Talk:Introduction to quantum mechanics/Archive 3

This article is intended as an accessible, non-technical introduction to the subject.
Fail. —Preceding unsigned comment added by 173.50.155.230 (talk) 06:42, 17 January 2010 (UTC)
 * I'm in chemistry I honors, and this article is EXTREMELY useful and detailed - it goes over the parts my teacher skipped for simplicity's sake! As long as you have a little background to quantum mechanics, whether it be from high school or a textbook, this article is an excellent supplement. Also, Physics 2000 is a GREAT website for understanding quantum mechanics.

Easy to understand??
This is supposed to be a "a generally accessible introduction to the subject"? I guess it might be easier to understand than the (non-easy) Quantum Mechanics article, but this is by no means something that the layman could understand. I know this is a complex subject, and that explaining complex things simply is difficult. Still, I hope that this article could be made from "easier quantum mechanics" to "actually easy and fairly simple to understand quantum mechanics". Above all, remember that we don't need to go into that much detail, because this is the "easy" article :). Some suggestions:
 * -The overview section is really long, maybe we could trim it down?
 * One of the things that might make the article easier to understand is if we took all the history out of the "Overview" section and put it into a new "History" section that details all the, well, history of QM, like Einstein, Bohr, etc. (see below)
 * Would it be possible to just put a few simple paragraphs explaining what quantum mechanics is, without going into a lot of detail just yet?
 * -History
 * I noticed that there is a TON of historical data floating randomly in this article. I don't know how important this is to quantum mechanics, and of course if it is an important point in the study of quantum mechanics to know who-did-what-when-and-why then of course these little snippets of history should be kept, but if this is not the case, then we have way too much history on our hands here. It seems like what's happening in this article is that instead of explaining QM in an easy-to-understand manner, we are writing about the major "players" in the development of QM. We are going through all these theories and concepts person-by-person, looking at "what Planck did" and then "what Bohr did" etc etc, and not at "what all of this actually is". The history, though an important part of QM as a whole, should not be the focus of the introductory article to the field. Thus, I think that the aforementioned "History" section might be a good idea. That way, we could have a brief discussion of what each genius did, and we can mention their experiments and everything, but we could also try to bring the focus away from the people and towards what QM actually is. Bottom line: what matters more, the who or the what?

Thanks for the time and effort, sorry if I have no idea what I am talking about...I don't know much about QM or even physics for that matter (hah! matter! no pun intended! but how amusing!). About the history, again, if its really important and integral, then I apologize, but it just seems to me, as someone who doesn't know much about the subject, that there is too history for an introductory article. Thanks, 71.178.238.238 (talk) 04:23, 19 May 2008 (UTC)


 * You might want to look at what some other secondary sources have done with the subject. Brian Greene has written a couple of good books that include chapters on the subject.


 * Just explaining what classical physics is can be a problem, yet it researches the stuff of everyday life. As soon as you hit Relativity theory, people start making simplistic interpretations that can only mislead others, but at least they are talking about effects that can be observed in things like global positioning satellites. Quantum mechanics deals with things that cannot be seen, and one of the really important lessons tied up with quantum mechanics is that it is essential to keep clear on what is observed vs. what is inferred.


 * It would be relatively easy to say what quantum mechanics does, i.e., what it explains, what it helps us do, how it directs technological initiatives, etc. But then the question would be, "Well, how does quantum mechanics provide for some of the useful things in our life?" One kind of explanation is like saying that a large box with windows and wheels, you get it, turn a key, and move across the terrain. That kind of explanation would do just as well for Cinderella's magic carriage. The other kind of explanation gets into fuel, pistons, mechanical and electrical connections, tires, etc., and even explaining a relatively stripped-down mechanized vehicle more specifically than saying that you get it and it goes will turn out to involve a long chain of explanations.


 * I started reading about quantum mechanics sometime before 1958, and my first impression of it was that it had something to do with an "uncertainty principle." For a long time I thought that it was possible that the things in the real world were all at actual points in space and time, and that our knowledge was just limited by the fact that we inevitably mess with these real locations when we try to measure them. It turns out that I had gotten it wrong.


 * If you don't want people to get misled, then you have to be really careful. You have to include things to head people off from taking some things the wrong way. Furthermore, you can't jump into the middle of the story. You have to provide a road between the things that readers already understand and the new insights you want to teach. P0M (talk) 15:50, 19 May 2008 (UTC)


 * I've just been through the article again. The intro section gives readers the basic "consumer's view of QM" (equivalent to: Car -- you get in, you get delivered, you get out). Everything else in the article has to do with quantum phenomena, so if the reader wants some flesh on the idea that quantum mechanics deals with how nature works on the very small scale and why that should matter to us then you must work through some concrete examples.  But these examples also tell the story, in digestible quantities at each stage, of how the answers to problems that cropped up in the labs each contributed parts to the jigsaw puzzle that was eventually assembled to account for everything except for gravity.


 * Would a timeline help?P0M (talk) 09:16, 20 May 2008 (UTC)


 * I agree with both User:71.178.238.238's criticisms. The history is too much, and the overview needs to be simpler.  What this introduction to QM needs to address is why QM is so much harder for people to understand than classical mechanics.  What about an approach like Richard Feynman uses in his Lectures on Physics?  He starts out by saying: "Things on a small scale behave like nothing you have any direct experience with.  They don't behave like waves, they don't behave like particles, they don't behave like clouds, or billiard balls, or masses on springs.  Even the experts don't understand it the way they would like, because all of our human intuition applies to large objects.  But small objects just don't act the same way."  Later he goes on to enumerate in simple language how small objects' behavior is different: wave - particle duality, inability to measure variables with arbitrary precision, probabilistic results of measurement, the ability of objects to be in different states simultaneously.  These are the things beginners have trouble with in QM, and they should be faced head-on in this article.  -- Chetvorno TALK 22:59, 21 May 2008 (UTC)
 * Your plan sounds good to me. Why don't you write a new front end? P0M (talk) 21:01, 25 May 2008 (UTC)


 * I warmly applaud the fact that Wikipedia, recognizing the nature of the beast, includes 3 distinct entries seting out quantum mechanics, with this entry intended to be the least technical. That said, this entry leaves something to be desired, if only because many of its sentences and paragraphs are too long. Quantum mechanics and electrodynamics are probably the greatest theoretical achievements of the 20th century. The quantum mechanical theory of the electron orbital grounds all of chemistry. Quantum electrodynamics is the most thoroughly verified scientific theory of all, and is the deep physics behind all information technology. Perhaps the most important fact of the 20th century is the discovery and subjugation of the electron, and the electron is the star of the quantum mechanical play. This story must be told.


 * (An aside. I propose that the first "quantum insight" was George Johnstone Stoney's 1881 prediction that electric charge was carried by a tiny particle he named the electrene, and that all electrostatic charge was an integral mutiple of the electrene's charge and hence quantized.)


 * At the same time, I must admit that it has proved very very difficult to communicate this achievement to educated lay people, and that's not for lack of trying. Many comments on this Talk page reveal that this difficulty extends to this entry. Not that this esoteric topic is lacking in human interest, and dramatic tension and irony. Should anyone doubt this, I refer them to Michael Frayn's play Copenhagen, on the clash between Bohr and Heisenberg. Also to Pascual Jordan's Nazi sympathies, Bohr's presence at Los Alamos, Pauli's intense work with Carl Jung, and Schrodinger's unconventional attitude towards marriage and paternity.123.255.30.126 (talk) 18:59, 14 December 2008 (UTC)

Since the initial criticism was entered above, I've changed the lead. I hope that I've increased the ease of comprehension of the article. It will be a continuing balancing act to avoid short reports that are accurate but so lacking in context as to make them hard to understand on the one hand, and something that grows, topsy-turvy, into something that is too long and contorted. P0M (talk) 00:08, 15 December 2008 (UTC)

Maintenance
I've archived older content to save space here. Old content is available by clicking the archive links at the top of this page. P0M (talk) 00:46, 15 December 2008 (UTC)

Moving new comment to the end of the article. P0M (talk) 21:17, 22 May 2011 (UTC)

One
Rereading the lead and the top parts of the article it occurs to me that some drawings might make the necessarily abstract assertions much clearer to the new student of the subject. For instance, the assertion that electrons and photons do not always show up where everyday experience would anticipate their appearance might be dealt with by a cartoon in which a copyright safe version of Captain Kirk, Captain Quirk, is given a new double-barreled photon rifle for testing. The viewer the looks over his shoulder and sees him drawing a bead on a target directly in front of him. Each time he pulls the trigger a different target is hit, and once somebody behind the bulkhead gets a hole through his chef's tall hat. It should even be possible to do this with GIF images and make it into a little motion picture. The familiar Young's interference pattern emerges, and Quirk returns the rifle with the comment, "Entirely up to specifications Mr. Smock." The cartoon could be linked to a description of how one can actually reproduce much of that scenario with a laser pointer and a few brads fixed into a frame.

Doing things that way should appeal to high school students and other just beginning to understand that physics is mysteriously cool. P0M (talk) 01:10, 15 December 2008 (UTC)

Another cartoon could show a moth flying at a leisurely pace in a large room. Somebody with a butterfly net tries to catch it, but is unsuccessful. To improve her chance of nabbing it, she closes a partition, trapping the moth in half the original space. But that doesn't help because the moth moves more rapidly and erratically. Closing the volume down farther only makes the moth's position more unpredictable.

I think that these two visual analogies would make the main assertions about the weirdness of QM more concrete without being too misleading.P0M (talk) 01:21, 15 December 2008 (UTC)

For the part that introduces the main figures in early QM, how about some pictures, maybe like these? To the new reader, these are just some strange-sounding names. We should select photos that show, e.g., how young Heisenberg was when he figured out his matrix theory. Students probably would otherwise find pictures of these important figures when they were old and famous. P0M (talk) 04:51, 15 December 2008 (UTC)


 * I made a composite of 10 pictures of individuals who were important in QM. Einstein looks rather older than the rest of the people who were so productive in the early years. I was generally able to find pictures of these individuals that were taken within a few years of their early important discoveries. I put in Feynman just to prevent leaving a blank space. His contributions came much later, but just look at how young he looked when he was working on the fission bomb! No wonder he was always breaking into safes and leaving prank notes. P0M (talk) 03:52, 17 December 2008 (UTC)

Two
I'd like to know what other people feel about the discussion of "h-bar." To me, it is only a computational issue. It may well be worthwhile to direct readers to a discussion elsewhere since the two constants are similarly named and, sometimes, on-line discussions write "h" when the appropriate thing would be "h-bar." But the discussion takes up a huge amount of space and, as far as I can tell, does nothing to elucidate the natural phenomena. P0M (talk) 05:41, 15 December 2008 (UTC)

Three
Is the bit about dimensionality going to be helpful to the beginning student in any way? Is it essential? To me it just seems to be something added in for no good reason. P0M (talk) 05:52, 15 December 2008 (UTC)

The most eminent of physicists have warned...
The most eminent of physicists have warned that if an explanation of quantum physics "makes sense", then that explanation is very likely to be flawed. Is this intended to be a paraphrase of Bohr's "Those who are not shocked when they first come across quantum theory cannot possibly have understood it" and Feynman's "I think I can safely say that nobody understands quantum mechanics"? If so, I think that we should find a wording which more closely matches the original intent of these. -- Army1987 – Deeds, not words. 16:52, 26 January 2009 (UTC)

In the late 19th century, classical physics appeared to some as nearly complete?!
If I remember my history correctly, in the late 19th century physicists and chemists could not agree on whether atoms were the smallest particle, or if matter was infinitely indivisible. Thermodynamics and statistical mechanics were relative new fields that were developing. No one understood black body radiation or the photoelectric effect. In the last 6 years of the 19th century x-rays, radioactivity and the electron were discovered.

Complete my butt! Technotaoist (talk) 02:18, 23 March 2009 (UTC)


 * There is no need to be crude.


 * The statement mentioned above can be substantiated. If I recall correctly it is actually based on a published statement by some eminent figure of the time who said something like, "All that remains is to figure out what is going on with problem x and problem y." The trouble was that x and y were the points where the whole thing was going to come unraveled. It's probably worth digging that quotation out just to demonstrate how successful Newtonian physics and Hamilton's work on electro-magnetics had been.


