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Particle-Wave Duality Contention

  1. Jul 21, 2010 #1
    This problem borders with the question of either wave only or particle only descriptions of duality, and I think it could possibly even end up being a personal opinion of the (hopefully qualified) repliers.

    In a normal atom, are there electrons orbiting around the nucleus? [This seems like a no-brainer: "Yes" but I don't believe that is true per QM.] Or, is there only an electron wavefunction of probable locations around the nucleus? This is to specifically ask whether there are really actual electron particles (as we would assume them to exist as fermions) each with their own velocity orbiting in an atom that is not being observed, or are there no physical electrons extant?

    I think QM gives wishy-washy open interpretation to this. Strictly, does QM not say that unless the electron is observed and the wavefunction collapsed, then the electron does not exist in one place with one velocity, but only probabilities of locations and velocities? But this does not jive with our idea of what fermions are.. This could be expanded to question whether fermions ever actually exist in one place in spacetime at any time other than when they are observed.

    (The question could be rephrased as a question regarding electrons as point particles in the double-slit experiment. When the slits are not being watched and electrons are fired individually, an interference pattern results. It seems then that the electrons go through both slits having two directional velocities, but neither one nor the other. This would mean that while the electrons were in flight they did not actually exist as fermion point particles except upon firing and being received at the end.)

    How then are the electrons -- if not extant as particles when not being viewed -- subject to gravitational acceleration and maintain inertia/momentum while in flight?
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  3. Jul 21, 2010 #2
    Wavefunction duality exist in our brains, not in nature.
    You can think about the point particles, but then use sum over histories of all their possible positions. You can use waves. Both mathematically give the same predictions.

    Particles + Sum over histories = Waves

    Finally, the concept of collapse is no longer used
    Both things (duality and collapse) are something from old popular books.
  4. Jul 22, 2010 #3


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    I would describe the duality differently.

    A photon (and any other elementary particle) is a quantum object which is strictly speaking neither particle nor wave because there are effects which are inconsistent with both classical particles and waves. One such effect is that depending on the experimental setup or the formulation it behaves like a particle or a wave.

    So duality is a concept which tries to bring quantum objects and quantum processes close to classical concepts and explanations; sometimes it works (in the photoelectric and Compton effect the particle description is OK), sometimes it fails (entanglement cannot be described by classical concepts at all).
  5. Jul 22, 2010 #4
    I understand all these points; and I must contend entanglement is an entirely different issue. What we are speaking of here is that a wave cannot have weight and mass. Weight and inertia are only possessed by particles. Waves, on the other hand, cannot posses momentum or weight.

    The wavelike properties of fermions in QM experiments are only fragments of reality due to our not being able to know where the particle is, e.g. the interference patterns in the double-slit experiment do not necessarily say that the electrons weren't each in one place at all times.

    What I am saying could be argued to be a particle-only truth for fermions. Any wave-like properties of fermions produced by QM experiments are due to lack of evidence for which place a particle is, or was, in. Oppositely, bosons are always waves, only showing particle-like properties when altered by abnormal monitoring of their QM situations.

    So, my answer to the question asked, "Do electrons orbit around the nucleus in an atom?" is "Yes' there are electrons orbiting."

    You on the other hand have no answer for this question. ("Yes~and~no" does not count.) This lack of having an answer is due to the interpretation of experiments which try to determine where a particle is when it cannot be determined. This has led to confusion and not understanding the reality of fermions.
  6. Jul 22, 2010 #5


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    You may want to start by read the FAQ thread in the General Physics forum.

  7. Jul 22, 2010 #6
    This is good example, you make some intuitive assumptions (based, probably, on our newtonian/classic 'common sense reasoning'). These assumptions are wrong in QM. In QM, wave has well defined momentum

    The next part is also wrong:

  8. Jul 22, 2010 #7


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    I don't know, what you guys understand under "wave". My understanding of "wave" is that you mean a field quantity which obeys a wave equation.

    If you associate with "wave" fields, then of course, classical fields carry energy, momentum, and angular momentum. Fields are entities not much different from point particles in this respect. The only difference is that these quantities are spread over all space. In relativistisc field theories, this is quantified by the energy-momentum and the angular-momentum-boost tensor whose time-time and time-space components give energy and momentum or angular-momentum) density, respectively.

    The expressions for these densities follow from Noether's theorem (for both fields and point particles).

    In quantum theory, both concepts are nicely united to the notion of quantum fields. There is no conceptional difference between the description of matter and fields anymore, and whether you describe more "wave like" or more "particle like" properties depend on the preparation of the system in question in a certain state. So Fock states tend more to the particle aspects. They are states of sharp particle number with particles having certain momenta and spin. The coherent states tend more to describe field-like aspects. They have a certain phase.

    Of course, quantum theory also includes the description of phenomena which are totally unknown in classical physics, mostly in terms of strong correlations at far distances (entanglement).

    All together, so farquantum theories subsumes all known phenomena in a coherent concept of description, and thus one should abandon old-fashioned concepts like "wave-particle duality" which obscure quantum phenomena more than they explain them.
  9. Jul 22, 2010 #8


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    I can only repeat what I said above: "duality" is an idea to harmonize two incompatible concepts. So my conclusion is that quantum objects are quantum objects and neither particles nor waves.

