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What is light?

  1. Sep 15, 2008 #1
    Sometimes light exists in the form of a wave and sometimes light exists in the form of a particle or wave/particle duality. Light existing in two completely different forms does not make sense to me but the experiments have proved this right? I have a theory that light is actually a stream of particles/photons moving in a wavelike up and down pattern that would prove wave/particle duality true in one existing form that I could believe in.

    The particles are moving so fast they appear to us as a wave and the experiments that prove light is a particle are misleading in that they destroy the wave. Any comments?
  2. jcsd
  3. Sep 15, 2008 #2


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    At the quantum level, light exists in a single form: as photons, which are quantum-mechanical objects described by the theory of quantum electrodynamics (QED). Some aspects of their behavior are particle-like and others are wave-like, but it all comes from the same mathematical description.
  4. Sep 15, 2008 #3
    jtbell: What do you personally think of my theory? Do you think I could be right about this? I am kind of saying what you are saying or believe that light is a stream of photon particles at the quantum level making up a wave?
  5. Sep 15, 2008 #4


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    You are missing the point: "waves" and "particles" are classical concepts and light is purely a quantum mechanical phenomena (albeit one that can often be well described by classical equation like Maxwell's equation); there is no such thing as "classical light". If you want an accurate description of light you need to use quantum electrodynamics(QED)

    Hence, it is not possible to explain what light is using concepts that "make sense" to us; light is -just as most quantum phenomena- simply very weird.
    Fortunately this does not stop us from formulating very successful theories that can describe light (i.e. predict the outcome of experiments) using math.
    Quantum electrodynamics is a very good theory and is -as far as we know- the "whole truth" about light (as long as gravity is not involved).

    Nowadays we can do all sort of funny things with photons in the lab, see e.g.
  6. Sep 15, 2008 #5
    Ok but what shape or form does the light in my office exist in? It has to have some physical shape or form if light exists and moves around?
  7. Sep 15, 2008 #6


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    What shape or form is the water that you drink?

  8. Sep 15, 2008 #7
    I remember seeing a theoretical illustration of Einstein running alongside a beam of light and the light in this example was in the form of a wave? Are you both trying to tell me that light does not have any shape or form whatsoever?
  9. Sep 16, 2008 #8


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    Shape and form are to a large extent classical concepts.
    Let me give you another example: The electron is -as far as we know- a point particle; i.e. it does not have a size (zero volume) but it still has mass.
    Hence, it would obviously be wrong to attribute a "shape" to an electron.
    But -and this is the important part- even though no one can really "visualize" an electron this does not stop us from describing it mathematically, the same is true for light.
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