 * The ultra-violet catastrophe was probably either x or y, and that was a "little detail" that had to be cleared up in the account of black body radiation. P0M (talk) 05:20, 23 March 2009 (UTC)
 * Yes, IIRC black body radiation and the associated ultraviolet catastrophe were explicitly flagged up as something they knew they didn't understand -- the surprise was that the can of worms uncovered was just so much bigger than anyone expected. --Michael C. Price talk 07:25, 23 March 2009 (UTC)
 * No, as correctly described in Ultraviolet_catastrophe, the concept of "ultra-violet catastrophe" was recognized in 1905. It played no role in Planck's derivation of the blackbody radiation law.
 * The "eminent figure" was Lord Kelvin, who, in his lecture presented On 27th April 1900, considered (classical) physics as almost complete, apart from "two clouds", the null result of the Michelson-Morley experiment and the problem of deriving the blackbody radiation law.--Belsazar (talk) 22:19, 24 March 2009 (UTC)
 * Let's use that quotation. Do you have a citation handy? P0M (talk) 03:29, 25 March 2009 (UTC)
 * Actually, Belsazar, the equipartition article says that Lord Rayleigh envisaged the need for some new principle to reconcile the equipartition principle with thermal equilibrium in 1900 (which is in the 19th century, and the same year that saw Rayleigh's first derivation the $$\lambda^{-4}$$ dependence of the Rayleigh–Jeans law and hence implied the UV catastrophe) he noted the need for a new principle that would provide an "escape from the destructive simplicity" of the equipartition theorem.[29]" The reference is JWS Rayleigh (1900). "The Law of Partition of Kinetic Energy". Philosophical Magazine 49: 98–118." So we have another ref to go with the Lord Kelvin quote.
 * Re Lord Kelvin, I'm assembling the "two clouds" quote (which may be disputed) over at Lord Kelvin's wikiquote entry. Kelvin is talking about the luminiferous ether (not Michelson Morley directly) and the equipartition of energy (not black body radiation directly). This quote seems to be confused with a similar 1894 statement by Michelson, which would also be relevant to this article. Have a look.
 * --Michael C. Price talk 08:57, 25 March 2009 (UTC)

". . . an accessible, non-technical introduction to the subject . . ."
In accordance with some of the comments on this page, I am submitting to the WP community this revised version of the simplified article concerning quantum mechanics. I have reorganized it and stripped it of its repetition and also placed within it some new links to Main Articles that will be helpful to the advanced reader. I've also deleted almost all the graphics, which are confusing and not at all "accessible and non-technical," in the words of the note at the top of the page (the wp:hatnote). The deleted material can be found at User:GeorgeLouis/QM.Rejects or in past versions of this present article; portions of this material might be added to the "expert" article at Quantum mechanics. As an aside, I note that the supposedly "accessible" article was composed of 82,419 bytes on 27 May 2009, with the "expert" article weighing in at only 51,037. Yours very sincerely, and with great good wishes for a fine Introduction to quantum mechanics (the basic principles of which are not really too hard to understand if presented simply enough), I remain your friend, GeorgeLouis (talk) 07:36, 28 May 2009 (UTC)

Article severely truncated --- opinions?:
A new editor has made some strong comments about the adequacy of the previous version of this attitude and has taken matters into his own hands. Please look at the results and give your opinions. P0M (talk) 16:45, 28 May 2009 (UTC)


 * I've reverted to the old version. The new version reads more like an account on the historical development of quantum mechanics, which is not the same as an introduction to quantum theory. Now, there already exists an article about the history: History of quantum mechanics, so perhaps the reverted edits can be included in there. Count Iblis (talk) 23:42, 28 May 2009 (UTC)


 * I am on the verge of being able to finish a re-write of the matrix mechanics part, pursuant to which I have been pestering my colleagues in the physics department. Probably much of that part should go into a sub-article as it takes quite a bit of explication to give a novice reader a clear idea of what caused the breakthrough that ended the "old" quantum mechanics. It was not the matrix idea, but the idea that found clearer expression in matrix form.
 * I have been hoping to get the Heisenberg part behind me and to go on to clear out some of the excess baggage in later parts of the article. It may be that some things will need to be tucked into sub-articles if they are not deleted. I will bring up major changes on this talk page before I make them. P0M (talk) 00:11, 29 May 2009 (UTC)

(OD) In the spirit of bold, revert, discuss, I suggest that GeorgeLouis now use the Talkpage to propose large scale revisions, perhaps on a section by section basis. This is not to disparage his good faith -- the article was long and somewhat rambling -- but rather an enticement to collaborate with many experienced editors to tighten the existing material.

P0M, when your rewrite is ready, I would be glad to offer feedback. Baccyak4H (Yak!) 03:18, 29 May 2009 (UTC)


 * I feel that GeorgeLouis's rewrite goes in the wrong direction, but it was at least a start. The previous article had way, way too much baggage. Here's my two cents: (1)I suggest omitting ALL the history.  We already have History of quantum mechanics and History of quantum physics and it is clear from comments on this page that people think the article had too much history.  (2)I'd also suggest omitting connections to relativity and other advanced topics; we need to keep the article short.    (3)It's clear from the comments on this page which direction this article should go.    What people want this article to address is why QM is so hard to understand.  It should just be a primer, in simple language, of how small-scale (quantum) objects behave differently from large scale objects: wave-particle duality, uncertainty principle, quantum probability and nondeterminism, superpostions, quantized energy levels, interference.  Yes, we have articles on these topics, but not in simple language.
 * I began a rewrite that can be viewed here, although I'm not satisfied the language is simple enough. -- Chetvorno TALK 21:56, 29 May 2009 (UTC)


 * Baccyak4H, and everybody:


 * I am stuck on the math, but in general the path up to Heisenberg's breakthrough is clear, and it is easy to explain how everything worked to explain things that had previously been unexplainable:
 * This is just an outline:
 * Mystery one: "Every element has its characteristic bright-line spectrum, but how can these irregular sequences be given a theoretical treatment? They don't make any rhyme or reason!" But then:
 * Balmer: λn=Å•3646•(n2/(n2-4) where (n=3,4,....) and later, in a more productive format:
 * Rydberg and Ritz: 1/λn = RH(1/4 - 1/n2) where (n = 2, 3, 4...)
 * Mystery two: "Light waves hit a metal surface but monochromatic light gives the same voltage on the (de facto) light meter. Stronger light gives more amperage, but the same voltage. What the hay?!?" Mystery solved:
 * E = hf (Planks's constant)
 * f = c/λ (nothing new here, but novices need to see how to get from frequencies to wavelengths and back.
 * Eelectron = hc/λ
 * Planck-Einstein relation:
 * Ephoton = Ei - Ej = hf
 * Mystery three: "The hydrogen spectrum is predictable, for the visible spectrum, but how about ultraviolet and infrared?"
 * Bohr's scheme of energy states predicts many spectral lines:
 * 1/λ = RH( 1/nf 2 - 1/ni 2 ) where (nf = 1,2,3... and ni > Nf)
 * Mystery four: "So what is with these bright lines? Why are some brighter than the others? Bet you can't explain that!"
 * On the existing basis, one could predict the spectral lines for hydrogen, and the energy of the photons associated with each of the lines. The only thing that would not be known on this basis would be the intensities of each of the spectral lines. By studying the best available secondary sources I have realized that the problem for Heisenberg, and the discovery that Heisenberg made to solve it, was how to account for the intensities of the hydrogen bright-line spectrum. Although every step in the math up to this point is almost too simple to believe that it can account for so much, the calculations that he had to perform take him about 16 pages just to sketch out -- and people in the field even complain that they can't understand it. If only he had written in a little more detail it would have been clearer. I say this because some people have since puzzled it out. Right now I'm trying to get a "proof of concept" grasp on the math so that I won't say anything ridiculous on how the matrices are to be written out. What Heisenberg actually wrote and published did not involve a single matrix, but my colleague in the physics department took one look at the equation that a secondary source spotlights as "Heisenberg's law for matrix multiplication," and said that it gave clear directions for how to write a matrix.  I do not think that the novice reader is going to object to the article's not giving a clear treatment regarding how the math was worked out. The important thing to see is that once this one step was taken there was a complete quantum theoretical picture of how hydrogen produces light. It also provided the key to the:
 * Yet another mystery, number five: Heisenberg indeterminacy principle -- discovered when a troublesome bug turned out to be a valuable feature.
 * "Help! Can anybody help with the math given in Heisenberg's 1925 paper and explained (to the satisfaction of people whose math is better than mine) in Ian J. R. Aitchison, David A. MacManus, and Thomas M. Snyder, 'Understanding Heisenberg's 'magical' paper of July 1925: a new look at the calculational details. arXiv:quant-ph/0404009v1 1 Apr 2007. Heisenberg figured out a way to compute transition amplitudes from the things already known. He gives a very sketchy treatment."
 * "If I could calculate the transition amplitudes for at least the visual part of the hydrogen spectrum then I could calculate the intensities for the visual part of the spectrum and compare the answers to empirical measurements. It's not that I want to put these results into the article, but that being able to see all of the matrices together I could be more sure of not writing something really ridiculous on the basis of some misunderstanding."
 * I am less familiar with the developments after that point. The math appears to be more abstract, which may be just the way things are, but some of the discussion like the "h-bar" part clearly do not help novice readers. The math up to the amplitude/intensity part should be stated, but it does not have to do anything other than to give readers the realization that there is nothing mystical or incomprehensible about it. I include them above mainly for concision in showing what needs to be covered.
 * I plan to finish my rewrite on the basis of what I know now, and keep trying to work through the math so that if I learn anything that contradicts what has been put up then I can correct it -- assuming somebody else has not already caught it. Maybe I can finish up the draft over this weekend. As far as I remember, the material up to Heisenberg is accurate. Historical details can be removed. P0M (talk) 19:30, 30 May 2009 (UTC)


 * I don't have the early papers you allude to, but trust you to draft something workable. Is it in your userspace?


 * Anyway, I sympathize with how simple some of the calculations might be and yet when you see where they are going, the mind is fried. I recall a simple work showing how Einstein apparently derived E=mc2 and was totally astonished at how easy it was.  I cannot remember where it was now, although it predated Larry Gonick's stuff. Baccyak4H (Yak!) 03:32, 31 May 2009 (UTC)

Request for comment
There are two WP articles concerning quantum mechanics. One, Quantum mechanics, is designed to be a full exposition of the subject for those who wish to explore the topic at depth. The other, Introduction to quantum mechanics is, in the words of the WP:Hatnote, designed to "an accessible, non-technical introduction to the subject. For the main encyclopedia article, see Quantum mechanics." The present user, your obedient servant, rewrote the article in what to him was the spirit of its title and introduced it on 27 May 2009. It was reverted with the suggestion WP:BRD. This is the place for that discussion. You can see the difference between the older, longer, article and the new one here. The comments of the entire Wikipedia community, not just physicists, are welcome, and indeed, sought. Yours sincerely, GeorgeLouis (talk) 16:53, 29 May 2009 (UTC)


 * The current version is similar to History of quantum mechanics. The main article: Quantum mechanics reads a lot like a basic introduction to quantum mechanics, so perhaps an introductory article is redundant. Articles that explain the mathematical formalism of quantum mechanics are spread out over a few wiki articles.


 * I think we should keep in mind that an introductory text explaining some physics topic and a historical account of how that topic was developed are two entirely different things. If these two things are confused, you get a very bad result.Count Iblis (talk) 17:03, 29 May 2009 (UTC)

-- Firstly, this is a noble idea. Difficult, but worthwhile.


 * The 'see also' is very long. This looks to me like a prime candidate for a navbox - a navigation box. I quickly knocked one up, please see user:chzz/quantum. If you edit it, you'll see that the code is not too complicated. I've made no good attempt at deciding the sections etc, I leave that to the experts, but I feel that if a good, organised navbox could be made about the 'Quantum' topic, this could usefully be used at the bottom of all of those articles. Please feel free to edit it, copy it, play with it, and make a template:navbox quantum.


 * I think this would be much better than the infobox used at present. For one thing, I'd like to see a more exciting photo at the top; was it Stephen Hawking who was told, every equation he put in his book would halve the readership? If this is an intro for us non-experts, then a nice, impressive picture would be a lot better than an equation which is going to be meaningless to us.


 * I think that the lede section should be much longer; an overview of the whole article.


 * I think that a lot of the language used needs work; it often borders on original research, and some of it sounds non-encyclopaedic and perhaps patronising; for example;

The idea of particles and waves is simply a mental model derived from everyday experience. Take, for example, the rainbow of colours reflected from a puddle of water when a thin film of oil rests on its surface. That phenomenon makes sense by thinking of light as waves...


