Talk:Quantum mechanics

Quantum mechanics is not just a description of nature at small scales

I'm a newbie to wikipedia so hopefully I haven't stepped on any toes. Apologies in advance if I have.

I've recently edited the Quantum Mechanics page and changed the first few lines to try to dispel the (often commonly held) belief that quantum mechanics is about nature at the "small scale". More accurately quantum mechanics describes nature at all scales but is *absolutely necessary* for describing nature at small scales.

I think that the opening line of the Quantum Mechanics article: "Quantum mechanics (QM; also known as quantum physics, quantum theory, the wave mechanical model, or matrix mechanics), including quantum field theory, is a fundamental theory in physics which describes nature at the small – atomic and subatomic – scales." is misleading in the sense that quantum mechanics is not only about the small scale. It applies at all scales. It explains the existence of metals, semiconductors, insulators, and the structure of the periodic table (which underpins all of chemistry, and is the basis of quantum chemistry). To a large degree solid state physics (which describes macroscopic objects) would not be understandable without quantum mechanics.

The misconception about quantum mechanics only applying at the small scale is somewhat clarified later in the "Quantum mechanics" article where there are several statements about quantum mechanics applying at all scales, such as: "Most theories in classical physics can be derived from quantum mechanics as an approximation valid at large (macroscopic) scale." and the entire section on "Relation to classical physics".

Nonetheless, I believe that the article could be improved by avoiding the "small scale" trap right off the bat. I would suggest changing the article to read

"Quantum mechanics (QM; also known as quantum physics, quantum theory, the wave mechanical model, or matrix mechanics), including quantum field theory, is a fundamental theory in physics describing the properties nature[2].

Classical physics, the description of physics that existed before the formulation of the theory of relativity and of quantum mechanics, describes many aspects of nature at ordinary (macroscopic) scale. Quantum mechanics explains the aspects of nature at ordinary (macroscopic) scales but extends this description to the small – atomic and subatomic – scales. "

Papaneeds (talk) 00:56, 5 March 2020 (UTC)papaneeds

The passages you have changed cite two sources - one by Nobel prize winner Richard Feynman and one 2014 published paper by Gregg Jaeger. It would be a good idea to verify that your new versions still summarize what these cited sources say. Dirac66 (talk) 03:36, 5 March 2020 (UTC)

No. QM is a description of the very small. That a few macro manifestations (such as superconductivity) can be observed at macro scales, does not alter this premise. By way of example, Relativistic theories are associated with the very fast, even though they apply in theory to everyday life (and GPS which isn't really that fast). That QM can manifest at larger scales is already mentioned, as you said. If QM explains the existence of "metals, semiconductors, insulators etc" then it does so by describing them at a SMALL scale. However, the requirement is that you quote a 3rd Party Reliable Source for your proposed change of emphasis. <Phecda109>. — Preceding unsigned comment added by 2407:7000:A244:E161:ADAA:4BDA:3348:BD42 (talk) 19:30, 16 May 2020 (UTC)

I agree, QM is the physics of small scales, numerous textbooks [1] p.8, [2] p.1, [3] p.3, [4], p.4 support this. I think the word small should be in the introduction. The current wording: "It describes physical properties of nature on an atomic scale." may be a little misleading, giving the impression that it applies only to atomic scale and not smaller scales. --Chetvorno^TALK 21:38, 3 August 2020 (UTC)

I'm late to the party, but I want to post this in case anyone else is wondering about the same. There is a very important nuance here that most people miss: Yes, Quantum mechanics is the foundation for all of modern physics and (most of) classical mechanics can be derived from it. However, and this is very important, it is completely impractical for describing the nature of objects on the human-scale. You cannot keep track of an Avogadro number of degrees of freedom. Statistical mechanics is useful in this region. Relativistic mechanics, as far as we can tell, is always valid but it is totally unnecessary at low speeds (v << c). Just as general relativity is not necessary to describe gravity on earth or the moon. Attempting to do so is, generally, folly. There are scales in physics, we have to make compromises (approximations) to make the best models we can with the information and resources at our disposal (hence statistical physics). In order to better appeal to nontechnical readers, I believe it is best that quantum mechanics and quantum physics are talked about as the physics of the small at the beginning, as that is what many of them are here to read about. Mentions, deeper in the article, to the applications of QM to these other fields seems appropriate. Footlessmouse (talk) 11:18, 16 August 2020 (UTC)

I agree with @Chetvorno:, the "atomic scale" sounds like other scales are excluded. But to say "small scale" would be immensely imprecise - small compared to what? QM is actually more about subatomic scales: we rarely use it to describe motion of atoms and molecules as a whole (He scattering), and more to describe their constituents. Shall we say the scale is the "particle scale"? How granular do we need to see Nature to start describing it by QM - that defines the scale. The effects can spread to mezzo and macroscopic scales, but the description starts with... particles. Your thoughts? Ponor (talk) 07:22, 18 August 2020 (UTC)

I think "atoms and subatomic particles" is sufficiently specific. QM certainly is required to describe interactions of atoms and molecules as a whole, in chemistry. --Chetvorno^TALK 16:36, 18 August 2020 (UTC)

