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So light has dual nature but I was wondering

  1. Apr 8, 2012 #1
    So if light acts like waves when interacting with huge objects and acts like regular particles when interacting with very small bodies like atoms and electrons.. now I know this might sound silly, but what if the photons were to be in the size of a tennis ball, and the electrons also relatively huge, will we still witness light to be acting like a regular particle ? like the electrons absorbing photons individually? or will light act like a wave?
  2. jcsd
  3. Apr 8, 2012 #2
    First I'm going to correct one of your assumptions: light always acts the same, and it's neither like particles nor like waves. It's something else entirely, described by a wavefunction.

    On to your question, it is really meaningless, because there is no way light would be that size. It behaves the way it does because it's that small. In fact, everything that size behaves the same way. Electrons, protons, photons, neutrinos, and even bigger stuff, atoms, and all of that, behaves exactly like light, with the weird non-particle non-wave nature.

    And also, since you are made of all of that, you, too, possess these properties of non-particleness and non-waveness. It's just that there are so many non-particles non-waves making you up that these effects mostly disappear for all practical purposes.
  4. Apr 8, 2012 #3


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    Also this view must be corrected since particularly photons, massless quanta of a vector quantum field cannot be described by a wave function but by a quantum field. The reason is that they are very easily created (e.g., bremsstrahlung by accelerated charges or in annihilation of a particle-antiparticle pair, etc. etc.) or destroyed (e.g., in the photoelectric effect, pair creation at a heavy nucleus,...). Thus one has to use quantum field theory which easily takes account of creation and destruction processes.

    A quantum mechanical state behaving most closely like a classical electromagnetic wave are the socalled "coherent state", which are a special superposition of states of arbitrary photon numbers (including also the vacuum, i.e., the state with no photons), i.e., they don't have a well-defined photon number at all.

    Also one cannot define in a naive way a position operator for photons. See Arnold Neumaier's physics FAQ on this quite subtle point of relativistic quantum theory of massless quanta:

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