Talk:Introduction to quantum mechanics/Archive 5

This article is far too complicated for the layperson
Hello chaps, I came across this article hoping to indeed get a non-technical, accessible introduction to the subject. I am not an idiot, I am also not uneducated in physics, and have read about quantum mechanics before (for example, I am familiar with the concept of probability waves and wave collapse), yet I possess no higher education qualification in physics. I.e.- I am the perfect person who this article is aimed at. Yet in the FIRST PARAGRAPH I found completely unnecessary nonsense. For example: "Action is a general physical concept related to dynamics and is most easily recognized in the form of angular momentum" why do I need to know exactly what 'action' means? It then goes on to use the phrase 'angular momentum' three more times, and brings in electron orbitals, Planck's constant and quantum numbers. All this in the FIRST paragraph, allegedly aimed at people who do NOT have a previous understanding in the subject. I did indeed read on, and found many other examples of unnecessary complexity- not least the sheer quantity of equations on the page. This is absurd.

I would like to echo what P0M said: "Many attempts that I have tried to make to keep the article comprehensible to somebody who has not had a couple years of college physics have been attacked by readers who have said that they feel that I am talking down to them." Surely anyone with a physics degree SHOULD feel like they are being talked down to in an 'introduction' article? — Preceding unsigned comment added by Mcplums (talk • contribs) 13:28, 9 May 2013 (UTC)


 * The first paragraph, at least, is easily fixed. An earlier version was much simpler, but an IP editor rewrote it - the same one who you agree with above. I have restored the earlier version. RockMagnetist (talk) 14:34, 9 May 2013 (UTC)


 * I agree completely with Mcplums. It also spends too much time on subjects of only historical interest, such as the obsolete Bohr theory.    I think the whole article should be rewritten.   Thank you, Mcplums, for an intelligent, cogently expressed critique. -- Chetvorno TALK 17:21, 9 May 2013 (UTC)


 * Indeed, see also here:
 * "Have you ever gotten the impression that the introductory physics textbook you are forced to use is a charlatan, that maybe it was designed by physicians and engineers purposely to make physics look boring, so that anyone with any imagination would be driven away? Generally such a book looks much more like a history book, and apparently the author thinks that the only way to learn from the mistakes of history is to repeat them. (Let's hope he didn't write the lab manual, too.) Or maybe he is just a disgruntled physicist, who thinks that, well, he had to learn it that way, so, by golly, that's the way you're going to have to learn it, too." Count Iblis (talk) 22:34, 9 May 2013 (UTC)


 * I think the implied criticism of P0M is a bit harsh. It's clearly been a labor of love and it has some excellent stuff in it. Some of the history is concerned with interesting and important applications of quantum mechanics. However, it is true that the Bohr model shouldn't be given so much weight in this article. RockMagnetist (talk) 22:57, 9 May 2013 (UTC)


 * What the article had, back in 2009, was intended to show the reader how people discovered quantum mechnics, what they were trying to do, why they needed to do it, etc. It depends on concrete occurrences and simple math, so it gives people an intuitive entry point. At some point it was replaced by lots of math that doesn't lead the reader to understanding what people are doing or why they are doing it.P0M (talk) 19:42, 10 May 2013 (UTC)


 * And it's way more readable than Quantum mechanics. RockMagnetist (talk) 22:59, 9 May 2013 (UTC)


 * I don't have time to patrol this article every day for odd additions. Thanks for calling my attention to the addition of a lot of math in systems of notation that probably only physics students could even read aloud.


 * One of the challenges of writing for something like Wikipedia is to get writers who are interested in communicating ideas to students, and not interested in proving how smart they are. Then you have to protect the good parts while accepting the changes that make sense.


 * The audience for an article like this can be anything from somebody in 8th grade who has heard about quantum mechanics and wants to know what it is about—in a general way, to somebody who has learned the basics of the subject as a physics major. Maybe for some reason this person just needs to be reminded of something that has grown a bit murky in the years since s/he graduated. In between these extremes there are people who have all sorts of different needs and preparations when they come to read the article. One person might do perfectly fine with some elegant math and a few words of explanation to string the equations together. Another person might work almost entirely by visualization, and might even need a clear "intuition" of what is going on before the math would make sense. People differ considerably in how they understand things. We should not drive anybody away by getting them confused. We should provide help for people with different learning "styles."


 * Somebody with a physics major should be prepared to have the obvious stated in many instances. Somebody who is not even familiar with much high school physics should be prepared to find some things beyond their ken. I believe that anybody has the right to look somewhere else if they don't find a book or an article meets their needs. I can't see, however, how an individual can insist that what may be good for some people or some groups of people should be replaced with something tailored for that individuals and (perhaps) other like him or her.


 * Anybody should be able safely to skip over equations, and introductory articles should be written so that skipping an equation will not get the reader lost. There may also be parts of an article that provide context that is useful for some readers but of no interest to others. Does anybody really need to know about Darwin's sea voyage to understand evolution? Maybe some readers will have an easier time absorbing general evolutionary ideas if they have some idea of what drove people to think up this abstract theory that seems to conflict with what everybody know.


 * The thing that a good article will not do is to lay traps for the reader by making statements that can be taken more than one way. Compare the writing of Heisenberg and the writing of Schrödinger. With the latter one often cannot be sure of what he really means. He appears to be cynical, ironic, sarcastic... It's hard sometimes to know whether he really means something or means for the reader to understand that he is showing off how clever he is and he is stating the position that he may think only an idiot would accept.


 * If you want to see a really good physics textbook, get the original MIT series written by Francis Weston Sears. It was incredibly useful to me as a freshman physics major, even though the official textbook for the course was the same series of books crammed into one volume. The difference was that when it became University Physics by Sears and Zemansky they took all the good stuff out. P0M (talk) 08:44, 10 May 2013 (UTC)


 * I didn't mean to criticize the editors involved. P0M, I agree with most of the points you made so courteously and intelligently above.  Especially the one about finding editors more interested in good writing than demonstrating their smarts.  I can see a lot of work went into this article.  It is a good article, and it is extremely difficult to write good articles for nontechnical readers about QM.  It sticks to its overall organization, and (except for maybe the intro) it avoids being too wordy, a common problem with QM articles.  As you say, different students respond to different approaches.  I can only call them as I see them.  My feeling is that the chronological organization makes the reader go through a lot of historical information that is unnecessary for understanding modern QM.   Ironically the article makes a better History of quantum mechanics than an introduction.  I think a conceptual approach would be better, that illustrated the central concepts of QM with a few well chosen examples.    I've never seen the Sears text, maybe I can look it up on the web.  I like the approach taken by Feynmann in vol. 3 of The Feynmann Lectures on Physics based on his introductory physics course at Caltech.  -- Chetvorno TALK 23:06, 10 May 2013 (UTC)


 * Amazingly, you can still get the Sears texts used on Amazon, e.g.,http://www.amazon.com/gp/offer-listing/B000H4MOUI/ref=dp_olp_used?ie=UTF8&condition=used
 * (the first one I found). Seeing, in the same list of books, a picture of the spine of Sears and Zemansky, I got reminded of how opaque it was compared to the books it compressed. I am reminded also of the guy who answered the question, "How come your book is so long," by answering, "Because it would have taken me too long to make it shorter." His point was that he would really have to work hard to write more concisely and not leave something out. There was nothing in the compressed version that was not covered in the multi-volume version, so I had always blamed Zemansky for taking all the good points out. Then I learned a little about him, and he seems like a fine person. Maybe some third party did the real work. It was a good idea as far as producing a textbook that people like me could afford, but to me cheap turned out to be expensive.


 * What would you list as the "central concepts of quantum mechanics"? I'm trying to see if a sequence of presentation of these concepts could be worked out so that the load of new ideas would not be overwhelming, in other words, how to manage the presentation of these ideas.P0M (talk) 08:23, 12 May 2013 (UTC)


 * @Chetvorno et al.:It is not very helpful to assert that something should be done in some way and then neglect to specify the most basic steps toward getting what you want.P0M (talk) 06:12, 6 June 2013 (UTC)

Great to read the above responses, especially since this is the first time I have ever tried to contribute to wikipedia. Chetvorno- I love your two ideas proposed, namely re-doing this article from the ground up and perhaps merging the existing article into History of quantum mechanics because as others have suggested, clearly a lot of time has gone into the present article, it would not seem sensible to remove it from wikipedia entirely. However, I would like some advice as to how to go about doing these things? I am a wikipedia noob and dont really understand the procedure. Would there need to be some consensus on this talk page first? Second, does wikipedia have a 'page under construction' function where the new page can be written before it replaces the current effort? As for writing a new article, I would absolutely love to have a crack at that- I am soon to have a lot of free time on my hands and contributing towards the new article sounds like the best way for me to learn about QM, which is after all why I ended up here. Mcplums (talk) 18:45, 11 May 2013 (UTC)


 * The equivalent of a "page under construction" would be to create a draft in your User space. Then you can get feedback before moving some of it to this page. However, you are probably underestimating the challenge - it takes time to learn how to write a good Wikipedia article, and writing an article on a subject as general as this one is a big deal. I think you would be wise to get experience making small improvements to articles. A good place to start might be to find a quantum physics stub and improve it; stubs are far more in need of improvement than this article. RockMagnetist (talk) 21:22, 11 May 2013 (UTC)


 * Haha perhaps you are right. We will see. Thanks for your help!Mcplums (talk) 10:30, 12 May 2013 (UTC)

Chaps, I have had a stab at re-writing the article, please see my sandbox. Please let me know your thoughts. I have yet to add pictures or sources, so dont judge it on that, but rather the content itself. Please note that it is only a draft, and also its my first attempt at writing a wiki article so any recommendations welcome. Mcplums (talk) 13:11, 25 May 2013 (UTC)

