Talk:Wave–particle duality/Archive 1

Flaws
In texts that talk about detecting light by means of either a "particle detector" or a "wave detector" no information is given as to the suitability of these objects to the tasks to which they are put. Why is the "particle detector" believed to be detecting a particle and not high tide. Conversely why is the "wave detector" detecting a wave-type light and not just showing its own distortion from being collided with a particle-like light.

Furthermore, no explanation is given as for how they know one and only one photon is emitted.

User:hackwrenchRobert Claypool


 * Wave detectors are instruments such as interferometers which rely on wave specific attributes such as diffraction and interference. Particle detectors are instruments such as photodetectors which rely on particle-specific attributes such as momentum and energy. -- Derek Ross | Talk 23:36, 12 October 2005 (UTC)

misleading or wrong
[The stuff below this line is misleading or wrong, I would recomend deleting it. The measurement problem is far more general then what is touched on here, and the ``rule of thumb'' is just plain wrong.]

Mathematically, electrons and other such creatures are modelled as waves. The question is, then, why they appear to be particles in certain experiments. This is called the measurement problem, and is solved differently in different interpretations of quantum mechanics.

An extremely simple (and possibly overgeneralised) layman's rule of thumb is that when fast and small, think "wave". When slow and big, think "matter".

Why is the rule of thumb wrong
Why is the rule of thumb wrong? Are there situations where it is advantageous to model, say, a cow as a wave? --AxelBoldt


 * Perhaps a cattle stampede can be conceptualized as a wave ? I particularly like to think of car traffic in that way.  When you see a stream of red brake lights moving in a wave backwards from a slowdown, or see the stream of cars divide and reconnect on the far side of an object in the road, it's hard not to think of traffic as a wave in a fluid.  To me, the individual cars are particles, yet collectivley they behave as a waves.

-

There are a number of problems with the rule of thumb. The big problem is that the key difference between what we normal think of "matter" and "energy" has nothing to do with particle/wave duality but rather the difference between fermions and bosons and the pauli exclusion principle. Also the rule just doesn't work. A standing radio wave is big and slow but you can think of it as a wave. A beam of X rays is fast and small, but is best conceptualized as a stream of particles.

-- Chenyu

explanation of what Wave-Particle duality means
I'd like to see more explanation of what Wave-Particle duality means and less incomprehensible history of how it was discovered by physicists. What is it supposed to mean that wavefunctions exhibit some properties of waves and some properties particles? For that matter, what does it mean for something to be a wave or a particle?

Key terms I'm looking for are: soliton and non-linear wave.

And given that we're talking about non-linear waves, terms like "frequency" should be avoided or explained; non-linear waves don't have an exact frequency or wavelength! (I'd prefer if it were explained since that would make explaining the Heisenberg "uncertainty" principle easier.)

Oh, and I'd like the first paragraph to explain that "duality" is a misnomer since the wave and particle theories of light are not equivalent. That's just a term tacked on by some loser who wanted to sell a mind-bender to a bunch of stuffy conservative physicists.

And "probability wave" is seriously misleading. Probability is not what most people think it is; mathematical probability has no relation to the everyday concept of probability. And since "probability" adds nothing to "wave" or "wavefunction", it should be junked.

Other misleading things: the ever popular misconception that quantum mechanics has anything to do with the travesty called Copenhagen. The impression that quantum mechanics recognizes a pre-observation and post-observation domain is seriously wrong and should be avoided at all cost.

And as long as we're explaining the history, why is Huygens left out of the picture?

IF YOU'RE GOING TO TALK.....BE SPECIFIC....YOU CAN'T JUST STATE WHY SOMETHING IS WRONG WITHOUT STATING YOUR REASONING. ISN'T THAT WHAT A PHYSICIST DOES? JUSTIFY WHY. THINK ABOUT IT

Rule of thumb
Wouldn't the ratio of mass to kinetic energy make for a better rule of thumb?

Photons: No mass, zero ratio = very wave-like Electrons: Low mass, low ratio = quite wave-like ... Deep-frozen chicken: Enormous mass, enormous ratio (compared with the others) = no measurable interference when shot through double-slit ;-)

understanding of QM POV
I'm made to recall Willis Lamb's statement that appeals to a "wave-particle duality" (among other things) reveal an individual's misunderstanding of QM...the historical discussion in this article is nice (and deserves expansion) but the physics needs serious updates. (Whoever wrote the above comment that ended in all caps needs to brush up on his physics...)

For starters, regarding the article, there is a glaring error, namely, that the "wave function" encodes all knowable information about a physical system. In relativistinc QM we have no "wavefuctions"--half-integer spin systems, for example, can't be described by a wavefunction. Wavefunction itself is somewhat of an anachronistic term--it's used either as a colloquialism for "state" or "state vector" or as the technical term for a continuous-basis (usually position or momentum) representation of a state vector. The latter usage probably merits an entry of its own, but I digress.

The "duality" is at best an historical paradox which was resolved by the development of quantum mechanics, although good resolution of the classical problem involving light interference (polarization filtering effects were more problematic and actually resulted in the earliest developments in quantum-mechanics--in 1804!) came from Maxwell's equations and Fourier analysis--the problem really arose when interference was observed for "matter" particles as opposed to the EM force field. "Particle" refers to spatial localization and treatment of some problems to good approximation using classical or semiclassical collision theory; "wave" is a code-word for linearity which can yield interference effects such as fringes and nodes, as observed in the Young slit experiment, for example.

A few comments on above statements: The person who apparently started this thread seems mostly on the right track.

The "rule of thumb" is wrong in part because comparing photons and electrons is like comparing apples and oranges. Photons aren't "particles" per se--they're not localized in free space. Some have taken the position that photons "do not exist" except as mathematical tools (either bases for a Fourier or mode decomposition or the extension of this in QED, etc.) and I have to say that I agree, although I qualify that agreement. It is certainly more proper unless you're in a quantum cavity to talk about excitation quanta--I may be being a pedant here, but this non-abuse of terminology does avoid much (especially popular) confusion. "Probability wave" is less misleading if one clears up what it means--that by definition its square yields a position or momentum-space probability distribution function, which does correspond to the everyday usage--the PDF is just a continuous version of the histograms that would arise when one talks of chances of winning the Lottery (equally likely for each number) or landing on Boardwalk as opposed to Illinois Ave in monopoly (not equally likely)

Why is the angry guy looking for discussion of solitons in this context?, and what the heck is a nonlinear wave? And why so mad about the use of duality?--the Huygens type wave theories and the corpuscular theories of light both turned out to be wrong--both were replaced by Maxwell's theory of light which (until quantization of the field became apparent from observations of line spectra and the photoelectric effect, and Planck's successful theoretical treatment of black-body radiation) resolved the "duality" for light. Regarding Copenhagen (and I'm a many-worlds guy, although I have reservations about the term), there is no credible interpretation of quantum mechanics which doesn't from some angle "look" exactly like Copenhagen, probabilities and all. What does the interpretation of QM have to do with this article, anyway?

Coming back to "nonlinear waves," QM is a linear theory. All solutions are linear. Observable operators are linear. Show me a soliton arising directly from the Schrodinger or Heisenberg equation of motion and I'll show you either an error. State vectors add like, well, vectors. The deBroglie frequency of matter particles is, again, an old approximation, and a theoretical tool which pops out of free-space treatments. In a potential it's meaningless. Physicists recognize this. We use mode-decomposition, which is related, as a theoretical tool and these modes can take on physical meaning in certain situations. Are you objecting to the mathematics? Does the Fourier transform (linear!) bother you? I don't understand what your objection is. You can't do a mode-decomposition of a "wavefunction" that's a soliton like a wave rolling onto a beach, but that would be like doing heart surgery--neither exist in the real world.

Wave-particle duality, historically, refers to observation of interference effects (linearity) such as fringes and nodes in experimental and theoretical treatments of matter particles such as electrons. It's not a concept considered to be accurate or enlightening by today's physicists and isn't referred to except as a metaphor used in teaching beginners. It is obfuscatory, but I don't understand your (the angry guy) side objections.

---

Planck
We need to add something about Planck! It looks as though E = hv is attributed entirely to Einstein so far... dave 01:14, Mar 25, 2004 (UTC)

Doubt
I've added a bit to the section on Doubt, noting that while complementarity [has been conceptually violated], the mathematics have not been. However, it is the first use of the term complementarity in the article on wave-particle duality. I don't think that's right. Complementarity should either be mentioned in the introduction, or have its own subheading. --ErikStewart

I am moving the entire section from the article to here, on the grounds that the result has not been peer-reviewed and so counts as unpublished research which is inappropriate for an encyclopedia. If and when it is published in a peer-reviewed journal, it can be moved back to the article. &mdash; Miguel 05:33, 2004 Nov 22 (UTC)

Doubt over wave-particle duality
There is currently (August 2004) some doubt over complementarity, the current description of Wave-particle duality, due to Shahriar Afshar's 2004 contradictory result using a variation on the double-slit experiment, which also appears to invalidate the Copenhagen interpretation. (See also: Geoff Haselhurst Biography) So far this revised experiment has only been carried out with photons, not electrons, neutrons or protons, and the results have yet to be peer-reviewed.

