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Wave-particle duality

  1. May 27, 2008 #1
    Photons are always called 'particles'. But through many experiments (by scientists such as Geoffrey Taylor), it has been found that photons show some strange characteristics which resemble those of waves. In fact scientists also reveal that electrons also show wave-like nature(in fact they have frequencies). So what can we call them-waves or particles? Or none of them? And how is the Heisenberg's uncertainty principle applicable here?
  2. jcsd
  3. May 27, 2008 #2


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    "Particles" is the appropriate word, but these are quantum particles, not classical particles. A classical particle can be thought of as small massive spheres, but quantum particles can't. If you're interested in how they are different, I can recommend the book "QED: The strange theory of light and matter", by Richard Feynman. It's a short book that doesn't use mathematics.
  4. May 28, 2008 #3
    Personally I prefer the term "warticle" ;p
  5. May 28, 2008 #4
    some think its particles guided by pilot waves (DeBroglie). heisenburg's uncertainty principle applies because quantum entities are expressed by probabilities, and these probabilities have standard deviations, and it is the product of the standard deviation in momentum times that of position that has a bound defined by heisenburgs principle. typically wavelike entities have better defined momentum because the DeBroglie wavelength is what shrodinger used to motivate his equation (i think).

  6. May 29, 2008 #5
    I sometimes used to picture them like packets, like a tiny box with a piece of wave inside, a space-limited (and time-limited) wave impulse.

    If you imagine each of them like in the attached picture then each is "space-confined", but many of them together forming a beam can be seen as a continuous wave (because the envelope is a piece of squared cosine, if you put many of them one after the other in the proper position and sum them all you should get a constant envelope).

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    Last edited: May 29, 2008
  7. May 29, 2008 #6
    Some people use the term wavicle.

  8. May 29, 2008 #7
    The uncertainty principle is, in fact, linked to Fourier theory. It is a principle of the Fourier transform of all signals (waves) that the time duration and temporal bandwidth product is limited to:

    [tex] \Delta t \Delta \nu = 1 [/tex]

    Further, the spatial frequency k is propotional to the momentum of the "wavicle" (with a constant 1/h-bar). So, we find that the width of the wavicle is constrained to:

    [tex] \Delta x \Delta p = hbar [/tex]

    So the link between the uncertainty principle and the wave property of matter is mathematical in nature. The wave property of matter, on the other hand, requires experimental evidence.

    For reading, google for "bandwidth time product". The Stanford Exploration Project has nice slides.
  9. Jun 4, 2008 #8


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    For the most part, electrons, photons, baryons and so on are detected as if they are particles, like very small ones. That's how the theory treats them. It is the probability structure that has wave-like properties. At a practical level, electrons and their associates are particles; not waves. Think of water molecules in surface water waves as a good and illuminating example.
    Reilly Atkinson
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