Guys its mcplums again, I have rewritten the article as I discussed above, and with regard to your points. Please discuss the rewrite here. To repeat, it is currently in my sandbox. I have rewritten it because: -This article is simply far too long. -The general language is FAR too technical. -There should be virtually no 'history' of QM- someone who doesn't even know what QM is (the target user) is unlikely to be interested already in the history of it. -There shouldn't be a single mathematical/physical equation. I can see an equation right now in the first section. -It should not reference to complicated principles which the layman would reasonably know nothing about, without defining it briefly within the article. Again, the first section references the Stefan–Boltzmann law, thermal radiation, Wien's displacement law, harmonic oscillators. -The intro itself is utterly underwhelming. -In my opinion, (feel free to disagree) there shouldn't be any topics at all in the article which are not either fundamental to QM, or reference something a layperson may have already heard about- probably they have heard how QM 'makes no sense' and are looking for examples. Mcplums (talk) 22:01, 20 March 2014 (UTC)

Part I
Guys its mcplums again, I have rewritten the article as I discussed above, and with regard to your points. Please discuss the rewrite here. To repeat, it is currently in my sandbox. I have rewritten it because: -This article is simply far too long. -The general language is FAR too technical. -There should be virtually no 'history' of QM- someone who doesn't even know what QM is (the target user) is unlikely to be interested already in the history of it. -There shouldn't be a single mathematical/physical equation. I can see an equation right now in the first section. -It should not reference to complicated principles which the layman would reasonably know nothing about, without defining it briefly within the article. Again, the first section references the Stefan–Boltzmann law, thermal radiation, Wien's displacement law, harmonic oscillators. -The intro itself is utterly underwhelming. -In my opinion, (feel free to disagree) there shouldn't be any topics at all in the article which are not either fundamental to QM, or reference something a layperson may have already heard about- probably they have heard how QM 'makes no sense' and are looking for examples. Mcplums (talk) 22:01, 20 March 2014 (UTC)


 * I've moved the above entry here so that new material will not be found somewhere in the middle of lots of other stuff.


 * This article was begun by a user in GB about 9 years ago. Over the years very many people have worked to improve it. Should it then be radically rewritten because a few contributors to Wikipedia feel that it is not what they would like for their own use?


 * An encyclopedia is different from a book. Brian Greene can spend around 500 pages to discuss things in The Fabric of the Cosmos, and the expectation is that the work will be clear, complete, and (within reasonable limits) it will contain all the needed support materials. An encyclopedia is expected to contain "everything" (if it's the encyclopedia of bait casting, everything about that kind of angling), but it need not repeat itself. A book on the care and tending of horses intended for a person first taking up riding and owning a horse needs to describe a disease such as "foundering" (technically called laminitis) well enough to warn the reader about how horses can get this condition and tell him or her about first-aid measures, the need to call the vet sooner than later, etc. A book on veterinary medicine will give considerably more detail intended for veterinarians and other specialists. An encyclopedia can have an article on horses with one of its sub-articles being "care of horses," and s sub-article can deal with laminitis in some detail.


 * An introduction to quantum mechanics should not, e.g., spend anything more than a possible mention on Schrödinger's cat. Many ideas, pertinent to quantum mechanics and not to be understood from the standpoint of everyday experience or even a complete classical physics background, must be understood before anything meaningful can be said about the problem without misleading the reader. So that's definitely something that only gets a link to a separate article on the subject. The inquiring reader should either find his/her way directly to that article, or get there by way of the main article. Considerable space needs to be devoted to the subject to make any sense of it at all.


 * Nobody should imagine himself/herself to have perfect knowledge of what would be unwanted by somebody with an inquiring mind. Our goal should be a well-rounded article that gives at least a link to a more information.


 * What you have put up in your sand box is frequently wrong. It is also limited to only four topics.


 * Here is substantiation for my criticisms:


 * Grammar/syntax mistakes:


 * sizes more familiar with human experience —— Dogs are more familiar with human experience(s) than jaguars. I think you mean something else.


 * (That's just one example.)


 * Questions of fact:


 * "The energy of an electron is limited to certain specific values." What does that statement mean?


 * Electrons can "carry" different amounts of energy, depending on what orbital of what kind of atom they currently reside in. Is that what you mean?


 * Electrons can be created by absorption of two or more photons whereupon the energy of the photons is converted into the mass of an electron, and when an electron collides with a positron the masses of the two can be converted into energy. Is that what you are talking about?


 * The energy that an electron carries due to being accelerated is not quantized.


 * "Unlike with water or sound waves, the waves of quantum physics do not correspond to the actual presence of matter." This statement is at least confusing. I think you mean that water waves are waves in a medium, water, and sound waves are also waves in some medium, air, water, steel..., but there is no medium that light waves are disturbances of.


 * "in actuality the photon is only ever at one place at a time." Actually, the indeterminacy of location of a photon is a prime characteristic of quantum mechanics. Nothing can be said about the "one place at a time" of a photon until we have actually measured it at that point. Then the momentum of the photon is lost, and the photon is also absorbed into the energy carried by an electron that gets boosted up to a higher orbital. You have to admit that, I think, because you immediately contradict the statement just quoted by saying that "The photon truly is, until we measure it, everywhere at once." That statement is technically not true at all, because a photon is held by most physicists not to have a definite position without its being measured. The right way to say it is that it could show up at any point. However, you still have to take account of transit time. Then you say that "this is known as quantum superposition." I don't know where you got that idea. Superposition with what?!! Typically, when researchers talk about superposition they are talking about a photon being in superposition with itself. Schrödinger's cat has to do with the superposition of two quantum states. Who said it had anything to do with an electron or a photon superimposed upon itself (as one would be at the detection screen of the double-slit experiment)?


 * "Theoretically, these probability waves exist throughout the entire universe[5]. That is, if the two slit experiment above is carried out in London, there is a finite probability that the photon would be detected in the Andromeda galaxy only a moment later. This applies to 'classical' objects too. A car is made up of nothing but atoms, each of which obeys the laws of quantum mechanics. There is a finite chance that a car in London could disappear and re-appear on Mars a second later (of course we would expect to wait many lifetimes of the universe to observe this, which is why we don't see it)[5]. Note that the 'movement' of objects in this way is not constrained by the speed of light- for more on this see quantum entanglement." Sorry, this whole thing is not true. An photon that leaves earth and heads out for deep space will show up wherever it shows up, but not at superluminal speeds. 	You are getting confused with entanglement.


 * Your account of entanglement is generally pretty good. However your final paragraph is not:


 * "Most scientists do not, however, consider this experiment to breach special relativity which (broadly) states that information can never travel faster than the speed of light. This is because it is impossible to use quantum entanglement to send information from one place to another instantly. The first electron's spin, when measured, is always randomly clockwise or anti-clockwise. It is this randomness that prevents information being sent at faster than the speed of light."


 * How do you mean "broadly"? Did you just think about an photon leaving the lab bench at Cal Tech and instantly landing on the planet of some distant star? The argument is that the researcher in one place can measure a photon but s/he cannot cause it to show up one way or the other. So the fact that the other experimenter measures his/her and finds a correlated result indicates absolutely nothing except that the first experimenter will get a correlated result. That doesn't tell either one of them anything about whether somebody did the measurement to try to say "yes" or to say "no." I want to say "yes," and that would be one quantum result. I do the measurement and only get to send the answer that I want to send with 50% probability. In that case we could forget about the whole thing and the other guy could just flip a coin at his end.


 * "we should be able to use both quantum and classical physics (specifically, general relativity) to describe its behaviour- that is, the two laws should be compatible with each other." Here is a very basic error. General relativity is not a part of classical physics.


 * "the laws of quantum physics break down and simply make no sense when applied to larger bodies" That statement is not true. What happens is that, e.g., the indeterminacy of the position of something the size of a grain of rice is so small that it could not be detected.


 * Main things the proposed draft discuses:


 * Wave-particle duality.


 * Probability waves and wave function collapse
 * Quantum entanglement


 * The Theory of Everything


 * What makes you think that these four things are the only possible kinds of information that somebody with an inquiring mind would want to know about?


 * I made this request before, a long time ago, and never received an answer from those who wanted to gut the article: Give me a list of things that the average well-informed reader will come to find out about, and the things that s/he might have to understand first to be able to deal with the answers to his/her question. P0M (talk) 02:32, 21 March 2014 (UTC)


 * Haha well I have to thank you for taking so much time to get back to me! I think I have been very naive about two things. 1) I thought that reading Brian Greene's 'Fabric of the Cosmos' once qualifies me to write this article accurately. 2) I completely underestimated how difficult it is to substantially change existing articles on wikipedia. I can see that even IF I one day succeed in getting through a complete rewrite it will have taken a lot of diplomacy. Anyway, ignoring my article for now, what are your opinions on the problems on the current article I outlined in my original post in this section? As to what makes me think those four things are the only possible things someone would wish to know, well what is your opinion on what they should know? And why? Do you really think the current article is better (in terms of topics covered, not the content!). Mcplums (talk) 10:11, 21 March 2014 (UTC)


 * I'd like to congratulate you. Although I agree with some of the above criticisms, I think that was a good first effort at presenting the really mysterious parts of QM for general readers.  This is one of the most demanding writing jobs on WP.    My feeling is that it is extremely difficult to write introductory articles on QM for nonscientists; particularly ones which also satisfy scientists.  -- Chetvorno TALK 14:53, 21 March 2014 (UTC)

Brian Greene is a very competent physicist, which means that he writes from depth. That, in turn, means that he is very unlikely to write something while forgetting about some wrinkle that will get him or his readers into trouble down the line.