    Think about a duckbill: you can call it duck or beaver. But it is neither a duck nor a beaver, it is a duckbill. The beak looks like that from a duck, but that doesn't mean that the animal as a whole is a duck. It isn't. It is a duckbill. Always.
  10. Jul 22, 2010 #9


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    I couldn't agree more. That's why I said, one should abandon the old-fashioned concept of "particle-wave duality" and just discuss quantum theory. Particle-wave duality is uperfluous for more than 85 years now!
  11. Jul 22, 2010 #10
    And we've also had our heads up our you-know-whats in the dark for these 85 years now, with no progress on uniting quantum gravity! You speak as if we've come so far in 85 years when we basically still have the same two foundations from then with not yet a single tie. So don't act like you're soooo above the quantum physicists from the 1930's who spoke of "wave-particle duality"; you're not.

    Answer the question instead of arguing your ability to think of fermions as particles and waves simultaneously.

    Are there electrons orbiting the nucleus in an atom??

    How can waves possess weight by gravitational acceleration?
  12. Jul 22, 2010 #11


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    At least some of the people here are physicists; you're not.

    Yes. Except 'orbiting' is a meaningless concept for something which has no classical trajectory.

    A classical wave is a displacement of matter, of course it has weight.
  13. Jul 22, 2010 #12


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    Classical electromagnetic waves do indeed possess momentum, as discussed in (probably) every E&M textbook.
  14. Jul 23, 2010 #13


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    We are - in a certain sense. We accept that quantum theory is weird. That's the main difference (it is ontological than physical)

    There are electrons, but they are not orbiting (in a classicsal sense)

    Because the source of gravity is energy-momentum density; energy-momentum density is perfectly understood since electromagnetism and GR; there is no problem with waves.

    The problem with quantum gravity is totally different and has nothing to do with wave-particle dualism.
  15. Jul 23, 2010 #14
  16. Jul 23, 2010 #15


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    I think you misunderstood me. I' not saying that we are "sooooooo above the quantum physicists from the 1930's". In fact, those quantum physicists (Heisenberg, Born, Jordan; Schrödinger; Dirac) were the ones who (with very good reasons) abandoned "wave-particle duality", which has been an important historical step to this development of modern quantum theory, but it has not been the final answer as we know since Heisenberg's "Helgoland paper" from July 1925.

    Further, I do not think of fermions (or also bosons for that matter) as particles and waves simultaneously. I think of them as being described by modern quantum theory, which tells me that they are neither classical particles nor classical waves but quanta.

    There's no simpler notion than quantum theory itself to describe the behavior of elementary particles or small compound systems. Nowadays, quantum theory is the most fundamental and most comprehensive theory we have to describe matter. Also the "classical behavior" of macroscopic systems is an emergent phenomenon, which can (at least in principle) be understood with quantum theory.
  17. Jul 23, 2010 #16
    Thanks all for answering. I thought the sharper prodding would help me get the more defined answers I was looking for out of you. I'm investigating all of the responses.

    I saw several "Yes" answers to there being electrons moving around in an atom. ("Orbiting" was a nomenclature error.) However, I am not sure if I am to take these individual's answers literally. It seems hard for physicists to commit to saying that there are any physical particles extant in the universe with certainty. I would figure this to be due to the great difficulty in really calling anything a true particle in regards to QM. But, of course, this is exactly what I was getting at.

    I must assert my view, if it has not already been clear, that there are at all times electron particles moving, each with their own individual speed and trajectory, continuously around the nuclei in atoms. With this claim, it would be understood that any notion a person has that atoms are not composed as such is due to faulty understanding of nature.

    Also, I want to say that I know we have made tremendous progress in QM, as the wording in that last post could be taken as insulting the way I worded it. It is actually GR that we have not been able to add upon; and there again is the gaping lack of reconciling the two. My thoughts are that GR gives the true core nature required in understanding gravity, and that the incompatibility between GR and QM for this must be a problem with our understanding of QM; thus, my questioning of dualism. Perhaps there is some such weakness in our conception of particles that may be contributing to our misunderstanding gravity.

    It seems I have having the same problem Einstein struggled with in QM: realism. Nature, to me, must have an ultimate realism, with particles always having one velocity - whether the velocity can be known to us or not is our problem in observation. And, as I alluded to earlier, the times fermions appear to not be in one place in our investigation is not due to their not being a particle at that time, but due to our not being able to define their location due to method of experimentation, forcing us render them at those times as waves. With this, it could be posited that fermions are never truly extant as waves in reality. This is an argument of realism, and that parts of QM may be an illusion, even though they are the best scientific conclusions to be made.
    Last edited: Jul 23, 2010
  18. Jul 23, 2010 #17
    In my arguing waves cannot have "momentum" I believe there was another confusion with my nomenclature.

    My intended meaning was that waves do not have inertia. Inertia is a property only contained by particles. So, if the electron is not extant as a particle during some moment in time, how then can it have inertia at that time?

    For instance, if the electrons in the double slit experiment were not particles that took one path and went through one slit each time, but phased out into a wave and then re-condensed into a particle, there would be a loss of inertia at the time the electron was not extant as a particle but only as a wave, and the momentum would be lost.
  19. Jul 24, 2010 #18
    Did you completely ignore the answers?
    Electrons do not 'switch' from one mode (particle) to waves and back from time to time. They behave the same way all the time.
  20. Jul 24, 2010 #19
  21. Jul 24, 2010 #20


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    As long as you search for answers along tracks of classical physics you will not succeed.
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