Talk:Spin (physics)/Archive 2

Archive 1

Archive 2

Cleaning up the Intro

The intro goes from an explanation of Spin in a classical mechanics to an explanation of spin in a quantum mechanics wihout significant emphasis that the two are not physical analogs. Though my familiarity with the subject is elementary, I am under the impression that Spin is only mathematically analogous (and loosely at that, since half-integers are allowed), and the use of the term arose from a lack of understanding at the time that electrons et al. are in fact point particles. I'm going to try to rewrite the intro to make it more clear that Spin in quantum mechanics is a consequence of Quantum Mechanics -- i.e., schrodinger equation, heisenberg's formulation, etc. -- and is not understandable with the original Newtonian Mechanics (F = dp/dt) and its later but equally classical formulations (Lagrange's equation, Hamilton's canonical momentum, etc.). Ryanluck 16:59, 27 February 2006 (UTC)

Agree. David Spector (talk) 01:01, 15 June 2023 (UTC)

More specifically, it is not the "atomic length scales" which give rise to Quantum Mechanical spin -- it's our formulation of quantum mechanics itself. As is well said in the article, classically a spinning electron at the classical radius would have surface speeds greater than c -- so clearly it's not the smallness but our understanding of the behavior of such small objects. Ryanluck 17:02, 27 February 2006 (UTC)

I disagree with your assessment of spin. I think of spin in the following way: spin is our word to describe how a system behaves under rotation. This has nothing to do with either classical mechanics or quantum mechanics, though of course both kinds of systems do have to have a specific behaviour under rotation. Angular momentum is the generator of rotations, so angular momentum is related to spin, and for classical objects, the angular momentum of a system is determined by how fast the system is revolving, which is where the term got its name. The only difference between classical spin and quantum spin is that quantum systems (whose space of states is a projective space) allow projective representations of the rotation group, while classical systems (whose space of states is a vector space) do not. Thus one sees half-integer spin in quantum mechanics, but not in classical mechanics. Certainly I agree with you that the smallness associated with quantum mechanics is not relevant, but I don't think Schrödinger's equation is relevant either. -lethe ^{talk +} 17:17, 27 February 2006 (UTC)

Ah, ok, that sheds some light. The rotation matrix as applied to spin states is where I first encountered a rigorous description of the weirdness -- the half-integer spins rotated 2*pi give you e^(pi*i) = -1 rather than the usual e^(2*pi*i) = 1, so your conception of spin as behavior under rotation makes sense. My intuition with the nature of the Hilbert space is still pretty weak, but your projective representations argument helps with that to. Thanks for the corrections and clarifications. Feel free to alter any of my edits as you see fit (not that such permission needs to be given or received in wikipedia). Ryanluck 17:58, 27 February 2006 (UTC)

Yes yes, that rotation matrix that acts on two component spinors is the projective representation of the rotation group. This means that it acts not on vectors in the Hilbert space of two component spinors, but rather on rays of that Hilbert space (the space of rays in a vector space is called a projective space). The reason for this is that phase is unmeasurable, because the measurable stuff in QM all uses magnitude squared. Some heavy duty mathematics can tell you that the projective representations of a group are just the representations of the universal cover (but only if the group is finite dimensional). So quantum mechanics requires you to consider the group SU(2) instead of SO(3) (SU(2) is the universal cover of SO(3)). -lethe ^{talk +} 18:11, 27 February 2006 (UTC)

Split?

Would it be useful to the reader to split this article? It seems like the discussion of spin in quantum mechanics would make a good article all by its self. Is it sufficently different from spin in the everyday world to warrant such a split? Or do they really deserve to be on the same page? Also, the physics bits of Rotation seem to share lot with he non-quantum bits of Spin (physics). Would it be useful to reader to merge those bits? (See also Talk:Rotation#Split?) Ewlyahoocom 12:57, 2 April 2006 (UTC)

But right now, almost the entire article is solely about quantum spin... -lethe ^{talk +} 14:27, 2 April 2006 (UTC)

It is a single concept. There is no justification for such a split. Removing. -- Xerxes 22:04, 2 April 2006 (UTC)