There are things that other physicists may not agree with. Greene is good about telling you when there are people with opposing conclusions or interpretations. (Interpretations are often the main problem. Nobody can do much with the basic equations. They are as they are. Einstein didn't like quantum mechanics because it seemed to imply that God plays dice with the universe and because the entanglement between remote twins looks like one operation "here" is causing an instantaneous reaction "there." But he had to accept the equations. All he could do was to try to work with the interpretation side.)

One of the introductory texts is very short. Not only is the page number low, most of what is on each page is in the form of cartoon illustrations. It's McEvoy, J. P.; Zarate, Oscar. Introducing Quantum Theory. I think neither of them is a physicist, but they've only slipped up in one place in the entire book. I believe it is a very well-received book. There were several copies available at my local Barnes & Noble, and they won't put anything out if it does not sell well. Check out the range of topics.

People have put some things into the article that I would disagree with in the sense that they probably aren't necessary. What if the person who put the stuff in disagrees with me? It's one against one. Besides, I don't think my judgment is necessarily better than that of someone else.

Readers should be the ones to determine what they "should" know, not article writers. Ideally, an introductory article would function like the finding telescope of 20x attached to an 8" reflector scope. The introductory article is there to point you at deeper resources if that's what you want.

One of the really influential introductory books on science is George Gamows One, Two, Three....Infinity. It has even been translated into Chinese. It was written by Gamow with his own son in mind. (Gamow is a major figure in the area of quantum nuclear physics, so he really knows what he is talking about.) His thinking was, "How can I give the needed stuff for my son or for anybody coming to a study of science with no prior background but a real interest?"

When I was growing up I conceived an interest in science. I heard about things like crystal radios and wanted to be able to build one. I looked for books. There was almost nothing available in my local library. I was undiscriminating in what I did buy on the subjects I was interested in. I filled in the explanations missing from the books with constructs of my own. Sometimes I was very successful, and sometimes I ended up filling my head with misconceptions that had to be rooted out later. The whole process was pretty inefficient because only Gamow had both the qualifications and the interest to write reliable and accessible stuff for kids who came to things without already having a year or so of college physics, college biology, etc.

English Wikipedia is read all over the world. Often it is used as the basis for articles in languages such as Chinese. Somewhere, maybe in Kabul, Afghanistan, there is a young person who wants to understand the universe. He or she may have only English Wikipedia available. The perfect match for this student may be a junior high student in a village of 300 somewhere in the U.S. These people are my idea of our target audience.

One of the early contributors to this article was a physicist whose opinion was that people who wanted to understand quantum mechanics should first learn the calculus (which would take more than a couple years) and then be given "the real truth" in the form of the Schrödinger equation. Anything else would mess up the potential student's mind. If somebody had an intense interest in and facility for math and calculus then I guess that might work, but how about the vast majority of people who wouldn't buy, "Just do four years of college calculus and then I offer you the mysteries of the Universe!"

So let's look at what the questions would be in the mind of a student who reads something about "quantum physics" in some mass media publication. (I remember getting interested in tesseracts because the idea of four-dimensional cubes was used in a science fiction story.) I can start a list of the questions that this proto-scientist might want answers to: (I've put in some of the usual misconceptions because they are what people are likely start out with.)


 * What is a quantum? I heard it means the minimum possible amount of energy. So, how much energy is a single quantum?


 * If this stuff is so hard and mysterious, how did people get onto it in the first place? What was motivating them to study something this arcane?


 * If it so badly messes up our usual expectations about what reality is, what are some good examples? Give me something I can understand without having access to a cyclotron.


 * What is this "Uncertainty Principle" about? Doesn't that just mean that humans can't get clear about something because of the limitations of our own senses or instrumentation?


 * What about this "complementarity" business? Waves of water are made of molecules of water, so waves are both waves and particles. What's the big deal about that?


 * I saw this really well-written chemistry book in the library that started out talking about quantums of energy, exclusion principles, and physicists who gave us the foundations of modern chemistry. I thought physics was physics and chemistry was chemistry. WTF!

I'm spending too much time on making this list. Other people can come up with other things. P0M (talk) 16:01, 21 March 2014 (UTC)

I have made a list of the topics covered in Quantum mechanics articles of a general nature listed on the first 5 pages of Google returns. If people need suggestions of things that need to be covered, see: User:Patrick0Moran/I2QM list P0M (talk) 19:35, 22 March 2014 (UTC)


 * Mcplums: I disagree with you - while the current article is a work in progress, I think your rewrite is a step in the wrong direction. Taking a few of your points:


 * -In my opinion, (feel free to disagree) there shouldn't be any topics at all in the article which are not either fundamental to QM, or reference something a layperson may have already heard about- probably they have heard how QM 'makes no sense' and are looking for examples.
 * I agree. The topics that I see as fundamental to QM are:
 * Electromagnetic radiation (quantisation thereof), how QM explains the spectrum of black body radiation
 * Atoms, electronic structure, how quantum mechanics underlies all of chemistry
 * Both matter and energy act as waves and as particles: wave functions, Schrödinger equation, wave-particle duality, uncertainty principle
 * Personally I'd not bother with quantum entanglement. It's not that it's a bad topic to talk about, it's just that I don't think you can explain why the "mysterious" parts are mysterious without a lot of background, and without that it just makes the article more confusing without leaving the reader any more informed.  Likewise I'd leave ToE out, it's too far beyond an introduction to QM to cover.


 * -The general language is FAR too technical.
 * That's certainly not the aim. It's a fairly technical subject, so I don't think we can avoid using technical language, I think the goal should be to explain the technical terms, not to hide them.


 * -There shouldn't be a single mathematical/physical equation. I can see an equation right now in the first section.
 * I totally disagree. It's a mathematical subject, it makes predictions which are best expressed as equations, and the experiment fits the predictions very precisely.  I know there has been discussion back and forth here about what the target audience for this article should be, and whether they are likely to be able to cope with (or be repelled by) equations or not, and I'm definitely on the side of including the equations.  We should express the predictions of the theory both in words and in equations; the equations allow you to make a very precise statement in a very compact way, trying to say the sam in words can be long and complicated.


 * -It should not reference to complicated principles which the layman would reasonably know nothing about, without defining it briefly within the article. Again, the first section references the Stefan–Boltzmann law, thermal radiation, Wien's displacement law, harmonic oscillators.
 * The article does exactly what you ask for, at least for the first three, it introduces them in context:
 * "Thermal radiation is electromagnetic radiation emitted from the surface of an object due to the object's temperature. ... In the late 19th century, thermal radiation had been fairly well-characterized experimentally. How the wavelength at which the radiation is strongest changes with temperature is given by Wien's displacement law, and the overall power emitted per unit area is given by the Stefan–Boltzmann law.  However, classical physics was unable to explain ..."
 * (I think I wrote the sentence about harmonic oscillators, and I agree it's not great.)


 * -There should be virtually no 'history' of QM- someone who doesn't even know what QM is (the target user) is unlikely to be interested already in the history of it.
 * As I've said before, I think the historical approach to explaining QM - we believe these (non-obvious) things about QM because they explain a whole bunch of things that we didn't understand previously, and the historical approach covers why, and takes us from the simpler stuff to the harder parts.


 * I think there's plenty to improve in the article, but I don't think that tearing it all up and starting again is the solution. Djr32 (talk) 01:03, 23 March 2014 (UTC)
 * My main problem with the existing article, which has also been raised by others on this page (see Archives) is it's chronological and historical approach. It is more a history than an introduction.  But we already have a History of quantum mechanics article.  I agree that this generally well-written and well-organized article shouldn't be thrown away; it has been suggested that the content be merged into History of quantum mechanics.   This existing article carefully describes how departures from classical mechanics motivated turn-of-the-century physicists to discover quantum principles step-by-step.   With respect, introductory readers don't care about that; they want to know, "How does it work?".  Some specific problems with the existing article:
 * Why should the Bohr atom be included? That is obsolete.
 * Why should the article start with black-body radiation, a specialized problem which can't be explained without complicated mathematics? It was important historically because in 1900 it was one of the few phenomena which couldn't be explained classically.  But now we know nothing on the atomic scale can be explained classically.
 * Why should the article have separate sections for the quantization of matter and light? One of the nice things about QM is that (barring small differences such as rest mass)  both matter and energy particles have the same particle/wave behavior.   The only reason to separate them is because it was discovered historically in that order; first Einstein's photoelectric effect and then De Broglie's waves.
 * QM is the science of how small-scale things behave.  Readers of this page are not here for the history, they want to know "how do quantum mechanical objects behave which is different from how large objects behave?"  This article should simply tell them, summarize the differences.  My other opinions:
 * I have no problem with a small amount of math
 * The double-slit experiment should be prominently included, probably right at the beginning. As Feynman says, it contains the "only mystery".
 * I agree that the more esoteric aspects of wavefunction collapse: entanglement, EPN, nonlocality, should be avoided, at least until the end of the article.
 * I agree that the Theory of everything should not be included.
 * -- Chetvorno TALK 14:27, 23 March 2014 (UTC)

I wondered whether there was a Quantum physics for dummies (there is), and if so how would they handle the material. The answer: they start with black-body radiation. And they don't avoid equations. RockMagnetist (talk) 20:47, 23 March 2014 (UTC)


 * Thank you for the research. Can we show readers the relevance of black-body radiation? (Wouldn't it be wonderful if our automobiles didn't get hot and need radiators, coolant, etc.?) The main problem with that starting point, from my point of view, is that it seems to involve a question that no reasonable person would want the answer to, or something that relates only to the age of steam engines. I don't mean that it is not important, but that the perception of the average well-informed reader may be that it is something irrelevant to daily life.


