User talk:Ldm1954/Sandbox/Duality

Doubts
On of the posts on the Wave-particle Talk threads (Third opinion) pointed to two meanings of duality: 1) a measurement-oriented summary/postulate and 2) a thing that is dual. Historically the physics work has been #1 and as you know I have been pulling strongly in that direction. The #2 category is, in my opinion, all over the map, for the reason that it hasn't experimental support so any thing goes.

If we include Alternatives, the implication is that we have a "thing that is dual" to contrast with alternatives. To say this another way: to discuss alternative interpretations implies that wave-particle duality is an interpretation rather than being essentially a non-interpretation.

This could turn out ok if we build up the aspect of wave-particle duality as being a non-interpretation, but I sense that you don't want to go in that direction. Johnjbarton (talk) 20:17, 13 August 2023 (UTC)


 * I think we agree about 1., although I am approaching it as probabilistic. Before we discuss 2., are you OK with my probabilistic approach, or do you mean something different? Ldm1954 (talk) 22:13, 13 August 2023 (UTC)
 * The probability is observed and the distribution computed from QM matches experiment: that is all great. Johnjbarton (talk) 22:55, 13 August 2023 (UTC)
 * If you are happy with 1., then the issue is 2 and the Alternatives section. I just copied much of it; whoever wrote that section doubted duality, so made them all seem plausible. I just pointed out that Duane's is wrong; you did the wave packet. I suggest we do the same for the others. Ldm1954 (talk) 23:05, 13 August 2023 (UTC)
 * I think we need to hit some of the confusion up front, calling a spade a spade. Ldm1954 (talk) 14:05, 14 August 2023 (UTC)
 * I did a bit more. I wonder about your para in the lead, it could be interpreted as pedantic.
 * We may want to include the two-gaussian image in the wave packet part. Side step a edit war. A section should be there, we cannot ignore it or call it Fringe science Ldm1954 (talk) 18:27, 14 August 2023 (UTC)
 * I guess my happiness is conditional ;-)
 * Discussing probability to explain the dots makes sense. But as a core issue for wave-particle duality, I'll quote a source about uncertainty relations: "Bohr has criticized Heisenberg for his suggestion that these relations were due to discontinuous changes occurring during the process of measurement and pointed out that the uncertainties in the experiment did not exclusively arise from the discontinuities (existence of quantum of action), but also from the fact that the position and the momentum of the electron cannot be simultaneously defined in the microscope experiment (‘Addition in proof’ in Heisenberg1 ) and we need to consider both the particle theory and the wave theory." This is the Sen review The uncertainty relations in quantum mechanics.
 * Duality and uncertainty are built in to the wave function. We encounter probability whenever we measure the wavefunction. Johnjbarton (talk) 19:13, 14 August 2023 (UTC)
 * That is combining the wave packet part? It is in the fully coherent limit of a probability approach. See how I have tried to combine them of late. Maybe some re-ordering, but coherence/density matrix includes all this. Ldm1954 (talk) 19:38, 14 August 2023 (UTC)
 * N.B., I don't think we are disagreeing, I think we have different language. We can add Heisenberg earlier if you want. Ldm1954 (talk) 19:40, 14 August 2023 (UTC)
 * Please explain what you are not comfortable about. I don't understanding. To me a wavefunction and it's higher level form is the description. Ldm1954 (talk) 20:31, 14 August 2023 (UTC)
 * Duality in wavefunction language is about Fourier transform pairs, like uncertainty but more extreme. If your apparatus is set up for detecting in one domain it will be (completely) insensitive to the other one. So probability doesn't figure in this aspect.
 * All of the math for the interferometry involves states, their interference, entanglement and so on, leading to predictions of distributions. Discussions end up comparing different distributions under different conditions. So probability only comes in when we get to comparing the distributions to experiment. That is the sense in which probability is not essential for discussing duality. Of course the probability is part of the overall physics, as it is for every QM experiment.
 * Since we are featuring an experiment the probability needs to be brought up to explain why we see what we see. But the duality aspect itself does not hinge on probability.
 * Does that help? Johnjbarton (talk) 23:18, 14 August 2023 (UTC)
 * Ok I just saw your comment on in the lead about probability and I realize there an aspect to duality related to probability indeed.
 * The relation concerns the meaning of the amplitude (according to some). Here a too-long quote I like:
 * "It is a general feature of delayed-choice experiments that quantum effects can mimic an influence of future actions on past events. However, there never emerges any paradox if the quantum state is viewed only as a “catalog of our knowledge” (Schrödinger, 1935) without any underlying hidden-variable description. Then the state is a probability list for all possible measurement outcomes and not a real physical object. The relative temporal order of measurement events is not relevant, and no physical interactions or signals, let alone into the past, are necessary to explain the experimental results. To interpret quantum experiments, any attempt in explaining what happens in an individual observation of one system has to include the whole experimental configuration and also the complete quantum state, potentially describing joint properties with other systems. According to Bohr and Wheeler, no elementary phenomenon is a phenomenon until it is a registered phenomenon (Bohr, 1949; Wheeler, 1984)."
 * From Ma, Xiao-song; Kofler, Johannes; Zeilinger, Anton (2016-03-03). "Delayed-choice gedanken experiments and their realizations". Reviews of Modern Physics. 88 (1). doi:10.1103/RevModPhys.88.015005. ISSN 0034-6861. Johnjbarton (talk) 23:27, 14 August 2023 (UTC)
 * To me, this is "interpretation": we have observed duality in myriad experiments, we understand it in our theories so now what do we make of it? We conclude there are no tiny flying things and the wave is just statement about what we don't know. We only know properties exactly when we measure them.
 * We can go in that direction, but to me this is one (very interesting, old and now modern) step beyond the concept that is wave particle duality. I would like to write more on this "measurement interpretation" ( there are plenty of refs) but I'm not sure it is in an article on duality. Johnjbarton (talk) 23:40, 14 August 2023 (UTC)
 * Ok, we are talking the same topic, but with different languages.
 * Now all we need to do is write it so a high-schools student will understand. I will sleep on it. Ldm1954 (talk) 00:54, 15 August 2023 (UTC)