Chemistry is mainly QM of the outer electrons, so we're still subatomic. We don't take neutral atoms and write wavefunctions for each without considering their electrons and stuff. But OK, we do have helium scattering, superfluid helium etc. where things are not too grainy. I didn't want to be disrespectful, but I reverted your "and smaller" edit. Subatomic particles already include everything from photons to nuclei. Ponor (talk) 16:57, 18 August 2020 (UTC)

No problem with your edit, "and smaller" was probably a bad idea. I do think "atoms" should be in there, as "of the order of subatomic particles" implies that quantum mechanics is not needed at atomic scale. Atoms are entirely quantum mechanical objects, wouldn't exist without QM. The wording is also supported by most sources: [5] p.8, [6], p.4 --Chetvorno^TALK 17:41, 18 August 2020 (UTC)

Atoms and subatomic particles are there to explain the scale, so we're describing anything between 0.1x and 10x of their size - I think we're fine! This is how I understand the scales: it's the smallest objects you need to use to describe your system. Atoms are quantum objects (when they absorb or emit light, bond to each other, etc.) because of their electrons. And are quantum objects because of their nuclei (when you probe nuclei). And nucleons (when you probe nucleons). And are quantum objects as a whole when they scatter off of surfaces (wavelike interference!), or condense in a superfluid, but in this case we don't care about their electrons that much (because energies involved do not excite them), we take them as quantum, 0.1 nm small billiard balls. Just saying... Cheers! Ponor (talk) 19:40, 18 August 2020 (UTC)

I agree with this. I think another major point is: there is no clear cut distinction. When trying to model a system, you start with the easiest model first (classical approximations) and, when it fails to account for experimental data, you upgrade to more complicated models. I think the new statement, after edits by @Chetvorno and @Ponor, are pretty perfect for the lead. It is clear and precise enough without going into too much detail. Footlessmouse (talk) 20:05, 18 August 2020 (UTC)

I agree that QM extends beyond small scale (I will try an edit). CaveWriting (talk) 21:37, 11 September 2020 (UTC)

I think a few of the effects of quantum mechanics, like superconductivity, superfluidity, and entanglement, are detectable at large scales, but they are still the results of interactions between particles at the atomic or subatomic scale. I think the addition to the introduction is misleading. --Chetvorno^TALK 21:55, 11 September 2020 (UTC)

The added statement, the new second sentence of the article, is very jarring. The lead is trying to convey the fact that quantum mechanics is only used in regimes where classical mechanics is insufficient. IMO, that is all it needs to do. Mentioning macroscopic quantum effects in the introduction to the quantum mechanics article is not particularly helpful to readers who don't understand quantum mechanics, I agree with @Chetvorno that it is somewhat misleading. Footlessmouse (talk) 22:12, 11 September 2020 (UTC)

We are entangled at large scales (nonlocality) because our constituent particles were at the same state during the Big Bang, which was the entangling event. At that level, we all share the same wave function (state). The laws of QM evolved our separate states going forward from that event.

References

--Ancheta Wis   (talk | contribs) 23:07, 11 September 2020 (UTC)

This is a fact that a god-like observer outside the universe would appreciate. Notes on how these concepts extend outside the realm of the particle-scale interactions should be placed lower in the article in a manner that is not confusing to readers unfamiliar with quantum mechanics. Quantum mechanics deals with systems in which we can keep track of all the degrees of freedom, maybe Quantum statistical mechanics is more appropriate for such notes. Footlessmouse (talk) 23:55, 11 September 2020 (UTC)

make page: quantum caustics

• https://www.google.com/search?q=quantum+caustics — Preceding unsigned comment added by 2A02:587:410E:CA26:4457:E00:4701:E3FC (talk) 14:47, 10 July 2020 (UTC)

Caustic (optics) — Preceding unsigned comment added by 2A02:587:410E:CA26:4457:E00:4701:E3FC (talk) 14:51, 10 July 2020 (UTC)

Splitting proposal

The following discussion is closed. Please do not modify it. Subsequent comments should be made in a new section. A summary of the conclusions reached follows.

The result of this discussion was to split Benica11 (talk) 03:31, 7 October 2020 (UTC)

---

I propose that Quantum mechanics be split from Quantum physics. It seems to me once (one or two decades ago) Quant mech and Quant phys were synonyms, but not anymore. From my experience quantum physics is the field encompassing Quantum mechanics, Quantum technology, Quantum information, Quantum field theory etc. Also, according to the current article, quantum mechanics = quantum physics = a part of quantum field theory. That is imo decidedly not so. Splitting could allow us to work out the "hierarchy", by lack of a better word, more rigorously. Laura sf (talk) 06:01, 3 August 2020 (UTC)

Quantum mechanics = formalism, quantum physics = application of the formalism to real problems? That would make sense to me. Before splitting, I'd think about what goes where so there's no overlap. But before anything else, how about we fix the first sentence? Do we really need all these old names listed? In what sense is QM *part* of QFT? The latter developed from QM, but the split is real... Most quantum mechanics :) never learn QFT. Ponor (talk) 12:07, 3 August 2020 (UTC)

I doubt whether sources really support separate definitions for "quantum mechanics" and "quantum physics"; this is a distinction without a difference. I think it would confuse general readers into thinking there are two theories. In addition, there is the question of whether the encyclopedia needs another QM article. We have numerous application articles quantum chemistry, etc. and Introduction to quantum mechanics which apply QM to real problems. This would involve a lot of redundant content. --Chetvorno^TALK 22:03, 3 August 2020 (UTC)

@Chetvorno I can say with 100% confidence that they are not a distinction without a difference. As with any science, there is often a distinction without a difference between 'the corpus of scientific theories' and 'the corpus of applications, associated professions, and areas of research'. I don't think that needs to be a problem here, as Quantum physics covers both and Quantum mechanics is only a small part of both.

