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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

    P.S.
    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

    tom.stoer

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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

    ZapperZ

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

    Zz.
     
  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

    vanhees71

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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

    tom.stoer

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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

    vanhees71

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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

    alxm

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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

    jtbell

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

    tom.stoer

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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

    vanhees71

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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

    tom.stoer

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    As long as you search for answers along tracks of classical physics you will not succeed.
     
  22. Jul 24, 2010 #21

    alxm

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    Says who? There are certainly physical particles extant in the universe, and this is not at odds with QM in any way.

    No, it's your understanding of nature which is flawed. (And obviously saying 'orbits' was not a nomenclature error because you just repeated the claim)
    Electrons in an atom do not have defined velocities or trajectories. You're blindly asserting they act classically. They do not. If what you said was true, electrons would simply 'fall in' to the nucleus and remain stationary there, because there would be no reason for them not to. Second, the electron of a hydrogen atom (for instance) has no angular momentum, and this is experimentally verifiable. Yet the charge density around a hydrogen atom is spherical, which is also experimentally verifiable. There is no way the electron can satisfy these two facts by moving classically. The electron can only be moving either 1) Non classically or 2) Not moving at all.
    Further there's the matter that even if you were to build a semi-classical model constraining the electrons (a la the Bohr model), any multi-electron atom would by unstable and chaotic, and would spontaneously ionize. Which they do not. Then there's the matter of electron tunneling, which is wholly impossible for anything with a classical trajectory, and also empirically quite well verified. Then there's the fact that electrons exist in a superposition of states, something which again bars them from having any kind of classical trajectory, and which is a property fundamental to chemistry. So is exchange energy, which is also entirely non-classical.

    What you're saying is simply wrong.

    Nature is not under any obligation to act in a manner you happen to find intuitive.
     
  23. Jul 24, 2010 #22
    But, if we make an experiment to look specifically in the atom's electron cloud to locate electrons, we will find electron particles there. Who is to say then, for sure, that there were not electron particles there while we were not looking? Do you see that at any time we can observe a particle directly, it is observed as a particle and that it is only when the particle cannot be observed that it seems to be a wave?

    The atom behaves in a way observable to us that the electrons appear to be in all possible locations at once due to the positions and trajectories of the electrons being indeterminate for us. This is an emergent quality resultant of it being improvable that the electrons have locked-in trajectories during that time.

    If the electrons have great enough speed in their orbits, wouldn't their momentum in the direction tangent to the nucleus keep them from falling into the nucleus? I can see how if they had no velocity or not enough momentum they would be pulled right into the nucleus. Moreover, if the electron with negative charge was spread out in a sphere around the nucleus, wouldn't it be even easier for the electromagnetic force to pull this negatively charged wave (that is not moving at all) straight down to meet the positively charged nucleus? And, if the electron is moving fast enough, the charge density of the hydrogen atom would smooth out and become spherical over time, as it is when we observe it over time and not instantaneously. This would also be true for multi-electron atoms. Is there not an equation which gives the speed that the orbiting electrons must have in an atom, i.e. the rate at which the electrons must revolve, such as revolutions per second, by the laws of physics?

    Also, superposition would be something that was also an emergent quality due to our not being able to define which place the particle is in, as well as electron tunneling. These seem to be the exceptions, not the standard behavior for the particle. I am not disputing that particles behave as waves sometimes through empirical evidence.

    What I am saying could be over-simplified to say that gravity never acts on a photon, as a photon is a wave (in its truly natural essence) [spacetime curves the paths of photons, but this is not gravitational action], and gravity always acts on electrons, as electrons are particles with rest mass in their true nature. A wave does not have rest mass. This is a realism that occurs at all times in the universe, making it the seemingly universal rule, while the odd characteristics that we are discussing now only arise through observational differences in certain situations. This would logically make a prevalent difference between photons and electrons in reality, not both the same type of particle-wave quanta, each being both and never one or the other.
     
  24. Jul 25, 2010 #23
    We never detect particles "directly"
    All our detection devices (photocameras etc) detect photons in areas which are big enough, say, 10x10 atoms minimum. Everything else is a result of calculations (scattering etc)

    There is no such speed.
    particle electron MUST radiate energy away.
    This is why the 'planetary' model of atom was rejected in the beginning of 1900 century.

    No.
    Our lack of knowledge, expressed in a form of 'probability wave', is always positive, so probabilities are always added. Wave, on the contrary, is complex-valued, so adding possibilities you can get 0.
    So it is not possible.
    For example, try to explain 2-slit experiment based on the fact that we dont know where the particle is.

    Photons are affected by the gravity, as well as, say, neutrons. This is confirmed by the experiments.