lead quote
I suggest losing Einstein and sticking with Bohr for both consistency and compact lead. Johnjbarton (talk) 22:21, 14 August 2023 (UTC)

I think we are close
I like your recent edits. I would leave the lead as is, because we need to explain, be inclusive and say what we will say. I had a look at some of the Y-Tube videos to get views. I think we need to tweak the wavepackets to include (coherent) superimposition. I wonder whether you want to add a Measurement section before the wavepacket. I think there is good, otherwise it could confuse. Maybe should include the Penrose collapse model, as it seems cute and possibly valid. Unfortunately I have my AL idiot to deal with... Ldm1954 (talk) 14:00, 15 August 2023 (UTC)


 * I restructured the beginning and end, adding "conventional interpretation" before wavepacket and rewriting it. Take a look.
 * I would like to replace the lead, starting right after the Bohr quote, to shorten it and match the current outline more closely. Here is my proposal:
 * The concept of wave-particle duality was proposed at the end of an exciting but frustrating 20 year period where many physicists, trained in classical wave and particle theories, confronted the confusing results from new quantum experiments. Adding to the confusion of some times wave, some times particle results, each experiment involved statistical averages over "quantum jumps". The current interpretation of duality -- that quantum properties are only revealed in measurements -- continues to be valid, including modern understanding of quantum entanglement.
 * Johnjbarton (talk) 16:54, 15 August 2023 (UTC)
 * I think that is too flowery and too complex for the lead; target high school? Also, we don't need to introduce "quantum jumps" as it does not come up elsewhere. I just cut it slightly, I think it is OK. When we have the rest finalized we can look again. Ldm1954 (talk) 17:59, 15 August 2023 (UTC)
 * Oh, and if you are good with the Conventional interpretation list of laureates I will add refs. Johnjbarton (talk) 17:31, 15 August 2023 (UTC)
 * I am ok with that. Others might think we are overdoing it a bit. Ldm1954 (talk) 18:36, 15 August 2023 (UTC)
 * Overdoing? You bet. Many QM articles I read on wikipedia imply that conventional QM was made up one weekend. Johnjbarton (talk) 19:04, 15 August 2023 (UTC)
 * I suggest taking the visualisation from the old page and using it, but remove the Briglie-Bohm. Merge with uncertainty & wavepacket Ldm1954 (talk) 20:14, 15 August 2023 (UTC)
 * Also use this or similar https://www.google.com/search?q=partially+coherent+wave+i&tbm=isch&ved=2ahUKEwjRvsP-vd-AAxVxPd4AHRbDCSUQ2-cCegQIABAD&oq=partially+coherent+wave+i&gs_lcp=ChJtb2JpbGUtZ3dzLXdpei1pbWcQAzIFCCEQqwIyBQghEKsCMgUIIRCrAjoFCAAQogQ6BAghEApQmg9YkxVgjxdoAHAAeACAAdABiAH_BpIBBTAuNC4xmAEAoAEBwAEB&sclient=mobile-gws-wiz-img&ei=c93bZJG5E_H6-LYPloanqAI&bih=1143&biw=686&client=tablet-android-samsung-nf-rev1&prmd=insv&hl=en#imgrc=schLHIWqbt4QoM Ldm1954 (talk) 20:28, 15 August 2023 (UTC)
 * I suggest taking the visualisation from the old page and using it, but remove the Briglie-Bohm. Merge with uncertainty & wavepacket Ldm1954 (talk) 20:14, 15 August 2023 (UTC)
 * Also use this or similar https://www.google.com/search?q=partially+coherent+wave+i&tbm=isch&ved=2ahUKEwjRvsP-vd-AAxVxPd4AHRbDCSUQ2-cCegQIABAD&oq=partially+coherent+wave+i&gs_lcp=ChJtb2JpbGUtZ3dzLXdpei1pbWcQAzIFCCEQqwIyBQghEKsCMgUIIRCrAjoFCAAQogQ6BAghEApQmg9YkxVgjxdoAHAAeACAAdABiAH_BpIBBTAuNC4xmAEAoAEBwAEB&sclient=mobile-gws-wiz-img&ei=c93bZJG5E_H6-LYPloanqAI&bih=1143&biw=686&client=tablet-android-samsung-nf-rev1&prmd=insv&hl=en#imgrc=schLHIWqbt4QoM Ldm1954 (talk) 20:28, 15 August 2023 (UTC)