As @Ponor states, quantum mechanics = the laws, the formalism ('machanics'). There is no profession associated with it. For example, no one will say that they work in 'quantum mechanics' just like no engineer will say they 'work in classical mechanics' and no biologist will say they 'work in Darwinism'. (Except of course, they would be theorists strictly occupied with that very specific part of the field. Same for physics.)

Quantum physics is the corpus of scientific work that encompasses the theory of Quantum mechanics and Quantum technology and the theory and applications of Quantum information and the theory and applications of Quantum field theory.

Some examples:

• Searches by non-experts
• The Arxiv uses Quantum Physics as subject indicator
• Nature as well. (Their definition: Quantum physics is the study of matter and energy at its most fundamental level.)
• The latter still has an invisible category for Quantum mechanics, with a significantly more restrictive definition than the one of quantum physics: quantum mechanics is the study of the dynamics of particles at its most fundamental level. The state of a particle, such as its position or momentum, is described by a statistical distribution given by its wavefunction. As this name suggests, this formalism gives matter many properties that are classically associated with waves.)

@Chetvorno I do strongly agree we do not need another semi-identical article on quant phys. I suggest either of two possibilities: (1) Quick-and-dirty: Change the main title of this article to Quantum Physics, rewrite the lead of the article and change the section 'Mathematical_formulations' to 'Quantum mechanics'. (2) Alternative: Make Quantum Physics a short page that sums up the subfields, and move contents of Quantum_mechanics#Applications here. This is approximately how it's handled in the Dutch Wikipedia. The Quantum mechanics page will be identical to the page today, minus section Quantum_mechanics#Applications. The important advantage here for the public is that when they look for 'Quantum physics', perhaps because they read something about quantum cryptography, computing, teleportation, etc from a person irl or in popular media (like what happened when Microsoft had their 15 minutes of fame for 2019) they will find an understandable page with an overview from which they can navigate further if necessary, instead of being served a monstrous article that starts with a plot of electron probability distribution functions and ends with a derivation of the 1-dimensional potential energy box or infinite potential well. Laura sf (talk) 00:33, 5 August 2020 (UTC)

@Laura sf My vote goes to your proposal #2: add Quantum Physics, update Quantum Mechanics beginning with something like "Quantum mechanics is a fundamental theory in physics. It describes physical properties of nature on an atomic scale and is the foundation of all Quantum Physics. ". If you're willing to write the new article, I think we should first ping a few people who were active on Quantum Mechanics, some of who are also admins here (my random choice @Headbomb, Materialscientist, PhysicsGal, Ancheta Wis, CYD, Chjoaygame, and DVdm:) to see what hey think. In my mind, QM is so 1920-1930, QP comes later and includes nuclear, particle, condensed matter, (...) physics. See Foundational quantum physics. Ponor (talk) 20:32, 5 August 2020 (UTC)

Sounds good, I'll await their input. This is making me excited to try and make this a GA again. Getting it back to its short-lived FA status from 2006 may be a bit of a stretch for now hehe—but the subject really deserves some TLC. Laura sf (talk) 11:54, 6 August 2020 (UTC)

The name is not as important as the statements of content. In school, we learned QM as the umbrella term for the concepts dating back to to the formative period, while quantum physics was more general and less technical. There are only a few exact solutions which we learn as quantum mechanics, which are then transmuted to general, vaguer statements. I am taking this opportunity to state a trick from Feynman: he said that "since it is so difficult to come up with solutions, we can turn this on its head, and let the physical situation (ie. cryogenic operation of ensembles of matter) model the mathematical computations". That is exactly the direction that quantum computing is taking. --Ancheta Wis   (talk | contribs) 21:13, 5 August 2020 (UTC), and 13:29, 6 August 2020 (UTC)

I'm new to all this, @Laura sf and Ancheta Wis:. Since there are no other comments on your proposal, Laura sf, before you lose all your excitement, maybe you should draft the new article and let others comment on it. You'll, I believe, need support of an admin to have your article added - Ancheta Wis would you be willing to do this? As I'm editing some other articles, I'm more and more convinced Quantum Physics should not redirect to QM. Ponor (talk) 23:50, 15 August 2020 (UTC)

If there is a consensus for a new Quantum physics article, I am in favor of Laura sf's idea (2) above: make it a WP:Summary style umbrella article having links to all our quantum articles. Quantum mechanics should also probably have a brief paragraph at the top laying out the different content of our top-level quantum articles: Quantum physics, Quantum technology, Quantum field theory, Introduction to quantum mechanics. Just keep in mind that a lot of readers coming to these pages will be middle school students, high school dropouts, single mothers studying to be x-ray techs, and English majors, who have no technical knowledge. Splitting content between a lot of overlapping similarly-named articles with no clear plan makes it very confusing for these readers. --Chetvorno^TALK 02:22, 16 August 2020 (UTC)