    3 puzzles for you.
    1. What do you think, can relatively big objects, say, molecules, form interference patterns in 2-slit experiment?
    2. Is neutron 'naturally' as you speak, a particle or a wave? What it consist of?
    3. How 'heavy brother' of the photon, Z-boson, can have rest mass?
     
  25. Jul 25, 2010 #24
    Thanks for the reply dmitry. Answers to your questions for me:

    1) My argument for the double slit experiment is that when objects (e.g. atoms) are individually shot towards the slits, they always hit the receiver as single objects, one by one. Any time one is shot, it is received on the other end as a particle; this is all we can tell when the slits are not being monitored. However, if the slits are monitored, we always find that the particle only took one path. There is nothing to prove that the atoms did not take only one path each when they are fired individually and the slits are not observed. When the individual atoms form an interference pattern over time, it does not necessarily prove that the particles each did not take one path.

    My suggestion for how the interference pattern occurs when the particles really each take only one path is that the interference pattern is a result of our lack of knowing the paths which the atoms took. This quantum effect of the particles seeming to act as waves (the interference pattern), by my depiction, is resultant of the impossibility for us to tell which path the particles did or did not take, due to our not having observed it.

    2) My depiction for the neutron is actually a spherical wavefunction of the triangle that the three quarks form when tied with gluons. When you take all of the orientations that the triangle can have, you result with a spherical wavefunction. In this way, the neutron is not three individual quarks connected by gluons, but rather a spherical waveform of one particle of the neutron. The neutron always exists in this form except if a quark within it is observed, at which time the spherical wavefunction diminishes and it is no longer one particle -for that moment- but three individual particles (which will each then be defined as smaller individual spherical wavefunctions -their smaller diameter correlating to their smaller mass). But again, when we have lack of knowledge of where the neutron is, we will find it appears to exist as a 'probability wave' and not a particle.

    I guess this description bears likeness to wave-particle duality, in which the fermion is a particle, but the particle is composed of a waveform, having no classical body; however, by my description, the fermion always exists as this type of spherical waveform particle at all times, having one position in spacetime and one velocity at all times (though it will seem to us to behave as a wave whenever we do not have evidence of it having one location in space -which misleads us to think that the particle is a wave, when it only appears to us to be wave).

    3) The mass of the W and Z bosons are, as I am sure you know, a type of freak bosons. They violate symmetry and have mass; this is proposed to be governed by the Higgs boson. I would argue that the W and Z actually have mass because they too exist as spherical waveforms as well. Do the W and Z ever travel through spacetime at the speed of light like a wave should? If the answer is "not provable" we might be able to say, with no evidence against us, that the W and Z are actually more like fermions than they are like light waves (which never have a spherical type waveform).


    I must argue against your position that light waves are gravitationally accelerated. We see that the paths of light waves are curved due to the curvature of spacetime around massive bodies, but we do not see that the waves have gravitational weight due to acceleration. This is a clear fundamental difference from fermions, which have gravitational weight. I find this to show proof that photons (wave quanta) and electrons (particulate quanta) are not the same type quantum object, that is, both wave and particle; if they were the same type of object (which Quantum Mechanics images them to be) there would not be such distinct differences between them as only waves being able to travel at c and not particles.

    I am not sure what you mean in saying that if the electrons in atoms were particles they would have to radiate energy away. Even by QM theory if we placed a detector on a portion of the electron cloud, we would always find there to either be a particle there or no particle there, never both.
     
  26. Jul 26, 2010 #25
    It does not explain why opening a second slit, adding more path to photons, decreases the intensity of light in some spots. Also, knowing how many experiments confirmed QM with extremely high precision, this "explanation" has no more value as something like "I suggest that tiny flying Unicorns hit some photons so the interference pattern is formed"

    How many gluons are there? :)

    Now here is an interesting contradiction in your view. Before you wrote:

    Then you write:

    Do you understand that we, as observers, and our measurement devices are nothing more than huge systemed built of atoms - and ultimately, of elementary particles? That there is nothing in nature that fundamentally distinguish 'observation' from any other type of interaction? And 'ultimate realism' is not consistent with the subjective view that something behaves differently just because it is 'being observed'???

    Z and W bosons are the examples of bosons with rest mass>0
    At the same time, neutrinos have mass=0 (very likely)
    Also, based on GR, photon gas gravitate.

    In general, I dont understand your position.
    If you are asking, then answers had been given you several times, you need to accept them, even if you dont like them.
    If you have your personal theory, which contradicts QM and as we see GR, then you should try it in a different place. The burden of proof will be yours, and it must be something serious - for the beginning, numerical agreement with all known QM experiments (blah blah stuff like 'I suggest that our lack of knowledge... leads to... does not count)
     
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