However, this experiment does not invalidate the Heisenberg equations on which the concept of complementarity was based. So similar experiments with other particles would almost certainly be successful. It seems that complementarity was an overly simple conceptual attempt to describe the mathematics, and will need to be revised. Peer review is still required to confirm this.

details
can we have more details about the electron gun experiment? what kind of detector is used? is this inside a vacuum tube? how do you specify that one electron per second is being output? is the interference pattern seen all at once, or is it an average of the pattern over time? etc. - Omegatron 02:09, Feb 4, 2005 (UTC)

orbits
when i first heard bohrs model of the hydrogen atom, it included electrons "snapping" to each energy level because they were forming a "standing wave", and there was a drawing of a wave going around the atom, and showing how it fit together at some radii, but interfered with itself at others. but then later in chemstry i learned about the lobe-things and the "probability clouds", so the older standing wave thing sounds like BS to me now. how does this fit in? - Omegatron 02:09, Feb 4, 2005 (UTC)

something like this:

http://www.wonderquest.com/images/2003-04-25-atom.jpg

http://hyperphysics.phy-astr.gsu.edu/hbase/imgmod/ewav3.gif

Request for comments: popularized part
Hello,

I (Cdang) made a popularized explaination that was removed by Afshar the 28 Jan 2005 at 15:28 with the comment: Removed oversimplistic and inaccurate "popularized" section.

Of course, I do not support this deletion.

First of all, the text itself:

To spare room, I put the last version before removal(i.e. 21:54, 14 Mar 2005) instead of the original version and not besides, which should imho not alter the unterstanding of the discussion &mdash; Cdang| write me 09:29, 25 Mar 2005 (UTC)

Popularised explanation: metaphor of the whirlpools in swift water
The original text of this part was published in French on the usenet forum news:fr.sci.physique the 13 September 2002, and is translated here under GFDL license with the author's consent, see.

Introduction
One of the main problem with quantum physics is to give images. Indeed, the human being needs images to think, memorise (see the article Cognitive psychology).

In the case of quantum physics, two different notions are required to represent the objects (elementary particles): waves and solid particles.

The images are necessary built by analogy with what we know, our everyday experience. Thus, when we think about a sound wave, we think about the waves on the surface of the water; when we think about a particle, we think about a ball. These two concepts are different and exclusive:

Note :
 * 1) impossible means in the « classical » physics ; the mass creation phenomena (creation of a electron/positron par from a &gamma; photon), of mass annihilation (disintegration) and nuclear fusion require precisely quantum physics

This causes a great trouble, a misunderstanding, which often leads to a mental block, especially when asking: "if a particle is localised during an interaction, why isn't it also localised between interactions?"

We will propose here an image, the whirlpools in swift water, to give a macroscopic illustration of this phenomenon.

The metaphor


Let us imagine a river with a rock in its middle. When the stream meets the rock, this gives birth to whirlpools. While the whirlpool moves away from the rock, it expands and vanishes. The object that is observed is the whirlpool, but is it itself an object, or is it just the interaction between two objects? It is possible to study the whirlpool itself: define its position, size, speed etc. but the whirlpool cannot exist alone, it is the result of the interaction between the stream and the rock.

Let us now imagine two rocks placed in a straight line in the stream. We can see a whirlpool after the upstream rock, and a whirlpool after the downstream rock. Can we say that it is the same whirlpool that travelled from a rock to the other? Certainly not, nor can we say that the whirlpool comes from the source of the river. The whirlpool forms locally by the interaction between the stream and the obstacle, but it has no existence between two obstacles.

Comparison with the photon
The photon is like the whirlpool:
 * both appear randomly; the frequency and the size of the whirlpool is determined by the strength of the stream and the size of the rock, the energy of the photon and the frequency of appearance is determined by the wavelength and the flow of energy of the electromagnetic (EM) wave;
 * if there is no rock, there is no whirlpool; if the EM wave travels in vacuum, there is no wave packet;
 * as well as the whirlpool vanishes, the photon, when it is scattered (i.e. when it is not absorbed), is only localised on a short distance after the interaction (the wave packet spreads).

This comparison can also be done with any elementary particle, just replace "electromagnetic wave" by "wavefunction".

Limits of the metaphor
But comparison is not reason. The metaphor does not reflect the wave packet reduction/collapse. In the case of the whirlpool, there is just a local concentration of kinetic energy, but the stream keeps its strength besides the rock. In the case of the photon, all the h·&nu; energy is concentrated in the wave packet. Thus, if the photon is absorbed by an atom, there can be no other wave packet reduction further; in case of a low energy flow (photons emitted one by one), if a photon "appears" on a metal plate with a slit, "a given amount" of time is required before a photon can appear on the photographic plate behind the slit (the higher the energy stream, the shorter the time).

Additionally, the whirlpool always follow the stream; the photon can be scattered in all directions (Rayleigh scattering).

The metaphor only presents the "wave point of view" of the duality, i.e. how a particle can arise from a wave. It does not present the "particle point of view", i.e. the wave function associated to particle, and the relationship between the particle momentum and the de Broglie wavelength.

Discussion
I noticed in my personnal and professional experience that many "science users" &mdash; engineers, but even some physics teachers &mdash; felt "uncomfortable" with this notion, and even did not accept it! And this notion is sometimes used for pseudo-sciences, to explain "bilocalization" (ethereal, extra-corporal experiences and such craps).

For these reasons, I think it is important to help the conceptualization for everybody. Additionally, I think that if a non-physicist reads the text, he should retain a little bit more than a few dates. This is why I wrote this text.

Now, I am aware that it has flaws that must be corrected, but I do not see the deletion as a correction. Afshar, please let me know what is wrong in this text, so I can improve it &mdash; or improve it yourself.

Cdang| write me 11:10, 7 Feb 2005 (UTC)


 * No news after 10 days... I put the section back, but let the tag. -- Cdang| write me  10:23, 17 Feb 2005 (UTC)


 * I don't understand particle-wave duality very well, but your analogy doesn't seem very accurate. It's usually better to not understand something like this than to understand it wrongly and be confused when you get further into the subject.  Your analogy just seems to say "here is an example of something that is sort of like a particle and sort of like a wave.  see?  things can really be both."  but, though I am not a physicist, I don't think the particle or wave properties of the whirlpools have any similarities to the real thing. - Omegatron 15:08, Feb 17, 2005 (UTC)


 * Dear Cdang, please REMOVE the analogy you have suggested. The photon is not like a whirlpool and I do not have the time right now to explain how the wave-particle duality can be popularized. But I promise to write something when I get the time. In the meantime I would appreciate if you place your analogy back HERE, so the uninitiated don't get more confused. Thanks! --Afshar 00:25, Feb 18, 2005 (UTC)


 * I also think the whirlpool analogy should be removed. I'll leave it to Cdang to do it, since Cdang's the one that put it in. Not only does the metaphor cause more confusion than it explains, it is also poorly integrated into the article. At the very least, it most certainly does not belong smack dab in the very beginning.

-
 * The metaphor is wrong for many reasons: Most fundamentally because it has nothing to do with complementarity which is really the main issue that should be discussed in this article (as someone pointed out above). Please remove the metaphor.CSTAR 05:42, 21 Feb 2005 (UTC)


 * At last some reactions!
 * The aim is that people figure out that it is possible to have both properties. Once the lock is removed, the mind is free to accept the results of the experiments, although it is unusual compared to the everyday experience (such as the diffraction of the fullerene or the diffraction of photons sent one by one).
 * I am well aware that it has a lot of flaws, i.e. the behaviour of a particle is far different from a whirlpool. There is a section called "limits of the metaphore" where you can put all these discrepancies.
 * Just make one experiment. Go and see your friends and relatives who made some physics studies (not the specialists of quantum physics, but the engineers, or scientists from other parts but who use these phenomena like the XRF, XRD, TEM, SEM user...), and ask them what they understand from wave-particle duality. You will probably be surprised.
 * If you have a better way to "break the lock", well yes please, write it down.
 * On my side, I will just put a warning at the beginning. I will not myself remove the text as I think it is usefull, it has an added value.
 * But you are also free to edit it, and thus to remove it back.
 * But please, please, give some arguments, examples, demonstrate your point of view... All I read above is "it is not accurate, please remove it"; well, give me some explanation why it is inaccurate.
 * To CSTAR : "Most fundamentally because it has nothing to do with complementarity which is really the main issue that should be discussed in this article"
 * Then the title of the article is wrong, or there should be just a redirect to Complementarity (physics). This is the rule of "minimum of ambiguity" that stand at the very beginning of the naming conventions.
 * Cdang| write me 09:05, 21 Feb 2005 (UTC)


 * The intent (I suppose) of the article was originally to show that dual descriptions are possible more generally; however, your metaphor suggests only how discrete localizable objects can arise in a continuous medium satisfying some non-linear PDE. That is not wave-particle duality.  Please remove it. CSTAR 14:44, 21 Feb 2005 (UTC)


 * Well, the original intent of the article is not the point. Wikipedia articles are the fruit of several authors and it is usual that an article takes various orientations when it is developped, as long as it is compatible with the title.
 * And yes, you are right about my metaphor, but it is wave-particle duality because generaly speaking, perturbations of the surface of a liquid can be treated by the wave formalism &mdash; or do you deny that waves are waves?
 * Additionally, as every popularisation inevitably leads to some approximation, do you (all who would liket he section to be removed) think that there should never be popularisation in Wikipedia? Why don't you simply add the flaws of the metaphor in the dedicated sub-section so everybody can be informed?
 * Cdang| write me 17:12, 21 Feb 2005 (UTC)


 * J'ai répondu d'une façon plus detaillée dans vôtre page discussion.CSTAR 18:10, 21 Feb 2005 (UTC)

Assessment quiz
From the discussion above, I think that the opposition comes from a misunderstanding. The popularised part is an analogy (the choice of the word "metaphor" in the section title is not neutral); it makes a comparison on only some aspects of the behaviour, not all.