 * A quick suggested rewrite;

Energy can be thought of as particles or waves; neither is the truth, but both models help us to think of quantum events in every-day terms. The rainbow of colours reflected from a puddle of oily water can be understood by thinking of light as waves...


 * ...the above is by no means perfect - a rough draft. The idea is to present the facts, and let the reader draw their own conclusion. Avoid saying "this is simple" and "makes sense by..." (maybe to you, maybe not to the reader), and "Take, for example" (not very encyclopaedic language).


 * I think that the article should focus more on an explanation of Quantum mechanics, and less on the history. If the history can still be covered whilst explaining the theory, then all the better.

All of the above - as everything I write - is #|IMHO. Explaining Quantum mechanics to non-experts is not easy, but exactly the sort of thing that Wikipedia can strive to do. I wish you the very best of luck with it.  Chzz  ►  05:26, 31 May 2009 (UTC)

---

I don't know how to insert the Navigation Template. Could you do it in lieu of the See Also section? The principal discussion of the Request for Comment is going on at http://en.wikipedia.org/wiki/Talk:Introduction_to_quantum_mechanics#Request_for_comment. I copied your lengthy message over there. Sincerely, GeorgeLouis (talk) 06:02, 31 May 2009 (UTC)

---

I am not sure why certain folks are taking exception to the simplification of this article. Could it be an example of WP:Ownership? I am willing to discuss any changes, but we should really start and end up with a simple, nontechnical article, as is promised in the title. It doesn't make any sense to add stuff that is totally incomprehensible to the layman and then insist on keeping it there. Remember, there is already a very complete article on Quantum mechanics and many other articles dealing with allied subjects in Wikipedia. This one is supposed to be nontechnical. Yours sincerely, GeorgeLouis (talk) 02:01, 1 June 2009 (UTC)


 * I like George's lead, which has been reverted. The old lead was looking too much like a history of quantum mechanics, which is of no relevance to the non-specialist and of doubtful pedagogical value. George's lead, by contrast, says the essential thing clearly: that particles are waves and waves are particles. --Michael C. Price talk 08:26, 2 June 2009 (UTC)
 * Michael, please check through the sequence of events. The whole article was replaced. Some of the material had serious problems. I attempted to adapt to the abrupt and unresponsive behavior of Mr. Louis by working on the text he had provided. But when I critiqued a section of the replacement text (see above), that critique was received with gracious words by Mr. Louis -- and then altered to a very great extent without any discussion whatsoever. When I complained about the lack of due process Mr. Lous did not make a responsive answer. He merely complained that my remarks about his behavior did not belong where I had put them but somewhere else.
 * I am not opposed to changes, and suggested many (see up near the top) to which nobody has responded as yet. I am opposed to a process of "communication" that consists of pronouncements from Mr. Louis but no responses to attempts at rational discussion.
 * The old lead had problems and will be changed. What needs to be done now is to make something that is not misleading and also not so free of real content that it does not serve the needs of a novice reader. It should be possible to arrive at changes by a collaborative process. Doing so means discussing large-scale changes beforehand, and giving responsive answers to criticisms. P0M (talk) 15:19, 2 June 2009 (UTC)


 * It's true I haven't followed the history of these changes, and didn't read past the lead. But I did think the revised lead had some very positive aspects.  Can't speak for the other changes without looking further, of course. --Michael C. Price talk 18:16, 2 June 2009 (UTC)
 * Mr. Louis gutted the corrections he had just thanked me for and replaced one paragraph with:

"The idea of particles and waves is simply a mental model derived from everyday experience. Take, for example, the rainbow of colours seen on a puddle of water when a thin film of oil rests on its surface. The different wavelengths of light reflected from the two layers of liquid are perceived as different colors. That phenomenon makes sense by thinking of light as waves.[5] Other phenomena, like the working of light meters in cameras, can be explained by thinking in terms of particles of light (called photons)."
 * What it boils down to is saying that light is perceived as having different colors when it has (a range of) different wavelenths. But that fact has nothing to do with the oil slick, and it does not explain why a wave explanation seems necessary to account for ambient light not being reflected in all its wavelengths. It's because he hsa cut out the explanation of the interactions of light "waves" coming off two surfaces of a very thin film. Similarly, he replaced an example of a phenomenon that cannot be explained on the assumption that light is a wave with a phenomenon that can be explained on the assumption is a wave. The light meter example is only relevant if one specifies that a wave explanation cannot account for why the intensity of the light does not increase the voltage but only increases the amperage.
 * We cannot make progress with this article if changes that matter are not discussed beforehand. I tried to fix the even worse misinformation provided by Mr. Louis, but his reaction was not constructive.P0M (talk) 19:35, 2 June 2009 (UTC)
 * Yes, the paragraph you quoted is basically a non-sequitur. And an over-eager editor is a pain. --82.31.28.46 (talk) 04:21, 3 June 2009 (UTC)

Article has been "unreverted"
I would not like to see progress on this article made by way of an edit war.

The change was made and then covered up by a minor edit with a notation appropriate to that minor edit. P0M (talk) 06:49, 31 May 2009 (UTC)

Point by point
(1) The current text has: Take, for example, the rainbow of colours reflected from a puddle of water when a thin film of oil rests on its surface. That phenomenon can be understood by thinking of light as waves, the length of which results in different colours. Other phenomena, like the working of light meters in cameras, can be explained by thinking in terms of particles of light (called photons) colliding with the detection screen inside the meter, the force of which is registered mechanically by a pointer or needle.

This is just plain wrong. The length of waves does not "result in different colours." The different wavelengths of light are perceived as different colors. And the fact that the waves of light have different lengths does not explain the "rainbow of colours" either. If the editor had bothered to read Sears he would have an understanding that would allow a correct explanation, not an exercise in the mystification of the novice reader.

Second, the description of the light meter suggests a device like the carnival strength meter in which a contestant strikes a lever using a sledge hammer and the other end of the lever hits a ball that then moves vertically alongside a measuring stick of some kind. Nothing could be farther from the truth. Even if the crude analogy of an electron as a bullet that strikes electrons and knocks them out of their original planetary orbits be accepted, the electrons do not then physically strike the end of a needle that then moves along a dial face. T

If this article is to be radically rewritten, it should be done so with both a clear understanding of what the true facts are and also with an eye to presenting those facts in a way that will not cause very damaging preconceptions to form in the mind of the novice reader.

It is the differences in phases between the light waves reflected by the air/oil surface vs. the phases in the light waves reflected by the oil/water interface that effectively "cancels" light of some wavelengths and permits light of some wavelengths to reach the eye of the observer from each different region of thickness of the oil film. You criticized the original diagram that clearly shows how interference occurs as "off-putting." But what have you put in its place?

It is the (mechanical analogy) pressure of the dislodged electrons that moves them off of the surface of the metal plate and through a wire to an electromagnet that attracts the spring-balanced needle which then moves in a way proportional to the induced amperage. Then they go through another wire back to the "low pressure" region of the metal plate. Even in modern light meters, it is all a matter of electrons moving in electrical circuits, not electrons pushing on lever arms.

Please be careful to give the most useful citations. I have discovered one citation that is a circular reference to a Wikipedia article by way of an external "encyclopedia." Also, the expression "Trojan wave packet" will not mean anything to the average well informed reader, hence serving only to create an air of mystery and incomprehensibility. I have already supplied a reference that distinguishes Trojan wave packets from other wave packets.P0M (talk) 18:02, 31 May 2009 (UTC)


 * Thanks for the fine corrections and the explanations therefor. We are all relying upon people with scientific expertise to make this the best article possible. (What a way to spend a Sunday!) Sincerely, your friend. GeorgeLouis (talk) 19:44, 31 May 2009 (UTC)


 * I object to the change that you just made. Can you please give evidence of good faith by discussing changes before you make them? P0M (talk) 21:29, 31 May 2009 (UTC)
 * Uh, the place to discuss all this is above, where it says "Request for comment." Sincerely, GeorgeLouis (talk) 01:49, 1 June 2009 (UTC)

Rewrite
While it's definitely possible to trim this article down significantly, doing it in one swell foop, without discussion, is not likely to be productive. I've reverted to the long version, and I'll put subheadings here to discuss the issues with the various sections.--SarekOfVulcan (talk) 23:42, 31 May 2009 (UTC)


 * One of the complaints about this article was the length. As of today the lengths of the two articles are approximately the same, and I still intend to cut more.P0M (talk) 06:42, 23 June 2009 (UTC)

Lede
Ok, for one thing, the lede on this article is longer than the lede in the QM article. :-) What can we do about this?--SarekOfVulcan (talk) 23:52, 31 May 2009 (UTC)


 * One thing to keep in mind is that Einstein's whole paper on Special Relativity was only 26 pages long (I think it was). His introduction might have been a couple of equations. Density is possible if people already know a great deal, and density is aided if a symbolic mechanism exists for cramming layers of meaning into simple symbolic representations. But when the reader is unfamiar with material then one thing left unsaid can stymie the whole process or at least slow it down greatly. P0M (talk) 01:34, 22 June 2009 (UTC)


 * Chetvorno had some useful ideas, which I quote from the material above:

"The history is too much, and the overview needs to be simpler. What this introduction to QM needs to address is why QM is so much harder for people to understand than classical mechanics. What about an approach like Richard Feynman uses in his Lectures on Physics? He starts out by saying: 'Things on a small scale behave like nothing you have any direct experience with. They don't behave like waves, they don't behave like particles, they don't behave like clouds, or billiard balls, or masses on springs. Even the experts don't understand it the way they would like, because all of our human intuition applies to large objects. But small objects just don't act the same way.' Later he goes on to enumerate in simple language how small objects' behavior is different: wave - particle duality, inability to measure variables with arbitrary precision, probabilistic results of measurement, the ability of objects to be in different states simultaneously. These are the things beginners have trouble with in QM, and they should be faced head-on in this article."
 * I still think his would be the best approach. Above I listed around 5 mysteries that might be listed with brief statements of what they are as the second paragraph of the lead. P0M (talk) 00:34, 1 June 2009 (UTC)

Draft, 325 words: Life gives humans preconceptions that fail drastically when experience is extended to the very massive and the very fast, and that also fail drastically when experience is extended to the very small and the very cold. On the large scale humans need relativity theory, and on the small scale humans need quantum mechanics.

Quantum physics deals with the unexpected realities of "neither-nor." Photons and other very small things are neither waves nor particles. They have spectrums, but the spectrums are chopped up instead of being continuums. The energies carried by particles are discontinuous and color coded. The energies, the colors, and the spectral intensities of electromagnetic radiation produced by something like a neon light bulb, are all interconnected by laws. But the same laws ordain that the more closely one pins down one measure the more wildly another measure relating to the same thing must fluctuate. Even more disconcerting, particles can be created as twins and therefore as entangled entities -- which means that doing something that pins down one characteristic of one particle will determine something about its entangled twin even if it is millions and millions of miles away.

The most elegant character on the quantum stage is the double-slit experiment. A single photon emitted by a laser or an electron emitted by a cathode will behave differently depending on whether one or two  slits lie in its path. With two slits present, the particle that arrives at a remote detection screen will be a superposition of two wave functions. Where a photon or electron shows up on the detection screen will show the resolution of those wave functions, sometimes called the "collapse" of the wave functions, and the location where this "collapse" occurs will be absolute in that it must appear in one of the bright "fringes" that will show up when many photons are run through the apparatus, but entirely unpredictable as to which of the fringes it contributes to.P0M (talk) 14:57, 2 June 2009 (UTC)


 * I'm not sure that we should follow the old section headings. I request feedback on the above. In the meanwhile, I have taken the suggestions given above, particularly from Chetvorno, and have drafted new text for the "old" quantum physics at: User:Patrick0Moran/Rewrite_QM
 * Thanks.P0M (talk) 18:11, 2 June 2009 (UTC)
 * I have started to pare the article down, starting at the top. If I have taken out things that others regard as crucial, please let me know. (It may be that I have it in mind to put some things later, but one way or another we should be able to agree on what needs to stay and what can go.) Please be aware that there will be a ripple effect. P0M (talk) 01:29, 22 June 2009 (UTC)

Overview
See "General trends of development"P0M (talk) 06:27, 22 June 2009 (UTC)

An elegant example
I added this section to get readers to jump into the cold pool.P0M (talk) 06:27, 22 June 2009 (UTC)

The unexpected
Combined with the following. P0M (talk) 06:27, 22 June 2009 (UTC)

How the unexpected came to light
Rewritten.P0M (talk) 06:27, 22 June 2009 (UTC)

Planck
I just added a brief section. Keep first things first. Cut some stuff that would have been duplications below. May still need to tidy up, but don't want to leave readers with any big holes to try to cope with. P0M (talk) 06:27, 22 June 2009 (UTC)

Spectroscopy and onward
So far I have just put in a diagram. This one equation gets reformulated a few times, and so it is made to mirror and explicate the structure of the atom (as regards its function of emitting photons) more and more closely.