Role of probability
We currently have a paragraph about sampling a probability distribution. I think this aspect can be shortened and used in the electrons-as-particles section to explain what the movie shows.

The "sampling of a distribution" is not to hard to explain and the current text works for that. The idea that duality implies non-deterministic mechanics is difficult to explain and the current text does not touch it, which is fine. But the current position and intro text mixes these up. I would rather not connect duality to sampling probability in this direct way. Johnjbarton (talk) 22:50, 15 August 2023 (UTC)


 * Ok I now remember a detail in Feynman's Quantum Behavior chapter that puzzled me. He start by describing a gun shooting at double slits:
 * "It is not a very good gun, in that it sprays the bullets (randomly) over a fairly large angular spread..."
 * So the pattern the classical gun makes fills in a probability distribution bullet by bullet. That's one kind of probability. It's related to source emission randomness (gun or quantum emission).
 * The second kind comes directly from duality: the slits confine the lateral position causing lateral momentum (uncertainty principle) and then the lateral position on the detector is random because (duality) the trajectory is only known as probability. I recall you said something before like gradients of probability amplitude: that's the kind of probability connected to duality.
 * I'll look for a ref, but this is the difference that keeps me on the fence about probability. Johnjbarton (talk) 03:10, 16 August 2023 (UTC)
 * The (grossly) overlong link to an image is very relevant. I am not good enough at graphics to redo this, it is not open source -- but IMHO matters. Ldm1954 (talk) 14:41, 16 August 2023 (UTC)

We don't agree
Incoherent electrons don't interfere, but still give diffraction patterns. Coherent electrons do both, and can give you interference in both real and reciprocal space. You only get interference in the two slit experiment if the wave is coherent enough between the slits. As an extreme example, use incoherent light, electrons, brownies with two, small circular apertures. Far field they won't give interference. Now put a second pair of slits in after the two apertures. Low and behold you will get two superimposed interference fringes as the wave exiting a small apertures has considerable coherence. Maybe rave-from-the-grave. With a standard thermionic LEED you can't get an image worth ¢¥#!. Now copy Ernst Bauer and put in a FEG (small source=coherence), apertures (more coherence) and... Ldm1954 (talk) 17:11, 16 August 2023 (UTC)


