Talk:Introduction to quantum mechanics

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.

Resolved

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:

• 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 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.

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

DRAFT: User:Johnjbarton/sandbox/introduction_to_quantum_mechanics#Quantization_of_matter

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.

Resolved

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#Proposal_to_create_and_adopt_"Teaching_quantum_mechanics"

Follow up there, one way or another.

Resolved

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)

Uncertainty principle without particles

The current intro says:

• One example of this is the uncertainty principle: if one can predict where a particle will be found, one cannot predict how it will be moving, and vice versa.

I understand that this is the conventional "party line", but it sets the reader into an incorrect mindset for understanding QM. It presumes that QM is a mechanics of "particles" whose properties are difficult to measure. Famously, no evidence supports this point of view. That is why the uncertainty principle is expressed in terms of measurement outcomes, not in terms of hypothetical particle properties.

I will attempt a fix. Johnjbarton (talk) 15:59, 14 November 2023 (UTC)