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B What is light exactly? Electromagnetic wave or photons?

  1. Dec 31, 2017 #21


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    It is not. You fire one photon at the screen and one dot appears; this behavior is exactly that of an indisputably particle-like rifle bullet.

    The "interference pattern" prediction of quantum mechanics is probabilistic, and it is impossible to observe any probabilistic phenomenon with a single observation.
  2. Jan 1, 2018 #22


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    I have to disagree with most of what you are saying. In this situation, you cannot say that as you add more photons, light becomes more like a wave. Not only is that a confusing statement, it is near incorrect. Light is always a wave, just that you can't really see it sometimes.

    Even if you shoot singular photons in completely separate experiments, you will see a distribution pattern.
    It isn't different. It is exactly like sending it through one apparatus just one at a time. The point of the experiment is that the wave nature is present at every instance, be it one photon or a thousand.
  3. Jan 1, 2018 #23


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    It's not the same thing. The electron is a (quantum) particle whose dynamic properties (position, momentum, energy, angular momentum, spin angular momentum) are governed by a "probability amplitude" function. This is usually called the "wave" function, but that is a coincidence of terminology that leads some people to get confused about whether it is "real" wave or not.

    In any case, you can (and should, in my opinion) learn QM without any reference to the wave-particle duality or "wavelike" behaviour of particles. I have two QM books:

    In Griffiths, wave-particle duality is mentioned once, as a historical footnote on page 420. And, in Sakurai it doesn't get a mention at all.

    Also, if you are new to QM, I highly recommend Feynman's Messenger lecture:


    And, especially, how he talks about "waves" and "particles".
  4. Jan 1, 2018 #24

    Mister T

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    The OP's question was about electromagnetic waves. Those waves are solutions to Maxwell's Equations and as such completely ignore quantum mechanics. Photons are purely quantum mechanical particles, and in quantum theory Maxwell's Equations are an approximation, valid only in the limit of large numbers of photons.

    Thus light as an electromagnetic wave is a picture that appears only when large numbers of photons are involved.
  5. Jan 1, 2018 #25


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    This entire post is completely wrong.

    The which-way experiment clearly shows that light does NOT behave as a classical wave. The anti-bunching experiments clearly show that light does NOT behave as a classical wave.

    Mister T is correct, that we tend to detect more and more of the classical wave nature when we are dealing with large number of photons, and when we are dealing with longer and longer wavelengths. So yes, there ARE regimes where the classical wave nature of light is INSUFFICIENT to describe what we observe.

    If you have the classical wave description to describe those two types of experiments that I mentioned above, I'd like to see it. Otherwise, you need to think twice before you spew such wrong information.

  6. Jan 1, 2018 #26


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    Ok @Mister T, thanks for clarifying my post. I was thinking of a quantum mechanical perspective but I seemed to have been missing the point of the OP's question.

    I'll revise my answers further next time.
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