It most certainly is not a single concept, just an ambiguous word used for two concepts. David Spector (talk) 01:10, 15 June 2023 (UTC)

I notice that there was recently (today?) an attempt to separate 'particle physics' out of 'physics' that was reverted, and here to have two articles about spin. There is already an additional article Spin quantum number. I agree that spin/tiny and spin/everyday are two very different concepts, so I urge a discussion about better organization of the articles about "spin" among advanced physics people. David Spector (talk) 01:10, 15 June 2023 (UTC)

Clarify the First Sentence to make definition easier to understand

I am guessing that this sentence would be easier to read if the clauses were re-ordered to keep all of the definition together and put the anti-definition at the end of the sentence:

INSTEAD OF : In physics, spin refers to the angular momentum intrinsic to a body, as opposed to orbital angular momentum, which is generated by the motion of its center of mass about an external point.

REVISE SENTENCE: In physics, spin refers to the angular momentum intrinsic to a body, which is the rotation of the body around its own center of mass; as opposed to orbital angular momentum, which is generated by the motion of its center of mass about an external point.

OR, TO MAKE IT EVEN MORE OBVIOUS: In physics, spin is the rotation of a body around its own center of mass. Spin refers to the angular momentum intrinsic to a body. This should not be confused with orbital angular momentum, which is generated by the motion of a center of mass about an external point.

Regards: Greg Chalmers

Such a revision changes the meaning of the sentence and would be incorrect. -- Xerxes 23:16, 5 April 2006 (UTC)

Xerxes, I don't see that. Can you explain, please? David Spector (talk) 01:11, 15 June 2023 (UTC)

Move the page to make it easier to understand

OK, I think I understand that this article is about quantum mechanics. But this is not clear from the lede or the title of the article. The phrase "intrinsic angular momentum" is presented as if that is supposed to clarify things, but it doesn't. People looking for the meaning of "spinning top" or "spinning wheel" or "spins round and round" would be better served by the information at Rotation or Angular momentum or even Billiards#English. Perhaps this page could be moved to e.g. Spin (quantum mechanics) or Spin (particle physics) or something like that. Ewlyahoocom 06:44, 7 April 2006 (UTC)

I'm against it. Exactly what sort of information did you have in mind to put in an article on spin? -lethe ^{talk +} 07:39, 7 April 2006 (UTC)

Against. People looking for the meaning of any of the phrases you mentioned would be more likely either to search Wiktionary for "spin," or to look up "top" or "wheel." The only field in which the term "spin" is used and is important enough to justify it's own article is physics. Linguofreak 17:58, 8 April 2006 (UTC)

Really? Then I guess most of the articles linked from Spin (disambiguation) derive their names from this quantum physics meaning, yes? Spin (public relations) actually refers to a spin-1/2 particle with non-zero magnetic moment? Figure-skating spin ("Pair spins", even!) has something in common with Pauli exclusion? Furthermore, I haven't suggested doing anything to Spin (physics) other than leaving it as the (automatically generated) redirect to the new name. With a new name, it would be more clear that the article is about quantum mechanics, and anyone arriving here by mistake would immediately know to click on the dablink to Rotation before wading through the article (for examples, see the above comments #Cleaning up the Intro, #Split?, #Clarify the First Sentence to make definition easier to understand). Ewlyahoocom 03:03, 9 April 2006 (UTC)

You've totally lost me. How will changing spin (physics) to spin (particle physics) make it easier for people looking for spin (public relations) to realize they're in the wrong place? -lethe ^{talk +} 17:23, 9 April 2006 (UTC)

Those comments are in response to Linguofreak's preceding comment that "The only field in which the term "spin" is used and is important enough to justify it's own article is physics." Ewlyahoocom 03:10, 10 April 2006 (UTC)

Ok, I admit, I made that point rather badly. Let me rephrase: The only field of physics where the term "spin" is used and is important enough to justify its own article is particle physics. Linguofreak 04:05, 10 April 2006 (UTC)