 * Perhaps we don't agree but not about anything you wrote above.
 * Coherence is essential and assumed in simple discussion of wave particle duality. Duality is exactly about the extreme coherent plane wave vs the extreme localized position.
 * The point of disagreement, I suggest, is how important is it to discuss incoherence in an article on a abstract concept targeting high school. Incoherence, the lack of extreme coherence, is complex multifaceted topic. Includes both classical and quantum aspects with quite a bit of confusing mixtures. It involves sources, geometries, vibrations at least. I would start from the work directly related to wave-particle duality (see Complementarity_(physics)).
 * A section on (In)coherence could work but it seems it would need to be a summary of Coherence_(physics) which is not horrible but also does not have any specific content about electrons. Unless it is a summary the topic will overwhelm the article.
 * Most of the continuous complementarity work is about coherence: any modification or failure in the apparatus that allows path information exactly alters the wave character, whether it was planned or not. Incoherence is just the messy middle ground. Unfortunately the quantum literature rarely uses the word "coherence", I suspect because of the reputation the word accumulated in optics.
 * Johnjbarton (talk) 18:41, 16 August 2023 (UTC)
 * I'm copying some of the comments from the text: (I am inlining)
 * L: Interference and duality are not the same.
 * J: agree.
 * L: You can get diffraction patterns from 100% incoherent electrons.
 * J: Disagree. 100% incoherent electrons are what? point localized or something. I suppose you mean that the coherence requirements for diffraction are not very stringent. I think this is the same effect as Young's visible light interference. Both cases are particular characteristics that make the coherence requirements weak.
 * Examples are Kikuchi lines (physics), EBSD and some types of CBED. In all cases the patterns are an incoherent sum in reciprocal space, but have minimal to no coherence in real space.
 * L: Dots are local, so not waves.
 * J: agree
 * L: Statistics of 10^N detections is a wave.
 * J: Adequate sampling the distribution is essential to see pattern, but each individual event is a result of the underlying probability. The wave property causes the lateral displacement leading to overlap and interference.
 * Disagree. It is in the probability and coherence. Without coherence there is no interference but there is still lateral displacement.
 * We apply the Born rule to continuous wave functions and produce a continuous probability distribution. It shows interference or not according to the experimental conditions. Duality works at this level. (In)coherence works at this level (determining visibility). Next comes some other not-very-often-discussed step where the continuous Born rule result is sampled. This sampling is time-dependent and most of the simple theory work is time-independent. A lot of "wave-function collapse" complaints center on this aspect. All interesting but not IMO directed related to duality. Johnjbarton (talk) 19:09, 16 August 2023 (UTC)
 * N.B., detection is statistical, so that is the right model -- and that is also quantum field theory. If you ignore coherence then, for instance, the neutron results you mentioned before are inexplicable -- why does it not go to zero? My view is in the sentence below the first quote -- probabilities. Duality is not interference, it is different modalities of detecting the statistics which can be either wave-like, particle-like or banana-like. Ldm1954 (talk) 19:35, 16 August 2023 (UTC)
 * N.B., for incoherence, suppose that we have complete incoherence in reciprocal space
 * $$\Gamma(k_1,k_2) = A(k_1)\delta(k_1-k_2)$$
 * Then in real space
 * $$\Gamma(r_1,r_2) = \int A(k)exp(ik(r_1-r_2))dk$$
 * The coherence length is the Fourier transform of the incoherent A(k), and non-zero. If this is wide then there is no interference possible in real space, but you still get diffraction. Ldm1954 (talk) 19:52, 16 August 2023 (UTC)
 * I'm unsure which topic we are on here, coherence or probability.
 * Interference and diffraction are not all or nothing, there is a continuous tradeoff. In duality experiments the tradeoff is described as visibility vs path distinguishability. See Wave–particle duality relation.
 * Classical coherence is closely related to duality. "when two beams are superposed, the absence of “which-way information” implies that the superposed fields are maximally correlated" Hochrainer, Armin, et al. "Quantum indistinguishability by path identity and with undetected photons." Reviews of Modern Physics 94.2 (2022): 025007. https://pure.mpg.de/rest/items/item_3348051/component/file_3389627/content.
 * The Kikuchi lines (physics) and EBSD examples are not incoherent. They are partly coherent. They use strong acceleration and collimation, the mechanisms to create longitudinal and lateral coherence. Perfect coherence is not needed for any of these experiments (or they would always fail). But so it is with experiments. When it comes to theory and concepts we can look beyond the specifics. In duality that means extrapolating to perfect coherence. So in explaining duality we should mention coherence, we can describe sources of incoherence, but that's all we need.
 * So just to reiterate, coherence is needed for duality -- its how we define the plane wave extreme -- but elaborating incoherence is needed to understand duality. Johnjbarton (talk) 23:02, 16 August 2023 (UTC)
 * Pro forma, both Kikuchi lines (physics) and EBSD are completely incoherent because all coherency is lost due to inelastic scattering. Neither acceleration nor collimation matter, after inelastic scattering the incoming coherency does not matter. The observed result is an incoherent sum. Incoherent electrons at twenty paces? (This is within my core competency.)
 * Diffraction is due to multiple scattering solutions of a relativistically corrected Schroedinger equation. It has not changed much since Bethe's paper. There is no coherence issue in diffraction, it is a single particle wavefunction.
 * Interference, however, involves coherence. Also diffraction observables can involve coherence, e.g. coherent and incoherent CBED following John Steeds work and, recently, psyctography -- I can dig up refs if needed. (Also core competency.)
 * As the graphic indicates, with no coherency there are no fringes in the two slit experiment -- but they are still waves, not particles. They are still described by probabilities. In all types of EBSD they are incoherent and can be treated as classical particles -- diagonal density matrix.
 * We are saying the same thing about probabilities, but I don't want to only use the fully coherent limit as it is unreasonable IMHO. Ldm1954 (talk) 23:26, 16 August 2023 (UTC)
 * Addendum. Suppose you have for unit amplitude and an incident direction $$k$$ the set of plane waves given by the response function $$T(k+g,k)$$ with reciprocal lattice vectors $$g$$, where the response function depends upon $$k$$. The response function is from coherent, elsstic diffraction. For Kikuchi & EBSD there is a range of incoherent $$k$$, so the pattern comes from an integral over $$|T(k+g,k)|^2$$. You get features near when the Bragg condition is satisfied, as these are where there is most variation. Diffraction is there, but no coherence or interference. (Remember that the silly Bragg's law diagram in intro books is just that, silly.) Ldm1954 (talk) 01:55, 17 August 2023 (UTC)
 * Ok sorry. We are far off track here. Johnjbarton (talk) 13:57, 17 August 2023 (UTC)

