Talk:Introduction to quantum mechanics/Archive 3: Difference between revisions

Revision as of 20:54, 3 December 2011

Revision as of 20:57, 3 December 2011

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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. [[User:Patrick0Moran|P0M]] ([[User talk:Patrick0Moran|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? [[User:Patrick0Moran|P0M]] ([[User talk:Patrick0Moran|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. [[User:Patrick0Moran|P0M]] ([[User talk:Patrick0Moran|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."'' [[User:Larryisgood|Larryisgood]] ([[User talk: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?[[User:Patrick0Moran|P0M]] ([[User talk:Patrick0Moran|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. --<font color="blue">[[User:Chetvorno|Chetvorno]]</font>^{''<small>[[User talk:Chetvorno|<font color="Purple">TALK</font>]]</small>''} 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. [[User:Patrick0Moran|P0M]] ([[User talk:Patrick0Moran|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. ([[User:TimothyRias|TimothyRias]] ([[User talk: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? [[User:IRWolfie-|IRWolfie-]] ([[User talk: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. [[User:Patrick0Moran|P0M]] ([[User talk:Patrick0Moran|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. [[User:Patrick0Moran|P0M]] ([[User talk:Patrick0Moran|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. [[User:Patrick0Moran|P0M]] ([[User talk:Patrick0Moran|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? -- [[User:Momotaro|Momotaro]] ([[User talk: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. [[User:Patrick0Moran|P0M]] ([[User talk:Patrick0Moran|talk]]) 01:05, 19 June 2009 (UTC)

::I haven't been following this debate (I came here from [[Wikipedia talk:WikiProject Physics#Introduction to quantum mechanics]]), 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. -- [[User:BenRG|BenRG]] ([[User talk:BenRG|talk]]) 18:52, 19 June 2009 (UTC)

:::(I come from [[Wikipedia talk:WikiProject Physics#Introduction to quantum mechanics]] 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'') <small>in [[it:Progetto:Fisica|Italian wikiproject physics]], where I come from, the answer was ''no'')</small>. Finally, I don't believe that using a copy of an existing article to create another article in wikipedia can configure as copyviol. --[[User:CristianCantoro|CristianCantoro]] ([[User talk:CristianCantoro|talk]]) 19:27, 20 June 2009 (UTC)

::::I saw this over at [[Wikipedia talk:WikiProject Physics#Introduction to quantum mechanics]]. 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. [[User:Ti-30X|Ti-30X]] ([[User talk: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. [[User:Patrick0Moran|P0M]] ([[User talk:Patrick0Moran|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. [[User:Ti-30X|Ti-30X]] ([[User talk:Ti-30X|talk]]) 22:58, 28 June 2009 (UTC)

(<=) I've added in [[Basic concepts of quantum mechanics]] a <nowiki>{{See also}}</nowiki> that points [[Introduction to quantum mechanics|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. --[[User:CristianCantoro|CristianCantoro]] ([[User talk: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. [[User:Patrick0Moran|P0M]] ([[User talk:Patrick0Moran|talk]]) 17:26, 11 July 2009 (UTC)

:Rambling to the point of (ironically) incoherence. Why not just replace it all with {{main|wavefunction collapse}}. --[[User:MichaelCPrice|Michael C. Price]] ^{[[User talk: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. [[User:MarkoZhuk09|MarkoZhuk09]] ([[User talk: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. --[[User:MichaelCPrice|Michael C. Price]] ^{[[User talk: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?

<blockquote>

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. </blockquote>

<blockquote>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.</blockquote>

<blockquote>"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. </blockquote>

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.[[User:Patrick0Moran|P0M]] ([[User talk:Patrick0Moran|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.