What are you talking about? Spin is important to all physics, not just particle physics. Atomic physics, molecular and chemical physics. Not to mention all of chemistry, in particular NMR, MRI, Open shell systems and radical chemistry, transition metal chemistry etc. It's a common and general physics concept, and it really does belong under "Spin (physics)". Also, spin is not a quantum mechanical phenomenon. So if someone comes to "Spin (physics)" expecting to read something else than what the entire physics world calls "spin", then that's their problem. --BluePlatypus 22:22, 13 April 2006 (UTC)

The word "spin" in physics is ambiguous. It refers to macroscopic spin, and to atomic-scale spin, which are totally different in properties and behavior. I'd like to see separate articles on "spin (classical)" and "spin (quantum)". David Spector (talk) 01:15, 15 June 2023 (UTC)

rename

Was this renamed from spin (physics) to spin (particle physics)? In any case, quantum mechanics requires angular momentum to be quantized for either elementary or composite particles. The two might have separate descriptions and separate articles, or separate sections within the article. Gah4 (talk) 18:53, 13 June 2023 (UTC)

Indeed it was, and I suggest moving it back by WP:CONCISE, and the fact that spin is not only relevant in particle physics but in other fields also, even if it on fundamental level is a property of elementary particles. It is of central importance e.g. in magnetism, and in that context it is awkward to refer to spin (particle physics). I would say that spin is similar to charge, which could be claimed to be a property of particle physics, but which also finds applications elsewhere, to put it mildly.

On the topic of separate pages: they might be useful for some subtopics, but there still needs to be a main page which discusses the concept of spin broadly (this page), and thus one cannot simply split this page into half (if that even was the suggestion). Jähmefyysikko (talk) 03:20, 14 June 2023 (UTC)

Is "Spin (physics)" ambiguous with measurements of rotation (e.g. angular momentum) of a macroscopic body in classical physics? Certes (talk) 23:00, 14 June 2023 (UTC)

I think the ambiguity can be address in the disambiguation page and the lead section on this page. See the following topic on this Talk page. Johnjbarton (talk) 01:16, 15 June 2023 (UTC)

What is spin?

I dug up a few good articles on the subject, namely "What is spin?", Ohanian, H.C., Am. J. Phys., 54(6), 500. And "Understanding electron spin", Boeyens, J. C. A., J. Chem. Ed., 72(5), 412. Both do a fairly good job of explaining how spin is not a quantum mechanical and/or relativistic effect. Perhaps something for the reference section? --BluePlatypus 22:29, 13 April 2006 (UTC)

I've been planning a rewrite of this article for a while which would eradicate from head to toe the notion that spin is either relativistic or a quantum phenomenon. Of course, it means that classical spin has to get some press time, which isn't really a concept that's used much, but well, I think it's worth it. My planned rewrite makes use of concepts from differential geometry, so it may not be as accessible to physicists as an article on spin deserves, so I'm a bit hesitant. Anyway, feel free to post references. Maybe I'd like to read them too. Are they online? -lethe ^{talk +} 23:57, 13 April 2006 (UTC)

I'd be interested in knowing your understanding of spin as a single topic, if you could share it here. But this was 17 years ago, so you may no longer be around. I see "spin" as two separate definitions united only in ambiguity of usage. David Spector (talk) 01:17, 15 June 2023 (UTC)

Cottage industry?

The study of the behavior of such "spin models" is a thriving cottage industry in condensed matter physics.

Cottage industry? I don't think that's the right phrase. —Keenan Pepper 15:45, 6 June 2006 (UTC)

You know, I saw that phrase a few weeks ago, and it seemed weird to me too, but my roommate who is in condensed matter physics says that it is used. -lethe ^{talk +} 16:08, 6 June 2006 (UTC)

There's another obscure term, "walled garden". Maybe best to avoid them? David Spector (talk) 01:19, 15 June 2023 (UTC)

Contradiction on definition of spin?

Can someone explain the following contradiction in the article, under the heading "Spin of elementary and composite particles"?

First it states:

Theoretical and experimental studies have shown that the spin possessed by these particles cannot be explained by postulating that they are made up of even smaller particles rotating about a common center of mass...