Expanding "Observations" with a Wheeler's delayed choice experiment
Based on our backgrounds, simplicity, and the availability of the single-electron double slit images we focused the observations section on some older experiments. Historically these experiments did not satisfy physicists involved in wave-particle duality research. I think that is why we have disagreements about their description.

From the earliest days Einstein, Wheeler, and others suggested better experiments. About 40 years ago these experiments became practical. All the modern work on duality uses them.

We have a short section on these now, but I think an expansion is needed. Some of the experiments are quite sophisticated but I think one of Wheeler's delayed choice experiments can be successful. These experiments involve two-arm interferometers with a switchable exit prism that can rapidly switch between interference and not. Both conditions involve probabilistic counting so that aspect is controlled.

Johnjbarton (talk) 15:36, 17 August 2023 (UTC)


 * You can add it, but to me it is not adding anything new. If there is no second splitter, there is no interference. It is a bit like the experiment where you put a detector of some sort before one of the slits. The interaction destroys the coherence between the two slits, so there is no interference (but still diffraction).
 * If you can find a way to put it into a section of two or so paragraphs that is simple, that would be fine.
 * N.B., I put in an archive to get rid of older discussions that were cluttering things up. Ldm1954 (talk) 18:24, 17 August 2023 (UTC)

Definitions needed
I did a little reading just now from Schiff, and he says (in words) what is in the Durt etc al paper - that complementarity is a generalization of the uncertainty principle. I am OK with that, BUT that is not probability or duality. We need definitions, as otherwise we are going nowhere:


 * A wave has properties such as diffraction and interference.


 * A particle does not, and is discrete in time and space.

I am OK with the first definition, I can't think of a better one for the second. Then we can discuss whether we consider these two as being complementary, which I am not currently convinced about. Ldm1954 (talk) 01:51, 18 August 2023 (UTC)
 * I really think this needs to be settled first.