[[User:Patrick0Moran|P0M]] ([[User talk:Patrick0Moran|talk]]) 00:15, 22 July 2009 (UTC)

:Patrick is someone talking about scrapping this article? Or are you talking about the "Basic" article? [[User:Ti-30X|Ti-30X]] ([[User talk: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. [[User:Ti-30X|Ti-30X]] ([[User talk: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.[[User:Patrick0Moran|P0M]] ([[User talk:Patrick0Moran|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 function'''s''' 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. [[User:Ti-30X|Ti-30X]] ([[User talk: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. [[User:Patrick0Moran|P0M]] ([[User talk:Patrick0Moran|talk]]) 07:32, 24 July 2009 (UTC)

==General trends of development==

I don't want to offend anyone, but I think the section entitled "[[Introduction to quantum mechanics#General trends of development |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 [[User:Ti-30X|Ti-30X]] ([[User talk: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. [[User:Ti-30X|Ti-30X]] ([[User talk: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. [[User:Patrick0Moran|P0M]] ([[User talk:Patrick0Moran|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. [[User:Ti-30X|Ti-30X]] ([[User talk: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. [[User:Patrick0Moran|P0M]] ([[User talk:Patrick0Moran|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. [[User:Patrick0Moran|P0M]] ([[User talk:Patrick0Moran|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. [[User:StradivariusTV|Strad]] ([[User talk:StradivariusTV|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... --'''[[User:Tone|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.[[User:Patrick0Moran|P0M]] ([[User talk:Patrick0Moran|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). --'''[[User:Tone|Tone]]''' 23:06, 26 September 2009 (UTC)

:::I understand your point. What other people have to say about the matter remains to be seen. [[User:Patrick0Moran|P0M]] ([[User talk:Patrick0Moran|talk]]) 23:31, 26 September 2009 (UTC)

:::: One month and no opinions. Seems noone cares... Can I remove the tag now? --'''[[User:Tone|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. [[User:Patrick0Moran|P0M]] ([[User talk:Patrick0Moran|talk]]) 18:07, 25 October 2009 (UTC)

== Planck and the ultraviolet catastrophe ==

The article currently reads

{{quote|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. [[User:StradivariusTV|Strad]] ([[User talk:StradivariusTV|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. [[User:Patrick0Moran|P0M]] ([[User talk:Patrick0Moran|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."[[User:Patrick0Moran|P0M]] ([[User talk:Patrick0Moran|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#Intended readership for introductory QM articles - discussion]]. [[User:Djr32|Djr32]] ([[User talk: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? [[User:Djr32|Djr32]] ([[User talk:Djr32|talk]]) 19:20, 26 December 2009 (UTC)

:This sounds good. [[User:StradivariusTV|Strad]] ([[User talk:StradivariusTV|talk]]) 04:43, 27 December 2009 (UTC)

== Problem in summary==

Enclosed in comment tags: Query n must be greater than m surely? [[Special:Contributions/86.141.115.30|86.141.115.30]] ([[User talk: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!) [[User:Djr32|Djr32]] ([[User talk: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 [[WP:content forking|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.

--[[User:Mcorazao|Mcorazao]] ([[User talk:Mcorazao|talk]]) 21:58, 7 June 2010 (UTC)

:I see that you have started discussions on the question of introductory articles at the [[Wikipedia:Village pump (policy)#Introductory articles|village pump]] and at [[Wikipedia talk:Make technical articles understandable#?Introductory articles?|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. [[User:StradivariusTV|Strad]] ([[User talk:StradivariusTV|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:WIARM]]----[[User:Steve Quinn|Steve Quinn (formerly Ti-30X)]] ([[User talk:Steve Quinn|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."----[[User:Steve Quinn|Steve Quinn (formerly Ti-30X)]] ([[User talk:Steve Quinn|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 [[WP:content forking|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. --[[User:Mcorazao|Mcorazao]] ([[User talk: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 [[Wikipedia:Village pump (policy)#Introductory articles|village pump]]. Also, [[WP:WIARM]] gives views of the policy. The actually policy is [[WP:IGNORE]], not [[WP:WIARM]].----[[User:Steve Quinn|Steve Quinn (formerly Ti-30X)]] ([[User talk:Steve Quinn|talk]]) 05:44, 8 June 2010 (UTC)