This is really the first difference equation and they are key to switching from classical physics that operated on the basis of infinite numbers of geometrical points (calculate the frequency associated with point 3384) to quantum physics that asks not what electron was doing in such and such an "orbit" or while it was in such and such an energy state, but where it started from and where it jumped to (energy state n - energy state m).

This equation, which started out like an NPR puzzle from Will Shorts, was the next major step after Planck's constant. The next building block will be the rule for multiplying grids filled with numbers arrived at on this basis or derived from numbers gotten this way. The third thing happened when Born realized that the rules of matrix multiplication were going to make pq - qp be something other than zero.

It's too late to do anything more. I'm keeping vampire hours already. ;-) P0M (talk) 06:27, 22 June 2009 (UTC)

Old quantum theory
I feel this whole section should be omitted, in compliance with the desire expressed by many people on this page for less history. There is already a History of quantum mechanics. This article should omit the history. -- Chetvorno TALK 21:59, 6 June 2009 (UTC)
 * As far as the history items, such as the (to me) interesting fact that Balmer was a pioneer who had no great status, a sort of one-hit wonder, I agree. On the other hand, the discovery he made is about as concrete as you can get. It's something that the average well-informed reader can understand. If you don't take the approach of showing the pathway in physics then you jump right into Schrödinger. Take a look at the Hyperphysics site (http://hyperphysics.phy-astr.gsu.edu/Hbase/hframe.html) and how they introduce quantum physics. The minute you get into Schrödinger it is entirely abstract, and terms such as "Hamiltonian" and "Hermitian" are used without definition. The full Wikipedia article starts with high level math. So in both those approaches the reader who doesn't know the math has to either work out the math or take conclusions on faith.
 * I haven't even edited the article form Schrödinger on, but I think that it is possible, on the basis of one of the graphs in the Hyperphysics (?) site, to show how the discontinuous picture of something like the hydrogen bright-line spectrum, which is sort of like a bar graph in appearance, can be converted into a continuous picture by means of Schrödinger's math. That way the reader gets an intelligible bridge from a Will Shorts kind of math puzzle to a higher math picture that really requires professional training to understand. The alternative is a "OU! AH!" kind of mystification.P0M (talk) 15:39, 10 June 2009 (UTC)

needed: Einstein
photoelectric effect

needed:Balmer
breakthrough equation, had more refined versions later

Reduced Planck's (or Dirac's) constant
As discussed above, several months ago, this section is rather pointless. The reduced Planck's constant is just the Planck's constant divided by another constant. So all the reader needs to know is about that much. I therefore will delete it if I do not hear arguments to the contrary. P0M (talk) 06:28, 4 June 2009 (UTC)
 * doneP0M (talk) 20:21, 6 June 2009 (UTC)
 * After I cut down earlier sections, the little paragraph on h-bar seemed totally out of place, so I have cut it.P0M (talk) 04:33, 23 June 2009 (UTC)

Bohr atom
It's pretty hard to talk about "orbitals" without a minimal understanding of "orbit."P0M (talk) 15:39, 10 June 2009 (UTC)

DeBroglie: Wave-particle duality
This part is central. I do not see how we could possibly leave this idea out.P0M (talk) 15:39, 10 June 2009 (UTC)

Full quantum mechanical theory (Heisenberg and Born)
I will replace the currently incorrect matrices with reduced size versions that are formulated in accord with Heisenberg's paper of 1925. If there is no objection to the draft at User:Patrick0Moran/Rewrite_QM I will make a full replacement in a couple of days. P0M (talk) 21:16, 6 June 2009 (UTC)
 * I feel the mathematics in your rewrite, although important, is just far beyond what should be in an "introduction". I think this article should have almost no mathematics, except possibly simple things like the Uncertainty principle and E = hν. -- Chetvorno TALK 22:54, 6 June 2009 (UTC)
 * Sometimes not having important content is more confusing than something that looks intimidating. The article could just say that Balmer had come out of obscurity to hand scientists the answer that they could not find, and the reader might carry away the impression that Balmer's formula must be something very difficult. When readers go to the advanced articles on quantum physics they are likely to be introduced to daunting equations in high math. In this article the only equations that would be that intimidating are those concerned with calculating transition amplitudes, and they clearly would not be suitable.
 * Fortunately not only are the equations that predict the bright-line spectrum simple, but there is a website that lets visitors plug in numbers and get back frequencies, wavelengths, etc. Readers do not even have to look at the equations to understand the text, but they are there if the reader wants them.
 * There is so much mystification involved with the matrices that readers deserve to have a demystified way into the subject. Heisenberg's "multiplication law" looks complicated, but it really is not. It explains in operational terms what a matrix does. And the matrix multiplications demonstrate why there is a difference when the complex thing called "p" and the complex thing called "q" are multiplied the results are going to be different. That in turn explains where the indeterminacy principle comes from.
 * Ideas like chain reactions in nuclear physics can be very abstract and mystifying unless they are made concrete to average people with demonstrations like the roomful of mousetraps functioning as catapults for ping-pong balls.
 * Take a look at Introducing Quantum Theory by McEvoy and Zarate, p. 127. It is a good example of how an over-simplification is a disservice to the reader.P0M (talk) 16:21, 8 June 2009 (UTC)
 * Seeing no further comment, let me suggest three equations, all of them first-year algebra. One gives the structure of the hydrogen atom, one relates frequency to energy, and one is just a schema for dealing with the fact that as far as radiation goes, it is not important what the electron is doing but what orbitals its transits between. P0M (talk) 12:08, 19 June 2009 (UTC)
 * I put up a diagram that indicates in a structural way how just the difference between energy levels (orbits in old QM) determines frequencies and wavelengths. The equation is absolutely central even though the math is so simple that you can see how it works without having to work out any examples unless you want to.
 * I replaced the discussion about Heisenberg because as I have chipped away at the layers of misunderstanding created in the secondary sources that are simplistic I have had to rely on the treatments by Van der Waerden, Aitchison et al., and the three volume series of the history of QM. I am taking the word of Aitchison et al. that Heisenberg actually computed amplitudes and thereby got quantum theoretical predictions that matched observed intensities, but frankly I can't find where or how he did it. Other than that, I think it states everything clearly and is or can be validated by citations to reputable studies. At least I trust it much more than what I wrote before.
 * Some things that come before this section in the article need to be changed next to accomodate these changes.
 * The third "equation" that I proposed above has also been included, but it is really only a "recipe" for writing a matrix. It just amounts to saying that you should multiply X × Y, X' × Y', and so forth, and then add them all up and store the results in the right slot.P0M (talk) 18:02, 20 June 2009 (UTC)
 * It is beginning to look like I may be able to off-load the more technical part of this section into a sub-article.P0M (talk) 20:20, 20 June 2009 (UTC)
 * Bad idea. In a recently purchased book I found assurance that the indeterminacy relationship comes out of the math. The math comes out of the matrices. The matrices come out of the weird C(n,n-b) = Σ A(n,n-a)B(n-a,n-b) business, and that in turn comes out of the 1/λ=R((1/m^2)-(1/n^2)) business. On the surface the whole structure is clear. (Why don't people supply the parts in order and context?) But the details quickly start to involve matrices each "cell" of which is itself a matrix, and the details get so intense that one has to have the "rules" of matrix math on the tip of one's tongue. That level of complexity can be glossed over with matrix mechanics, but the Schrödnger equations can't be handled that way. I think it is better to do all that we can dowith high school math.P0M (talk) 04:47, 23 June 2009 (UTC)

Schrödinger wave equation

 * The current section is an abstraction about an abstraction. There are easy ways to make equations such as f=ma concrete. With Heisenberg's matrix mechanics one can give readers the information that it allows the prediction of the amplitudes corresponding to each of the energy levels of the hydrogen atoms, and from them it allows the prediction of the intensities of the lines in the bright-line spectrum.
 * Since the Schrödinger model of the quantum world produces the same predictions as the Heisenberg model, it may be useful to point out that many models may equally serve human purposes.P0M (talk) 19:16, 5 June 2009 (UTC)
 * I've looked at several secondary sources and so far none of them have been able to say anything sensible about the Schrödinger equation without going off the deep end of the math pool. The math behind the relatively simple stuff that Heisenberg ended up with was already extremely difficult. So it may be that the novice is lucky that there is anything at all that does not have to be accepted on faith absent of a couple years of university physics and higher math. Introducing Quantum Theory doesn't spare the magic wand and fairy dust. I wonder if there is a way to make it clear to readers why the level of mathematical complexity gets so intense. P0M (talk) 19:12, 20 June 2009 (UTC)

Uncertainty principle
This is one of the main pillars of quantum mechanics. You can't even begin to explain it without the matrix picture or high level calculus. I think anybody can understand that if prices per gallon of gasoline vary by city, and city to city the distances are different, then if you top your gas tank of at each stop it may make a difference which way you travel between a series of cities.

Heisenberg's microscope is a reductio ad absurdum that depends on classical physics to defeat classical physics, so it is not ideal, but it does make part of the nature of the problem intuitively accessible to readers. Gamow used it in his ''One, Two, Three... Infinity.''P0M (talk) 12:42, 19 June 2009 (UTC)

The indeterminacy relationship was not an empirical discovery. It came out of the numbers. I found Born's own words from his Nobel lecture. So there is an organic connection among the main equations I have included, and at least up to this point they are simple. In Born's formula that gives the Uncertainty Principle, the "i" factor has to come out of the math somehow, and I suspect it either has to do with using an exponential i in phase relationship factors to some of the classical equations Heisenberg was taking inspiration from, or (more likely) it is something about matrix math that was already common knowledge, i.e., part of a regular formula, in use by clued-in mathematicians of Heisenberg's time.

There is no reason to dig out the origin of the use of "i" in this equation. But without the basic and simple math up to this point we would have the equivalent of a detective story that just said, "Someone was murdered. The butler did it."

It's late. I'll put the reference to the quotation from Born in tomorrow. P0M (talk) 07:20, 21 June 2009 (UTC)
 * Actually, both i and h come out of the math. The whole thing is derived in an appendix to Aitchison, et al. P0M (talk) 02:33, 28 June 2009 (UTC)

Wavefunction collapse
This topic has to be described in conjunction with superposition. The only situation wherein superposition is going to be clear to most people is the way a single wave function is divided in the double-slit experiment and arrives at the detection screen by paths of different lengths so that the waves are out of phase. While it is true that some readers may not be visual thinkers, it will be helpful to must people to have a drawing to show how waves may reinforce each other if in phase or cancel each other if out of phase. Such a drawing literally shows one wave superimposed over the other. How to explain the "collapse" is more difficult. It is possible that a "colllapse" occurs, potentially at least, at each point from the double slits to the detection screen, but for a photon to actually manifest its presence by boosting an electron in orbit there has to be an electron available. Occasionally, a photon may cause a scintillation on a dust particle flying in the beam, but most of the time photons will show up on the plentiful electrons of the detection screen. There seems to be a sort of cosmic roulette wheel that determines which of the bright fringes a photon will contribute to, but my understanding is that there is no mechanism proposed.P0M (talk) 19:11, 19 June 2009 (UTC)

This section starts out treating an electron but in the last sentence it seems to have changed to a photon. WmMBoyce (talk) 15:50, 24 January 2010 (UTC)

Eigenstates and eigenvalues

 * Is there any need for this section in an introductory article? I think readers who go beyond the scope of the article might encounter it, but their need would only occur at that point. Perhaps a very brief paragraph and then a sub-article? If I hear no objection I will reduce or delete this section in the next few days. P0M (talk) 18:16, 5 June 2009 (UTC)


 * I agree. -- Chetvorno TALK 21:53, 6 June 2009 (UTC)


 * I moved most of the content to a sub-article. P0M (talk) 18:05, 8 June 2009 (UTC)

The Pauli exclusion principle
This section is poorly written. It involves circular reasoning and/or the use of undefined terms, e.g., fermion. P0M (talk) 12:35, 19 June 2009 (UTC)

I don't see 'fermion', so I guess it's had rewriting. Should clarify that it's an electron 'within an atom' that has the orbital numbers, not an electron in a beam or otherwise unattached. WmMBoyce (talk) 16:06, 24 January 2010 (UTC)

Dirac wave equation
I think this section can be drastically pruned. The last paragraph is redundant. The rest of it includes details for which the average well-informed reader will have insufficient background to understand.