But a little further on it says:

The spin of composite particles, such as protons, neutrons, atomic nuclei, and atoms, is made up of the spins of the constituent particles, and their total angular momentum is the sum of their spin and the orbital angular momentum of their motions around one another.

Which statement is correct here? Mehrshad123 00:02, 14 December 2006 (UTC)

This is a really good question from 16 years ago, and deserves an answer. David Spector (talk) 01:20, 15 June 2023 (UTC)

Not really a contradiction...

Think of it this way: Just as a figure skater speeds up by bringing in her or his arms, thereby conserving angular momentum, the smaller a particle is, the faster its components must whirl about each other to maintain the same overall angular momentum.

While protons, neutrons, and other composite particles are certainly tiny, they have well-defined diameters that are sufficiently large to allow their constituents (quarks and gluons) to whirl about each other with enough separation to add significantly to the overall angular momentum of the particle. This is the "orbital angular momentum of their [quark and gluon] motions about one another" mentioned in the article.

An electron, in contrast, has never been found to have a measurable diameter no matter how closely one looks (where in particle physics "looking closely" translates into "no matter how high an energy one uses"). While very small components of electrons can (and have; see Preons) been proposed, the trouble is that no matter how one slice and dices and whirls such hypothetical pieces, they all must move within a region so incredibly tiny that they would have to exceed the speed of light many times over to provide significant additional angular momentum. This again is in sharp contrast to particles such as protons with diameters large enough to add angular momentum while whirling about at less than the speed of light.

Incidentally, the reason why the net angular momentum of a proton is a bit of a mystery is that from a theoretical perspective no one can quite pin down why all that whirling and twirling of the quarks and gluons seems to add up to... well... zero, more or less. That is, if you do nothing more than assume that two quarks have opposing 1/2 spins and the third one acts as a sort of tie breaker, you end up with a pretty good first guess at what the spin of a proton is: 1/2. Such unanticipated simplicity is a bit like looking down over a huge skating rink chock full of twirling dancers, some with arms locked together, some forming long chains moving at frightening speeds at the tips ... and yet finding that the only ones that really count when all is said and done were three smaller dancers dressed in red, yellow, and blue, all of whom were twirling at only half the speed of the very slowest of the other dancers. How, exactly, did all that other whirling and twirling by the other (mostly gluon) dancers manage to cancel itself out?

Terry Bollinger 02:01, 19 December 2006 (UTC)

A shorter way to say whatever he just wrote

It is not a contradiction because they are talking about different stuff. The 1st one is talking about elementary particle spin, which is the spin the article is about. The 2nd one is talking about angular momentum of non elementary particles. One is elementary, the other one is not. That's simple. —Preceding unsigned comment added by 128.54.72.182 (talk) 04:23, 2 December 2009 (UTC)

I think that people with a limited education in physics believe that there is only one concept of spin, and it applies everywhere. Physics articles should be correct, and not modified by otherwise well-educated WP editors, IMO. David Spector (talk) 01:23, 15 June 2023 (UTC)

Spin quantum number

Spin quantum number has some nice technical info about spin, and it does not really make sense to have these two as separate articles. --Itinerant1 21:25, 16 February 2007 (UTC)

I agree, I was looking for something in the article spin but the actual info was in Spin quantum number. Carnelain 07:41, 17 April 2007 (UTC)

The split is a mess. It would make sense to turn Spin quantum number into an specific, more general / chemistry - oriented article on electron spin and move the general features of spin physics into this article. 84.92.241.186 22:44, 27 April 2007 (UTC)

I agree, assuming that it is understood that the word spin is ambiguous: classical spin and quantum-level spin are completely different properties at completely different scales/regimes. David Spector (talk) 01:25, 15 June 2023 (UTC)

Outside Link: origin of spin

My website contains a mathematical derivation that shows clearly how the phenomenon of spin comes from a relativistic treatment of the Schrodinger equation for the electron. It also clearly shows how spin is hard to conceptualize by virtue of the fact that spin terms in the relativistic Schrodinger equation are imaginary. The site also contains a link to a .pdf file of all my handwritten notes detailing every tedious detail of the derivation. I think readers would benefit greatly from exposure to this. Please check it out, and if anyone thinks it is a good idea please link to it. The url is http://www.teraproofs.com/spin.html --Leiding 23:36, 18 June 2007 (UTC)