To make things clearer, and to discuss on facts, not on feelings, I propose below a kind of quiz. Everybody is invited to answer it:
 * edit the section and copy the table;
 * every time you meet a

just remove the  and   and let your answer to the statement
 * please sign your quiz by putting four tilde

Cdang| write me 09:12, 23 Feb 2005 (UTC)

New mode of discussion?
Set up a quiz. Marrant. C'est un piège ça?CSTAR 17:19, 23 Feb 2005 (UTC)
 * No trap. This is a scientific article so we should discuss about facts.
 * Well if you answer wrong to any of the topic, we can then talk about the accuracy of the exposed facts. As facts are facts, it will be easy to point out my errors.
 * If we all agree that the facts that are presented are right, we will then discuss about pedagogy, whether the presentation is relevant or not, which is completly different.
 * Cdang| write me 11:03, 24 Feb 2005 (UTC)

Possible compromise
OK here is a possible compromise:

1. The thing you propose is neither a metaphor nor an analogy. Please label the section soem other way. For instance visualization (to which you could add for some aspects of wave particle duality)

2. Remove the psychobabble at the beginning.
 * e.g One of the main problem with quantum physics is to give images. Indeed, the human being needs images to think, memorise (see the article Cognitive psychology).

3. Retain the contrast table, prefixing with some such thing as
 * Waves and particles are ordinarily thought of as being radically different kinds of entities; these differences are illustrated by entries in the following table

4. AFter the table make a comments such as
 * However, it is possible for some aspects of particle behavior to be displayed in a wave-like medium (ed. remark: I'm not sure what a wave-like medium is other than a continuous medium which supports wave propagation)

5. Please get another picture. It's too big, it's not clear to focus on. If you tell me what to draw, I'll draw it myself.

6. What does this mean?


 * if there is no rock, there is no whirlpool; if the EM wave travels in vacuum, there is no wave packet;

I assume you mean some aspect of wave propagation in free space;

7. State the limitations of the visual picture right away, not in another section and without making any idle speculations. e.g., remove But comparison is not reason.

CSTAR 16:38, 24 Feb 2005 (UTC)


 * if you like, but if you could explain me in why it is not a metaphor nor an analogy, it would be nice
 * OK, that's not the point here; it is just a way to justify why it is imho important to visualise things... The brain builds anyway pictures (a basis of pedagogy).
 * I agree that the contrast table is more general and could be in another section
 * If the table clearly states that it is a macroscopic and not quantic vision, then it is useless.
 * try the  option
 * it means that the particle is not localised if there is no interaction, or, which is thesame, that the wave packet disperses after an interaction
 * I don't get your point. It is right after, there is just a subsection title, and the subsection title precisely points out that there are flaws ("look, the flaws are so important that we created a specific section for them"). "Comparison is not reason" is the transposition of a French word which sounds exactly the same, if it does not sound good in English, no problem to remove it.
 * Does anyone else has suggestions ?
 * Cdang| write me 11:49, 25 Feb 2005 (UTC)


 * I am not a physicist, but I know enough to know that this is not a good analogy. I think it will hurt more than it will help. - Omegatron 03:14, Feb 28, 2005 (UTC)


 * Omegatron, what do you mean with "not good"? Do you have any wrong answer to put in the quiz? Otherwise, why do you think it is not good if you agree on facts ?
 * Cdang| write me 08:45, 28 Feb 2005 (UTC)

Sound
So sound travels in particles? In solids it travels in phonons, which make no sense to me. But what about in air and such? If radio waves travel in photons, then sound in air must travel in quantized packets, too. How does this work? I have a feeling that understanding this would help me understand the entire concept a lot better. - Omegatron 03:14, Feb 28, 2005 (UTC)


 * Well, the wave-particle duality does not mean that the wave and particle characteristics appear simultaneaously, or can be detected simultaneously. You can imagine that each sound quantum is too "weak", so you can never isolate one quantum, there are always a bunch of it so the wave always appears continuous.


 * Uhh... I definitely don't understand, then. - Omegatron


 * Concerning the phonons, it is not exactly the sound, but the vibrations of the crystal, including (and especially) the thermal agitation. You can look at springs: imagine two springs, horizontaly placed, one attached to the left, the other to the right, with a mass in the middle. You have one resonance frequency. If you put thousands of springs on a row, with thousands of masses, you will have a very complex system with a lot of resonance frequencies (bands with gaps, similar to electronic band theory). In such a configuration, you will have an heterogeneous deformation, with "concentrates" of elastic deformation at some places; this is an image for the phonons (yes, I love metaphors).
 * Cdang| write me 08:43, 28 Feb 2005 (UTC)


 * I understand your image of springs and masses. I understand the multiple resonant frequencies.  Still don't understand the phonons.  If phonons are the "concentrations" of elastic deformation, then they must come into existence and then disappear constantly, which doesn't make sense.  Sounds like the phonon article, which I've read several times and still don't get it. - Omegatron 18:39, Mar 1, 2005 (UTC)


 * Yes, that's it, concentrates of elastic deformation appear and disappear constantly, randomly. Thus, you can only define a probabylity of presence, of apparition.
 * Now imagine the spring network is 2-dimensional (like a bed springing, mesh-springing ? sorry, my vocabulary does not include furnitures); and imagine there is an heterogeneity, e.g. an object is blocked n between the springs. You can imagine that this will modify the probability of apparition of the concentrates, and that it may stabilise a concentrate (i.e. there will always be a concentrate near this object). And if you have several foreign objects, you will see concentrates travelling between the objects, if they are close enough. If they are far away, you will see a concentrate disappearing randomly from one object, appearing randomly next to the other, but no concentrate between (the concentrates spread between the stabilising objects).
 * The concentrates can also interact with each other. This explains that the thermal conductivity evolves with the temperature: the phonons, which "carry" the heat, interact with each other, thus the number of phonons (i.e. the temperature) influences their movement. They also interact with electrons (waves of course), explaining that good thermal conductors are good electric conductors too, and that the electric conductivity changes with temperature.
 * Do the clouds clear a little bit ?
 * Cdang| write me 19:17, 2 Mar 2005 (UTC)


 * A tiny bit. This doesn't seem right to me, though.  So it's really just waves adding on each other and bouncing off boundaries and such that happen to look kind of like particles every once in a while?  This mesh could be simulated on the computer pretty easily.  I'd like to see it.  Something like this http://www.falstad.com/ripple/ .  I don't understand how the "particles" are anything important in this example. - Omegatron 18:06, Mar 5, 2005 (UTC)


 * Well, the particle aspect of the thing is that the energy is quantified, e.g. a concentrate of elastic deformation carries a given amount of energy. Cdang| write me 13:38, 8 Mar 2005 (UTC)


 * ??? How is it quantized?  Aren't there also multiple particles taking up the same space?  Sorry this is losing me more and more.  I guess this discussion helps to come up with a way to explain this so that everyone can understand, though... - Omegatron 15:03, Mar 8, 2005 (UTC)


 * Sorry, I'm not sure I understand what you mean; several particles can take the same place as long as they are bosons (and if you imagine it as wave, it is obvious: interferences), but the energy of each particle stays quantified. Of course, if this energy is too small to be detected individually, you will see a continuum, it will be apparently unquantified (that's the difference between long wavelength electromagnetic waves such as radio waves, and the short wavelength such as light or X-rays).
 * I'm not sure there is a how: the quanitfication is a fact, and that's all. It was discovered with the photoelectric effect (the electrons are taken away only by ultraviolet and not by red light, so the energy comes in packets) and the black body (the energy spectrum must be discontinuous otherwise the radiative energy of a black body would be infinite).
 * That's where the representation of the phenomenon as a wave reaches its limit. There is nothing to understand because facts are not to be understood, they are to be accepted. You can go deeper and deeper in the explanation (i.e. description), you will always meet somewhere a fact that must simply be accepted &mdash; e.g. you know that you fall down, you know how (the cinetic law), you can tell that the same phenomenon make the planets turn around the sun, you can imagine gravitons, but still you just have to admit that you fall...
 * Sorry if I answered the wrong question.
 * Cdang| write me 19:29, 9 Mar 2005 (UTC)

My edits
(William M. Connolley 15:57, 5 Mar 2005 (UTC)) I came to this page via RFC expecting constant dispute but the page appears quiet for a week or more. I've added a new intro that is how I see it; and I've moved the popular exposee down to the bottom. I'm not really sure I like the analogy stuff at all, but I really didn't like it being right at the top, and very long, so that the casual reader might never get beyond it to the actual science.