Support. In the preface of Griffith's second edition (a widely adopted intro text for undergrads) it says "Every competent physicists can 'do' quantum mechanics, but the stories we tell ourselves about what we are doing are as various as the tales of Scheherazade, and almost as implausible... [the] purpose of this book is to teach you how to do quantum mechanics". That sort of summarizes what I think of QM, it is hard to put in words, but it is a collection of techniques and rules and the process of using those techniques and rules to solve problems related to physical systems. Just a thought. Footlessmouse (talk) 02:15, 19 August 2020 (UTC)

• Support As a first-year graduate student in physics, I can confidently say that some physicists do consider quantum mechanics to be distinct from quantum field theory and other quantum theories. QM is best described as being analogous to classical mechanics in the same way QFT is the counterpart to classical field theory. –LaundryPizza03 (dc̄) 03:25, 13 September 2020 (UTC)

It has been over a month and there is long-standing consensus for a split here and for @Laura sf:'s second proposal, namely "Make Quantum Physics a short page that sums up the subfields, and move contents of Quantum_mechanics#Applications [there]." Is there any experienced, uninvolved editor that can close this discussion and perform the separation? It would be appreciated. You only need to split out the Applications section, the newly created Quantum Physics article will be quickly expanded. I agree with @Laura sf that the split will make it easier to bring both articles up to GA standards. @Headbomb, DVdm, and Materialscientist:, any thoughts? Footlessmouse (talk) 04:12, 13 September 2020 (UTC)

The discussion above is closed. Please do not modify it. Subsequent comments should be made on the appropriate discussion page. No further edits should be made to this discussion.

Step one complete, much work left

Hi all, if the articles are to be split, does anyone mind if we copy over the philosophy stuffs to the other page? I do not think I am the only one who has said this page should be about quantum mechanics and no physics major is taught about this stuff in their physics classes, so it does not seem particularly relevant here, except maybe a very brief mention and links to other articles. History can also be trimmed with some of the content being used to fill out the History of quantum mechanics article. The example sections should be cut down drastically. Schrodinger equation is mentioned six times outside examples and is not defined. Matrix mechanics is not mentioned outside a single reference. Path integral formulation is mentioned as a side note. Pauli matrices are not discussed!!! These facts are absurd! I would say this article is much more about the history, philosophy, and applications of QM than it is about QM, which otherwise does not have a coherent article on this encyclopedia. Thank you for completing the split @Benica11:, that is step one.Footlessmouse (talk) 08:05, 7 October 2020 (UTC)

I'm not sure this split was adequately discussed, and I oppose it. If you want a split of the application parts then Quantum technology is a much better target. Quantum mechanics IS the physics of quantum behaviour. So I would say this split is inappropriate and is going to make a mess of our coverage of quantum physics as it is basically a content fork. Polyamorph (talk) 08:14, 7 October 2020 (UTC)

@Polyamorph: the discussion was open for weeks with consensus, why didn't you object before? Also, did you read my comment? This page currently has no substantive quantum mechanics material in it. We should work on expanding it with relevant material that will actually tell the reader what quantum mechanics is. I know we physicists like to be lazy with words when talking with other physicists, but this is an encyclopedia and words matter. Philosophy and history and applications are NOT quantum mechanics. They are simply philosophy, history, and applications of a subject. Quantum mechanics is not discussed in a meaningful way. (How can you possibly pretend to have learned anything about quantum mechanics at all if you were not even shown Pauli matrices???)Footlessmouse (talk) 09:18, 7 October 2020 (UTC)

Um, just because it was open for a few weeks does not mean everyone got a chance to see it - I didn't object because I didn't see it. This is such a fundamental subject that I don't feel the comments from a handful of users on this page can possibly represent the true consensus. Just because the page is bad is no reason to split and potentially create deleterious content forks. It's instead a case of working to improve the existing content. Regarding history and philosophy, this is an encyclopedia and full coverage of the subject is indeed appropriate. If such sections get out of hand they can then be split into independent articles and referenced using {{main}}. Polyamorph (talk) 09:23, 7 October 2020 (UTC)

@Polyamorph:, they already have main articles and what is on this page is supposed to summarize, but goes into too much detail. I must admit, I do not care about "quantum physics" and only wanted the split to get rid of all the junk on the page that is supposed to be about "quantum mechanics". They can all be summarized, but currently the whole page is summaries of those things with absolutely no meaningful exposition on quantum mechanics. It's not a matter of improving the content, it's a matter of writing a large amount of new content to replace what's here. I would support a move of the page "Quantum physics" to a "Applications of quantum mechanics" if that appeases others.Footlessmouse (talk) 09:42, 7 October 2020 (UTC)

Why support something that you don't think is the optimal solution. We can't create pages just to put "all the junk" somewhere else, that's just kicking the can down the road. Polyamorph (talk) 09:46, 7 October 2020 (UTC)

