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Photons wave-like behaviour

  1. Aug 11, 2009 #1

    Edi

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    When a photon is travelling in a wave like manner, what happens when it hits some absorptive material? The material is a small ball, but the wave is large, wide... wave. Will the whole wave shrink and get absorbed or a small part of it will be absorbed?

    Actually, where do we see photons travelling as waves in nature? What else but the double slit experiment indicates that they do?
     
  2. jcsd
  3. Aug 11, 2009 #2
    Hm...most of the time we would use the particle theory to explain absorption of photons...never really considered how the size of the wave and the size of the ball weigh up...
    In any case, it is not possible for "a small part of [the wave]" to be absorbed. Einstein's postulate states that these discrete packets of energy (photons) are indivisible and hence we cannot have part of it being absorbed - as aptly evidenced by the intensity problem in the photoelectric effect.
     
  4. Aug 11, 2009 #3

    RUTA

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    This is related to the measurement problem and wave-particle duality, both of which have many explanations. My answer is, as I just posted in two other threads, not to think of the photon as a "thing" at all. Rather, the only "things" which exist are the actual pieces of experimental equipment -- the detector, source, beam splitters, mirrors, etc. -- and detector clicks are subsets of the detector resulting from its placement in the experimental arrangement.

    This is not a widely held view, but not everyone who subscribes to it is a crackpot, e.g., this quote from a couple Nobel Laureates (Bohr & Mottelson):

    “Indeed, atoms and particles as things are phantasms (things imagined).”

    A. Bohr, O. Ulfbeck & B. Mottelson, “The Principle Underlying Quantum Mechanics,” Found. Phys. 34, Mar 2004, p. 405.
     
  5. Aug 11, 2009 #4

    DrChinese

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    Actually there are plenty of other wave-like indications. How about refraction (change in direction) when light moves from one medium to another? Much of classical optics is wave-like.
     
  6. Aug 11, 2009 #5
    From my knowledge, the photon would get absorbed or it could get partially absorbed. If you are using a absorptive ball, likely the photon will be absorbed.

    Photon being absorbed is shown in the photoelectric effect. So you need to imagine photons as particles of EMR waves. This is kind of confusing, but imagine small segments of EMR waves that that would be the photon. In the photoelectric effect the photons are absorbed by bundles of these EMR waves which carry energy. However in the photo electric effect the photon is hitting a metal plate. But the photon is so small that hitting a ball would be like hitting a absorptive metal plate.

    Photons, being particles as well, carry momentum defined by p=h/lambda, the Compton Effect. Compton fired a photon into an electron and observed a change in wavelength of the photon, change in direction of movement of photon, and the movement of an electron. The change in wavelength determined that some momentum was absorbed by the electron. So in this case, kinetic energy was transferred to the electron, so in essence the photon was partially absorbed and its wavelength changes accordingly to its energy loss.

    Multislit diffraction also shows that photons can act as waves.
     
  7. Aug 12, 2009 #6
    I wish I knew the math to support the things I say, but before the photon is absorbed, it will be traveling it's wave-like path. This means that it is traveling along an infinite number of straight lines, simultaneously, but it doesn't (yet) exist as traveling along only one. It's pretty close to the "real" (mathematical/experimental) description to think of this wave as an imaginary wave, and along each of the infinite paths is an imaginary particle. We know, without a doubt, that these are imaginary, because if they were real particles, really traveling along an infinite number of paths, then this would equate to an infinite energy. You can only consider the energy as applying to a single one of these infinite paths, but the "idea" of the energy is "delocalized" such that every imaginary particle along every possible path would have access to this idea. When such an event occurs that the quantum state must reduce to a single path, this "idea of the energy" now "manifests" for a single one of these imaginary particles which travel just a single one of these infinite paths, as though it had been traveling that single path the whole time. This particle-wave nonsense is just that: nonsense. Quanta of energy do not act in any way that we can directly imagine, so we use our closest descriptions for the behavior we witness. Sometimes you look at a cloud and you see a cow, or a face, or maybe you'll see a particle, or a wave. But when you get right down to it, it's just a cloud.
     
  8. Aug 12, 2009 #7

    Demystifier

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    Such a view is fine from a purely experimental point of view. However, the problem with such a view is that we are not able to explain the results of such experiments in terms of a theory that operates only with such macroscopic degrees of freedom. On the other hand, a theory that involves a photon (quantum mechanics) works remarkably well. It is hard to believe that it is a mere coincidence.
     
  9. Aug 12, 2009 #8

    RUTA

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    Theoretically speaking, instead of particles or waves, you can consider elements of the spacetime symmetry group as the fundamental entities of quantum mechanics. That's the point of the paper I cited. Here is a quote from an earlier paper on this idea:

    “It would appear, however, that the role of symmetry in relation to quantal physics has, so to speak, been turned upside down, and it is the purpose of the present article to show that quantal physics itself emerges when the coordinate transformations (the elements of spacetime symmetry) are recognized as the basic variables.”

    A. Bohr & O. Ulfbeck, “Primary manifestation of symmetry. Origin of quantal indeterminacy,” Rev. Mod. Phys. 67, 1-35 (1995).
     
  10. Aug 12, 2009 #9
    http://www.physlink.com/Education/askExperts/ae176.cfm



    In electromagnetic field theory, when one solves for the distribution of a field in and around a conducting surface, one finds that electromagnetic waves do not penetrate very far through holes that are less than about a wavelength across. Equivalently, the reflection of electromagnetic waves from a conducting surface is not much affected by holes (or other irregularities) in the surface less than about a wavelength across. Therefore, it is possible to make a Faraday Cage or a satellite dish with 'holes' without materially affecting performance, provided that the holes are less than about a wavelength across.
     
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