If we are going to eliminate history from this article, then not much is left to talk about in regard to Dirac. Unless I hear otherwise within a day or two I will prune this part and then we can discuss reactions to the changes. P0M (talk) 10:18, 19 June 2009 (UTC)

Quantum entanglement
This section is pretty bad. The main thing that it fails to do is to point out that two entangled photons have superpositions of psi wave functions and that means that each of them could turn out to have the characteristic of one superimposed wave or the other, but the Pauli exclusion principle shows us that the entangled twin could not the same characteristic. The weirdness comes about because by the time one photon is forced to reveal a characteristic the entangled twin may be a great distance away, but if in the next instant the second photon is interrogated it must reveal the complementary characteristic. That's about all that can be or needs to be said on this topic, no? P0M (talk) 10:30, 19 June 2009 (UTC)
 * I've rewritten this section. The article still needs something more about superposition, and the place for that is in talking about the double-slit experiment because anyone can see the results of superposition for the cost of a laser pointer and some brads, not to mention that the photographs are rather spectacular. P0M (talk) 02:30, 28 June 2009 (UTC)

I removed this section, it was an inexact analogy, with an unencyclopedic tone, and sounds like it's been lifted from a book.
 * "Suppose that some species of animal life carries both male and female characteristics in its genetic potential. It will become either male or female depending on some environmental change. Perhaps it will remain indeterminate until the weather either turns very hot or very cold. Then it will show one set of sexual characteristics and will be locked into that sexual status by epigenetic changes, the presence in its system of high levels of androgen or estrogen, etc. There are actually situations in nature that are similar to this scenario, but now imagine that if twins are born, then they are forbidden by nature to both manifest the same sex. So if one twin goes to Antarctica and changes to become a female, then the other twin will turn into a male despite the fact that local weather has done nothing special to it. Such a world would be very hard to explain. How can something that happens to one animal in Antarctica affect its twin in Redwood, California? Is it mental telepathy? What? How can the change be instantaneous? Even a radio message from Antarctica would take a certain amount of time." Larryisgood (talk) 15:00, 13 April 2011 (UTC)

Interpretations

 * The current section repeats points that would appropriately be handled elsewhere, and says nothing about interpretations except that people make different interpretations. It does not even say what is involved in making an "interpretation." Maybe we need to say something about "waveform collapse" and "alternative universes," and leave the link to the main article.  My memory of discussions of the Copenhagen "interpretation" is that everybody has a different idea of what that means, and my feeling is that the alternative views result from its really being more of an attitude toward the connection between models and realities than any willingness to favor any one set of  assertions about what is "really" going on in quantum phenomena.
 * Has anyone found good surveys/definitions of the interpretations?P0M (talk) 18:43, 5 June 2009 (UTC)


 * Interpretations are an advanced, speculative subject, and mostly irrelevant to the observed results of experiments, which is the everyday use of QM. All the interpretations agree on what is observed - wavefunction collapse.  It's going to be hard enough in this introduction to explain wavefunction collapse and wave-particle duality in a way that nontechnical people will understand.  I suggest not getting into interpretations. -- Chetvorno TALK 23:06, 6 June 2009 (UTC)


 * I'm not even sure about wavefunction collapse. ;-) Maybe the best idea is to take the whole section out, at least until such time as something makes it seem imperative to have anything more than a link to someplace else. P0M (talk) 00:58, 7 June 2009 (UTC)


 * No offense, but wave-function collapse is on of the major differing points between interpretations. Many interpretations tend to rely solely on decoherence instead of wave function collapse.
 * Anyway, interpretations are probably the part of quantum mechanics that a lay reader is most interested in. They can also be explained in a non-technical way, which makes them a very good candidate for the intro article. (TimothyRias (talk) 13:59, 19 June 2009 (UTC))


 * My point was that wavefunction collapse is just one way of talking about what is observed. Everybody can perhaps agree about what is observed, but not everybody agrees on wavefunction collapse as the way to explain what is observed. One of the raps against this article is that it is too long, so we are looking at things that can either be cut or be put into subsidiary articles.


 * Another problem is that there is misinformation behind some of the things that may the average well-informed reader interested in interpretations. For example, as far as I can tell Schrõdinger was saying that if you took the idea of superposition of seriously then you would have a cat the condition of which was "smeared out" (his words if I remember correctly) between life and death. Most people take the idea of the neither-alive-nor-dead cat seriously. (I think there was even a Star Trek episode in which several Spocks and Scotties were superimposed over each other.)  I think there are already articles on interpretations, and that going into any detail at all would entail several tens of Ks of text.
 * does an introduction require a section on interpretations at all? IRWolfie- (talk) 00:20, 15 January 2011 (UTC)
 * I don't know whether it's a good idea or not. It might be easier for people to get clear on the basic ideas first. On the other hand, people are likely to have come to this article with misinformation about interpretations, so perhaps some guidance regarding interpretations is worthwhile. See what I said earlier, immediately below. P0M (talk) 04:54, 15 January 2011 (UTC)
 * The one thing that we might say in a short paragraph or so is that the equations all work out beautifully and have been used in so many practical applications with tight tolerances that people are very, very confident that the equations give reliable results. However, one can use these abstractions as the components in several competing but compelling narratives. P0M (talk) 19:11, 19 June 2009 (UTC)

Summary
I've added a summary at the end. Maybe I should call it a conclusion, but my intent is to draw together the multiple reclarifications of Balmer's formula, the "numerological" clue to the structure of the atom. My intent is that the reader understand that what began by looking like a mathematical curiosity fit for some puzzle magazine turned out to give an abstract picture of how and why electrons produce photons. The main thing left to explain in the hydrogen atom after that is the intensities of the lines. They turn out to require heavy computation, and that very fact explains to the reader why Schrödinger's equation can't get a satisfactory explanation here. All we can say is that the math is very hard and very useful.


 * There is a little left to do. There really should be a section on Richard Feynman, even if all it really does is to point out that he was a prominent figure in the recent past and that the field continues to develop.


 * Even without changing actual content it should be possible to shorten the article somewhat by striving for conciseness -- always remembering that what is too compressed becomes an unneeded burden on the reader. (For the sake of extreme concision we could probably quote a few equations and have done with the whole thing, but then readers can already go to the senior articles if that is what they want or need.) Probably there are some more things that can be cut now that the total structure of the article is clearer. I have in mind things like the discussion on h-bar that has already been removed. P0M (talk) 08:22, 11 July 2009 (UTC)

Basic concepts of quantum mechanics
Now we have a fork of this article at Basic concepts of quantum mechanics, written by User:GeorgeLouis, which started with a copy of this article at User:GeorgeLouis/Quantum and may therefore also be a copyvio. Links to the fork start appearing everywhere. Any suggestions what to do with it? -- Momotaro (talk) 15:14, 18 June 2009 (UTC)


 * Mr. Louis originally deleted "Introduction to quantum mechanics," supplied a copy on his own user space in an attempt to maintain the appearance of civility, and replaced the original article with what has now become his fork. I gather that he then visited all the pages that originally linked to this article and replaced the links there to links to his fork.


 * This "Basic concepts" is a fork that was made after Mr. Louis's uncollaborative edits to this article were rebuffed by other editors. I wondered where he had gone.


 * I have tried to communicate with this editor, but have never received a responsive message in return. After thanking me (see above) for correcting errors in the alternative version (now the fork), he quietly chopped the guts out of the revision I had made and reintroduced an error even though I had explained on this discussion page why the way he had it was incorrect.


 * Mr. Louis wants an article on quantum mechanics that uses neither math nor graphics. There is one essential equation that needs only beginning algebra to work with and has an on-line calculator that is essential to seeing how humans first gained entry into the quantum mechanical world. Without that simple math one has an "It's too wonderful for words!" kind of explanation. But people who want to understand these things can be given this mathematical model without overwhelming them -- and if they don't want to bother with working out a couple of examples with their hand calculator then they can just ignore the formula. Any reader who understands fractions and squaring can see at a glance what is going on.


 * In principle I do not object to another, lower level article that is even simpler than "Introduction to quantum mechanics," but it has to be both factually accurate and also not potentially misleading.


 * Wikipedia is a community that has to maintain certain norms of behavior.  P0M (talk) 01:05, 19 June 2009 (UTC)


 * I haven't been following this debate (I came here from Wikipedia talk:WikiProject Physics), but my impression is that the "basic concepts" article is entirely worthless and should be deleted (or just blanked and redirected here). It's poorly written, vague, and at times just ludicrous. It used to contain (before I deleted it) a link to File:Christmas.lights.jpg with the caption "An artist's vision of the speed of light". It has crazy lines like "Quantum mechanics is a physical theory that has practical application" and "Many experiments have been carried out to prove the concept", followed by a seemingly random list of three papers. I'm fairly sure that the article content represents pretty much GeorgeLouis's entire understanding of quantum mechanics. Sometimes you can make the case that a poor article should be kept because it will encourage the creation of a better article, but in this case we already have a good article on the same subject, namely this one. -- BenRG (talk) 18:52, 19 June 2009 (UTC)


 * (I come from Wikipedia talk:WikiProject Physics and I've followed the previous debate). Maybe I was expecting worst but I don't believe Basic concepts of quantum mechanics is so bad. Maybe some things need to be adjusted (as, the already mentioned artist version of speed of light and others), but it is mainly history of physics, not physics. So I don't see so much the problem of compatibility with this article. The real question is:are we ok with having this kind of articles? (i.e. introductory articles that have to be simple, maybe simplicistic, for construction) in Italian wikiproject physics, where I come from, the answer was no) . Finally, I don't believe that using a copy of an existing article to create another article in wikipedia can configure as copyviol. --CristianCantoro (talk) 19:27, 20 June 2009 (UTC)
 * I saw this over at Wikipedia talk:WikiProject Physics. An article that is simple, and conveys information is OK by me, as long as editors can keep the information accurate. Sometimes I think some of the articles are too technical for the general reader who is interested in physics. This article, here, seems to be a really good one. No doubt the result of consensus, collaboration, and cooperation. Ti-30X (talk) 22:46, 22 June 2009 (UTC)
 * This article has been around for several years, and interested readers have corrected many mistakes and made many improvements. I have thus far restricted myself primarily to the material up to Heisenberg because my math is not good enough to understand much of the later stuff, and because I was stuck on some things regarding Heisenberg. (The old "for the lack of a nail" chain... A little more detail in some secondary sources would have increased my rate of progress greatly.)
 * The technical accuracy of statements will depend on people with degrees in physics. About all general editors like me can do, after they reach their depth limit, is to make sure that the writing is clear enough to convey something to the average well-informed reader.
 * The writer of the fork wants one level of writing beneath articles like Matrix mechanics that jump right in with advanced math, a level that uses no math and no diagrams. To me,that point of view abandons consideration for the needs of inquiring minds who have not yet had access to university math and physics classes but who are trying to really understand, to the extent possible, what is really going on.
 * The problem with the fork writer is that he has removed all links to this article and replaced them with links to his own article. Read that article carefully. No matter how simple it is, an article should neither provide misinformation nor lead the unsuspecting reader to draw false conclusions. P0M (talk) 04:29, 23 June 2009 (UTC)
 * Patrick, I have to agree that no article should provide misinformation and I certainly don't agree with replacing the links to this article. I wanted to address the links issue in my last response, but didn't. I think that it needs to be addressed. In truth, this article is enough for the non-technical, general reader, who is interested in physics. Is anyone able to take any action on this matter? Sorry, it took this long to respond to your response. Ti-30X (talk) 22:58, 28 June 2009 (UTC)

(<=) I've added in Basic concepts of quantum mechanics a that points here, I didn't know about this thing of replacing links. I agree with the fact that articles should not be misleading, so I will check the "basic concepts" article and look for errors. But, I repeat, that's mainly history and IMHO the two articles are not incompatible. --CristianCantoro (talk) 07:50, 4 July 2009 (UTC)

Please, someone with expertise, check the following:
The section /* Wavefunction collapse */ was written by the third person to get seriously involved with this article. Could someone who is very familiar with Schrödinger's equations please check it for accuracy? Thanks. P0M (talk) 17:26, 11 July 2009 (UTC)
 * Rambling to the point of (ironically) incoherence. Why not just replace it all with . --Michael C. Price talk 20:04, 11 July 2009 (UTC)


 * Greetings. The interpretation for a wavefunction collapse is somewhat accurate (although the last sentence is completely irrelevant). I would suggest replacing it with something along the lines of:


 * Wavefunction collapse is the replacement of the description of the uncertain state of a system by a description of the system in a definite state. The nature of the process is controversial.