 * I think there is a good reason for using black-body radiation. If you do not start there with an explanation of what a quantum of energy is, then you have to do two things: 1) You commit yourself to giving a definition of "quantized," and 2) you have to give a full explanation of what quantum means. That means you plunge the reader into a bewildering mass of abstract definitions. It's the rare person who can absorb a definition of "action" and understand h as a "quantum of action" and not as a tiny slice of energy from which all larger sausages of energy are assembled. Even assuming that the reader does not get hung up on this point, there are other fundamental concepts to explain at the same time, and there will be questions in the reader's mind such as 1) Who in the world would care? and 2) How did they get these weird ideas in the first place? So there is still the need for an accessible example as starting point.


 * When you start at one of the places that people really started, you don't have to commit yourself to explaining any more than the experimenters explained. Readers who can at least handle graphs can easily see that the two ways of understanding things were far off the mark. Physics was clearly failing. So here came this idea of a collection of vibrating bodies that were discrete entities of finite number and could only crank out one vibration at a time. People can understand how physicists could get a measure of frequency and a measure of energy and ask what the mathematical relationship is between them.


 * There may be an even better place to start. If so, what is it? I think I came upon the idea of quantum in random mentions. Use of the term often makes its sound as though there is a single thing called a quantum. To me it was never quite clear what anybody was doing until I came upon the black-body explanation simply because of the way the original analogy was made. Is there a clearer example to show that you need something that reliably produces a photon of a definite frequency, you need some process to store energy into the photon producer, that the energy comes out as a function of the frequency of the photon, and that the total energy produced by your apparatus depends on how many photon producers there are and whether they get stoked up or are standing around doing nothing for lack of incoming energy? P0M (talk) 18:31, 24 March 2014 (UTC)


 * No, that isn't clear at all, because you haven't explained in all that blather why the assumption of quantized rather than continuous energies prevents the ultraviolet catastrophe. Folks, why do we need the black-body example in this article at all?  It is one of the worst, most abstruse examples I can imagine for an Introduction to quantum mechanics.  It has to go into a lot of radiation physics, Rayleigh-Jeans law, the Stefan-Boltzmann law, and then it just says "quantized harmonic oscillators prevent the ultraviolet catastrophe".  There's no way to make clear, without mathematics, why that is so.  The explanation in this article and every other one I've seen is just hand-waving.  If you think it is an "accessible example" then try to explain, to a nonscientific reader, exactly why assuming quantized harmonic oscillators prevents the ultraviolet catastrophe.


 * When it comes to introducing the idea of quantized systems, there are a gazillion examples that are clearer than that. The article could go with the classics; the photoelectric effect or spectral lines, or  or with newer examples,  the application of the particle in a box to quantum wells, or even the quantization of vibrations in a nanobeam. -- Chetvorno TALK 21:08, 24 March 2014 (UTC)


 * I think the photoelectric effect might work well. P0M (talk) 03:37, 25 March 2014 (UTC)


 * I'm not convinced that black body radiation ("Why does the Sun look like it does? Why do hot things glow red?  How do lightbulbs work?") is really more obscure than the photoelectric effect ("Why does a current flow if I shine a blue light on that lump of metal, but not if I use a red light, even if the red light is really really bright?").
 * You're right that there is a certain amount of handwaving going on in the article, though I think the solution to the ultraviolet catastrope can be stated more clearly without being technically wrong (old prediction = "all of the infinite number of modes should have the same energy", Planck = "no, the high frequency modes should have (effectively) no energy").


 * But my preference for the historical approach is probably related to it being the approach that I was taught QM through - it worked for me! I think it's worth trying out the idea of starting with the double slit experiment.  (IIRC, it's what the Feynmann lectures do, so copy from the best!)  You don't need to delete the rest of the article to do this, just write a section on the double slit experiment and put it above the Planck bit.  I think this needs to cover matter as much as light as otherwise you're saying "wave-like phenomenon behaves in wave-like manner" which doesn't require QM (which is what I didn't like about the Mcplums version).  Djr32 (talk) 22:55, 25 March 2014 (UTC)


 * I agree that the black body business is understandable. The graphs of predictions of the two classical predecessors show why they wouldn't work without the need for any equations to be worked out in the article.


 * The double-slit experiment can be explained from the beginning as working for both photons and electrons. One of the interesting developments in the last couple of years is that people are starting to talk about both light and electrons as superpositions of wave and particle. See "A quantum delayed choice experiment" by Alberto Peruzzo et arXiv:1205.4926v2 [quant-ph] where they have shown you can't have one without the other, even at one moment in time. The way amplitudes add and multiply to account for probabilities is one important aspect of quantum mechanics. However, we also need to tackle the relationship between frequency and energy. There is a natural connection between the slit-width, slit-separation, and photon frequency that means that by measuring the dimensions of things that exist on a macro scale we can compute frequency. The next step might be to consider how the different frequencies of light interact with the camera's light meter. And we are all familiar with the effects of UV radiation.


 * I think we ought to keep in mind that different people learn in different ways. Does anybody know how to do one of the "buttons" that swings a block of forbidding math into view for the brave or foolhardy, and then pops it safely behind doors if the reader is too scared of it? The math that leads to the structure of the hydrogen atom and its orbitals is not hard. I think it would be appealing and easily assimilated by some.P0M (talk) 00:40, 26 March 2014 (UTC)


 * Seriously?!? Here's the result (copied from Hydrogen atom):
 * The normalized position wavefunctions, given in spherical coordinates are:
 * $$ \psi_{n\ell m}(r,\vartheta,\varphi) = \sqrt {{\left ( \frac{2}{n a_0} \right )}^3\frac{(n-\ell-1)!}{2n(n+\ell)!} } e^{- \rho / 2} \rho^{\ell} L_{n-\ell-1}^{2\ell+1}(\rho) Y_{\ell}^{m}(\vartheta, \varphi ) $$
 * where:
 * $$ \rho = {2r \over {na_0}} $$,
 * $$ a_0 $$ is the Bohr radius,
 * $$ L_{n-\ell-1}^{2\ell+1}(\rho) $$ is a generalized Laguerre polynomial of degree n − ℓ − 1, and
 * $$ Y_{\ell}^{m}(\vartheta, \varphi ) \,$$ is a spherical harmonic function of degree ℓ and order m.u
 * I remember grinding through this as an undergrad, I really can't see a situation where it's going to fit into Wikipedia's Introduction to quantum mechanics article! Djr32 (talk) 09:07, 26 March 2014 (UTC)


 * I was thinking of something like this: http://hyperphysics.phy-astr.gsu.edu/Hbase/hyde.html#c4 But I guess it perhaps ought to be regarded as a steppingstone along the way. The values are close, but not, I think, exact. P0M (talk) 19:23, 26 March 2014 (UTC)


 * P0M, that's far too complicated for this introductory article. A number of people have said on this page they don't want any math at all. -- Chetvorno TALK 19:45, 26 March 2014 (UTC)


 * Ah, OK, that's not what you asked for above - it's not "the math that leads to the structure of the hydrogen atom and its orbitals", it's just a statement of what the result is. (In fact it's as accurate as the wavefunction I posted above, it's the corresponding energy levels. They're the eigenstates and eigenvalues of the Schrodinger equation (i.e. no relativistic effects, reduced mass, fine structure, Lamb shift, hyperfine structure...), but I digress!)  I think that stating that QM predicts the energy levels of hydrogen in terms of fundamental constants is an interesting and relevant fact. (It's also identical to the Bohr model result - in fact, I note that hyperphysics also takes the approach of working through the Bohr model first...) Djr32 (talk) 21:00, 26 March 2014 (UTC)


 * In one place I've tried hiding the math behind a fig leaf for those whom the numbers and symbols would frighten. Feel free to revert. I just wanted to see how it would look.P0M (talk) 00:40, 27 March 2014 (UTC)


 * The addition of info to the bit above the collapsed part works well. I would like to put the sentence you've commented out at the end because I want to alert readers to the fact that the expansion of the quantum picture of nature will continue (on one path at least) from this point.P0M (talk) 22:32, 27 March 2014 (UTC)


 * I've made a few changes, and hopefully this now does what you suggest, though in a slightly different way. Firstly I got rid of the subsection heading - I thought that it wasn't a good idea to split a section that's only 4 paragraphs long into a main section and subsection - so now the "to be continued" part is in the last sentence of the whole section, and also at the end of the collapsed box.  I also made sure that we introduced the issue of different intensities earlier on - previously we hadn't mentioned them before we said that various models had failed to predict them, which read a bit odd.  What do you think?


 * Your changes all look very good to me. P0M (talk) 00:57, 29 March 2014 (UTC)


 * A separate question: Now that we have collapsed text for more mathematical content, should we put the more mathematical description of the Bohr model that you removed last year back? Djr32 (talk) 22:25, 28 March 2014 (UTC)

I think that can be done. However, I'd like to make the thinking behind the derivation clearer to those who may come to the discussion with little prior background. Could we say something like this for the first part?

Louis de Broglie suggested that an electron might exist as a standing wave in the orbit that it takes around the nucleus of an atom. If that is the case, then the circumference of the orbit would either equal the wavelength or be an exact multiple of the wavelength of the electron.

Since this discussion aims at the Bohr radius, the above relationship will be expressed as:

nλ = 2πr

Louis de Broglie provides the equation to calculate the momentum of an electron with a certain wavelength:

λ = h/mv

or

nλ = nh/mv (in the case that two or more waves fit perfectly into one orbit)

It follows that 2πr = nh/mv

or

mvr = nh/2π

I'd like to make it clear that Bohr didn't just take a wild stab at something emerging from the depths of his unconscious. P0M (talk) 05:39, 29 March 2014 (UTC)


 * No, I don't think that's a good idea. The Bohr model was from 1913, de Broglie came along a decade later - basically de Broglie started the move from the Bohr model to the modern QM model of the atom (as is already discussed in the "Application to the Bohr model" and "Development of modern quantum mechanics" sections).  Bohr's argument for why angular momentum should be quantised is complicated and doesn't match very well with modern QM understanding - to me it's the sort of historical stuff that we have rightly been encouraged not to put in this article.  Djr32 (talk) 10:56, 29 March 2014 (UTC)


 * Yikes. I've become an anachronist! That's not a good idea. P0M (talk) 16:49, 29 March 2014 (UTC)

Part 2

 * Sure. I think a little math is necessary, but this introductory article certainly shouldn't include anything as complicated as differential equations. That's my point about complicated examples like the black body spectrum.  I don't mind the article mentioning the black-body example, the changing colors of hot objects, in a simplistic way to illustrate the Planck equation; the energy of a photon is proportional to its frequency and hotter objects radiate more energetic photons.  I just don't want the article to use it as QM texts use it, as it was used historically, as evidence for quantized energy levels in atoms; that requires difficult math to see the connection.


