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Behaviour of electron as wave and Particle

  1. Feb 18, 2010 #1


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    Sorry to ask a very fundamental question: But I never understood this?

    We know that sometimes electron behaves as a particle and some times as a wave. But we know that the characterisitcs of particle are very different from wave. For ex. particle has mass but a wave doesn't have. So, what happens to the properties of particle, for ex.mass when it behaves like a wave?
  2. jcsd
  3. Feb 19, 2010 #2


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    Nobody knows. Your question is in the realm of interpretations of quantum mechanics. In the context of standard quantum mechanics, or the Copenhagen interpretation (CI), what you have asked is simply not a meaningful question, in that it does not ask a question that can be answered by making an experimental measurement. (See for example my post in https://www.physicsforums.com/showthread.php?t=379260"). Note that interference has also been observed in the two-slit experiment with molecules as large as Buckminsterfullerene .. a 60-atom "soccer-ball".

    A different interpretation is deBroglie Bohm or dBB, which hypothesize that particles travel with something called 'pilot waves', which carry the wave-like properties, while the particles remain discrete. The dBB interpretation, like the Copenhagen interpretation, has been shown to be consistent with all experimental results to date. However, there is no independent evidence that it is any more correct than the CI ... it is just more palatable to some people because it at least attempts to address questions like your own, and give them "meaningful" answers. I am still learning about the dBB interpretation, but I believe that in the context of dBB, the answer to your question would be, "the particle and all of its associated mass goes through one of the two slits (although we can't know which one), while the pilot-wave travels through both slits and interferes with itself."

    There are many other interpretations of Q.M., but I think most of them have been shown to be inconsistent with one experimental result or another, and thus are considered to be wrong.
    Last edited by a moderator: Apr 24, 2017
  4. Feb 19, 2010 #3


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    Actually, a lot of people do know, or think they know, the answer to this and similar questions. The problem is that they disagree with each other, and it's not possible to decide among them by experiment because in the end, they all come up with the same predictions for the results of actual experiments.
  5. Feb 19, 2010 #4


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    Ok .. so nobody knows for sure. :tongue:
  6. Feb 19, 2010 #5
    By the way, Arxiv published today an interesting paper on this subject:


    where wave properties of the electron are referred to mass density oscillations.
  7. Feb 19, 2010 #6
    Are Positivism and Phenomenology DEAD?! :cry: SpectraCat knocked this one out of the park in my opinion. To summarize: "Conclusions pending, experiments ongoing, communication ends." :rofl:
  8. Feb 19, 2010 #7
    Think of it is a large number of waves covering all space. A particle would exist where the linear combination of the energy of these waves is high enough to be detectable.

    Where the linear combination is roughly zero due to peaks and troughs there is no detectable particle. Because with a very large number of waves the average will in most places be close to zero this would create the illusion of particles or energy clumps in certain spots.
  9. Feb 19, 2010 #8
    This doesn't quite work, though. A set of waves at one time may possess a totally different number of peaks as at a different time. Additionally, the single-particle wave function can exhibit arbitrarily many peaks without implying production of extra particles. The peaks simply correspond to maximum likelihoods for measuring a particle. They don't imply that a particle will be found at each peak.

    If I use the Copenhagen interpretation, the existence of a few tall peaks in a wave function only implies that I have a good idea about where to place my detector if I wish to measure a particle. Even with a smooth wave function you will have the experience of energy clumps in certain spots because when the detector fires you will know that a particle was incident on the active region of the detector.
  10. Feb 19, 2010 #9
    You try to think the electron as the "real" mass density oscillations?

    But I think it is difficult.
    Because the electron always has "spin" in QM.

    The very strange "spin" can be described only by the mathematical methods, if it exists.
    Because the spinning electrons don't return by one rotation.(See this thread ).

    The electromagnetic waves has spin 1 in QM, so it can be described by the "real" things.

    I think any interpretaion can not interpret this "spin 1/2".
    Last edited: Feb 19, 2010
  11. Feb 19, 2010 #10

    There are tables of elementary particles, e.g. electron has such and such mass, spin, charge, etc. but there is no table of "elementary waves". In this literally sense I assume particle is more fundamental than wave.
    I prefer "(quantum) particle behaving as (classical) wave" to "(quantum) wave behaving as (classical) particle", perhaps it's just a matter of taste.

    Last edited: Feb 19, 2010
  12. Feb 19, 2010 #11
    It is a matter of taste in the sense that you choose the Interpretation which matches your set of beliefs. Barring more evidence, they're just distracting and entertaining.
  13. Feb 19, 2010 #12
    For a simple explanation, I would reccomend The Fabric of The Cosmos by Brian Greene.
  14. Feb 19, 2010 #13


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    Yet another interpretation to add to the pile! :rolleyes:
  15. Feb 19, 2010 #14

    Quantum particle and quantum wave are wavicle that could be a convenient word for conciliation.:tongue:

  16. Feb 19, 2010 #15
    Do wavecicles come in cherry flavour? :rofl:
  17. Feb 19, 2010 #16
    So, in your opinion, in the Young two slits experiment, the photon goes not only the two slits, but all across the wall that contains the slit. Is this supposition correct ?

    Best Regards,

  18. Feb 20, 2010 #17
    Depends on your interpretation of QM (especially if it's SQM vs. dBB). The interence pattern appears only after a number of hits on the detector, and to add another measurement before the 'slits' (polarizers, etc) would destroy the pattern. There is no way to tell just how the photon makes its transit, but rather a probability of finding it at any given point. Even that can be unsure in DCQE experiments, but what all of that means is still a matter of ongoing debate and personal opinion.
  19. Feb 21, 2010 #18
    Ok, but let me check your opinion in this case. In the two slit experiment, sometimes physicists say that the wall containing the two slits represent and infinite barrier to the wave function (except for the slits region itself, naturally). Your conception, according to which everything is superposition principle, seems to invalidate this hipothesis of infinite barrier. So you seem to consider that the wave function in the two slit experiment traverses the wall at every single point of it.

    Is it a correct estimation of your reasoning ?

    Best Regards,

  20. Feb 21, 2010 #19
    I would say all things are always wave-like in that they can be described by a Schrodinger wave function. In the case of a electron and the two slits the electron travels both ways and the two paths are constructive or destructive depending on their phase relationship. If you block one slit then the electron goes through the one slit just like a wave going through one slit (i.e. no interference).

    More correctly it is a wave packet. Not a single frequency wave. A wave packet can have any degree of localization we want. High energy, high frequency, high localization.
  21. Feb 21, 2010 #20
    I got interested in this last part of your saying. What about momentum dispersion in this sentence?

    Best wishes

  22. Feb 21, 2010 #21
    1) I do not know
    2) it must be a soliton
    3) what is a soliton? a wave packet that does not disperse
    4) knowing nothing about solitons this is all I can say
  23. Feb 21, 2010 #22
    On the other hand, I may not know the math but, I do know that electrons do not disperse so the wave packet must be such that it does not disperse with time. I will leave it to the mathematicians to explain the math.
  24. Feb 21, 2010 #23
    edpell, I'm not sure what you mean by that. The wavefunction for an electron can certainly disperse -- as in cease to be localized at a particular location in space. It can only be detected at a single location, but this isn't the same thing as localization of its wavefunction.
  25. Feb 21, 2010 #24
    You are right.

    I guess I do not know what the question is wrt dispersion.
  26. Feb 21, 2010 #25
    Are you speaking of an atomic electron or a free one?

    Best Wishes

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