 * In slightly more detail, a system's wavefunction represents the probability of an event occurring in the system. This event could, for example, be the arrival of a photon at a detector (e.g. the surface of a photographic plate). Before the photon arrives there is the probability of the photon arriving somewhere across the entire surface, and so the wavefunction is distributed across the surface.  After the photon has been absorbed we know with certainty where the photon was (i.e. somewhere in particular) and so we update the wavefunction to represent this certainty.  Hence, upon detection of the photon, the wavefunction is said to have 'collapsed', as the probability of the event occuring has turned into a certainty. In general, any measurement performed on a system collapses the wavefunction.


 * Although having said that, it may be better to remove that section altogether as I don't think it adds much to the article. Just my 2 cents. MarkoZhuk09 (talk) 05:20, 13 August 2009 (UTC)
 * The topic needs to be addressed. Your text is better than what is there currently, we don't need to consider the double slit experiment to talk about collapse.  I've taken the liberty of applying updates directly to your proposed text, rather than cut-and-paste, to save space. --Michael C. Price talk 11:29, 13 August 2009 (UTC)
 * Un-indenting:

The statement that wavefunction collapse is a replacement of one description by another description is too solipsistic for me. Something clearly happens, and humans can account for parts of it. But our torn and tattered maps are not the reality.

The average well-informed reader is likely to want to know why a change of descriptions is called a "collapse." I think there are understandable reasons but the main thing the reader needs to know is that "collapse" is a figurative way of talking about something that is not understood the way the collapse of a building is understood.

How about the following as an alternative that gives the reader a bit more context for understanding why the term is used and argued about? That measurement of a quantum system causes the "collapse" of its wave function is fundamental to quantum mechanics.(ftn.1 ) But the meaning of the word "collapse" can only be given an operational definition. That is to say that according to Bohr's model of reality photons or other such quantum scale entities propagate like waves, and only receive unambiguous values of momentum or of position when that quantity is measured. When such a measure is made, the photon is manifested as a particle.

So, if one wants to understand what "collapse" means, all that can really be said is that "collapse" is whatever happens when momentum is measured, when position is measured, or some similar operation is performed and the photon ceases to propagate.(ftn. 2) A measurement is performed, information is gained, and indeterminacy is replaced by a determined description as the state of the system changes. (ftn. 3) The limitation of quantum mechanics is that prior to measurement only probabilities can be predicted by theory. The question is whether this limitation is attributable to the shortcomings of the theory or reflects the fundamental characteristics of nature. The term "collapse" is evocative. It suggests the idea of a long list of possible values and the probability for each of them being what will eventually be found, and then that list suddenly emptying of all but one value with its probability equaling unity. However, the use of the word "collapse" is optional. Whatever one wants to call it, it is the "underlying reality" question that is the real focus of interest.

"Was the system really in a specific eigenstate before the observation, with that knowledge 'hidden' (not in the wave function), or did the system collapse into that eigenstate after 'the dice were thrown', and by who/what?" (ftn. 4) According to Einstein, et al., the photon has to have a well-defined position and momentum all along. Otherwise, since measurement reveals a well-defined state, measurement might be understood to have created this state. While Heisenberg rejected the idea that measurement in this context necessarily implied human consciousness (e.g., of a piece of exposed photographic emulsion), even the restricted idea of measurement determining reality was too close to solipcism for many thinkers and scientists. For them, wherever a photon shows up (for instance, after passing through a double-slit apparatus),it was always going to show up there. There is no "collapse" or whatever one would choose to call the phenomenon, just as there are no probabilities as to where any given photon might end up.

Footnotes all apply to the first couple pages of: "Wavefunction collapse, quantum reality, EPR, Bell's Thm (sic), and all that," Alan Weinstein, Caltech, 1996

See: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.27.6299 for several on-line sources of the same study.P0M (talk) 23:14, 16 August 2009 (UTC)

Swap out template for "truth in advertising"
This article has come under attack for not being "accessible." It does involve high school math, and exponents. So to try to resolve this issue I have taken out the template somebody added that perhaps makes it seem that no thought is required.

I hope this article still merits its B grade. Perhaps someone could go over it for any factual errors one more time. I will keep fussing with the wording and cut out any wordiness that I can find. Thanks.

Anybody who does not think this article ought to be scrapped might want to participate in the discussion of its "merger" with the "basic" fork. Thanks. P0M (talk) 00:15, 22 July 2009 (UTC)
 * Patrick is someone talking about scrapping this article? Or are you talking about the "Basic" article? Ti-30X (talk) 04:51, 23 July 2009 (UTC)
 * The person who did the "basic" article originally deleted all of this article and replaced it with that article. The effect was to freeze the form of this article into what you see as the "basic" article now, since that editor resisted changes so strongly. (See the talk page for this article, earlier on.) So my suspicion is that the only way the two articles to be merged is to lose most or all of the content of this article. (I originally thought maybe I could put some of this content back as sub-pages of the "basic" content. Then a senior editor reverted everything back to the original "intro" order. Then the "basic" fork appeared.


 * Patrick - it looks as though someone replaced that template (for this article). I am in favor of removing it, if that's what you want to do. The template is really kind of humorous. Also, I noticed your comment about the wording and wordiness, above. If you don't mind I think I can help out with that. Ti-30X (talk) 04:51, 23 July 2009 (UTC)
 * I replaced the template. Somebody put it in at some point and I never disputed it, but it was providing a rationalization for scrapping this article since the article uses high school math and dares to show people a real matrix or two. I welcome your editorial help. I am sensitive to collections of words that don't really mean anything, but looking over my own work I can often see where I could have tightened the wording. One objection to "Intro" is that it is too long. My feeling is that if a paper is shorter than it needs to be then it is a stumbling block for learners. On the other hand there is no reason to have unhelpful words bloating the prose.
 * I would also appreciate help with User:Patrick0Moran/Aitchison_article. I have been trying to work out the actual numbers that would go into a corner of the infinite matrix for amplitudes. Things like Introducing Quantum Theory by McEvoy and Zarate are fine for beginners until they start on Heisenberg. Then they say, "qp ≠pq" and don't even explain that q and p are matrices not ordinary variables. If the "Intro" article has any advantage over other sources for beginners it is that it carries people as far as they can go without having to take at least a year of university physics. But in order to write in the shallow end of the pool I have to have some knowledge of the deeper stuff, and exactly how Heisenberg figures intensities looks a little... tricky. (It's not the square of the amplitude.) I have some problems that could have been avoided if Aitchison et al. had just defined their symbols. For instance, they use both e and ε0 in some of the same equations.  In Sears Optics (which I used as an undergraduate physics student), ε is written for what Aitchison writes as e (I think). So it's pretty confusing to people like me who would not recognize, let's say, ν as the ordinary symbol for frequency. (It took me a while to figure out that ν and v are different. But I knew that frequency belonged in the equation where I saw the "nu" so it wasn't a problem.)  There are a few conventions that I list at the top of that page that I haven't doped out yet.

Thanks.P0M (talk) 05:27, 23 July 2009 (UTC)
 * Patrick, I like what you did with the "An elegant example" section. I was dillegently hoping to provide clarification as well, but you got back to it first. I do have a question, though. When the wave interference occurs is it really a collapse? So far I understand wave function collapse - it occurs when, say, the position of an electron is measured, according to prediction. Then the probability wave collapses. All the other possible positions of the electron, are nill, once it is measured. There is a wave function involved (in the double slit experiment) because probabilites about which slit an electron will pass through can be calculated. I am thinking that the wave function can only collapse if detectors are placed at one or both slits, to accurately determine which slit the electron went through  and the path that each electron takes to impact on the sreen. I think wave interference is being confused with wave collapse.
 * If detectors are placed at the slits, then the wave function will "collapse" there (unless the wave function sneaks by and doesn't get registered). If detectors are not placed at the slits, then the wave function will "collapse" where there is a detector, and the next one encountered will be the big detection screen. So the wave functions can "collapse" there.
 * Also, it may be that this section of the article is trying to express the paradox that occurs. The paradox is that both an interference pattern occurs (as a wave) and the electron strikes the screen as a particle. I am thinking this is one of the features of quantum mechanics that the author of this section wishes to express, in this section.
 * Right.
 * If a photon were truly a particle like a bullet, it would go through one slit or the other and hit straight-line at a point that is the extension of a geometrically straight line from light source (laser or whatever) to detection screen.
 * If a photon were truly a wave (like a water wave or a sound wave), then a disturbance would be manifested across a fairly wide span of the detection screen. (E.g., you could hear most clearly across from the center of the double slits, then as you moved more to the side the sounds would get weaker and stronger.)
 * One more thing, do you have an opinion on removing the "General trends of development" section. Perhaps some of this material can be used as a third introductory paragraph. But it definitely needs to be less confusing. Ti-30X (talk) 04:35, 24 July 2009 (UTC)
 * First. all of these ideas have to do with models. What "really" happens is what human-made models try to get close to.
 * Wave interference occurs all the way from somewhere near the two slits -- when the wave-fronts have spread out wide enough to get in each other's space -- all the way to the detection screen. (Actually, once in a while a mote of dust somewhere in between will be where a photon shows up.)
 * Second, what the model shows occurring at the detection screen (first at the center and then spreading out to infinity) is one wavefront from slit A and another wavefront from slit B. The probability for a photon showing up at each point at the detection screen is the product of the values of the two wavefronts. (If there were a single wavefront it would be the square of the values of the wavefront at different points along the screen.)  That's all clear, at least as far as models go.  It is analogous to the explanation that came out of old-fashioned "light is a wave that spreads out from the emitter" theory as analyzed by Huygens and Fresnel. But instead of a series of single circular (centered on the light) wave fronts the modern theory has to take account of one wavefront for each photon, or, when two slits are interposed, two wavefronts for each photon and each has its individual straight path.
 * So, at some point x on the screen there is a probability for the appearance of a photon of x%. and at y there is a probability of y%, but if you are watching single photons they don't show up in percentages of their individual energies along the points x, y, ...etc. The photon shows up at one point. Why does one photon show up at point x and the next photon show up at point a and the third photon show up at point r? There are different "explanations" for that fact. Hidden variable theorists will say that there is something about the photon that pegs it to point u (or a line moving toward some unique point u) from the time it is generated by the "leap" of an electron from one "orbit" to another, lower, "orbit." Other people says, no, Bell proves that there can be no hidden variables. So it just shows up.
 * Saying that the wave functions "interfere" just means that they are both there together, and means that the fact that they are together in a certain configuration makes a difference. (The experimenter can shift the two wave functions more in or out of phase by various means. For one thing, the distance between slits makes a difference.)
 * The idea of "measurement" is often misunderstood. Heisenberg gives a good explanation, and demystifies it, in his book that popularizes his theory. "Measurement" just means anything that happens to make a photon (or an electron or anything else) "show up" at a certain point, something that would make it possible for us to know it had been there if we happened to be looking (scintillation, for instance) or maybe even if we looked much later (exposed photo film, for instance). In the case of the double-slit experiment the "cleanest" experimental situation is one where the detection screen is a piece of photographic emulsion. A photon comes out of the candle or the laser or whatever you have at the other end. It goes through the slit apparatus. A single dot appears on the photographic emulsion when that photon "shows up" at that point and triggers a chemical reaction.
 * If the experimenter does anything to try to detect which slit the photon goes through, it changes the experiment. Feynman is particularly clear about this point. Let's suppose that you make the experiment in a darkroom. You have a laser device that is set up so that it only fires off one photon at a time. (It's neat how they do that now. In Young's time they just attenuated the beam so much that on average you only saw one photon get through at a time.) Now you put semi-transparent sheets of photographic emulsion in each slit, and you put your usual photographic emulsion in the detection screen position. Here is what will happen (according to Feynman, and presumably everybody who has tried anything remotely like this experiment has gotten the same result -- else they would be famous). One possibility is that there is no photon detected at either slit because the photographic emulsion is thin enough that the photon goes right on through the slit apparatus.  If you collect that photon where it shows up on the detection screen (actually, maybe you use a big CCD and a coincidence counter because otherwise you are going to have to use a new piece of photographic emulsion for every single photon you fire through the apparatus) it will contribute to the interference pattern that eventually will develop.  On the other hand, if it "shows up" by blackening a spot on either piece of photographic emulsion in a slit, then it will not form part of an interference pattern at the detection screen. Possibly all the energy of the photon will end up in the emulsion at slit A or possibly it will end up in slit B, But if all of the energy shows up there then that will be the end of the matter. The other possibility is that the photon has lots of energy, so maybe it boosts an electron high in some atom in the emulsion of one slit, part of its energy goes to expose the film, but the remaining energy is re-radiated as a new photon.  In that case you do not see anything coming out of the other slit. What you then have, ala Feinman, is two paths beginnings and two path termination; The first path goes from the laser to the emulsion in one slit. (The wave-function for that photon gets "collapsed" at that point.) The second path goes from somewhere in the photo emulsion in that one slit to the detection screen. So in that case what you get will contribute to a diffraction pattern keyed to the involved slit.  So you've "measured" one photon at slit A or slit B, and you've "measured" another photon at the detection screen.  As Heisenberg says, it doesn't matter whether anybody even develops and looks at the photographic emulsion. The essential thing is that a physical interaction between the wave and the emulsion has actually occurred.
 * It's really interesting to ask what happens when there is a hole in the detection screen, and behind it is the open sky. It's possible that the photon does not show up on the detection screen (and that is especially likely if the hole is right in the middle of the screen.  Where it shows up, eventually, is anybody's guess.  The two wavefronts are still interfering. Their products (their probabilities then), for that truncated part of them anyway, is what it was before they went through the hole. If you put a secondary detection screen a relatively short distance behind the one with the hole in it, you will see a whole set of fringes appear back there and it will be easy to see that it's all part of the same picture of interference fringes.  So predicting a probability for showing up at some point along the interfering wavefronts only gives a statistical picture. Another interesting thing is that if you lose a photon through the hole, it would seem that the parts of the interfering wave fronts that have already arrived at the screen are now "dead" even though the rest of the interfering wave fronts, the parts that went through the hole, may not do anything until they hit a planet circling a star in some other galaxy. But there are, it seems, always exceptions or at least the possibility of exceptions. If, ten minutes later, a photon showed up on the intact part of the detection screen, how would anybody know for sure that it wasn't the one from ten minutes earlier? Well, because light moves a c, so obviously anything to do with the original photon emitted by the laser has to be very far away after ten minutes. At least that is what theory indicates. But nobody can watch the photon, and how do you tell one photon from another?
 * This stuff is inherently confounding. I made my own apparatus out of the thinnest brads I could find in a hardware store, some plastic railroad tracks for very small model railroads (because it was the right size for what I wanted and it was on sale), some black spray paint (so I wouldn't fry my retinas by laser light reflected from the steel brads), and a laser level. To me it is always helpful to have the real world in my hands (even if I cut myself sometimes) because I can do things like cut a hole in the detection screen and put another sheet of paper behind it. I had the right intuition on what would happen, but sometimes I don't have the right guess.
 * The nice thing about writers like Heisenberg and Einstein is that they can write about this stuff, never get it wrong (obviously) but also never get their leaders lost or mislead their readers. It is intrinsically very difficult to keep from importing macro-world assumptions (such as, "an electron is a thing, so it either goes through the left slit or the right slit") into thinking about a world fro which those words may not have referents.