:I agree. [[User:Patrick0Moran|P0M]] ([[User talk:Patrick0Moran|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. [[User:Patrick0Moran|P0M]] ([[User talk:Patrick0Moran|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. [[User:Dauto|Dauto]] ([[User talk: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. ----[[User:Steve Quinn|Steve Quinn]] ([[User talk:Steve Quinn|talk]]) 06:07, 4 July 2010 (UTC)

== Discontinuous and colour coded sequence. ==

Anon {{user|161.203.19.1}} had [http://en.wikipedia.org/w/index.php?title=Introduction_to_quantum_mechanics&action=historysubmit&diff=384050379&oldid=383013061 removed] the phrase "''and colour coded sequence''" from the statement "''Photon energies form a discontinuous and colour coded sequence.''". User {{user|Steve Quinn}} then [http://en.wikipedia.org/w/index.php?title=Introduction_to_quantum_mechanics&diff=next&oldid=384050379 reverted], asking for a source. I did a little google books search ([http://www.google.com/search?q=Photon+energy++%22colour+coded%22] and [http://www.google.be/search?q=Photon+energy++%22color+coded%22]) 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. [[User:DVdm|DVdm]] ([[User talk: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. ---- [[User:Steve Quinn|Steve Quinn]] ([[User talk: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 [[User:DVdm|DVdm]]. ---- [[User:Steve Quinn|Steve Quinn]] ([[User talk:Steve Quinn|talk]]) 07:21, 11 September 2010 (UTC)

:::Ok, I did the rest. Looks better now. Cheers - [[User:DVdm|DVdm]] ([[User talk: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? [[User:Patrick0Moran|P0M]] ([[User talk:Patrick0Moran|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...) [[User:Djr32|Djr32]] ([[User talk: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 "m_l" since magnetic moment depends of the second quantum number, "l."

I note that http://hyperphysics.phy-astr.gsu.edu/hbase/spin.html writes "m_l, which differentiates that value from the product of m and l. [[User:Patrick0Moran|P0M]] ([[User talk:Patrick0Moran|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 <math>l_n</math> -- 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 <math>m_l</math> (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? [[User:Djr32|Djr32]] ([[User talk:Djr32|talk]]) 21:27, 11 November 2010 (UTC)

::That sounds fine to me. [[User:Patrick0Moran|P0M]] ([[User talk:Patrick0Moran|talk]]) 02:41, 12 November 2010 (UTC)

:::OK, done. [[User:Djr32|Djr32]] ([[User talk: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? [[User:Djr32|Djr32]] ([[User talk:Djr32|talk]]) 17:04, 28 December 2010 (UTC)

:Done. [[User:Djr32|Djr32]] ([[User talk: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. <span style="font-size: smaller;" class="autosigned">—Preceding [[Wikipedia:Signatures|unsigned]] comment added by [[Special:Contributions/76.24.17.170|76.24.17.170]] ([[User talk:76.24.17.170|talk]]) 04:54, 22 January 2011 (UTC)</span><!-- Template:UnsignedIP --> <!--Autosigned by SineBot-->

: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.)[[User:Patrick0Moran|P0M]] ([[User talk:Patrick0Moran|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? [[User:Petersburg|Petersburg]] ([[User talk: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.[[User:Patrick0Moran|P0M]] ([[User talk:Patrick0Moran|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 [[Introduction_to_quantum_mechanics#application_to_the_hydrogen_atom|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?

[[User:RevenDS|RevenDS]] ([[User talk:RevenDS|talk]]) 11:40, 27 March 2011 (UTC)

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

:I fixed the offending article. [[User:Dauto|Dauto]] ([[User talk:Dauto|talk]]) 19:25, 27 March 2011 (UTC)