Removed
Whether correct or not, the "popularised explanation" is a piece of essaying and therefore not appropriate for Wikipedia. Having it there with the warning messages is just ridiculous. There are many places on the web more suitable for things like this. Fredrik | talk 02:27, 20 Mar 2005 (UTC)
 * Agree. CSTAR 04:02, 20 Mar 2005 (UTC)
 * Disagree: Fredrik, you didn't give any argument proving the text is wrong.
 * A "piece of essaying", well, what do you mean? If all the facts are true (nobody ever pointed a false fact in this text, i.e. nobodyever put a wrong in the quizz), how can you say it is inappropriate?
 * If someone wrote the hydraulic/electric analogy (you know, voltage~pressure and intensity~flow), would you also say it is an essay? If not what is the difference between both cases?
 * Cdang| write me 13:37, 23 Mar 2005 (UTC)
 * I thought "the following section is not a scientific presentation" would be sufficient. The question is, is this metaphor used in any physics textbooks? If so, references should be cited and the discussion of whether it is scientific should be integrated into its description, not presented in the meta-text. If the best reference is an anonymous Usenet post, the metaphor certainly fails the no original research policy. In either case, the text is also inappropriately worded. It does not present facts; it attempts to have a dialog with the reader. This might be more appropriate for Wikibooks, if really correct. Fredrik | talk 17:57, 23 Mar 2005 (UTC)
 * the "the following section is not a scientific presentation" is just a precaution; it means that it does not add any fact (it just repeats the facts presented above) but present them in another way. I can change the sentence if it is the problem.
 * The reference to the Usenet post is just to avoid copyrights problems (I am the author of the post). The other references are all the physics books because all the facts presented in the section are in the general consensus. It is just the fact to put besides hydraulics and quantum mechanics that is unusual.
 * Cdang| write me 08:02, 24 Mar 2005 (UTC)


 * I agree that it should be removed, but I think an article on the water/electric current analogy would be a good thing. I might start that...  :-)  I think this "popularization" is more misleading than helpful, though. - Omegatron 15:39, Mar 23, 2005 (UTC)
 * Well you judge this popularisation is good and that one is misleading&hellip; Great, we have a referee for pair review.
 * Come on, Wikipedia has a deletion policy, if you delete this section, you have to do it according to this policy:
 * not encyclopedic? Sorry, the article as it is is imho as useful as a blank page: people who know quantum physics already know this (it is the basis of QP), and people who do not know QP can't catch a word.
 * Original research? Certainly not, nothing new, only consensual facts.
 * Vanity page?
 * Copyright infringement? No copyright infringement.
 * Dictionnary definition?
 * Patent nonsense?
 * Vandalism?
 * So which point(s) of the policy does the section violate?
 * Cdang| write me 08:02, 24 Mar 2005 (UTC)


 * For me? Non-encyclopedic original research.  It's very large and all it attempts to say is "some things behave like waves and particles at the same time".  That's where the analogy ends, though.  It's a very loose analogy.  I am one of the aforementioned people who doesn't know QP, but I have read enough in trying to learn this concept that I know yours is more misleading than helpful. - Omegatron 17:54, Mar 24, 2005 (UTC)

(William M. Connolley 10:09, 24 Mar 2005 (UTC)) For myself, I simply found it unhelpful: too long, too vague, well I never really finished reading it. I didn't remove it, but I'm happier with it removed. IMHO the new text I added at the start is far clearer and far more helpful for people to understand what is going on.


 * For Omegatron : unencyclopedic, well, it is a very vague thing, an information about a fictitious video game character such as Dark Force has its place on Wikipedia, but not an attempt to make understand to the non-physicists one of the main concept that governs the electronics that fills their pockets&hellip; Original research certainly not, as I pointed out all the facts are known since more than 50 years, but the Shahriar Afshar's experiment which is refered to in the article is original research. Do Wikipedia considers two different types of contributors?
 * I just noticed that Afshar's experiment has been removed from the Double slit experiment article, sorry for this Cdang| write me 09:23, 25 Mar 2005 (UTC)
 * Additionally, you said "this "popularization" is more misleading than helpful", could you tell me in which way it is misleading so I can improve it (not necesserily for Wikipedia)? Which false idea came to your mind when you read this?
 * For William M. Connolley, OK, you find it annoying and vague, but you did not try anything to improve it. Yes the text you added is far clearer and far more helpful and I thank you for that, but it does not clear all the clouds for the novices.
 * Now, let's try to be constructive: a student comes to you and asks (as it happened to me): "uh, I didn't understand one thing: how can you say a particle is not localised? For the double slit experiment, if I put a photographic plate, I can see the photon, if I move it a few millimeters away, I can still see it, thus little by little I can track the photon; the photon has a trajectory and thus does not go through the both slits".
 * What would you answer to him/her? Propose an answer and put it on the article, then the article will be more useful than a blank page&hellip;
 * Cdang| write me 08:59, 25 Mar 2005 (UTC)
 * (William M. Connolley 15:57, 25 Mar 2005 (UTC)) I think you have to tell them that only things that can be observed really make sense; thus to speak of a trajectory (for an individual photon) when you don't observe that trajectory is dubious; and of course the results of the double split expt don't make sense if you believe in trajectories.


 * Why was Ashfar's experiment removed? It looks interesting...
 * Un-encyclopedic
 * By this, I simply mean "not accurate". You asked which of those categories it belonged to, so I picked the closest.  A whirlpool can move through the water in a straight line and collide with and interact with other whirlpools, but this is not the same thing as the effects seen in the double-slit experiments.  The whirlpool probably has more in common with things like solitons.  It's really just a special type of wave...
 * Original research
 * Well, yes, of course whirlpools really do exist, and really do travel in straight lines, but your essay on using that "duality" to make an analogy to quantum wave/particle duality is original, no? Do others use the same analogy to teach this?
 * The article as it currently exists is as useless as a blank page? I disagree.  I would like a better "popularized" explanation, though. - Omegatron 15:22, Mar 25, 2005 (UTC)


 * To William M. Connolley :
 * when you don't observe that trajectory is dubious; &rarr; but they do see a trajectory when putting a photographic plate; you see, the student could not imagine why the photon would act differently with or without a photo plate. That's why I imagined this metaphor, to show him an object can exist when there is an interaction and not exist when there is no interaction.
 * (William M. Connolley 09:43, 30 Mar 2005 (UTC)) No they don't see a trajectory: they see a measurement of a photon at a point. If they think they are seeing a trajectory, then here is where you can explain the difference to them.
 * and of course the results of the double split expt don't make sense if you believe in trajectories &rarr; of course, but that's what you already told during the lesson: "the result of the double slits experiments proves that you must forget etc."; if the message did not work the first time, I doubt it will work by just repeating it. The reason why I tried to find a different way (and I think it worked).


 * To Omegatron :
 * A whirlpool can move through the water in a straight line &rarr; yes, that's precisely why the last section points out the flaws of the metaphor.
 * and collide with and interact with other whirlpools &rarr; interact yes, not colide (just like quantic particles)
 * but this is not the same thing as the effects seen in the double-slit experiments. &rarr; of course not, that's why it is called "metaphor" or "analogy"; if my student doesn't know the difference between a fact and an analogy, I just send him to read a dictionary.
 * your essay [...] is original, no? &rarr; when you teach, you have to adapt your message to your public; a teacher must be original, i.e. find new solutions when new difficulties of understanding arise (and mind that you are always at least 10 years older than the students and it never decreases, so the generation discrepancies come one day or another).
 * The article as it currently exists is as useless as a blank page? I disagree. &rarr; well, just ask a young science student (e.g. first year of university) what he/she can do with it; and just ask a curious person who did not follow science studies. We will never write "Quantum physics for dummies", but we can try anyway to make some concepts as reachable as possible, can't we?
 * I would like a better "popularized" explanation, though. &rarr; I would be happy too, but for the moment, I didn't see any other try. You think that nothing is better, I think not.
 * Cdang| write me 17:23, 26 Mar 2005 (UTC)

I applaud the whirlpool simplification/visualization effort
The whirlpool analogy seems useful to me to aide in visualization. If the physicists here object to it's inclusion in this article, I suggest you include it in a new article, such as visualization of wave-particle duality and add links from/to this article. I have found there is an impenetrable divide between those who write for the masses and those who write just for post-grads. The first group likes to include simple, if not rigorously correct, models, like a globe to represent the Earth. The post-grads are aghast at such an approximation, as the globe is a hollow paper sphere with a metal rod as an axis, and the Earth is not. They prefer higly complex theory, impossible to visualize, and understandable only to themselves. Since there are far more non-post grads than post-grads, you would think they would have the majority in any vote, but, since they spend much less time here than the PhDs, the reverse is the case. Keeping the two groups away from each other's throats by giving them each their own article may be the only way to "compromise". StuRat 12:45, 8 October 2005 (UTC)

Reader's comments
Consider me as an intelligent non-physicist, someone who would look up an encyclopedia to understand Wave Particle Duality. In this light, I believe my first impressions would be useful in updating the article. I expected the first section of the article to introduce the idea, the next to give a brief history and the last to explain the prevailing consensual model and explanation. I also expected the last section to tell me what I should already know to understand the explanation being presented.