I'll think about just deleting that problematical section. Probably that is the right thing to do if the rest of the article is clear enough without it. P0M (talk) 07:32, 24 July 2009 (UTC)

General trends of development
I don't want to offend anyone, but I think the section entitled "General trends of development" is unecessary. The opening introduction is clear and I think it is good. But the next section, "General trends of development" is not very clear and I think it is redundant. It is not redundant with respect to the introduction. It appears to be redundant in regards to the rest of the article. The information in that section is explained much better in different sections throughout the article IMHO. Does anyone else agree that maybe this small section should be removed? I really don't think it adds anything to the article. In addition, the nebulous wording stands in the way of the rest of the article. IMHO Ti-30X (talk) 04:41, 23 July 2009 (UTC)
 * Allow me to add one further comment. Like I said, the introduction is good, and it renders a certain focus to the article. Then when I skip over "General trends of developement", and read the next section entitled "An elegant example", then go on and read the next two sections "How the unexpected came to light", and "Planck and the constant h" - the article retains its focus, and its flow.
 * Now, when I go back and read through the introduction, again, and then read "General trends of development" I start to get bogged down, and a little confused. So that when I read the next few sections after that it seems the article has lost its focus and flow. Maybe others could try this reading "experiment" and be able to see what I mean. Thanks for your time. Ti-30X (talk) 21:59, 23 July 2009 (UTC)

single dot
I see one inaccuracy in the current double-slit discussion. If light passes through any single slit there will be diffraction. In fact, one can even see diffraction around the edges of things like back-lighted razor blades. Most of the time we don't notice these phenomena because the amount of light bend going around edges is small relative to the size of books and most things that we look at. However, as the photographic image shows, when one slit in the double slit apparatus is blocked the result is not a single dot. People writing popularizations may like to leave out this detail, but then it comes back to bite us when people make additions to the article such as saying that one can see an interference pattern by looking through the narrow space between two fingers held knuckle to knuckle. They are definitely seeing something, but it is diffraction rather than interference. P0M (talk) 18:00, 1 August 2009 (UTC)
 * Yes, that was an oversight on my part. I was relying on memory, and I wrote it real fast just to get the idea in the section, because I was pressed for time. Hopefully, I would have caught the error when I came back to it later. Either way you saw it, and accuracy is now included. Ti-30X (talk) 11:40, 2 August 2009 (UTC)

recent changes
When adding material to the article, please be aware that you may be putting things in at a point earlier in the article that are already handled as new information later in the article. It may be, then, that the more recent information would fit into the general flow of the article if it were used to replace the later mention of the same stuff. Or it may end up making more sense to change the later part of the article. Failing to do either will make the organization of the article bad.

Please do not use undefined physical constants. This is an article for the well-informed general reader. It is not intended for readers who already know enough to recognize Greek letters and what most physicists take them to mean. P0M (talk) 01:50, 17 September 2009 (UTC)

I've supplied definitions for e and φ. There is no reason to expect a bright high school student to know what these are. P0M (talk) 02:56, 17 September 2009 (UTC)
 * The organization of the article is already shockingly bad, with information repeated multiple times and the same topic spread out into different sections. Leaving off the definitions of some of the constants and variables was not done intentionally. Thank you for adding the information. Strad (talk) 19:10, 17 September 2009 (UTC)

"This article is accessible to those with a command of high school algebra."
I believe it is totally inappropriate to have such a tag on the top of the article. First, what is "high school algebra"? Checking the article, there is little math in it and it does not seem very complicated for me. Then, what is actually the purpose of the tag? Telling kids not to read the article because they will not get it? The same reason could be used for any article with complicated formulas - "This article is accessible to people who know advanced concepts of particle physics" for example. In my opinion, this is a bad use of tags since a better thing exists - hyperlinks. Who does know what eigenvalues are, can easily click the link... --Tone 20:47, 26 September 2009 (UTC)


 * Many other people have strong opinions on this subject too. I think it ought to be possible to have a civil discussion about the matter and reach a consensus rather than taking unilateral actions.
 * In the beginning there was no "intro" tag, so no promises were made about level of content. A few months ago the entire article was deleted and replaced by one written by George Louis. (That article was later turned into a fork of this one.) The rationale was that this article carried the "intro" tag and that therefore it should have no math, no diagrams, etc., etc. I do not agree with that assessment. There has to be a middle ground between no math and university math. After intervention from several editors the original Intro article was restored.
 * It does not matter to me whether this article has an "intro" tag or not. But in an attempt to avoid further edit warring I put up the qualification that some math is required. It does not matter to me whether this article has that tag or not either. What does matter is that the article not be gutted.
 * I fully agree that the math should not be a real problem, and I cannot imagine explaining things without some use of it. If students are not frightened or subdued by the presence of the equations I find it hard to believe that they would be scared off by a a mere statement about their presence.
 * Bright students deserve to have available all that can be understood without the necessity of a couple of years of the kind of calculus classes that physics majors need to take. That information may motivate them to take the university classes. Those who already have that level of calculus can go to the senior articles.
 * Let's see what some of the other people involved in discussing this article think about the "some math" statement.P0M (talk) 22:44, 26 September 2009 (UTC)


 * Hm, I am just saying that there should be no tag at the top of the article, I am not arguing the content... Actually, at the moment the only non-elementary math in the article is about the uncertainty principle. Regarding the other intro article, the AfD is about to end tomorrow (after I've relisted it in order to get some feedback what to do with it). --Tone 23:06, 26 September 2009 (UTC)


 * I understand your point. What other people have to say about the matter remains to be seen. P0M (talk) 23:31, 26 September 2009 (UTC)


 * One month and no opinions. Seems noone cares... Can I remove the tag now? --Tone 13:53, 25 October 2009 (UTC)
 * Since some of the discussion on a recommendation for deletion of the fork to this article (which insisted on no math) ridiculed the idea of talking about physics without math, and since I basically agree, let's give it a try. If anybody who reads the article does not understand basic algebra I guess that they will have to skip over the equations. That should not leave them any worse off than if the equations had been edited out. P0M (talk) 18:07, 25 October 2009 (UTC)

Planck and the ultraviolet catastrophe
The article currently reads "The way out of this "ultraviolet catastrophe" was prepared by Max Planck, who determined that the energy content of a beam of light of frequency f comes multiples of a quantum of energy hf. He was not aware of the ultraviolet catastrophe, however, and only was trying to fix the problem he knew about—that the existing models did not yield the right energy distribution for black-body radiation."

What I glean from this is that Planck was aware that the classical models were wrong, but he was not aware of how they were wrong (e.g., that the Rayleigh-Jeans model blows up at high frequencies). Is this correct? If not, it should be clarified. Strad (talk) 18:09, 27 September 2009 (UTC)
 * I need to re-read some stuff and then rewrite that part. Basically, Planck was working on a very limited problem the solution of which had immense consequences. But popularizations have tended to jam things together and mess up the time line. Planck knew nothing about atoms, for starters. There was a problem with Wien's law in the infrared region. Planck assumed that the energy units were discontinuous, and that allowed him to get an equation that made the predictions fit the facts. Unless I have missed or forgotten something, I think he stopped there. It would appear that the full consequences of the classical view had not been noticed yet. So in a way he solved the problem before it appeared.
 * I should be correcting papers now. I don't like the "content of a beam of light" wording because it is too divorced from the black-body apparatus. Planck wasn't thinking about any beam of light, just about the beam of light that came out of one particular kind of lab apparatus. Maybe I'll just fix that part and then review tomorrow night. P0M (talk) 19:04, 27 September 2009 (UTC)
 * From the Planck's law article: "Planck did not consider the equipartition theorem to be universally valid, so he never noticed any sort of "catastrophe" — it was only discovered some five years later by Einstein, Lord Rayleigh, and Sir James Jeans."P0M (talk) 19:32, 27 September 2009 (UTC)

Intended readership for introductory QM articles - discussion
For a variety of reasons, there are currently two different introductory articles on Quantum Mechanics on Wikipedia (in addition to the Quantum mechanics article itself):
 * Introduction to quantum mechanics, which aims to be accessible to those with a command of high school algebra, but which has been criticised for going into too much technical detail and mathematics for an introductory article.
 * Basic concepts of quantum mechanics, a more descriptive article with less mathematical detail, but which has been criticised for going too much into the history and a lack of mathematical detail.

Arguably this is at least one too many introductory articles, and various ways of dealing with this issue (by merging, moving content, deleting, etc.) have been suggested without ever coming to a consensus view. Possibly the problem is that we haven't yet answered the more fundamental question: what level(s) of readership should the introductory article(s) be targeted at?