It is against WP policy to reference your own self-published work. This would violate two policies: WP:OR and [[[WP:RS]]. I'm surprised that no one has pointed this out in almost 20 years. David Spector (talk) 01:27, 15 June 2023 (UTC)

Spin IS rotation

And I thought elementary particles DO rotate. That's what "spin" means! How can anything have angular momentum if it doesn't revolve or rotate? By the way, what letter stands for spin in particle physics?--Mathexpressions 18:53, 12 July 2007 (UTC)

Elementary particles may spin, but this is not what quantum spin describes. Quantum spin terms in the relativistic Hamiltonian are imaginary terms, and this implies that we cannot easily conceptualize exactly what quantum spin is.--Leiding 16:28, 19 July 2007 (UTC)

The magnetic moment we observe as 'spin' isn't from the electron spinning. It'd have to be rotating with a surface speed faster than c to create the moment we observe. It's simply an intrinsic property of fermions. (I say 'simply'. Of course, I've no doubt there are fuller models for it at a level I don't understand.) The opening part of the article contradicts this at present, implying it's due to a rotation of the body. I'll have to dig up a few citations and correct this. 314159 00:13, 20 July 2007 (UTC)

This section is an example showing that physics articles ought to be edited only by those with an advanced physics education. David Spector (talk) 01:29, 15 June 2023 (UTC)

redirect

Recent edits on many articles change Spin (physics) to Spin (particle physics). I am not so sure that is correct. In many cases, the articles are describing composite particles like nuclei or even protons. Those would be better described as the former, as they are not the subject of particle physics. Currently there is a redirect, but it isn't so obvious that they should change. Gah4 (talk) 07:17, 13 June 2023 (UTC)

Nuclei or protons not being subjects of particles physics? What are you talking about? Those are textbook examples of particle physics. Headbomb {t · c · p · b} 08:28, 13 June 2023 (UTC)

By WP:CONCISE, the title should be just Spin (physics). @Hári Zalán: I do not understand the reason you gave in the edit summary, could you elaborate a bit? Jähmefyysikko (talk) 14:08, 13 June 2023 (UTC)

I agree with the previous comment. @Hári Zalán: the phrase "the momentum also called spin" doesn't make sense and cannot be used to motivate moving this article to a new title. What was wrong with Spin (physics)? Plumbum208 (talk) 17:15, 13 June 2023 (UTC)

Protons are the subject of nuclear physics. Studying the insides of protons is the subject of particle physics, more usually called high-energy physics. Protons are used in high-energy physics, as they are easier to accelerate to high energy. In fact, though, in the LHC it is quarks colliding and not whole protons. (Or maybe gluons.) In any case, it is usual to consider intrinsic spin of elementary particles separate from that of composite particles. Links for composite particles are best links to Spin (physics), and not to Spin (particle physics). Gah4 (talk) 19:07, 13 June 2023 (UTC)

That's a completely arbitrary and unnecessary artificial division of topics. Headbomb {t · c · p · b} 17:59, 14 June 2023 (UTC)

Sorry, I made a mistake. Zalán Hári (talk) 03:05, 14 June 2023 (UTC)

I take this to mean that we can move the page back to its previous name. I suggest you revert the renames. (@Dr vulpes, please note) Jähmefyysikko (talk) 03:29, 14 June 2023 (UTC)

Hey @Jähmefyysikko, thanks for the ping. It's not a problem I'll take care of it over the next couple of days. I should have dug a little deeper instead of just going along with the request. Is by Friday an acceptable deadline for the reverts or is this super urgent? Dr vulpes ^{(💬 • 📝)} 04:25, 14 June 2023 (UTC)

Thanks, and no, it is not urgent. In fact, I also plan to move the page back to its previous name only tomorrow, to allow a little time for possible objections. Jähmefyysikko (talk) 04:39, 14 June 2023 (UTC)

The change of name was inappropriate and should be reverted together with the edit spree that followed it. Further, the proposal to change the name should have been taken to this notice board before action was taken. Xxanthippe (talk) 06:09, 14 June 2023 (UTC).