That said, I found the article dense with information but disorienting. The external link [http://hyperphysics.phy-astr.gsu.edu/hbase/mod1.html Nave, R.,Wave-Particle Duality. HyperPhysics, Quantum Physics] was more useful. Presently, the article headings are anchored around scientists (Fresnel, Einstein, Broglie). I would find it more meaningful to see section headings based on the conceptual history that underpin Wave-Particle Duality than on physicists.

For now, I would suggest folks above to skip the Whirlpool argument. The overall format of the article needs revision and the current argument above is moot till the article takes better shape. I'll stick around and work with anyone who responds. -Selva 15:01, 16 Apr 2005 (UTC)


 * I like your ideas. - Omegatron 17:12, Apr 16, 2005 (UTC)

help me someone
all i want to know is WHAT IS wave/particle duality and de broglie hypothesis. ive being bugging on understanding this for months. if anyone knows any books/sites/mag that gives a easy AND detailed introduction to them PLEASE tell me (just not too hard please) - thanks for your time

edit: for the probability wave of a particle, does it really exist in phyiscal terms? like electromagnetic waves? because i really don't know why they call it a 'wave'


 * If I understand it correctly, there is no known physical wave property of electrons, at least, but they are called waves since their behaviour matches that expected by mathematical models of a wave. To me, this means there is some physical manifestation of a wave, we just haven't identified it yet. StuRat 15:36, 9 October 2005 (UTC)


 * quantum mechanics really defies interpretation, hence the Copenhagen "Interpretation". The wave here is the complex wavefunction which is not measurable directly. yes it behaves just like a wave (mathematically) but really isn't anything we can point at, just an intermediate step in solving a problem. The probabilities, which we can measure, are from its squared amplitude. It's all just a bunch of math that fits experiment really well I would say. keith 01:43, 30 October 2005 (UTC)


 * Well, if you put a beam of electrons through a diffraction grating, you get an intensity pattern just like if you've used a beam of light. I don't think I'm disagreeing with you guys, per se, but that seems like the obvious thing to mention.  -- SCZenz 01:46, 30 October 2005 (UTC)


 * yeah that's an easier way to describe where the "wave" in wave-particle duality can be seen. I was talking about the "probability wave" asked about above.


 * As for wave phenomenon, I would go even farther and argue that you could in principle also demonstrate wave-particle duality by heaving bowling balls at a pair of appropriately-sized slits to produce an interference pattern. btw the article is a bit overly focussed on light (sorry couldn't resist).keith 02:42, 30 October 2005 (UTC)

Disliking: a simple example using light
Well, in particular: Also, if light only had a wave nature, we would not expect it to be able to travel through a vacuum.. AFAIK light is a happy electromagnetic wave and propagates in vacuum without worrying about being a particle. This seems a throwback to some very old physics. But... perhaps the more knowledgeable will comment. William M. Connolley 10:30, 8 October 2005 (UTC).


 * Hmm, so you're saying a pure wave phenomenon can travel without a medium ? In that case, why doesn't sound travel through a vacuum ? StuRat 11:51, 8 October 2005 (UTC)


 * Errrrrrr... that really is old physics. Sound is a wave in air (or other elastic medium) and is the particles of the medium moving. That much is well known and has been for ages. Electromagnetic radiation is just interlocking electrical and magnetic fields and requires no medium. There is no need to invoke wave-particle duality. William M. Connolley 12:44, 8 October 2005 (UTC).


 * In that case, you aren't just disputing my contribution to the article, but the entire article, in that you deny any wave-particle duality exists for light, which is mentioned other places in the article, as well. StuRat 13:14, 8 October 2005 (UTC)


 * No, only that you need W-P to explain electromag prop across empty space: you assertion of this is the first time I've seen that. - Unsigned by William M. Connolley


 * I still can't tell what you are trying to say. Are you saying that the wave-particle duality of light does exist, but is unrelated to the ability of light to travel through a vacuum ?


 * Yes. William M. Connolley 20:02, 8 October 2005 (UTC)


 * If so, I don't get your argument. My argument is that a pure wave phenomenon requires a medium, thus, if there is no medium in a vacuum, light must not be a purely wave phenomenon.


 * Its not an argument, its an assertion, made apparently by analogy with sound.


 * Which portion of that logic chain do you disagree with, exactly. Don't just say it's wrong, tell me WHERE it's wrong, please. StuRat 18:44, 8 October 2005 (UTC)


 * There is no chain of logic, just a bald assertion. William M. Connolley 20:02, 8 October 2005 (UTC).


 * There most definitively is a chain of logic, even if you disagree with it. I will state it even more clearly for you.  To say that it is incorrect, you must identify which PART or PARTS are incorrect, otherwise you are just being argumentative:


 * Light travels through a vacuum. Do you agree ?


 * A purely wave phenomenon requires a medium in which to travel. Do you agree ?


 * A vacuum contains no such medium. Do you agree ?


 * Therefore, light must not be a purely wave phenomenon. I won't ask if you agree here, since this is the only logical conclusion, if you agree with the first 3 premises.


 * StuRat 21:42, 8 October 2005 (UTC)

I think I just deleted this while section; maybe that will solve the argument. As to the train of thoughts above, 1) Light travels throughy a vacuum, 2) A wave phenomenon most certainly does not require a "medium". It does require a "field" and the distinction is subtle, but there is a distinction. In particular, the electromagnetic field is relativistic, as was demonstrated in the Michelson-Morley experiments; see aether theory for details. I am somewhat disconcerted that some of the article editors are not familiar with the basic history, philosophy and interpretation of modern physics, and yet feel confident to edit this article. linas 22:40, 8 October 2005 (UTC)


 * I take it you are saying that a field does exist in a vacuum, sufficient for wave propagation ? At least you took the time to identify the part of my logic you disagreed with, I thank you for that.  However, you not only took out that part, but the rest of the section, as well, without explanation.  I therefore restored the rest.  As for the implication that only PhD's in physics are qualified to edit this article, I would say there are two qualifications for any editor, an understanding of some, if not all, of the concepts involved in the article (which I have) and an ability to communicate effectively to a wide audience (which I have and many PhDs apparently lack).  I try to limit my contributions to areas where I am competent (notice no contributions in the detailed theory sections), but may occasionaly overreach.  If so, other editors will point out any errors in short order, and I will correct them. StuRat 23:46, 8 October 2005 (UTC)


 * Well, according to modern quantum field theories, which are far and away the best (for certain things, the only) model of reality we have, here's how "fields" work:
 * There is a "field", everywhere, for every particle. It's a function of all space and time.
 * A particle is a wave packet, with reasonably well-localized position and momentum, of the field.
 * Of course, in classical electromagnetism, which is pretty damn good, there are waves with nothing resembling a medium whatsoever. Certainly nobody is saying that only PhD's in physics should edit articles, but the issue of whether light waves need a medium was debated a century ago and settled shortly afterward. -- SCZenz 17:12, 9 October 2005 (UTC)


 * That could be a matter of interpretation. One could say that the feild IS the medium in which waves travel. Also, if you are saying that the majority of the general population know that waves do not require a medium, I disagree. StuRat 17:21, 9 October 2005 (UTC)


 * The field is closer to being the wave itself, I think, but if we're really going to go into a detailed discussion of the philosophy of quantum field theory, we will need someone more knowledgable than me. -- SCZenz 17:34, 9 October 2005 (UTC)
 * I am not saying that the majority of the public knows that waves don't require a medium. Rather, I'm agreeing with linas that understanding the modern (or, at least, the 1920s) answer to this question is a prerequisite for effectively editing this article.  (It's generally something one learns about in a physics program as an undergraduate.)  Note I'm not suggesting for a moment anyone should be excluded, but a little brushing up on some of the relevant articles might not hurt.  -- SCZenz 17:34, 9 October 2005 (UTC)

New "Theory" section
A new section was added by Arnero which was originally named "Intro". I renamed it to "Theory" and performed a LOT of cleanup in spelling, wording, punctuation, and format. While this editor appears to have good info to contribute, they don't seem to do a very good job at proofreading their own work. I would also like an expert in the field to review it for technical accuracy, particularly suspect is the following statement:


 * If Psi(x,t) is a state with the lowest Eigenvalue, one says: The pendulum contains zero phonons.
 * If Psi(x,t) is a state with the next higher Eigenvalue, one says: The pendulum contains zero phonons.

If they do both mean zero phonons, then the case of more than zero phonons needs to be described. StuRat 15:11, 8 October 2005 (UTC) ..UPS sorry a translation error from http://de.wikipedia.org/wiki/Welle-Teilchen-Dualismus I know I should have used Google. I already planned to bother a therotical physicist friend of mine. Arnero


 * I took the bold action of just removing the whole section. I found it clear as mud, and felt it contributed nothing to the article. If someone wants to talk about phonons, they should say something like The phonon is another example of wave-particle duality, see phonon for an elementary explanation of what a phonon is. linas 22:27, 8 October 2005 (UTC)

I admit to be no native speaker and even in German peoply boldly throw away my work even if I asked for help. But I got a diploma in physics. And physics starts with mechanics (both historically and in school). And quantum physics starts with quantum mechanic. And thus the phonon has to be the first example, followed by light and electrons. User:Arnero.