 * See my answer in article. Johnjbarton (talk) 04:09, 18 August 2023 (UTC)
 * Oh darn! As soon as I finished I realized I fell into a fallacy!
 * Wave particle duality is about the duality of position and momentum wave function representations. A pure position eigenfunction is a localized point, delta function unit probability; completely unspecified momentum. A pure momentum wave function is a plane, completely delocalized in space. These are the complementary dynamic variables; the Fourier transform pairs.
 * So duality isn't really about dual mechanics.
 * To then go off about particles and waves is really to ride off with the words "wave-particle" with out paying attention to what the duality means.
 * Nevertheless what I wrote is correct-ish and I like the cloud chamber image (or the alpha particle one). So maybe it can be rescued IDK. Johnjbarton (talk) 04:26, 18 August 2023 (UTC)
 * Maybe useful for a quantum particle
 * https://www.quantamagazine.org/what-is-a-particle-20201112/
 * https://www.energy.gov/science/doe-explainsquantum-mechanics
 * I would combine the discrete part and the measure part from the first with also discrete properties such as energy, momenta, spin (so photons are in). Yes? Ldm1954 (talk) 11:56, 18 August 2023 (UTC)
 * Let's not worry about anything more than the definition at the moment. I adjusted it to be 4, first classical then quantum as you had mixed the two. Also, waves are not everywhere, Schiff has a nice intro on wavepackets.
 * Later we will define duality. Ldm1954 (talk) 11:36, 18 August 2023 (UTC)
 * Well this too seems like it will be a challenge. How can we possibly have a discussion of quantum waves and quantum particles in an article devoted to the concept that such things cannot be observed, as has been shown through 100 years of fruitless searching and a theory that forbids the possibility? Johnjbarton (talk) 14:04, 18 August 2023 (UTC)
 * I don't agree. Quantum wave is easy, quantum particle is not bad using the links I sent. I will make a stab shortly.
 * We must settle this first. Ldm1954 (talk) 14:26, 18 August 2023 (UTC)
 * Well we agree that we don't agree ;-)
 * The Quanta article would be a great addition to interpretations of quantum mechanics. It has nothing to do with duality. Duality claims that no particle model will ever succeed because for every experiment demonstrating particle properties there is another demonstrating wave properties. Similarly no wave model.
 * The probability wave amplitude is literally a figment of our imagination, a list of all possible outcomes and their estimated frequency. It has no reification, it can't collapse because it "isn't" in the first place.
 * But duality does not say this either. It only says no particle or wave model works. Johnjbarton (talk) 15:13, 18 August 2023 (UTC)
 * Again, you are running ahead. Without a definition this article has no focus. Ldm1954 (talk) 15:15, 18 August 2023 (UTC)
 * Addendum, remove position from what I have for the particle. Then everything is fine, as a quantum wave does not have a discrete charge etc. Have to go now Ldm1954 (talk) 15:42, 18 August 2023 (UTC)
 * The first two sentences give the definition. The references are quite consistent with this point of view. That is why I've been trying to convince you that our previous understanding was off the mark.  Read the references. You'll come to really understand why Einstein, Schrodinger, Leggett, in fact everyone was unhappy. Like Bohr pointed out, the concept is a lot like relativity: very hard to believe in your heart, even if your head says it has to be so. Johnjbarton (talk) 16:28, 18 August 2023 (UTC)
 * I do not know what two sentences you mean. The current definition of a quantum wave and particle is consistent; an interference pattern is multiple quanta etc. Ldm1954 (talk) 17:08, 18 August 2023 (UTC)
 * Oh sorry. You said "definition this article" so I meant:
 * Wave–particle duality is the concept in quantum mechanics that quantum entities can have both particle and a wave properties according to the experimental circumstances. It expresses the inability of the classical concepts such as particle or wave to fully describe the behavior of quantum objects. Johnjbarton (talk) 17:54, 18 August 2023 (UTC)
 * Can we settle first on the definitions of quantum particle and waves. Ldm1954 (talk) 17:57, 18 August 2023 (UTC)
 * We can describe quantum states as exhibiting behavior consistent with mass, point charges, etc. We can't ascribe any property to a quantum entity, particle or wave. There is a (too long) quote in Wheeler%27s_delayed-choice_experiment from the Ma et al paper that is worth a look.  The experiments say the properties exist when the experiment is done.
 * The phrase "quantum particle" is really an oxymoron unless prefaced by lots of caveats. That's why I wanted to avoid using it. Particle physics of course uses it a lot, but it always really means "exhibiting behavior". For our famous high schooler I believe the phrase creates a too vivid a mental image which leads away from the topic.
 * Same actually goes for waves but the caveats seem to be applied afterwards. That's when we fall into the whole collapse pit. Not really waves but em er a wavey thing that collapses?
 * To me the duality concept is limited: we can see particle properties or wave properties depending on the experiment and that result agrees with the QM theory. It's been so for 100 years up to the latest Nobel prize. As soon as we start with what a quantum state "is" we are off on a much larger topic full of pits and dragons. Johnjbarton (talk) 20:08, 18 August 2023 (UTC)
 * Again, I disagree and I think you are over making everything too complicated. An electron has a quantized charge and and spin. A photon has a quantized momentum and energy. These do not depend upon measurement, they are absolute (ignoring reference frame issues).
 * A quantum wave does not have a quantized momentum, charge etc.
 * I am not talking duality. Ldm1954 (talk) 20:22, 18 August 2023 (UTC)
 * Yes, yes! That is exactly what I have been saying: you are not talking about duality. Duality is simply not about what particles, waves, or quantum states "are". Come up with what ever definition of particle or wave you like: it won't be relevant.
 * In many other articles on QM I would not complain about "an electron has quantized charge". That is an effective shorthand, even if it is not strictly correct. But in this article, about duality, the shorthand will only cause grief. The shorthand will be immediately contradicted by the references in the article.
 * The properties you mention do depend upon measurement. That is what the reference say. That is why this entire topic has been troublesome for so long. That was Bohr's conclusion and generation after generation of physicists have eventually had to concede that it is the only conclusion that fits the data. Duality is not about some wavey-particly thingy. It's just not. The evidence mounts that the properties only exist at interaction. Johnjbarton (talk) 21:52, 18 August 2023 (UTC)
 * The article is called "Wave-Particle Duality". That is what we are revising.
 * I am only discussing the definition of quantum waves and particles, as without a definition I believe no article is possible. Ldm1954 (talk) 22:06, 18 August 2023 (UTC)
 * N.B., if you want to write an article on quantum complimentarily that is an interesting thought. However, it would be a different article. Ldm1954 (talk) 22:08, 18 August 2023 (UTC)
 * Please see User:Ldm1954/Sandbox/Duality, Complementarity_(physics) and Scully, Marian O.; Englert, Berthold-Georg; Walther, Herbert (1991-05-01). "Quantum optical tests of complementarity". Nature. 351 (6322): 111–116. doi:10.1038/351111a0. ISSN 0028-0836.
 * Wave particle duality is complementarity limited to the case of position-momentum complementarity. Yet another thing I did not know until reading the refs. Johnjbarton (talk) 22:16, 18 August 2023 (UTC)
 * If we do not say what a quantum particle is, and what a quantum wave is, we cannot say anything. Ldm1954 (talk) 22:41, 18 August 2023 (UTC)
 * Would you accept position eigenfunctions as a particles, as the dots on the screen, and momentum eigenfunctions as waves which interfere to create the pattern?
 * In wave-particle duality, the wave and particles refer to classical waves and classical particles. Johnjbarton (talk) 03:19, 19 August 2023 (UTC)
 * No, I would not, as this makes the photoelectron effect irrelevant (as a start). Ldm1954 (talk) 08:35, 19 August 2023 (UTC)
 * Please do a Google search on "photoelectric effect wave particle duality". Ldm1954 (talk) 08:44, 19 August 2023 (UTC)
 * I did such a search and I didn't see anything inconsistent with what I have been saying.
 * The better sources carefully avoid defining "quantum particles". They say things like "light exhibits particle properties". Johnjbarton (talk) 14:18, 19 August 2023 (UTC)
 * Sorry, but I do not agree that wave-particle duality is just Complementarity (physics), and neither do the sources I have looked at. Complementarity is an extension of the uncertainty principle, and I have no problems with that. However, it says nothing about particle properties, which all sources connect to discrete values of energy, charge etc. Ldm1954 (talk) 09:26, 19 August 2023 (UTC)