I support moving this back to Spin (physics). Per WP:PRECISION, Usually, titles should unambiguously define the topical scope of the article, but should be no more precise than that. This renaming was, IMO, in direct opposition to this principle. WP:CONCISE also applies, which has already been mentioned. Also, the idea that the difference between "(physics)" and "(particle physics)" will be understood to disambiguate between two topics, or even subtopics, is kinda strange. Even Spin (quantum mechanics) would be preferable to Spin (particle physics) if one wanted a more precise title. Spin is even referenced in chemistry, which, last time I looked, was not a sub-discipline of particle physics. —Quondum 11:38, 14 June 2023 (UTC)

I too agree the name should be Spin (physics). Headbomb {t · c · p · b} 15:55, 14 June 2023 (UTC)

I also agree. XOR'easter (talk) 18:47, 14 June 2023 (UTC)

Ok edits fixed all the edits. I just reverted the words because there were a lot of minor clean ups or tags added to the articles. If there's anything else just ping me. @Jähmefyysikko Dr vulpes ^{(💬 • 📝)} 00:19, 15 June 2023 (UTC)

On account of the consensus on this page, I changed the title back to Spin (physics) and fixed the double redirects. Jähmefyysikko (talk) 03:20, 15 June 2023 (UTC)

This article makes no sense to non-physicists

I'm not a physicist and it doesn't make sense, which just proves my statement. The amount of confusing jargon here is ridiculous.

It even seems to contradict itself by implying that "spin" is not the same as it is in classical mechanics.

The introductory section talks more about what spin is not than what it is. After you tell me about classical rotation, you fail to finish your thought and tell me what quantum spin actually is. The introductory paragraph says that it doesn't mean "rotation" yet then you later mention how you have to rotate a spin-1/2 particle 720 degrees to return it to its original quantum state. But you don't mention what that "quantum state" really means.

The very first paragraph in the body of the article has a completely meaningless formula: $[S_{i},S_{j}]=i\hbar \epsilon _{ijk}S_{k}$ - which could maybe be more useful if you said what those variables are, but probably not.

"Spin in quantum mechanics" is also a silly section name given that, as far as I know, the entire article concerns itself with that subject.

How about you start with introducing spin for a layman and then get to the formulas that could only possibly help a physicist later on?

njaard (talk) 01:07, 15 April 2008 (UTC)

unfortunately, the quantum world is a very confusing place, it takes a litte faith to understand that 'spin' is just a name that is given to a property of quantum particles, it is not actually comparable to classical spin, i.e a ball spinning, and unfortunately by trying to compare it to classical spin to make it more understandable, it usually just ends up more confusing, just think of it as a property of the particle that happens to be called spin, rather than imagining an electron spinning like the earth does 193.60.83.241 (talk) 14:40, 14 May 2008 (UTC)

I recognize that. So why the comparison to classical spin at all? Just say "it has nothing to do with rotating bodies" and leave it at that. njaard (talk) 06:18, 15 May 2008 (UTC)

I agree, but have finals soon so do not currently have the time to amend 193.60.83.241 (talk) 20:11, 15 May 2008 (UTC)

I hate to disrespect, but non-physicists are not supposed to be able to understand quantum theory. Richard Feynman is quoted as saying that "No-one understands quantum mechanics", is he not? The reason the article is littered with jargon (seemingly incomprehensible to us novices) is that quantum theory is designed around very particular jargon, and none of it is particularly comprehensible at all, unless you take the years to study in a university wherein you could acquire mastery of this jargon.