 * Phonons are not even mentioned in Quantum Mechanics courses I'm familiar with. They appear in solid state physics courses instead. So I can't imagine why they'd be the first example. -- SCZenz 16:57, 9 October 2005 (UTC)

Starting from an electron as a particle may have some historical reason as {deBroglie 1924, Schrödinger 1926: Wave} was later than {Milikan: 1910). And chemnistry long ago said: "particles". But the way quantum physical systems are simulated is the other way round. Formulas are the other way round und textbook orders their parts the other way around ( "Quantum Field Theory" from Ryder ). I have the feeling most people are to lazy to accept quantum physics to be more than a corpuscel theory and have billard balls roll before their eyes. The confusion with solitons in this discussion almost made me sick. Arnero


 * I thought your section looked useful, after the wording was cleaned up (by me), but I'm not qualified to talk about the technical value. It might be a good idea to include it here and let people other than linas comment on whether it's worthy of inclusion. StuRat 15:28, 9 October 2005 (UTC)

Thank you for clean up --Arnero 20:27, 9 October 2005 (UTC)

Basis: Quantum Mechanics
A classical pendulum is described by a function x(t). Quantum mechanics recognizes that a complex wave function, &Psi;(x,t), better matches experimental results. The classical calculation is then the approximation for the special case that &Psi;(x,t) is a wave packet. The differential equation for &Psi;(x,t) is fitted to the differential equation for x(t). The differential equation for &Psi;(x,t) has a discrete number of Eigenstates with their respective Eigenvalues. If &Psi;(x,t) is a state with the lowest Eigenvalue, one says: The pendulum contains zero phonons (a phonon is a particle). If &Psi;(x,t) is a state with the next higher Eigenvalue, one says: The pendulum contains one phonon. And so on (the phonon is a boson).

Superposition of oscillator modes leads to Quantum field theory
A popular type of the pendulum around 20MHz is the oscillating quartz crystal. In it one can excite higher modes. The superposition results in the function: Displacement(x,y,z,t). A function of all space coordinates is called a field. Some special superpositions result in waves.

Other wave-particles
The coupling between different shells of the DeBroglie wave with different EM modes can be taken from the classical calculation.

Inclusion of "Theory" section ?
->Please comment on inclusion of the above "Theory" section here:


 * Support inclusion, provided the phonon error is corrected. StuRat 15:30, 9 October 2005 (UTC)


 * Support inclusion, phonon error is corrected. Bold for particle and wave. Bose-Einstein-condensate added. User:Arnero 17:37, 9 October 2005 (UTC)


 * Oppose inclusion, these are narrow examples, based in specific ways of thinking about the problems, that are going to confuse things. "Photons" and "EM waves" exist quite independently of "cavity resonators", and likewise for electrons and atoms. -- SCZenz 17:03, 9 October 2005 (UTC)


 * Oppose inclusion same as above. -- Afshar 18:09, 9 October 2005 (UTC)


 * Oppose inclusion, there are multiple technical confusions/misleading statements/errors, and thus the above text shouldn't be inserted into the article because of this. (I'll critique in next section below). linas 23:23, 12 October 2005 (UTC)


 * Oppose inclusion. William M. Connolley has a point about the poll. But what the heck. Let's throw it out. Give 'em hell linas. --CSTAR 23:30, 12 October 2005 (UTC)

I'm unhappy that StuRat has suddenly decided to start a poll here: it doesn't look very useful. Voting/polls on wiki shouldn't be a first resort. I say: let people who clearly understand this have a go. Its already clear that StuRat *isn't* in that category, however well meaning he may be. Also second SCZ's comments above. William M. Connolley 17:42, 9 October 2005 (UTC).


 * It's also clear to me that you aren't in that category, as you were unable to find the specific flaw in my section (the field vs medium flaw), despite repeated questioning. However, there is no need to have any technical expertise at all to attempt to build a consensus, using polling as one such method.  Frequently somebody not involved in the discussion can be a better moderator than someone rigidly on one side or the other.  I didn't write the material in question (although I did clean it up), and I'm just fine with it being included or excluded, whichever the consensus is.  User:Arnero did apparently spend a fair amount of time writing this material, however, so to simply remove it without any discussion seems quite rude to me. StuRat 18:34, 9 October 2005 (UTC)


 * From my reading, the two of you somewhat misunderstood each other in the initial discussion. William did have a legitimate point, that it's quite unnecesary to use wave-particle duality to explain light propogation in empty space, but he stated it quite briefly.  It's not useful to label each other as not understanding the content of the article, either.  As for removing content, it is pretty standard to be bold and remove stuff you know isn't right, as long as you explain it.  If it's disputed, obviously we need to build consensus--I prefer discussion to voting, but the same consensus is going to come out either way in this case. -- SCZenz 19:08, 9 October 2005 (UTC)


 * I agree, except that I think voting is quicker, it gets everyone's opinions listed right up front, instead of trying to read thru pages of dialogue to try to extract each person's opinion. I'm all for settling issues as quickly as possible and moving on, rather than engaging in endless debate, or even worse, edit wars. StuRat 19:47, 9 October 2005 (UTC)


 * As for removing things which are incorrect, I agree there, too, but don't feel the "Theory" section falls into that category. As near as I can tell, it's not wrong, just perhaps not the best way of explaining wave-particle duality.  In this case, whether it is useful is opinion, and I believe that building a consensus is valuable in such cases. StuRat 19:53, 9 October 2005 (UTC)

Double slit is confusing and as specific. Fourier transformation is a limit of fourier sequence for very large spaces. Thus waves are a limit of modes (Born von Karman). Can we split the whole discussion (which I haven't read) and the article into two sections:

1) particle-wave duality

2) other stuff like spin, relativistic effects, horror vacui, sound in amorph solids, fluids, gas and more very hard to calculate systems like cats and measuring humans? Fermions and fermi dirac statistics -> MAtter. Bosons -> Gauge Fields -> Lights

I better do not bother my particle physics or my Bose Einstein condensate colleage. -Arnero 20:36, 9 October 2005 (UTC)


 * I rather like the double-slit discussion, although it certainly isn't introductory level material. I especially like how it leads from wave-particle duality into a discussion of the many worlds theory. Schrodinger's cat is always a fun way to discuss "collapsing the probability function", but again, is not introductory level material.  Since both of those sections are down in the depths of the article, not at the top, I'm just fine with having them here.  Similarly, I'm fine with Arnero's material, as long as it's not near the top. StuRat 21:27, 9 October 2005 (UTC)

Theory section critique
Below are some comments about the proposed theory section, which should explain why I was against it. The original text italic, my comments are indented. linas 23:50, 12 October 2005 (UTC)

''A classical pendulum is described by a function x(t). Quantum mechanics recognizes that a complex wave function, &Psi;(x,t), better matches experimental results.''


 * To most people, a "pendulum" is a gravity-driven pendulum, and is a very non-quantum object. It would be very very unusual to try to quantize a gravity pendulum. Maybe you meant simple harmonic oscillator?

''The classical calculation is then the approximation for the special case that &Psi;(x,t) is a wave packet. ''


 * No, it is and it isn't. Its more subtle than that, and this statement is misleading.

''The differential equation for &Psi;(x,t) is fitted to the differential equation for x(t). ''


 * That's not right either. I think that what this statement wanted to describe was naive quantization, where one substitutes ihd/dx for the classical momentum. But there are two problems: 1) one makes this substitution not in the classical differential equation, but in the expression for the energy, 2) naive quantization is correct only in simple cases.

''The differential equation for &Psi;(x,t) has a discrete number of Eigenstates with their respective Eigenvalues. ''


 * Too fast. the discussion went from very simple language to the sudden use of an advanced concept. If someone knows how eigenstates and differential equations are related, they will already know quantum mechanics, and won't need to be reading this. And if they don't know, then this sentence will not help them.

''If &Psi;(x,t) is a state with the lowest Eigenvalue, one says: The pendulum contains zero phonons (a phonon is a particle). ''


 * The ground state of the simple harmonic oscillator is never described in terms of phonons. Phonons are lattice excitations, and are far more complex objects.

''If &Psi;(x,t) is a state with the next higher Eigenvalue, one says: The pendulum contains one phonon. And so on (the phonon is a boson).''


 * Again, false.

''A popular type of the pendulum around 20MHz is the oscillating quartz crystal. ''


 * Radio crystals are not pendulums. Also, the vibration modes of a crystal are not quantum mechanical. Although one could describe them in terms of phonons, if one wanted to, the basic theory would be like that of a vibrating guitar string or violin string: the vibrations are not quantum mechanical. Finally, there is nothing special about 20MHz.

''In it one can excite higher modes. The superposition results in the function: Displacement(x,y,z,t). A function of all space coordinates is called a field. Some special superpositions result in waves.''


 * No. While there are higher modes, to the first approximation, these are classical, just as they would be for a violin string.

The coupling between different shells of the DeBroglie wave with different EM modes can be taken from the classical calculation.


 * Maybe. Only with the greatest of difficulty. The beauty of quantum mechanics is that it is a much simpler theory than the semi-classical theory involving de Broglie waves.