Incremental progress
Should we consider moving that part of the current draft that we agree upon into the main? Specifically we could branch the current draft in to eg DualityNG or something, then each edit to remove things we don't agree. Any remaining material could be moved into the main by sections. I'm thinking specifically about History and perhaps Interpretation. Johnjbarton (talk) 14:11, 19 August 2023 (UTC)


 * Sorry, while I don't have problems with those sections, to me the article cannot proceed at the moment:
 * 1) Wave-particle duality is not Complementarity (physics).
 * 2) You cannot talk about anything until you have defined the quantum meaning of particle. Defining it in terms of a quantized entity with definite spin, magnetic moment as appropriate then includes photons, your eigenfunctions of position/momentum do not (plus in general neither is an eigenfunction of the SE or higher-order forms).. The two-slit pattern etc is not quantized, it is a statistical probability when many quanta have been detected.
 * Sorry, to me this seems obvious and I am going to be stubborn about it.
 * I am leaving the country on Aug 27th for 3 weeks. While I might do something, it will be family plus two conferences so I may not do much. It would be good to have some concensus before then. Ldm1954 (talk) 16:33, 19 August 2023 (UTC)
 * 1) If you don't want to talk about complementarity there is not much to say about wave-particle duality beyond some history and link to the complementarity article. That's fine by me, though I think the duality-related complementarity content makes more sense here. You can decide that one. (I would of course oppose any unconventional explanation of wave-particle duality however, as the references are very clear.)
 * 2) The reason you are having a difficult time with quantum particle is really simple: no such thing. Einstein was also stubborn, but Bohr kept coming up correct. The story continues right up to the Zeilinger. I won't be able to help with a definition, they don't exist. Measurements induce properties.
 * Johnjbarton (talk) 20:10, 19 August 2023 (UTC)
 * I see no evidence that complementarity is wave-particle duality, zero sources. It is that there are operator pairs -- fine. But that has nothing to do with wave interference, diffraction or the photoelectron effect. It should be removed, and there is no need to change anything.
 * I have no problem with a quantum particle defined the way I have. Without this you have to remove the photoelectron effect completely as irrelevant. You appear to be rejecting my definition. Why? A wave does not have a defined charge, spin or momentum.
 * We are at an impass. Ldm1954 (talk) 20:20, 19 August 2023 (UTC)
 * Your definitions include a particle and a wave that "have" properties. But that is contrary to the evidence in many of the references. There are not entities with properties. The properties emerge during measurement.
 * I'm not objecting to your definition, I'm objecting to defining "quantum particle" at all. Quantum systems exhibit properties, including defined charge, spin, momentum, interference and diffraction. Some of these properties are things we associate with particles, some with waves. How can that possibly be true?? Well we really don't know but if we define a wave equation and a born rule all of the properties can be quantitatively reproduced and new predictions achieved. Complementarity falls out of that and provides an explanation of the duality. Wave particle duality is about classical wave and particles not working for quantum systems. We can't make them work by putting "quantum" in front.
 * Anyway I encourage you to read the references with an open mind. Johnjbarton (talk) 21:26, 19 August 2023 (UTC)