This discussion has been raised in order to generate a consensus view on this issue, which can then inform discussion of what to do with the articles. In order to avoid having the same discussion taking place on three different talk pages, please direct all comments to Talk:Basic concepts of quantum_mechanics. Djr32 (talk) 11:19, 25 October 2009 (UTC)

Wave-particle duality section and related subjects
This topic is currently covered in a fairly disjointed way, with the double slit experiment being introduced right at the top, then another section on the double slit experiment later down, and finally a section on wave-particle duality and the de Broglie hypothesis. I would like to reduce this to a single section, probably after the section on the Bohr model, i.e. at the end of "old" quantum mechanics, just before Heisenberg and Schrodinger. I would also intend to make wave-particle duality the central concept, demonstrated by the two-slit experiment, Davisson and Germer's experiment, etc. (As it stands, I think the two-slit description doesn't really emphasise the main point as it relates to QM: that it was well known that light had wave-like properties but it was more surprising that matter did.) Would anyone object to this idea? Djr32 (talk) 19:20, 26 December 2009 (UTC)
 * This sounds good. Strad (talk) 04:43, 27 December 2009 (UTC)

Problem in summary
Enclosed in comment tags: Query n must be greater than m surely? 86.141.115.30 (talk) 17:48, 25 January 2010 (UTC)
 * You are entirely correct - now fixed. (Arguably, n > m gives the emission spectrum and m > n gives the adsorption spectrum, but the section is already too convoluted to get into this!)  Djr32 (talk) 21:16, 25 January 2010 (UTC)

Content fork
I know that I am not the first to bring it up but this article is a major content fork. Looking at the history it appears that the article was created because the Quantum mechanics article was to one degree or another violating WP:NOTTEXTBOOK. That article has improved, though, perhaps not enough. Regardless, creating two articles on the same topic is a serious violation of policy (for good reason), regardless of whether the articles are intended to serve two different purposes.

I hope the editors who have been working on the two articles will reconsider the path they are on. If these types of violations of Wikipedia continue to develop I believe Wikipedia is in danger of falling apart.

--Mcorazao (talk) 21:58, 7 June 2010 (UTC)
 * I see that you have started discussions on the question of introductory articles at the village pump and at Wikipedia talk:Make technical articles understandable. I also see from these discussions that there is no consensus that such articles are a violation of Wikipedia policy or even a bad thing. Until such a consensus is reached, there are no grounds to characterize this or any other introductory article as a "serious violation of policy" simply for being an introductory article. Strad (talk) 02:31, 8 June 2010 (UTC)
 * The QM article did not "violate" anything. It may be that some editors saw that it was difficult to understand and saw the need for this introductory article. Since there is a focus on "violations" then there might be interest in this WP:IGNORE,which is an accepted "English Wikipedia policy". Here is a page that explains that policy in more detail WP:WIARMSteve Quinn (formerly Ti-30X) (talk) 04:50, 8 June 2010 (UTC)
 * "Wikipedia has many rules. Instead of following every rule, it is acceptable to use common sense as you go about editing. Being too wrapped up in rules can cause loss of perspective, so there are times when it is better to ignore a rule."Steve Quinn (formerly Ti-30X) (talk) 04:50, 8 June 2010 (UTC)

Yeah, well, looking at the responses on village pump it appears some editors agree and some don't. What's disturbing is that some of the disagreement amounts to "maybe it is a content fork but I still think it's ok". I believe the content fork policy was created for good reason. I understand the aim of WP:WIARM (bearing in mind that this is an essay, not a policy) but if we don't learn from our mistakes then Wikipedia will never mature (i.e. if we are considering violating a long-established policy, we should consider that a big deal, not just something to do on a whim). It's actually easy to come up with all sorts of reasons to content fork. But I have yet to see a case where it was actually necessary. --Mcorazao (talk) 05:15, 8 June 2010 (UTC)


 * It is not a content fork. That is an oversimplification, and ultimately a mischaracterization. For more detail on this view see my response at village pump. Also,  WP:WIARM  gives views of the policy. The actually policy is WP:IGNORE, not  WP:WIARM.Steve Quinn (formerly Ti-30X) (talk) 05:44, 8 June 2010 (UTC)


 * I agree. P0M (talk) 17:28, 10 June 2010 (UTC)

"seems to be" vs. "is"
A recent editor did not like the sentence, "The principles of quantum mechanics are difficult for the human mind to understand, because humans are accustomed to reasoning about the world on a scale where classical physics is an excellent approximation." and wanted to say that classical physics only "seems to be an excellent approximation." That way of saying things would imply that within classical limits there are cases where classical physics is something less than an excellent approximation. But that is not the case. The math is such that the farther from the small end of the scale predictions are made by both theories, the less is the difference between the two results, and the discrepancy quickly becomes so small that it cannot be detected. An "ap-proximation" is a "getting close to" something, and the discrepancy/distance continually decreases. A case where classical physics were not an excellent approximation would be a world in which ball bearings of most sizes were well behaved, but at a certain mass and diameter they were palpably smudged in their space-time locations.

The founders of quantum mechanics paid deference to the excellence of approximations of classical physics by arguing that quantum mechanics should never predict results within classical limits that disagreed with classical theory. This idea was, I think, fundamentally a practical consideration. The laws of classical physics had by then been so well tested that any theory that predicted different results (within the domain of classical physics) was almost surely going to be found false when subjected to experiments in the laboratory -- because the experiments had all been done over and over again in hundreds if not thousands of labs and true anomalies had not been discovered.

I have reverted the change to the above-cited sentence. P0M (talk) 14:01, 3 July 2010 (UTC)


 * There are situations where classical mechanics do not give good results even for macroscopic systems. For instance, classical mechanics spits a whole lot of nonsense when you try to calculate themal radiation (heat) emited by a body at a iven temperature. Dauto (talk) 19:05, 3 July 2010 (UTC)


 * I agree with Patrick regarding this edit. I almost reverted it myself, but hesitated. I see classical physics as an excellent approximation, and I think science progressed a great deal via classical physics. Also, it seems that it would have to be at least an excellent approximation for it to be useful in any period. Steve Quinn (talk) 06:07, 4 July 2010 (UTC)

Discontinuous and colour coded sequence.
Anon had removed the phrase "and colour coded sequence" from the statement "Photon energies form a discontinuous and colour coded sequence.". User then reverted, asking for a source. I did a little google books search ( and ) and, I think we should indeed get rid of the phrase. There are many sources talking about figures and diagrams in which the photon energies are colour coded, but I don't think we will find any source that says that photon energies are inherently colour coded. So I think we better get rid of it. Furthermore, i.m.o. we can remove the entire remaining statement ("Photon energies form a discontinuous sequence."), as it then simply repeats the stmnt immediately before it. DVdm (talk) 22:44, 10 September 2010 (UTC)
 * It was not my intention to restore that phrase. I thought I was removing it, and asking for a reference. Sorry about that. And, yes, I agree, remove the entire remaining statement. Thanks for catching my error. Steve Quinn (talk) 07:14, 11 September 2010 (UTC)
 * I reverted my error. Feel free to do the rest. The rest of the statement probably needs to be removed as per DVdm. Steve Quinn (talk) 07:21, 11 September 2010 (UTC)
 * Ok, I did the rest. Looks better now. Cheers - DVdm (talk) 09:32, 11 September 2010 (UTC)

Recent changes by djr
I think the recent changes are good.

As far as possibly removing the more technical parts that have been improved in reading, I think I would be against that. My reasoning is simply that the Schrödinger equations are never, to my knowledge, described or explained in any sensible way. So anything that can be said that makes them more than a set of squiggles for the average well-informed reader is of great benefit. Somewhere I have a book that I will have to dig out that, if I remember correctly, provides visual representations of the "electron clouds" for each of the consequences of the equations. Something that would visually show the reader how our mental picture of the atom changed as a result of Schrödinger's work would probably be the best we can do.

I just did a quick count of diagrams on commons, and there are at least 50. Those 50 could be put into a grid. To me, they actually look more meaningful when you scan a whole group of them and try to arrange them into meaningful patterns. Maybe a sub-article just to show the possible n, l, and m variations and their consequences? P0M (talk) 21:39, 24 October 2010 (UTC)


 * Glad you like it! I was a bit shocked to realise that I hadn't done anything useful to this article for about 9 months, but I've dug out some of my old undergrad notes and might have a bit more time over the next few weeks.


 * There are a few articles I know of which discuss this sort of area, though I agree that it's hard to find anything that describes Schrödinger's equation at a suitably introductory level. Have a look at Atomic orbital for pictures - some of these could be useful here.  (You're right that for some reason there are a lot of pictures available - the same is true of the Bohr model, where there seem to be about 10 slightly different pictures used across different articles...)  Djr32 (talk) 22:34, 25 October 2010 (UTC)

quibble
The text currently states: "This number is denoted by either m or ml, because the magnetic moment depends on the second quantum number l."

This way of saying things could encourage some readers to believe that m and ml are two different variables, and that there reason there are two different variables is that another variable, l, can have values that sometimes yield an "m" and at other times yield an "ml."

How about saying: "This number is sometimes written as "m," but some authorities prefer to write it as "ml" since magnetic moment depends of the second quantum number, "l."

I note that http://hyperphysics.phy-astr.gsu.edu/hbase/spin.html writes "ml, which differentiates that value from the product of m and l. P0M (talk) 02:50, 11 November 2010 (UTC)


 * If you think that people might get confused then we should fix it. I don't really like the sentence as it stands anyway -- when I was moving some of this text around recently, I did think that I would come back to it later.


 * I'm not convinced that the subscript l is used to point out that the value depends on l -- after all, the possible values of l depend on n, and l is never written as $$l_n$$ -- but rather because it also measures angular momentum, and angular momentum is conventionally denoted by L. Perhaps something like:


 * The third quantum number, the magnetic quantum number, describes the magnetic moment of the electron, and is denoted by $$m_l$$ (or simply m). The possible values...   The magnetic quantum number measures the component of the angular momentum in a particular direction.  The choice of direction is arbitrary, conventionally the z-direction is chosen.


 * What do you think? Djr32 (talk) 21:27, 11 November 2010 (UTC)


 * That sounds fine to me. P0M (talk) 02:41, 12 November 2010 (UTC)


 * OK, done. Djr32 (talk) 20:34, 13 November 2010 (UTC)

Article length and the "Summary" section
I'm not sure what the "Summary" section is aiming at - to me it seems to just repeat some randomly chosen pieces of information from the article, in a relatively "wordy" form. Given that the article is still quite long (69 kB), would anyone object if I removed it? Djr32 (talk) 17:04, 28 December 2010 (UTC)
 * Done. Djr32 (talk) 18:28, 8 January 2011 (UTC)

Photon instead of electron?
In "Wavefunction collapse is a forced term for whatever happened when it becomes appropriate to replace the description of an uncertain state of a system by a description of the system in a definite state. Explanations for the nature of the process of becoming certain are controversial. At any time before an electron "shows up" on a detection screen it can only be described by a set of probabilities for where it might show up. When it does show up, for instance in the CCD of an electronic camera, the time and the space where it interacted with the device are known within very tight limits. However, the photon has disappeared, and the wave function has disappeared with it. In its place some physical change in the detection screen has appeared, e.g., an exposed spot in a sheet of photographic film."

I think the first mention of "electron" should say "photon" instead. —Preceding unsigned comment added by 76.24.17.170 (talk) 04:54, 22 January 2011 (UTC)


 * To be consistent with the rest of the paragraph the word "electron" did indeed need to be changed to "photon." (The issue is logical/grammatical. An electron would, I think, also have an indeterminate position before it "shows up" at some point on a suitable detection screen.)P0M (talk) 05:21, 22 January 2011 (UTC)

Quantum theory replacing classical physics?
I believe that the sentence "This article describes how the limitations of classical physics were discovered, and describes the main concepts of the quantum theory which replaced it in the early decades of the 20th Century" in the second paragraph is inaccurate. Quantum mechanics/theory does not replace classical physics, it merely complements it. Simply put, quantum theory describes the small world, general relativity the large world, and classical physics anything in-between, i.e. our humanly comprehensible world. Thoughts? Petersburg (talk) 00:23, 23 March 2011 (UTC)
 * Quantum theory reduces to classical physics within classical limits. There are not two varieties of physics, one for the macro world and one for the micro world as you seem to believe. The same situation exists for relativity physics. Two people walking away from each other each have "slow" clocks from the other one's perspective -- but the correction is so small that it would never be noticed.P0M (talk) 01:59, 23 March 2011 (UTC)

"The possible values for l are integers from 0 to n"
There appears to be a contradiction in the article under Application to the hydrogen atom. In the article Azimuthal quantum number, which is linked to in the section in question, it states (under the heading Derivation, third paragraph under the table) "the possible values of ℓ range from 0 to n − 1".

Which is right? Or are there a specific conditions governing whether l can range from 0 to n or from 0 to n - 1?

RevenDS (talk) 11:40, 27 March 2011 (UTC)


 * The range from 0 to n − 1 is correct. Dauto (talk) 14:26, 27 March 2011 (UTC)


 * I fixed the offending article. Dauto (talk) 19:25, 27 March 2011 (UTC)