 * Thanks for the critique, linas. I think the pendulum is a translation error from his native German.  Perhaps oscillator would be a better translation. StuRat 00:23, 13 October 2005 (UTC)

Eigenvalues is a math term. Students learn this before quantum mechanics. But it is not for the layman, I am really looking for an alternative. Pendulum may really be the wrong start, though it is certainly quantized.

The Eigenvalue Article is on the title page of wikipedia! What do you think of the GRIN-optics glas-fibre model? --Arnero 15:43, 1 November 2005 (UTC)

>While there are higher modes, to the first approximation, these are classical

Yeah right! You got it. Simple classical math and we get from quantum mechanics to quantum field theory!

Uhhh I did that mistake again. The higher mode stuff is not important. Product-wave function is important. Either the product of all harmonic oscillator wavefunctions or the product of all single particle waves (suitable for electrons). --Arnero 15:43, 1 November 2005 (UTC)

> The beauty of quantum mechanics is that it is a much simpler theory than the semi-classical theory involving de Broglie waves.

de Broglie waves are completely classical. Bohr, Heisenberg, Plank are semi. Schrödinger and de Broglie are completely classical. But somehow no one sees it this way. But I have read it this way. --Arnero 19:45, 17 October 2005 (UTC)

Reverts about the theory of light.
Hi Stu, I reverted the last edit for three reasons: first, its redundant with what is stated in the introduction. Second, it does not fit into the literary flow of this section. This section is attempting to establish some of the history of the theory of light. The history is a debate of light as particle or wave; I'm trying to get to the point of saying "particle and wave". The third reason is that I find the bald assertion to be rude, crude and out of place. Physics is subtle and difficult; its wrong to blurt "we know that" because it sounds like religious dogma and not science: we only know this or that due to the difficult efforts of many people. It is not at all obvious that light is a particle and a wave, and one shouldn't talk about it as if it were obvious.

I would have found the following edits acceptable: At the start of the section:
 * It took physicists many centuries to realize that light could be understood to be a particle and a wave. Christian Huygens ...

Or, maybe at the end of the section:


 * Thus, at the dawn of the 20th century, physicists were poised to discover that light is a particle and a wave, thus setting aside the argument between Newton's and Huygen's theories.

Either of these would have fit with the flow of the paragraph. Either of these would have worked well, and would segue well into the next section, which goes into what happened in the 20th century. linas 00:56, 16 October 2005 (UTC)


 * 1) It's not all redundant. For example, I saw no mention of how color relates to the wave characteristics of light elesewhere.


 * 2) Since my material was there before the rest of the section was added, I would be more justified in saying the new material "doesn't fit into the literary flow of the existing material" and removing it. We can always make it a different section, say, "introduction to the duality of light".


 * 3) The "we know that" verbage has been gone for quite some time now, you really should read things before you delete them.


 * StuRat 02:20, 16 October 2005 (UTC)

Suggestions for improvement
Here are aspects of the anon re-org that I would hope are preserved: The introduction in the "higher standard" edit was two sentences long, too short to satisfy readers wanting even the quick summary, let alone the second group listed above.
 * The first section after the introduction should be a more detailed overview of the present-day understanding of the article's topic. As the Guide to writing better articles encourages,
 * some readers need just a quick summary (lead section),
 * more people need a moderate amount of info (a set of multi-paragraph sections)
 * and yet others need a lot of detail (links to full-sized separate articles).


 * I attempt to do that. However, I am concerned that there is a buried conflict here: since the present-day understanding of the article's topic can be taken to mean a review of quantum mechanics as well as a review of duality. I try to do both, but I beleive that wave-particle duality really is little more than a recap of the debate over the paradox, since, to this day, you can scratch QM pretty hard and come up with nothing in particular (see, for example, the silliness of the Afshar experiment). Basically, this is not the article to review QM in its entirety. Anyway, take a look at the current version, I beleive its close(r) to what you envision. linas 19:29, 22 November 2005 (UTC)


 * The article is much improved in its current form, thanks to the work of you and other editors. 66.167.138.98 08:15, 23 November 2005 (UTC).


 * Essay-like connecting remarks like the following should be avoided:
 * This article reviews the history of the development of the notion of wave-particle duality.
 * Quantum mechanics is a deep and broad subject, and it is impossible to give it justice in only a few paragraphs. However, the explanation of wave-particle duality by quantum mechanics can be briefly descried as follows.


 * I eliminated the first, I don't know how to eliminate the second. In order to debate the topic at a mathematical level, one must dive very deeply into quite a large amount of math. And once one finally understands that much math, one realizes that wave-particle duality is kind-of the wrong debate over the wrong topic. So, for me, its a conndrum.


 * Honestly, I'd rather not be editing this article; I have other articles I wanted to work on. However, this article was so appallingly bad, that after one recent edit, I just got angry and went to fix it as best I can. linas 19:29, 22 November 2005 (UTC)


 * This issue has been addressed, too. 66.167.138.98 08:15, 23 November 2005 (UTC).

66.167.253.84 18:48, 22 November 2005 (UTC).
 * The "See also" section references articles that need to be incorporated into the article itself, so that a reader unfamiliar with the terms have some context about those topics.
 * No. The house style is that "see also" is a list of possibly-related topics that haven't been mentioned in the article. If these get incorporated into the article, then the see-also section won't be needed. linas 19:29, 22 November 2005 (UTC)


 * I should have been clearer. I was suggesting that the See also section go away in favor of putting those items in context elsewhere in the article.  I don't understand why those two particular Category:Interferometers merit inclusion over others.  The Hanbury-Brown and Twiss effect article is written clearly enough that I quickly understood how it relates to Wave-particle duality.  I can't say the same for the Sagnac effect article, so again I wonder why this particular interferometry topic was chosen instead of others.  Given the other progress, my See also points are quibbles, so I'm content to let them lie unaddressed if need be.  66.167.138.98 08:15, 23 November 2005 (UTC).


 * You seem to have a sense of literary style and balance, which is perhaps a bit more than what has come heretofore in this article. Please consider getting a named account, so we don't have to try to remember you by number. If you wish to stay anonymous, you may work under a pseduonym; we have several "famous" people here working in this fashion. linas 19:29, 22 November 2005 (UTC)


 * Thanks. I've been contibuting anonymously for several years because it means my contributions usually receive closer scutiny which almost always improves them.  It also encourages my contributions to be judged on their individual merits.  I realize there are disadvantages but so far I've been willing to live with them. 66.167.138.98 08:15, 23 November 2005 (UTC).


 * I agree with that. However, Linas, you should not just assume all edits by anon I/P's are vandalism and revert them out of hand.  Many fine contributions have been made by them. StuRat 20:14, 22 November 2005 (UTC)


 * Sorry. I just finished a long, multi-hour edit, staying up wayyy past bedtime to finish it, and then, within minutes, saw the whole thing mercilessly jumbled. I reverted and went to bed.linas 00:09, 23 November 2005 (UTC)


 * I understand. But you must understand that "mercilessly jumbled" is in the eye of the beholder.  All the authors of the version prior to yours could say the same thing about your edits of their work. StuRat 00:33, 23 November 2005 (UTC)


 * PS: It looks like you fell asleep before you got a chance to use a spell-checker. I fixed those spelling errors I found, except those I think might be proper British English spellings. StuRat 00:37, 23 November 2005 (UTC)


 * I guess what you think are British spellings are still typos, come on Linas is from Texas. :) It is good if there is only one spelling style per article, which in this case will be American I guess. And no, no duality accepted. Oleg Alexandrov (talk) 00:41, 23 November 2005 (UTC)


 * Yes, my spellchecker doesn't do British English, so I just have to guess if something might be British or is just spelled wrong. StuRat 21:25, 23 November 2005 (UTC)

light is particles
I see a lot of confusion about "wave-particle duality".

At one time, it was confusing to everyone. Each of the theories of light ("light is particles" vs. "light is waves") made predictions that matched reality sometimes, but were incorrect other times.

However, physicists have finally figured out a single theory of light that makes predictions that match reality in all experiments.

(Forgive me for giving this Appeal to authority, rather than actually explaining quantum electrodynamics:)


 * It is very important to know that light behaves like particles, especially for those of you who have gone to school, where you were probably told something about light behaving like waves. I'm telling you the way it does behave -- like particles. ... waves can combine or cancel out, and the calculations based on this model matched the results of Newton's experiments, as well as those done for hundreds of years afterwards. But when instruments were developed that were sensitive enough to detect a single photon, the wave theory predicted that the "clicks" of the photomultiplier would get softer and softer, whereas they stayed at full strength -- they just occurred less and less often. No reasonable model could explain this fact. So there was a period for a while in which you had to be clever: You had to know which experiment you were analyzing in order to tell if light was waves or particles. This state of confusion was called the "wave-particle duality" of light, ... It is the purpose of these lectures to tell you how this puzzle was finally "resolved". -- Richard Feynman, in QED (book) (1985).

Would this quote (perhaps trimmed down a bit) be something good to stick in the article? Does this mean that "wave-particle duality" is now merely a historical footnote, like Phlogiston theory? Or is it still a useful idea, even if we now know it is not exactly true in all cases, like Newtonian physics?