But yes, I would say Applications of quantum mechanics would be a better target. IMO QM is the Physics. Applications are technology. Polyamorph (talk) 09:49, 7 October 2020 (UTC)

@Polyamorph: I apologize, that is fair. I also really wanted to close that discussion so we could move on to discussing the content. I will support your move to Applications, it is very appropriate. To be honest, the literature has always ambiguous when it comes to quantum mechanics versus quantum physics. I have always held, though, that quantum mechanics is simply the adaptation of Hamiltonian mechanics to situations where it was previously invalid, requiring an inherently probabilistic approach that is nonsensical from a classical perspective.Footlessmouse (talk) 10:05, 7 October 2020 (UTC)

No problem @Footlessmouse:, thanks for understanding! cheers! :) Polyamorph (talk) 10:38, 7 October 2020 (UTC)

As a professional physicist, I want to add that we use quantum mechanics and quantum physics as synonyms. Neither is very well-defined, but generally include all quantum theories. When we want to be precise, we specify that we are working with non-relativistic quantum mechanics, or QFT, or quantum information, or QCD, etc. Tercer (talk) 10:13, 7 October 2020 (UTC)

Side note, even those terms are dependent upon your specialty, part of the reason so many terms are ambiguous. As a CM physicist, I can state as a matter of fact that we never refer to it as non-relativistic quantum mechanics, as (in most specialties) our systems of concern are non-relativistic. There should be a Wikipedia article about terms in science with a disclaimer that says most terms scientists use are context dependent.Footlessmouse (talk) 10:25, 7 October 2020 (UTC)

I concur with Tercer — I've pretty much always heard those terms used effectively synonymously. In my own writing, I employ both, just so the phrasing doesn't get too repetitious. XOR'easter (talk) 18:45, 8 October 2020 (UTC)

When @Laura sf proposed the split, it seemed like she had a clear idea of what to do. We pinged her a few times since then, and there was no response. So I think this split came a bit too soon. Quantum physics (QP) is not just applications of quantum mechanic (QM), it's almost everything that happened in physics since ~193* (after They were done with developing QM). Would I say that quantum statistical physics is part of QM? No, I would not. Is it a branch of QP - yes it is. Nuclear physics, particle physics, atomic physics, condensed matter physics? They're all branches/fields of QP, not QM. In my opinion, QP article should be about fields that have QM in their foundation. It should say that they emerged from our need to describe Nature at the most fundamental level (el. particles and energy quanta), and give a one-sentence introduction to each. Condensed matter deals with interactions emerging in many-body systems of valence electrons and atomic cores. Nuclear physics deals with QM description of protons and neutrons bound by nuclear interaction. And so on. Then there can be sections with more specific examples/applications from each of these high-level fields, that will more or less point to separate articles. When it comes to QM article, I think it's better to keep it short: it can mention perturbation methods, but does not need to elaborate on them. It can say in which cases we need them, but not how we use them. It can mention Pauli matrices (what they're used for), different formulations of QM (elaborate on the most prevalent one), but should not try to say everything about them. All low-level details should stay one click away. Your thoughts? Ponor (talk) 19:59, 7 October 2020 (UTC)

@Ponor:, we do already have articles on Modern physics and Classical physics and I think your definition may be a duplicate of the content that belongs in modern physics. It would otherwise require turning modern physics into a disambiguation for quantum physics and relativity. I get both sides of the argument and am a little torn. Woe us, if only some authoritative literature could help us out!Footlessmouse (talk) 21:06, 7 October 2020 (UTC)

@Footlessmouse: I know... that's why I hoped Laura sf would do it. Does is hurt to leave the two articles like this for some time (no changes is QM until QP is written) and see how things evolve? For in the third sentence of Modern physics we have: "Notable branches of modern physics include quantum physics (sic!), special relativity, and general relativity." Also, Modern physics in an unsearchable term; you may only stumble upon it. Quantum physics, to me, is much more real. It might be interesting to see what pageview counts QM and QP will have. Ponor (talk) 21:37, 7 October 2020 (UTC)

@Ponor and Polyamorph: What if we create a new page titled "Quantum (adjective)"? It is unambiguous and could be used to disambiguate popular jargon and list all fields that utilize QM, just like the QP article would. As regards to Modern physics article, it is highly underdeveloped and it should have said quantum mechanics rather than quantum physics, mentioning it in one breath with the relativities. If it said, "Notable branches of modern physics include astrophysics, cosmology, and quantum physics, I would agree, but in this case I think the wording of the page is wrong.Footlessmouse (talk) 21:51, 7 October 2020 (UTC)

I feel Quantum (adjective) would be insufficiently specific; articles about adjectives are more dictionary entries. We need to title articles with enough specificity so general readers can find what they are looking for. A list of all fields of study in QM would not take up much space and could be incorporated in this article (or whatever toplevel QM article is decided on). Another possibility is List of quantum physics articles or List of fields of study in quantum mechanics. --Chetvorno^TALK 22:38, 7 October 2020 (UTC)

