT are objects that have some properties reminiscent of waves and some that are reminiscent of classical particles.

    My short answer would have been that it is neither, but it has some properties that we typically ascribe to particles and waves.
  4. Jan 21, 2015 #3


    Staff: Mentor

    You can also see our FAQ:

    However if you want to learn the technical detail and have an understanding way beyond popularisations a wonderful book has recently been released:

    I am studying it right now and my knowledge of QFT has benefited a lot.

    Its big advantage is that your background in ordinary QM doesn't have to be at an advanced level - Susskinds book is good enough:

    Last edited by a moderator: May 7, 2017
  5. Jan 21, 2015 #4
    What about the concept of phonon in the context of condensed matter ? Is there similarity between these two concepts that can be use to better understand the concept of photon defined in a given theoretical framework ?

  6. Jan 21, 2015 #5


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    Guineafowl, to add to what has already been said (with some repetition), the best SIMPLE way to express it is to simply say that light is a quantum object (as are electrons, for example, and this means it is not a particle and not a wave, it is it's own thing which is neither but has some of the characteristics of both)
  7. Jan 21, 2015 #6


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    Sure. They both use similar QFT methods. Its not any easier however.

  8. Jan 21, 2015 #7


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    Is your friend also a veterinarian? Because this is like saying that vets haven't even decided whether a frog is a fish or a reptile. It has properties of both, and yet it's neither.
  9. Jan 21, 2015 #8
    Thanks for all your replies. My friend is actually an acquaintance, and is really a Jehovah's witness who came to the door, but my original thread with this information got deleted.
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