--DavidCary 21:47, 30 November 2005 (UTC)


 * In Quantum Field Theory, which is the general modern theory of particle physics, a photon is treated as a particle just like any other (except for having a different mass, spin, etc. than others, of course). However, all particles are subject to wave-particle duality.  -- SCZenz 22:34, 30 November 2005 (UTC)


 * All particles are waves. Feynmann probably says that a few paragraphs over. linas 00:31, 1 December 2005 (UTC)

For the record
This may not belong in the article, but I just wanted to mention for the record that the whole issue basically goes away in modern quantum mechanics. The wave model was particular to early quantum mechanics. This is sometimes called "Wave Mechanics" today, to distinguish it from modern QM. Typically, undergraduate courses in quantum mechanics never get beyond this. Modern QM deals with states of quantum systems as abstract objects&mdash;points in Hilbert space, a complex vector space. These can be manipulated with various kinds of mathematical operators, some of which correspond to physical measurements that can be performed on the system. Like an ordinary 3D vector, the states can be expanded in terms of a set of basis vectors. One can extract the "wavefunction" corresponding to a particular state by expanding it in terms of the basis set of position vectors if you like, but you don't have to do this in general.

None of that probably belongs in this article, but my point is that in modern QM an object is neither a wave nor a particle. It is what it is. If you choose to describe the system in a position-space representation you can describe it as having wave-like properties. You're perfectly free to choose another basis set, however, in which case the description may be quite different even though the results are the same. There are an infinite (IIRC) number of basis sets to choose from, so there is nothing particularly special about "waves" or "particles", except that they are kindof intuitive.--Srleffler 01:57, 13 December 2005 (UTC)


 * Actually, the section called "Theoretical Review", near the bottom of the article, was meant to contain such statements. I didn't feel like writing a grand review of what QM is, so I left it vague, but it is clear from previous edits to this article that many readers are thirsting for a technical rather than a historical presentation. Feel free to add or re-write that section; however, please don't oversimplify analogies, I'm sick of deleting "particles are like guitar strings" type content. You're scaring me with the "IIRC" comment.linas 15:23, 13 December 2005 (UTC)


 * I agree with Srleffler's above setiments, however the statement about infinite basises - yes there are an infinite number to choose from, however the most useful ones tend to be eigenfunctions of important operators. The "wave" function space in free space is important because it is the set of eigenfunction (at least in nonrelativistic QM) of the momentum operator, which is of course very important.  Same with the dirac delta being the engenfunction for the position operator.  These choices are not merely intuitive, but mathematically necessary to study the results of these operators.  I do agree, however, that the whole wave/particle concept is now pretty irrelevant, however to understand the history of physics, it is absolutely vial.  I agree with Linas that the final section should be improved, but we do have to be sure to stay away from oversimplification. - JustinWick 15:43, 13 December 2005 (UTC)

Picture
I complied with your "Good Article" request, but it would be great if this article had a picture. I'm not sure what you could add a picture of, but it looks like this needs one. joturner 17:35, 25 December 2005 (UTC)

Update of Treatment in modern quantum mechanics
I have updated the section "Treatment in modern quantum mechanics" to reflect the common understaning of field theory put forth by Weinberg. There were several comments stating that it needed clarification. I hope that this is considered the best approach at explaining it. Please do not remove any of the added content unless you have read "The quantum theory of fields" by Weinberg. That said you are welcome to expand or edit what I have done.

~Dr. Edmonds — Preceding unsigned comment added by 174.4.58.66 (talk) 08:50, 2 February 2012 (UTC)

Regarding the final sentence in the first paragraph:

Particles without mass, like photons, have no solutions of the Schrödinger equation so have another wave.

I can't parse this as English starting after the word equation. Is it supposed to end with "wave equation" instead of "wave"? If so, it would at least read clearly, though I still wouldn't quite understand the meaning (i.e. it would imply that the equation for describing a photo and other mass-less particles is not the Schrödinger equation but some other equation).

--James Synge (talk) 19:03, 29 January 2017 (UTC) James Synge

Reference issue
Ref. #6 ( http://www.hep.princeton.edu/~mcdonald/examples/QM/thorn_ajp_72_1210_04.pdf ) is not accessible (AJP paper). Changed the reference to point to the article on the journal's website.

Do it faster Mr Ishizaka (talk) 16:57, 18 July 2018 (UTC)

Shorten sentences in the black body radiation section?
Hi there, I am not a native speaker, but the all section about black body and Planck's theory is composed of uselessly long sentences. Let's take this one: "By demanding that high-frequency light must be emitted by an oscillator of equal frequency, and further requiring that this oscillator occupy higher energy than one of a lesser frequency, Planck avoided any catastrophe, giving an equal partition to high-frequency oscillators produced successively fewer oscillators and less emitted light."

I do not even understand the end of it: "[...] Planck avoided any catastrophe, giving an equal partition to high-frequency oscillators produced successively fewer oscillators and less emitted light."

Aren't a couple of mistakes here and there? oscillators? oscillations? giving? given? or a coma somewhere maybe?

Globally most sentences in the whole section could be cut in half and still convey an equivalent meaning. Keuj6 (talk) 14:03, 10 February 2019 (UTC)

Both particle and wave view
In this section, I propose the deletion of the quote from "L.E. Ballentine, Quantum Mechanics." It is quite long and from a very dated textbook. The lead-in sentence suggests that duality is not a mystery, but the long quote simply says the wave pattern is statistical and the particles don't obey classical rules which we knew anyway. The quote tells us nothing... CometKeeper (talk) 22:56, 23 April 2021 (UTC)

Wave-particle Duality on Busy Roads
An anonymous contributor introduced above (see Archive 1) the idea that motor traffic, especially at night when only the rear lights are visible, can show particles behaving like waves when the stream of traffic splits to avoid an obstruction.

Everyday experience on fast main roads includes the phenomenon of heavy traffic repeatedly slowing down, sometimes to a standstill, and bunching up, before moving off to spread out again. This is explained by Boris Kerner's three-phase theory of traffic flow, in which a "wide moving jam" entails a "congestion shock wave" which propagates backwards at what turns out to be around 20 kilometres per hour, whatever the forward speed of the main traffic flow may be.

The wave-form is not easily seen from within the stream, but can be seen from the side when traffic has to form a queue to leave the carriageway. Cars in the inside lane can be seen slowing down, possibly even stopping, while those ahead speed up and separate, leaving enough room for faster traffic in the adjacent lane to cut in. There may be several such segments. To the onlooker this looks like a sound wave, the direction of oscillation being the same as that of propagation.

I have not seen this happen when happen when humans or animals, or even people on horseback, walk or run in the same direction: it seems to be specific to vehicles controlled by humans, rather than a property of the road layout. Perhaps the next generation will discover whether self-driving cars behave this way. Whatever the basis, this seems to me the most visible example of particles behaving like waves. NRPanikker (talk) 17:39, 15 February 2019 (UTC)


 * The archived introduction was probably also off-topic per wp:talk page guidelines. - DVdm (talk) 19:08, 15 February 2019 (UTC)
 * It's only off-topic if we have to confine ourselves to mathematical models of imaginary objects. But the point of these models is to explain real events in terms of things we can imagine. The archived account helped by offering an analogy with something we can actually see. Waves and particles were originally brought in as metaphors to explain things that we can't see. NRPanikker (talk) 01:44, 16 February 2019 (UTC)
 * But it is off-topic because we must discuss changes to the article here. We cannot discuss the subject or aspects thereoff. See wp:TPG. - DVdm (talk) 12:57, 16 February 2019 (UTC)
 * One point of talk pages is to discuss matters that might be worth putting in the article. It would be pointless to refuse to consider things because they aren't already in it. NRPanikker (talk) 11:43, 17 February 2019 (UTC)
 * Right. Can you bring a reliable source (as in WP:RS and WP:DUE) that would support the content —and its documented relevance— to be put in the article? With such a source we can discuss. Otherwise it remains off-topic. - DVdm (talk) 12:42, 17 February 2019 (UTC)

Unfortunately none of Boris Kerner's papers appear to be accessible without payment. However the Traffic wave page on Wikipedia has an external link to a YouTube video from Japan showing cars driving around at a steady speed under the Nagoya Dome. They soon start to bunch up, slow down and then accelerate away: the narrator assures us that the "congestion shock wave" we see moving backwards is doing so at 20 km/h. This is the phenomenon I spoke of above. Regarding its relevance, I can only say res ipsa loquitur. I hope that this will be enough for a nihil obstat and eventually an imprimatur from a WikiBishop. NRPanikker (talk) 01:25, 18 February 2019 (UTC)


 * I don't see any reference to the subjects of quantum mechanics or wave-partucle duality in the Traffic wave and Boris Kerner articles, nor do I find any link between the subjects and Boris Kerner in a Google Books Search or in Google Scholar Search. Perhaps this is some kind of wp:original research of your part? In that case we obviously cannot discuss it here. - DVdm (talk) 18:38, 18 February 2019 (UTC)
 * That's right. No mention of the phrase, "wave-particle duality." Just lots of stuff about particles acting like waves. QED. NRPanikker (talk) 20:59, 18 February 2019 (UTC)