 * The reason intro QM texts include the black-body example or Schro's eq for the H atom is not because it is an easy example but because they have to cover the history of QM. But we have History of quantum mechanics and Timeline of quantum mechanics to do that.  This article does not have to take a historical approach, and to do so is kind of redundant, given those other articles.  Djr32, my idea for the article is something like a simple version of Feynman's Lectures, Vol. 3.  In the preface Feynman explains why the historical approach is the wrong way to introduce QM: it requires taking the most complicated examples first: black-body radiation and Schrodinger's equation applied to the atom.  Instead, in his course Feynman did not start from classical physics, but used simple examples to describe how quantum objects act, starting with individual particles in space.  I'd like to see a rewrite take that direction. -- Chetvorno TALK 10:49, 26 March 2014 (UTC)


 * I don't think that's the case - they don't have to cover history at all, they talk about the hydrogen atom because "QM explains all of chemistry" is a really important result. Fair enough that Feynmann takes a different approach, but a lot of QM textbooks do take the historical approach (apparently including Quantum physics for dummies) and they do so because their authors believe that it's the best approach to teaching the subject.  The problem in the other direction is that 1D particle in a box is a good starting point if your goal is to work through the maths, but it's a bit of a stretch to relate it to the real world. Djr32 (talk) 23:06, 26 March 2014 (UTC)
 * Every time I come back to this article I get jazzed up about at how well it is written. I agree that this article does not need a major rewrite. Also, this article is not overly concerned with the history of QM. Instead, the article communicates the basics of quantum mechanics, starting with fundamental ideas - such as quantization. Additionally, it is not designed to teach why this or why that. Wikipedia is not meant to be a teaching tool, it is not a textbook. Rather it is meant to be an Encyclopedia, a reference work. Hence, the article means to say this is what the concept or idea is - with links to other articles for further explanation. Also, in this instance the idea is keep things as simple as possible - because it is an introductory article.


 * Also, by convention and guideline, Wikipedia is edited according to consensus of mainstream sources. Consequently, it appears that most mainstream sources communicate (or teach) QM in a format similar to this article.


 * Additionally, Feynman's lectures were cited earlier. Even in Volume 1, Feynman explicitly overviews what physics was like before 1920. And in the previously mentioned preface in volume 3, it is clear that this was an experimental and innovative method of teaching physics. There were no constraints on mentioning concepts before a certain stage of the course. Feynman was throwing things into earlier lectures that would be fleshed out in later lectures. In this way he could relate more advanced concepts to earlier concepts.


 * Also, I believe one of his themes throughout the course - is that he is teaching approximations which lend themselves to corrections as the course progresses. So his style in these lectures is different from course textbooks. It is a unique case, and does not seem to mean that we should rewrite the whole article based on Feynman's innovation. And, this is the same preface as Volume 1, which is simply entitled "Feynman's Preface".


 * Finally, I am not seeing where Feyman's Volume 3 says "explains why the historical approach is the wrong way to introduce QM". I cannot see where he makes the history of QM an issue at all. Can you provide a link to where he says this? Thanks.


 * It appears to me that he references historical examples throughout the course. On this page, (Vol III) he mentions Newton; and an issue resolved in 1926, 1927 by Schrödinger, Heisenberg, and Born. --- Steve Quinn (talk) 04:33, 28 March 2014 (UTC)


 * "...The usual way of dealing with quantum mechanics makes that subject almost unavailable for the great majority of students because they have to take so long to learn it. Yet in its real applications - especially in its more complex applications, such as in electrical engineering and chemistry - the full machinery of the differential equation approach is not actually used. So I tried to describe the principles of quantum mechanics in a way which wouldn't require that one first know the mechanics of partial differential equations." - Feynman, Vol. 3 preface


 * This is referring to the organization of Vol. 3, not the whole series. What he's talking about is starting with Schro's equation applied to the atom, which historically was one of the first applications, which was the course taken by many of the QM texts of the time, as well as this article.   I'm not suggesting leaving out the application of QM to the atom and chemistry, just leaving it to the end of the article, as Feynman does in Vol. 3. -- Chetvorno TALK 17:18, 28 March 2014 (UTC)


 * Regardless, I'm just saying this article could devote more space to its subject - introducing quantum concepts - by devoting less space to historical aspects and obsolete theories like the Bohr theory.  There are many additional elementary concepts which should be covered: what a wavefunction is, quantum vs. classical randomness,  intro. to bra-ket notation, spin and polarization, the difference between Fermi and Bose particles, quantization of energy, more.   I think this article's purpose should be to give introductory readers the conceptual tools to understand other articles on quantum mechanics, not be a historical overview.  However I agree the existing content is very well-written, and should become the new History of quantum mechanics article, since it is better than the existing article. -- Chetvorno <i style="color:purple; font-size:smaller;">TALK</i> 16:36, 28 March 2014 (UTC)


 * It seems the consensus does not support my view of what the article should be, so I'll stop pushing the issue. Just want to make clear that my criticisms were only with the article's conceptual organization; for what it is the article is clear, well-thought-out, well-organized, and presents the material well.   Whoever worked on it, congratulations and thanks.  I'm glad to see that with all the smart people that seem to devote their attention to the advanced QM articles, there are some of us who care about the introductory ones.   -- Chetvorno <i style="color:purple; font-size:smaller;">TALK</i> 17:18, 28 March 2014 (UTC)

I'm curious to know how you would introduce wavefunctions, quantum/classical randomness, bra-ket notation, etc. without getting into more than the little bit of math (never going beyond secondary school algebra) that you cite above as a reason for rewriting this article. I would like a clear explanation of some of these things, too, but I don't see how to do it without a high degree of abstraction.

I favor giving a fair representation of quantum mechanics as an abstract system that can be treated of in English by means of one or another interpretation, but there seems to be a number of people who reject the abstract or the theoretical in favor of "no math" and (presumably) narratives about weird phenomena. (I just read a treatment of some quantum mechanical ideas in the latest Analog Science Fiction and Fact, and I think the physicist author went too far in the direction of describing results that appear to be paradoxical. He was good to us readers because he used no math and entertained us with ways that might explain psi(chic) phenomena.)

What is the proper relationship (as regards conveying useful information) between what people can see in the real world (in a lab if necessary) and what they can gain from abstract laws and equations? P0M (talk) 18:24, 28 March 2014 (UTC)

Spin
User:Patrick0Moran asked in a html comment "Is there anything more about spin that should be said here?"

Yes! The fact that it's something we can actually measure, i.e. the Stern–Gerlach experiment.

Which then leads nicely on to what the consequences of the Stern–Gerlach experiment are. And they're vital: that QM is probabilistic, that measurement affects the thing being measured (wave function collapse), etc. Right now we don't explain any of this, though the section on entanglement relies on all of these concepts. Djr32 (talk) 22:23, 1 April 2014 (UTC)


 * I think the article on the Stern-Gerlach experiment is already about as suitable to an introduction as it needs to be. The thing that we may need to concentrate more on is the idea of something being quantized. If we can clearly explain that idea then we can fan out to cover polarization, spin, etc. as instances of phenomena involving quantization. We could then refer to the main experimental observations with their quantum characteristics, and give links to the main articles.P0M (talk) 21:31, 2 April 2014 (UTC)


 * OK, so maybe we could add a "Spin" section between "Wave–particle duality" and "Development of modern quantum mechanics"? As you say, we could take some material from the Stern–Gerlach experiment article, though I think the focus here needs to be on the fundamental QM concepts that it illustrates, rather than on the experimental details. Djr32 (talk) 14:03, 5 April 2014 (UTC)

I've just wikilinked quantum state and exclusion principle in the Spin section, but these terms are just thrown in without explanation, so it talks over the target reader's head. Could somebody in the know make that part of the intro go a bit slower, please? Thanks everyone for a very helpful article. --Stfg (talk) 11:27, 16 April 2015 (UTC)

Quantisation
Before we do anything special on spin, which is pretty hard to understand because it is a kind of analogy to macro-world spin, I think we need to set things up by discussing quantisation.

Quantisation is something that is so pervasive that it fades out of the discussion and into the background in most writing on quantum mechanics. When it is discussed by people who do not come with a clear understanding of fundamentals, they may believe that frequencies can't have fractional values or that a wavelength that is some fraction, e.g., 1/3, of some known wavelength is impossible in nature. It is important to introduce the idea that the physical process determines how much energy is absorbed or freed in one event, e.g., the fall of an electron in a hydrogen atom from a higher orbital to a lower orbital, that sets both the frequency of the photon involved, its wavelength, and its energy. The early researchers were dealing with hydrogen lamps in a single intertial frame, and they may have unintentionally implied that anybody measuring the energies of the visible hydrogen spectrum would get the same results (even if they happen to be in a spaceship approaching earth at some substantial fraction of c).

To go from that kind of quantisation to the kind that is involved in spin or polarization is going to be difficult. I am not sure yet of how (or whether) to say anything more about it than that it happens — it's either spinning this way or that way, with nothing in between.