I meant that it would discuss how the adjective modifies the rest of the term. Explaining the difference between classical and quantum physics is far beyond the scope of any dictionary. My main argument this whole time was that all that stuff doesn't belong here, I think this page desperately needs be rewritten to actually discuss QM, like, you know, for starters, Pauli matrices, wave mechanics, matrix mechanics, path integral (I'll even take sum over histories). The current article is a long expose of quantum caveats with some examples, applications, history, and philosophy mixed in. There is no mechanics.Footlessmouse (talk) 22:59, 7 October 2020 (UTC)

@Footlessmouse: I'm not sure about this, before creating any new articles I think it would be useful to generate a list of articles wikipedia already has on quantum theory, see which ones overlap, and then see if we can formulate a merge/split/cleanup/expand plan to ensure full and proper coverage of quantum theory/physics/technology. Hope that makes sense. Polyamorph (talk) 07:57, 8 October 2020 (UTC)

@Footlessmouse: I kind of agree with you that the mathematical basis of QM like the Schrodinger equation and Pauli matrices is given sort shrift in this article (I understand why, there's a lot of other stuff to cover). An option I've thought about is rewriting Introduction to quantum mechanics to make it a technical introduction. The current Introduction to quantum mechanics is more about the history of QM. We could move the historical content of that article into History of quantum mechanics (where it really belongs) and replace it with a proper mathematical introduction to QM touching on the stuff you mentioned, maybe along the lines of Feynman. --Chetvorno^TALK 23:04, 7 October 2020 (UTC)

@Chetvorno: This is a decent idea. I would be okay with it if the hatnote mentioned that "This is an overview of topics relating to quantum mechanics, for a mathematical introduction to the subject see..."Footlessmouse (talk) 23:14, 7 October 2020 (UTC)

Splitting proposal 2

Following the recent split discussed above of content from here to Quantum physics, it has been suggested that since much of the content moved to Quantum physics deals with various applications then Applications of quantum mechanics might have been a better target. I'm therefore re-opening the split discussion with three options. 1) Keep the two articles Quantum Mechanics and Quantum physics split as they are. 2) Move Quantum physics to Applications of quantum mechanics and redirect Quantum physics to Quantum mechanics. 3) Merge content currently at Quantum physics to Quantum technology and redirect Quantum physics to here. 4) Undo the split to Quantum physics entirely and focus on cleanup of this article. 5) Other (please elaborate).

!Votes

• Option 2 or 3 In my opinion Quantum mechanics is the physics of quantum behaviour, so it makes sense for Quantum physics to redirect here. The short section on Applications of quantum mechanics can remain with the {{main}} target updated to Applications of quantum mechanics. However, Applications of Quantum Mechanics and Quantum technology are arguably synonymous. So I would also support a merge of the applications content to Quantum technology. Polyamorph (talk) 12:09, 7 October 2020 (UTC) EDIT: Following XOR'easter's comment I agree there are applications of quantum mechanics that are not technology so I'm striking option 3.Polyamorph (talk) 09:14, 9 October 2020 (UTC)

• Option 2 or 3 While, in my opinion, quantum mechanics is mechanics, an inherently mathematical modelling of physical systems, I agree with the other points.Footlessmouse (talk) 16:12, 7 October 2020 (UTC)

• Option 2 or 3. "Quantum physics" is something you find in popular science descriptions, but what they mean is almost always quantum mechanics. A separate article for that doesn't make sense. --mfb (talk) 19:37, 7 October 2020 (UTC)

• Option 1 Quantum mechanics is the foundation. Its development was over in 1930s. That's where most textbooks on QM stop. What emerged were different fields that used QM (AND statistical physics AND field theory AND many, many approximations) to describe Nature at the most fundamental level (el. particles and en. quanta). Those fields are part of quantum physics. So no, QM and QP are not the same. No, QP is not a popular science thing (Nature:Quantum physics). More thoughts in the previous section... Ponor (talk) 20:14, 7 October 2020 (UTC)

• Option 2 or 4 In 20+ years of working with physicists, reading physics papers and books, and doing physics myself, I've never heard a clear-cut distinction made between "quantum physics" and "quantum mechanics". To illustrate, MIT calls its undergraduate courses "Quantum Physics" (8.04 through 8.06), while Caltech labels its undergrad classes on the same material "Quantum Mechanics" (Ph 125 abc). It's possible that some people do have a distinction in mind, but we should not presume that a reader would pick up on it, or that everyone who makes a distinction does so in the same way. All this talk of moving, merging, splitting and renaming is making my head spin, and I don't think it will ultimately lead to any clarity. Nor do I quite follow the rationales that have been advanced so far. No, the term "quantum physics" is not restricted to pop science; "quantum technology" is not the same thing as "applications of quantum mechanics" (the latter might include, for example, applying quantum physics to calculate the spectral lines of a quasar, something with no technological application — it is a much more general turn of phrase). XOR'easter (talk) 19:10, 8 October 2020 (UTC)

• Option 2 makes the most sense to me. Nerd271 (talk) 18:03, 9 October 2020 (UTC)