Taking A. Messiah's approach
Perhaps we can adopt Messiah's approach to duality. Just before he introduces (pg 59) Schrodinger equation he has:

''Universal Character of the Wave-Corpuscle Duality

"We conclude from all this that microscopic objects have a very general property: they appear under two apparently irreconcilable aspects, the wave aspect on the one hand, exhibiting the superposition property characteristic of waves, and the corpuscular aspect on the other hand, namely localized grains of energy and momentum, There exists a universal relationship between these two aspects, given by equations (II.5)"''

$$E=h\omega\ \ \boldsymbol{p}=h\boldsymbol{k}\ $$(II.5)

is described as "...relations between dynamical variables of the particle and characteristic quantities of the associated wave."

Then in Chapter IV on interpretation he says:

''"18. Wave-Corpuscle Duality and Complementarity

If one adopts the principle of complementarity, the wave-corpuscle duality ceases to be paradoxical: the wave aspect and the corpuscular aspect are two complementary aspects which are exhibited only in mutually exclusive experimental arrangements. Any attempt to reveal one of the two aspects requires a modification of the experimental set-up which destroys any possibility of observing the other aspect."''

So in this description wave-particle duality is equivalent to de Broglie's hypothesis and complementarity is the explanation of wave-particle duality based on Schrodinger's equation within the Copenhagen view.

Obviously we have a good reference for this approach and I think we can make it work.

Messiah is available in openlibrary if you don't have a copy. Johnjbarton (talk) 19:42, 19 August 2023 (UTC)


 * Messiah's definition of a quantum particle is the same as what I have been saying and you apparently have been rejecting. His definition of a quantum wave in terms of superposition is incomplete as it excludes diffraction through an aperture, but that can be remedied. Ldm1954 (talk) 20:24, 19 August 2023 (UTC)
 * Plus...complimentarity only helps overcome what some see as a paradox, nowhere does he claim that it is the wave-particle duality, which is what I am continuing to say. Ldm1954 (talk) 20:25, 19 August 2023 (UTC)
 * It's perfectly reasonable, based on Messiah, to reduce the discussion of complementarity in the article to just a summary as I believe you desire. I'm completely agreeing to that line of reasoning.
 * Also based on Messiah, complementarity is an explanation for wave-particle duality in conventional ("Copenhagen") QM. I assume that is why all of the conventional physics papers about wave-particle duality are about complementarity.
 * However, the same logic -- not discussing an explanation for duality -- would also exclude any other conventional QM discussion. How can it make sense to discuss conventional QM in an article about duality but not talk about the conventional QM explanation for duality? Johnjbarton (talk) 17:04, 20 August 2023 (UTC)
 * I am jealous ggling guests, a paper, travel and a calculation that fails. With luxk I will get to this, but maybe not. At most complimentarity goes towards the end. Ldm1954 (talk) 18:47, 20 August 2023 (UTC)
 * I see na rationale that complimentarity is needed to explain probability. Ldm1954 (talk) 18:47, 20 August 2023 (UTC)

Some editing
I found time to do a little coherent editing, although now AL has decided again to interfere in Triboelectric effect so more waste-of-time to come.

Please expand a little the complimentarity section, I think that is the right place for it. I really don't think it does anything useful to introduce it early. Plus the language should be simple.

Also, the current uncertainty and eraser sections IMHO don't provide useful info as currently written. See how I edited the history so it does, plus other pieces. Ldm1954 (talk) 03:06, 23 August 2023 (UTC)


 * Feel free to delete the those sections. Based on our discussions and others on the wave-particle duality page editors don't want an article about the science of wave-particle duality.
 * I think we should go back to our original simple-for-high-school concept. Johnjbarton (talk) 15:29, 23 August 2023 (UTC)
 * Here is a cut-down high-school version of the page User:Johnjbarton/sandbox/duality. By necessity many topics are omitted. But it gets close to the entry-level, focuses on phenomenology not jargon and formula, allows us to ditch the current mish-mash page.  Limited topics also give limited scope for complains. Please consider it with an open mind.
 * I think we should use the other material we developed here in other places. Johnjbarton (talk) 17:39, 23 August 2023 (UTC)