When I read one of Einstein's books intended for the general public while in high school I was quite impressed with the way he would set the reader up with all the information needed to anticipate the conclusion he was going to announce. He was like a writer of a detective novel who wrote so that the readers would always figure out who did it before the detective announced why he was arresting somebody. If we can supply beginning readers (i.e., readers who do not already know what the answer is) with an adequate understanding, then we can forestall their going off in some wild direction and getting themselves thoroughly confused. Einstein seemed never to throw out false leads. (Maybe he just had a good editor, but I doubt it.)

I must attend to grass mowing to forestall problems with city government, so I'll have to come back to the problem a little later. P0M (talk) 17:51, 6 April 2014 (UTC)


 * Don't we already discuss quantisation? Quantisation of energy emitted in thermal radiation, light being quantised as an explanation for the photoelectric effect, quantised energy levels in the atomic models... I can think of a really nice demonstration of something else that's quantised, it's called the Stern–Gerlach experiment...  (Thinking about it further, I don't really want to talk about spin at this stage, more about the things I mentioned above, i.e. QM being probabilisitic, the effect of measurement, etc.  Exactly what it is that is quantised is difficult to explain, and I agree with you that probably best to just state that it happens.) Djr32 (talk) 21:58, 6 April 2014 (UTC)

I think there must be an energy quantum connected to angular momentum. Spin and counter-spin would then be numerically positive and negative (in the same sense that if motion toward the east is calculated on the x axis from an arbitrary 0 point to or toward a positive value, then motion to the west is "negative"). P0M (talk) 20:35, 6 April 2014 (UTC)


 * There is a quantum number connected to angular momentum, and also one connected to spin. As you say, the different quantised values can be labelled as +ve and -ve, for example see the Pauling quote in the article.  It is not "an energy quantum".  Djr32 (talk) 21:58, 6 April 2014 (UTC)

Overview Too Long
For brevity and quick reference by the average reader, maybe condense the opening overview.--Lucas559 (talk) 17:32, 20 June 2015 (UTC)

copyright issue. copy and pasted from the web
user: 183.83.151.17 https://en.wikipedia.org/w/index.php?title=Introduction_to_quantum_mechanics&diff=667204247&oldid=666392559 Please paraphrase this edit.--Lucas559 (talk) 17:36, 20 June 2015 (UTC)
 * This content was removed. RockMagnetist(talk) 23:36, 25 October 2015 (UTC)

Postulates of Quantum Mechanics?
This article doesn't seem to go into the postulates of quantum mechanics (aside from a brief discussion about eigenstates without really explaining what eigenstates are). I don't think it would be too difficult to explain the postulates of QM in a beginner-friendly way, and not explaining the postulates would mean that readers don't get to learn about the heart of the theory. Plus, the point where students grasp the postulates of QM is usually the point where QM finally "clicks" with them and they realize how simple it is, so if the postulates could be explained, then this article might be a lot less confusing to beginners.

So are the postulates of QM beyond the scope of this article, or is it okay if I (or others) include an explanation of the postulates? --J00cy (talk) 09:41, 25 October 2015 (UTC)

Intent to add and the immediately remove an image of horses.
Horses are gone, but preserved in the history page. FYI, some of us are trying to start a wiki Journal that selects quality articles and preserves them so that teachers may confidentally use the approved version. See First Journal of Science.--Guy vandegrift (talk) 03:47, 11 January 2016 (UTC)

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Duplicate interaction
The diagrams showed that the electromagnetic force is the interaction of photons between interacting particles.

If the particles are only interacting because of the photons, this expression is confusingly redundant, is it not?

Would amending this to read 'exchanged between' add clarity, or subtract accuracy? If the later, that could be explained somehow, probably making the sentiment a lot more clear to nonspecialists along the way. &mdash; MaxEnt 17:32, 16 October 2018 (UTC)

Do you mean to replace the first or second segment? The correct sentence should be "The diagrams showed that the electromagnetic force is the exchange of photons between interacting particles, I have fixed it. IntegralPython (talk) 21:50, 16 October 2018 (UTC)

Schrödinger's equation
There should be slightly more detail about exactly what Schrödinger's equation says. A reader should be able to roughly imagine what the evolution described by the equation looks like. I'm not necessarily looking to provide a perfect understanding of the equation, but the page is more vague than it should be Ramzuiv (talk) 00:52, 4 November 2019 (UTC)

Problems with introduction
The introduction is way too long; it should be no more than 4 paragraphs (MOS:LEADLENGTH). The elementary explanation is good, but my feeling is that some of the more peripheral topics like superfluidity and Ehrenfest’s theorem could be moved to the body. --Chetvorno<i style="color: Purple;">TALK</i> 18:08, 5 August 2022 (UTC)


 * Agreed. This is supposed to be an introductory article, and the lead, in particular, should concentrate on the basics. MichaelMaggs (talk) 22:07, 5 August 2022 (UTC)
 * My specific proposals:
 * 1) Remove from the first paragraph: "This article describes.." through to the end of that paragraph. The historical content in the article can be grouped, making this material redundant with structure.
 * 2) Move the entire paragraph "Light behaves in some aspects ..." to Applications
 * 3) Remove the Ehrenfest content to a new section on connections to classical physics.
 * I'll move forward until someone yells. Johnjbarton (talk) 02:19, 28 June 2023 (UTC)
 * Ok down to two paragraphs. Lots of reorg. The Einstein material is still duplicated and the photon section is dubious, but the major character of the article is, IMO, in better shape.
 * Please check.
 * Johnjbarton (talk) 17:25, 28 June 2023 (UTC)

Wave-particle duality section border-line incorrect :-(
The movie with the bouncy sound track is both incorrect and inconsistent. The first example, BBs through holes has a weird distribution: it should be sharp shadows of the slit, particles cant get around them. That's the point. The last example, observer, should identical to a single slit wave case, not the uniform dots shown. The simulated electron wave packets are dubious.

The single/double slit image is simply wave interference, no duality shown. Johnjbarton (talk) 16:59, 29 June 2023 (UTC)

Ehrenfest's theorem
Copying conversation from my talk page, as it seems best to continue here:

"Hi MichaelMaggs I am a little confused by your comments concerning Ehrenfest's theorem and quantum mechanics, could you elaborate on why you believe it doesn't cure apparent quantum-classical paradoxes?


 * --Best Bosonichadron2 — Preceding undated comment added 20:58, 3 August 2022 (UTC)


 * It's not correct to say that "Many of these paradoxes can be cured", as that implies that QM is wrong in some way. Most of the so-called 'paradoxes' are in truth things that appear from a day-to-day perspective simply weird. We should be explaining to beginner readers that such weirdnesses are unavoidable and are real, no matter how counterintuitive they may at first appear. They are not things that can be explained away by Ehrenfest or any amount of classical analysis. If there are particular and specific examples of beginner missapprehensions that Ehrenfest's theorem can help dispel, by all means let's include them. But we do need a specific reliable source for that, not just a statement to that effect. MichaelMaggs (talk) 10:02, 4 August 2022 (UTC)
 * I respectfully disagree with your first sentence, because if we take the definition of paradox as Webster defines it (using 2a) and replace it in the sentence that I wrote originally:
 * "Many of these paradoxes can be cured using Ehrenfest's theorem, which shows that the average values obtained from quantum mechanics (e.g. position and momentum) obey classical laws."
 * with the definition paradox:
 * Many of these statements that seem contradictory can be cured using Ehrenfest's theorem, which shows that the average values obtained from quantum mechanics (e.g. position and momentum) obey classical laws.
 * The above sentence certainly does not make a value judgement on the correctness either of the two classical or quantum "statements" it simply says that there are apparent contradictions.  But then goes on to say that many of them are not contradictions at all, because of Ehrenfest's theorem.
 * With paradoxes like
 * "How is it that Newton's laws are wrong at the atomic scale, but then perfectly correct when dealing with systems which are simply large collections of atoms?"
 * easily being cured by Ehrenfest's theorem. These questions being the most natural, obvious and fundamental a student might bring up, mention of Ehrenfest's Thm is extremely helpful if not absolutely necessary.  As to the point of citations, the entire purpose of Ehrenfest's Thm is to answer questions/paradoxes like the above and therefore satisfy the correspondence principle.  I could add a citation, but it would just be a copy of the citations which are already present in the main article on Ehrenfest's Theorem, which I linked to and is well-written, so I believe a citation would be inappropriate for that reason.
 * What are your thoughts? Bosonichadron2 (talk) 16:41, 4 August 2022 (UTC)

MichaelMaggs (talk) 12:02, 5 August 2022 (UTC)
 * The third paragraph, with Feynman's quote, is all that needs to be said in the lead. Ehrenfest's theorem is far too subtle and sophisticated to be included in the lead of this beginner's article. No beginner following that link would be able to glean anything useful from even the first sentence of the Ehrenfest's theorem lead. More useful to a beginner would be a non-technical explanation of the Correspondence principle, which is referred to lower down, but is not developed.