• Option 2 for reasons above. I think this article should be what it already is: a nonmathematical introduction to QM and WP:summary style umbrella article on all Wikipedia's quantum content. This article has a readable prose size of only 52kb so there is room to add stuff. I also share Footlessmouse's concern that Wikipedia has no proper mathematical introduction to QM, giving Schrodinger's equation, Born probability eq, postulates of QM, uncertainty principle, unitary matrices, etc. Without the mathematical introduction, the Examples section of this article is pretty incomprehensible. I suggest either adding a brief mathematical introductory section to this article, or creating a new article covering this. One option I suggested above is to rewrite Introduction to quantum mechanics as a nathematical introduction, moving the existing historical content to History of quantum mechanics. --Chetvorno^TALK 00:10, 10 October 2020 (UTC)

Are people still interested in this reorganization? It looks like the proposal that gained the most support was to Move Quantum physics to Applications of quantum mechanics and redirect Quantum physics to Quantum mechanics. XOR'easter (talk) 01:58, 12 December 2020 (UTC)

Quantum physics has a life of its own, and since 17 August 2020 a growing number of readers (inc. from 100 to 600 a day). An article called "Applications of quantum mechanics" will be nearly unsearchable; if "Quantum physics" bothers anyone, its contents should just be put back into "Quantum mechanics". "Quantum physics" was and still is in Modern physics, as one of its branches. Please also remember that polls should not be used for article development, per WP:Vote. I'd like to see a broader consensus before proceeding; though I don't see how having Quantum physics hurts. Your quantum physicist (quantum mechanic?) for 22+ years, Ponor (talk) 07:13, 12 December 2020 (UTC)

There was an extensive discussion already, and consensus has emerged. You were the only one arguing for keeping things as it is. I think having "Quantum Physics" does hurt, for two reasons: first most people think of quantum physics and quantum mechanics as synonyms, the readers won't be able to find the correct article to get the content they want even if we here manage to come up with a sensible distinction between them. The second reason is that the actual content of the Quantum physics article is indeed just applications of quantum mechanics, it's much more helpful to have a title that matches the content. Tercer (talk) 13:11, 12 December 2020 (UTC)

I would do the deed myself but Applications of quantum mechanics already exists as a redirect, so we need an admin to delete that before we can do the move. Tercer (talk) 13:27, 12 December 2020 (UTC)

I've filed at Wikipedia:Requested moves to move Quantum physics over the redirect. XOR'easter (talk) 17:34, 12 December 2020 (UTC)

XOR'easter, I've completed the move to Applications of quantum mechanics. ─ The Aafī ^(talk) 18:13, 12 December 2020 (UTC)

@Tercer:I don't see any discussion, I only see a few people voting. A few months ago we had consensus to start Quantum physics, the "splitting" (spin-off) proposal was announced at Project Physics list and people were invited to comment. Unfortunately, the original proposer vanished and the split was rushed. Then the Applications section was removed from Quantum mechanics (with that consensus in mind, I assume), and now we're creating another article with what should really still be in Quantum mechanics as its very important part (most readers will be interested in what QM is, and how it can be taxed). How about we follow some procedure: revert everything to the status quo ante, start discussion on whether to create yet another quantum article called "Applications of quantum mechanics", invite members of WikiProject Physics to comment, etc. Btw: who is "most people" for you? If you follow my google scholar link in the previous posting, you'll see thousands of researchers listing "Quantum Physics" as their research field. It would be nice to actually discuss all this for a change. Ponor (talk) 18:16, 12 December 2020 (UTC)

We ... did have a discussion? (Just because people summarized their opinions with a little bold text here and there doesn't mean they were voting — that's why the section heading was "!Votes", after all, with the bang denoting negation.) We discussed, almost everyone found option 2 to be acceptable, the discussion petered out, and now we've implemented the change that consensus had settled on. This is Wikipedia procedure.

As for the Google Scholar bit, sure, people list "quantum physics" as their research field. Others list "quantum mechanics". That's not evidence we should prefer one terminology over the other. XOR'easter (talk) 18:29, 12 December 2020 (UTC)

Procedure was followed. This is how a discussion and consensus looks like. Your current proposal to revert everything and start discussion anew was actually one of the options there, which was not supported even by yourself. About Google Scholar: I'm not sure what it is that you're to prove. That many people use the term "quantum physics"? Sure, nobody is disputing this. What I said is only that "quantum physics" and "quantum mechanics" are effectively synonyms. Tercer (talk) 20:01, 12 December 2020 (UTC)

Agree with Tercer, I am strongly against reopening the proposal. We had an adequate discussion above, and 6 editors voted to redirect Quantum physics. The only reason it wasn't implemented immediately was to give people plenty of time to comment. They've had plenty. Time to close this discussion. --Chetvorno^TALK 21:36, 12 December 2020 (UTC)

Article structure may be problematic

Hi

While I have been editing Wikipedia for many years in different topics, many of them in physics, I have refrained so far from editing this particular page, as I am mainly interested in either correcting errors or adding new material. However, I must admit that I find the structure of this article problematic. While the article is very impressive in the amount of material and in elaborating the history and the mathematical tools used in quantum mechanics, I feel it is too focused on the history and less on the subject matter at hand, and the subject matter itself is mainly presented by mentioning the mathematical tools used, with very little explanation of the reasons behind using these tools, which I feel have a much better understanding today compared to when they were first invented.