 * The assertion that Ehrenfest's theorem (which is technically quite specific) "cures statements that seem contradictory" seems far too broad, and a reliable source for the exact wording to be used really is essential if it is to be mentioned. The E th article discusses nothing about apparent or real contradictions, let alone that the theorem can be considered a 'cure'. Few if any physicists would maintain that contradictions can be cured without (at the very least) a solution to the measurement problem. MichaelMaggs (talk) 12:02, 5 August 2022 (UTC)
 * @MichaelMaggs
 * " The assertion that Ehrenfest's theorem (which is technically quite specific) "cures statements that seem contradictory" seems far too broad, and a reliable source for the exact wording to be used really is essential if it is to be mentioned. The E th article discusses nothing about apparent or real contradictions, let alone that the theorem can be considered a 'cure'.  "
 * After reading the article again, I think this is a good point, I'll find a citation.
 * Is the word "beginner" defined anywhere? Bosonichadron2 (talk) 12:21, 5 August 2022 (UTC)
 * These "Introduction to..." articles are supposed to provide a non-technical overview of a subject for non-specialists, but with repeated edits there is a tendency for them to become more and more complex. Rather than "beginner" it would perhaps have been better to refer to the "non-specialist" or "non-physicist" reader. MichaelMaggs (talk) 12:39, 5 August 2022 (UTC)
 * Yes, "beginner" should not be used of someone with roughly a high school education who is curious about quantum mechanics and some of its specific topics. "Newcomer" also seems a bit judgmental. The legal definition "reasonable person" doesn't feel right. Is there such a thing as an "average person"? That would be my choice. Otherwise, I am fine with "non-physicist", except that many non-physicists may be fine with mathematics. In QM, as I've said, the truth can only be expressed fully in mathematics--that is the way that Nature actually works at the atomic scale; but WP articles ought not to include any mathematics in their lead or first few paragraphs, so as not to be off-putting. David Spector (talk) 15:40, 8 July 2023 (UTC)
 * Both mathematics and "Ehrenfest's theorem" are forms of jargon: specialized vocabulary expressing complex ideas quickly to those trained in the subject. To be successful an "introduction" needs to focus on those un-trained in the subject but nevertheless interested. For a complex fundamental topic like QM, I would expect 'interest' to grow out of a curiosity and thus exposure to scientific and technical ideas. We shouldn't have to explain "atoms" or "electrons" as general concepts for example, but neither should we expect such a reader to be excited about the constants in Planck's blackbody radiation formula. Johnjbarton (talk) 15:55, 8 July 2023 (UTC)

The theory of relativity?
The lead paragraph mentions the theory of relativity. The word relativity is ambiguous and this paragraph suggests that there is only one such theory. There are at least two such theories: special relativity, which deals with causation and the constancy of the speed of light in a vacuum as measured in any inertial frame of reference (a frame of reference that is not being accelerated by any force), and general relativity, which deals with the physics of acceleration, especially that caused by gravity. The subject matter of these two theories is clearly, from these brief definitions, quite different. The equations that embody these two theories are different. In fact, the time differences caused by these two theories, which must be corrected by the Global Positioning System for it to function with adequate accuracy, are of different magnitudes. David Spector (talk) 22:09, 10 July 2023 (UTC)


 * @David spector I would support removing mention of relatively altogether in the lead. Johnjbarton (talk) 22:27, 10 July 2023 (UTC)
 * I see references in papers and on the Web often to "relativity" and it really annoys me, because I can't always tell which theory is being referenced. The relationship between QM and these two theories is important, yet not fully understood in physics today. David Spector (talk) 22:45, 10 July 2023 (UTC)
 * The ambiguous mention of “the theory of relativity” in the lead of this article on quantum mechanics is minor, perhaps even trivial. In the lead it is blue linked to the Wikipedia article, and the title of that article includes the singular “theory”. The article then proceeds to resolve the ambiguity and explain the subject.
 * If Wikipedia has a problem on this matter, that problem is embedded in the article on the theory of relativity, and that is where it should be fixed. The lead to this article on quantum mechanics appears fine to me. <i style="color: green;">Dolphin</i> ( t ) 00:09, 11 July 2023 (UTC)
 * Independent of the importance of relativity to QM the topic does not belong in the introduction to the Introduction unless the subject dominates the article, which it does not. This article is about one revolution and has enough to do on that topic. So I boldly fixed this. Please check. Johnjbarton (talk) 00:45, 11 July 2023 (UTC)
 * I'm glad it's gone, thanks. David Spector (talk) 01:07, 11 July 2023 (UTC)

Merge history -> History of quantum mechanics
Currently history takes more than 50% of this article; the history outweighs the article is supposedly summarizes.

To correct this imbalance and make room for new content here, I propose to merge the history with the main page. Then we can summarize the historical context for each concept selected for the introduction, linking the corresponding discussion in History of quantum mechanics.

I believe this will make both articles stronger. Johnjbarton (talk) 14:09, 7 July 2023 (UTC)
 * First of all, following the history of QM is how one is introduced to QM, at least in that article. It is not about redundancy, the history has a purpose. It is not simply extra content weighing down the article, Deleting the history in Intro to QM may be detrimental to that article. If you want to do some summarizing then that might best be suited for the History of QM article. If you want to do some copy editing in the Intro to QM that is fine. Steve Quinn (talk) 15:25, 8 July 2023 (UTC)
 * I agree that history is one path to learn QM, but only one and it has its pluses and minuses. Fortunately we don't have to choose: we can have both a history and a non-historical introduction. That is what we have been considering.  Specifically we are proposing an almost non-mathematical introduction.
 * Before my merge, the History page was weak. It lacked adequate material, was disorganized, and had some small amount of incorrect material. By pulling from the Introduction the new page is (in my opinion) dramatically improved.
 * This page, the Introduction, had a large amount of history (over half the content) providing no real hint of "introducing" QM. The material was not selected nor presented to introduce QM but rather was focused on encyclopedic history. That is, it was perfect for the History page!
 * Despite that approach, the Introduction page had numerous links claiming that the Main page was the History page. It claimed that the Introduction content was a summary. Now that we have a stronger History page, this Introduction page can legitimately summarize the History page.  That would be the next step for the Introduction.
 * If you are interested in the History of QM I encourage you to help us improve the History of quantum mechanics page. It's a bit scruffy and certainly could use more content.
 * I hope this clarifies my point of view and I hope it also reflects, at least approximately, the views of @David spector and @XOR'easter. Johnjbarton (talk) 15:24, 8 July 2023 (UTC)
 * Well, it could be that editors have added extraneous 'history' content over time. I haven't looked at this article in awhile. It sounds like you have a good plan. I didn't notice that this page claimed to summarize the main History page. I'll have a look at the History of QM page. I would like input from the other editors that you pinged and hear their take on the matter. ---Steve Quinn (talk) 15:50, 8 July 2023 (UTC)
 * I haven't looked at the history issue due to lack of time. I agree that following the historical development of QM is an excellent way to learn about QM, but definitely roundabout, especially as QM history is littered with mistakes, such as a demand for local realism or the belief that atomic energy states are quantized because only so many waves can fit on a string that is constrained not to move at both ends, or the belief that hidden variables can explain everything without invoking nonlocality.
 * Because of such mistakes, because of the eternal misunderstanding of Feynman's remark, and because it is indirect, I would mildly oppose including much history outside of the main History of QM article. Let's just directly describe QM, okay? And let's definitely try to avoid too much talk about the mysterious named terms (axioms) that got codified around 1927 and haven't budged much since.
 * David Spector (talk) 16:03, 8 July 2023 (UTC)
 * Thanks very much for your responses. Your arguments are very convincing. So, keep up the good work. And all of you are doing a great job. This was probably a change that needed to happen awhile ago. I don't have a problem with any of this. ---Steve Quinn (talk) 21:25, 8 July 2023 (UTC)


 * Support the merger. In its current state this article mainly just reprises History of quantum mechanics.  In general, I agree with David Spector that a minimum of history should be included here.  We desperately need a real introduction to QM.  I think there should be a simple section on the math - wavefunctions, bra-ket notation, Born rule, etc.  As Feynman pointed out in his Lectures, the elementary math of QM is not difficult. --Chetvorno<i style="color: Purple;">TALK</i> 22:00, 8 July 2023 (UTC)
 * Please see Talk:Introduction_to_quantum_mechanics below; my replacement for the history in this Introduction article is ready for review. The only major question outstanding is whether to shrink the blackbody discussion to a sentence. Johnjbarton (talk) 02:34, 14 July 2023 (UTC)

Why are uncertainty principle, eigenstates, and Pauli exclusion under Copenhagen?
While historically these things emerged before alternative interpretations (except de Broglie/Bohm I guess), no modern treatment would make such an outline. Johnjbarton (talk) 02:28, 28 June 2023 (UTC)


 * I massively reorganized the article outline and added a few small sections to keep the flow.
 * Please check.
 * Johnjbarton (talk) 17:26, 28 June 2023 (UTC)
 * I don't think any of these aspects are part of the Copenhagen interpretation. They are part of QM. The purpose of QM is to predict the behavior of nature in very tiny scale. QM does this successfully, to high precision. However, QM doesn't include ontology, the explanation of how nature actually works. That is the domain of interpretations. For example, Many Worlds is a very explanatory conjecture due to Hugh Everett that can never be proved (it is not falsifiable), since it requires the existence of infinite universes, only one of which we can ever experience.
 * However, the interpretation of David Bohm actually does make a prediction that was verified by experiment, (it was that particle paths are deterministic, which is counter to the Copenhagen belief), so it is scientific. Certain other parts of Bohm's later "implicate/enfolded order" conjectures are unlikely to be falsifiable. Admittedly, these are all fine points, but truth is truth. David Spector (talk) 16:45, 13 August 2023 (UTC)

Draft replacement for History section ready for review
I am proposing a shorter, more focused history section for this Introduction. Personally I would be ok with no history but I know others want one and I think we should focus our energy on getting a good Introduction rather than debating whether history is part of it.

My draft aims for these goals: I anticipate we will use the photoelectric effect, photo-absorption, and Stern-Gerlach in the new Introduction, but not blackbody. Nevertheless I don't think we can have a history without blackbody. Thus I put a bit more text in to blackbody radiation to satisfy the "intro" requirement.
 * no math, intro level.
 * short, beyond summary short.
 * accurate.
 * cover only phenomena likely to be discussed in Introduction.
 * emphasize "quantum/quanta" not particle-wave.

I left 'photon' to the end for accuracy and for 'quanta'.

DRAFT: User:Johnjbarton/sandbox/introduction_to_quantum_mechanics

Please review this draft only for "scope" or similar overall-ness. If it seems like we are likely to agree on the character of a replacement, I will add sufficient references and ask for a second detailed review. Johnjbarton (talk) 18:52, 11 July 2023 (UTC)


 * John, I'm not following at all why black-body radiation should be in a summary or an introduction to QM, historical or not. The classical Maxwell–Boltzmann distribution of particle velocities does a fine job of explaining temperature. The leap from that to describing the distribution of black-body radiation involves using a model of bound harmonic oscillators and thus mathematics to a great extent. I don't see the value of including it in a summary or an introduction, especially if mathematics is not to be included. I do agree with the first concept being the photoelectric effect, although the Millikan/Fletcher oil drop experiment showed quantization as the number of free electrons on the surface of each droplet, without any of the further strangeness of QM, in around 1900. I would leave out black-body radiation from any readable introduction to QM. David Spector (talk) 19:39, 11 July 2023 (UTC)
 * All QM histories I have read start with Planck. I believe this is because the main participants of the day viewed Planck's blackbody paper as the key starter event. Planck -- a deeply old-school physicist -- was "forced" in to using quanta by the experimental data, much the way the rest of QM unfolded. Einstein's paper photoelectric effect paper was primarily aimed at Planck's blackbody work. The statistical analysis was used again and again esp. by Einstein (eg Bose-Einstein statistics).
 * However I am not against removing the text I wrote, condensing it to a single sentence.
 * (The Millikan/Fletcher oil drop experiment was completed in 1909.) Johnjbarton (talk) 23:04, 11 July 2023 (UTC)
 * I'm looking forward to seeing your draft, thanks. David Spector (talk) David Spector (talk) 19:41, 11 July 2023 (UTC)
 * I put the link above, thanks. Johnjbarton (talk) 23:04, 11 July 2023 (UTC)
 * I have replaced the two history sections with my draft. Please review the new page content.
 * Johnjbarton (talk) 16:51, 16 July 2023 (UTC)

References on teaching QM
There are a quite a number of educational studies and surveys targeting better QM instruction for non-expert students. For example there are even meta-reviews.

I think reading through these and applying their insights would be helpful.

I wonder: should we create a "Teaching Quantum Mechanics" page that summarizes these articles and some of the key findings? Johnjbarton (talk) 15:09, 12 July 2023 (UTC)


 * I'm sure some WP editors would reply that an article on good teaching methodology for topic X is off-topic for any article about X, but I disagree. Since so many have difficulty learning QM from scratch (which is clear from the comments on QM articles on YouTube), an article discussing how to teach/how to learn QM would be an excellent idea. It could summarize how QM popularizers like Don Lincoln teach QM. There could be a number of steps in which the experimental evidence is reviewed (including descriptions of the lab equipment used), followed by steps for learning the basic mathematics needed to understand the theory, followed by the ontology, the general way in which Nature works in tiny scales. I would, please, leave out the historical development, since the order in which concepts were discovered is likely not the best order in which to learn about QM. David Spector (talk) 16:06, 12 July 2023 (UTC)
 * I was thinking of a completely separate page, to avoid the off-topic/meta discussion issues.
 * I cooked up a page that provides some links to review of educators doing studies:
 * User:Johnjbarton/sandbox/teaching_quantum_mechanics
 * I'm pretty sure this is not what you are thinking but I think it's a start. Refs to secondary articles and everything ;-)
 * I already got many ideas from these reviews. I'm inclined to create it as a real page. Feedback? Johnjbarton (talk) 01:45, 13 July 2023 (UTC)
 * Wonderful! Your new article should be helpful for those new to QM. Don't forget to put some back links to it in good places in other articles.
 * I know I've found several interesting ways to learn QM over the years, different from each other, that at least helped my intuition about tiny physics. My memory is not good: there was an approach (from a public MIT course?) starting with a light source and three plane-polarizing filters, that eventually reached an explanation of the Pauli functions of QM, there were several different approaches to proving Bell's Theorem, that shows how unnatural Einstein's intuition about locality was, there was Don Lincoln's course (for "The Great Courses/Wondrium") that used mostly a simplified model of the Mach–Zehnder interferometer to describe basic QM effects involving beams of light, there are the various presentations in videos and in papers/books of David Bohm's deterministic interpretation of the double slit and Stern-Gerlach/spin experiments, and there were several different approaches to reasoning with matrices and operators that were perhaps more important than all the others. David Spector (talk) 11:13, 13 July 2023 (UTC)
 * I've proposed to put my draft up as a page: Wikipedia_talk:WikiProject_Physics
 * Follow up there, one way or another.
 * Johnjbarton (talk) 16:54, 16 July 2023 (UTC)

The Uncertainty Principle is not Part of Quantum Mechanics
I'm not sure why so many physicists have stated that Heisenberg's Uncertainty Principle (HUP) is a basic part of the strangeness of QM. It is not any such thing.

I would ask them, is the equivalent inverse precision principle due to Joseph Fourier (and others) between the amplitude and the frequency of an audio or electromagnetic signal also part of QM? Or can you physicists out there finally admit that the inverse precision of measurement of complementary variables is entirely due to the interdependence of the two variables, one of which is the derivative or the Fourier transform of the other?

The HUP is usually expressed as $$ \sigma_{x}\sigma_{p} \geq \frac{\hbar}{2} $$. But this scales up without difficulty to the classical regime, in which complementary pairs of variables are not treated as a mystery, merely as the natural result of measurement: it takes one measurement in time to fix the position of a particle, but many such measurements in time reduces the accuracy. Inversely, it takes many measurements in time to measure velocity accurately, but measuring only once reduces the accuracy. David Spector (talk) 16:22, 13 July 2023 (UTC)


 * I think considerations like this might fit on Uncertainty principle but I don't think we should get into Fourier analysis on this page. Fourier analysis applies to other waves than quantum probability amplitude, so yes if you accept matter waves then uncertainty principle is not additional information. However, it is a consequence and not something you expect if you are, well, unsure about matter waves. Johnjbarton (talk) 17:06, 13 July 2023 (UTC)
 * You're right in the sense that the uncertainty principle is inherent in the properties of all wave-like systems. But it is an important aspect of QM (and is almost always taught as such) due to the matter wave nature of all quantum objects. What learners find 'weird' is that the Principle applies to things they'd always thought of as particles, not waves. So of course it is important to discuss it on this page. MichaelMaggs (talk) 17:22, 13 July 2023 (UTC)
 * @MichaelMaggs oh uncertainty yes, Fourier no. Johnjbarton (talk) 18:16, 13 July 2023 (UTC)
 * Absolutely. Agreed. MichaelMaggs (talk) 19:34, 13 July 2023 (UTC)

Matter waves really exist, but have nothing specifically to do with the HUP. Also, matter waves are not a complete description of matter. While position and momentum are included, mass is not. Gravity is not yet a part of QM, and it would be misleading to imply otherwise. Since matter waves are not yet complete (they do not account for mass/gravity), and since they are not a justification for HUP, they are irrelevant to the discussion of HUP.

These objections by John and Michael do not address the points I actually made. Nor do their points justify the continued inclusion of the HUP in this Introduction article. David Spector (talk) 17:57, 16 July 2023 (UTC)


 * It would be perverse not to discuss the uncertainty principle in an introductory page on QM. I can't see any statement on the page that misleadingly implies that gravity is part of QM, but I don't see that that has much relevance to whether the uncertainty principle should be discussed in any event. MichaelMaggs (talk) 18:08, 16 July 2023 (UTC)

I did not claim that there was an implication that gravity is part of QM. I complained that using matter waves as an excuse to keep the HUP as peculiar to QM, as John did above, is invalid. I agree with Michael that matter waves, as John introduced them, has nothing to do with the HUP, and I already stated so. My original point above was that Heisenberg's insistence on the HUP is just fine, and is relevant to QM, but is not specifically a unique part of QM and therefore does not deserve to be listed as a peculiarity of the tiny regime or of QM. As I said, it does not belong in an introduction to QM. I gave convincing reasons: Heisenberg did not discover something new, or something that was specific to the atomic scale of physics when he discussed the Uncertainty Principle. The principle had already been discovered centuries before. David Spector (talk) 18:19, 16 July 2023 (UTC)


 * My proposal on uncertainty principle for this article has two parts:
 * 1) Replace the paragraph in the introduction that features uncertainty with a paragraph on interference. In my opinion interference is so much more important to QM.
 * 2) Rework the uncertainty section in this article to focus on the modern, practical use of lifetime-energy uncertainty.
 * I find the position - momentum uncertainty much over discussed and ultimately without impact. I don't know of any interesting experiments related to it and yet much ink is spilled.
 * The historical issues should be covered in History of quantum mechanics and referenced here. Johnjbarton (talk) 00:31, 17 July 2023 (UTC)
 * I like this proposal a lot. I agree that wave interference patterns and linear superpositions of wave functions are both central to QM, while the HUP is central to no important part of QM ontology of which I am aware. I agree that an important application of HUP is to determine particle lifetimes in high-energy collisions. I agree that simultaneous position/momentum uncertainty, even though relatively far larger than in the classical limit, is of not much real importance to theory or experiment in QM. HUP is certainly part of QM history, but not of central relevance to understanding QM. I have been saying this for years, yet am usually ignored due to the mystical weight of the Copenhagen interpretation, which goes far beyond experiment in its enshrinement of mysticism in its set of axioms. Recall that calling a conjecture an axiom means you never have to prove it. This is the dirty little secret of many QM physicists, in my opinion, and perhaps the real meaning behind Feynman's outrageous statement. David Spector (talk) 01:41, 17 July 2023 (UTC)
 * That sounds good. Although the uncertainty principle should be mentioned and briefly discussed, there is no need to devote whole paragraphs to it in this article. MichaelMaggs (talk) 10:49, 17 July 2023 (UTC)