I believe it would be very difficult for a student to understand what is going on from reading this article. Having finished a PhD in string theory many year ago, I personally have no problem with this, but having taught many new students in the past, I think they would find it very difficult to gain good understanding of quantum mechanics from reading this article alone.

Therefore I suggest to add an "overview" part before the history part, which will cover the fundamental issues and main ideas and results in a compact way. I have in fact started working on this.

I would love to hear your opinions/suggestions/(dis)agreement on the matter.Dan Gluck (talk) 14:56, 24 November 2020 (UTC)

I would also like to see progress made on this page, an overview section sounds reasonable to me. We have also discussed creating a technical introduction aside from this article that would be more along the lines of what a calculus-knowledgeable physics student would read if they were interested in learning more, which I think is a good idea as well. Footlessmouse (talk) 23:02, 24 November 2020 (UTC)

Agree with both the above. I'm not knowledgeable enough to help write such a section myself, but I would support it if you guys want to do it. --Chetvorno^TALK 22:01, 12 December 2020 (UTC)

There's an overview section now (added by Dan Gluck on November 30). XOR'easter (talk) 02:35, 13 December 2020 (UTC)

I'm rather unhappy with the resulting "Overview" section. It is rather long, give too much detail, and mixes precise mathematical statements with arguments that do not actually follow. For example, it claims that Every basis vector may have different values of these, so position and momentum must be defined as linear operators in quantum mechanics, having different results on different basis vectors. and that This relation is identical to the one found in Fourier transform, so that a description of an object according to its momentum is the Fourier transform of its description according to its position.. This needs to be fixed. But instead of chopping it down now, I'll start adding actual mathematics to the "mathematical formulation" section, which only has mathematics in form of words (I find this bizarre, mathematics in mathematical symbols is much easier to understand). Then we can remove the inappropriate material from "Overview". Tercer (talk) 20:09, 14 December 2020 (UTC)

Actually, I think that after the overview we should have a section about the 5 postulates. There is no justification to put the math in a separate section. Dan Gluck (talk) 21:38, 14 December 2020 (UTC)

I think it is a good idea to start with an overview of what the important concepts are, before diving down to the mathematics. I put the sections closer together, but I think keeping them separate is better. As for using formal postulates, the problem is that with Wikipedia's usual growth-by-accretion such a list tends to become garbage. See here, for example. To compound that, there's no well-defined or consensually accepted list of what the postulates are, on the contrary, one can do the postulates in several different ways that work just fine.

Either way, postulates or flowing text, we need a mathematical description of the theory. I wrote a bit about Hilbert spaces, quantum states, observables, and measurements. It's not good, but it's much better than the dumpster fire that was there before. Notably missing is still anything about composite systems and the uncertainty principle. Tercer (talk) 15:56, 15 December 2020 (UTC)

I like the idea of starting with a big-picture view of the concepts before diving down into the Hilbert spaces and Hermitian operators and tensor products. Some of what's in the "Overview" section now feels like it already wants to start diving. I moved the "uncertainty principle" material into the next section, where it seems to fit better. XOR'easter (talk) 18:15, 15 December 2020 (UTC)

I added a little bit about composite systems and entanglement. XOR'easter (talk) 03:05, 16 December 2020 (UTC)

Should the article introduce Dirac notation? XOR'easter (talk) 00:27, 22 December 2020 (UTC)

I was wondering about this as well. I decided not to do it, because I assume that the target audience of this article is kids that are taking their first quantum mechanics course, and very often this course is done without the use of Dirac notation. There's also the question of where it would help. There are only a couple of equations when we talk about measurements that would be clearer in Dirac notation, the rest would stay the same. So I don't think the benefit is worth the effort in introducing it. Tercer (talk) 09:48, 22 December 2020 (UTC)

That's fair. The question occurred to me when I thought about writing something about Mach–Zehnder interferometers and realized that I was instinctively going for $|0\rangle$ and $|1\rangle$. XOR'easter (talk) 19:44, 22 December 2020 (UTC)

Hehe I need to make a conscious effort to use regular vectors instead of kets. I started gathering some material about the Mach-Zehnder in my sandbox, feel free to use it. Tercer (talk) 21:11, 22 December 2020 (UTC)

OK, I mixed that with some text I had on hand and added the result to the "Examples" section. It probably needs some reworking and/or expansion. XOR'easter (talk) 21:53, 22 December 2020 (UTC)

I reworked it a lot. Maybe I put too many details, but I find this example fascinating because the math is so easy, even a schoolkid can follow it, so I think it is worth being completely explicit. Tercer (talk) 13:59, 23 December 2020 (UTC)

Good article?

I've fixed all the problems I've noted with this article, and am going to nominate it as WP:GOOD. Before, though, I thought I could ask here if there's some problem that escaped my attention but is obvious to somebody else's eyes. Tercer (talk) 22:06, 30 December 2020 (UTC)

I have no objection to GA nomination. I've fixed all that I've noticed; further progress will probably require a fresh set of eyes that aren't so accustomed to the text that they see what's supposed to be there. XOR'easter (talk) 02:50, 6 January 2021 (UTC)

Thanks for the feedback, I nominated it. Tercer (talk) 14:18, 6 January 2021 (UTC)