As humans, we generally aren't good enough to write up everything in an equation as simple as "E=mc^2", our world doesn't work so "cleanly", so to speak. (and rumbles in the scientific community are starting to indicate that relativity may be due for revision)

Should anyone figure out a way to explain quantum physics to novices, their effort would be hailed as a breakthrough unparalleled in human history. To use a favored turn of phrase, that's just the way it goes. Quantum physics is confusing. The sky is blue, grass is green, and politicians lie. Feel free to eviscerate me over my opinions. CameronB (talk) 11:43, 23 May 2008 (UTC)

I agree it is very hard to understand for those not familiar with physics at a degree level, but by no means should that mean we should no try, and certainly not discourage people from trying to understant, if we go around telling people 'im not going to explain this because youll never understand it' then physics in the public eye will not improve, we must strike a compromise between how likely people are to understand a given concept, and the importance of not excluding the public from the world of physics193.60.83.241 (talk) 14:08, 24 May 2008 (UTC)

"No-one understands quantum mechanics" was a wry comment, not a theorem or a statement of fact. To quote it to justify insisting on QM being difficult to understand is a great shame, and not consistent with all the efforts by many people to popularize physics. The basics of QM can be explained simply, but it does require many steps to get from there to understanding the more specific results in QM. One problem is the unduly mysterious Copenhagen interpretation, which I discuss elsewhere on this Talk page. David Spector (talk) 11:03, 15 June 2023 (UTC)

CameronB I challanged you by creating a new section in the article called introduction to spin. I know it is far from wikipedia standard, I really wish that someone would fix it for me, but at least I have succeeded to explain spin in language that njaard-ites can understand. My nick is arielgenesis, can't be bothred to log in. 04:20, 2 December 2009 (UTC) —Preceding unsigned comment added by 128.54.72.182 (talk)

"The amount of confusing jargon here is ridiculous." WP is an encyclopedia for everyone, not just experts in a field of study, so I must agree with this assessment. Every piece of jargon should be a wikilink at first appearance. An example of a violation of this (should be a) rule is in the first paragraph: "quantized wave property" means nothing to someone with no education in physics. It should be a link to an article that starts with a very elementary explanation.

On another point, I don't agree that QM is necessarily a difficult or mysterious topic. There should always be an initial explanation that our commonsense physics applies only to our scale of nature, with a wikilink to an article explaining these differences in detail, with emphasis on the fact that classical and commonsense physics results from summing up trillions of individual wave functions, just as temperature results from summing up a range of elastic collisions of individual molecules.

Even the strange idea, generally accepted, that particles have no paths until they are measured or transformed is just a mystery/leftover from the Copenhagen interpretation, and is not actually required by QM. There should be a wikilink to an explanation of the big difference between QM and its standard (Copenhagen) interpretation.

Such strange nondeterminism is accepted by many physicists as an axiom (and therefore need not be proved), a neat way to sidestep the part of physics that requires theories to be tested by experiment.

In 1952, David Bohm published a simple interpretation of QM that permitted predictions of deterministic paths and other strange features of QM. His theory (nonlocal and hidden-variable, where the hidden variable is simply the initial position of each particle) was championed by John Bell around 1964 but was still ignored by most physicists. In 2003 an experiment to test for Bohm's theory was proposed, and in 2011 it was done and published. Still, the deterministic interpretation of QM is ignored by most physicists.

However, making use of Bohm's proposal would make much of QM more accessible to the educated person who is not very familiar with physics. The only mystery that would remain would be the Schrödinger equation, but I have no doubt that it can be interpreted in a simple way as a description of where and when energy is located in the atomic regime. David Spector (talk) 10:57, 15 June 2023 (UTC)

The proton is not a point particle.

The proton is not a structureless point particle. —Preceding unsigned comment added by 128.230.195.113 (talk) 16:28, 13 June 2008 (UTC)

Also, even though the proton carries mass, it isn't actually a point particle. It doesn't have a fixed size, and is frequently represented as a point particle (just as collections of particles can be represented by their center of mass). "Size" is a classical property, not one that always makes sense in the quantum/atomic regime. Sometimes it makes sense, such as in lining up a row of atoms, and sometimes it doesn't make sense, as in the way nucleons function in atoms and in collisions. David Spector (talk) 11:11, 15 June 2023 (UTC)

Daily Spin?

In the introduction in "For example, the spin of the Earth is associated with its daily rotation about the polar axis" I removed the redundant word "daily". Surely the fact of the Earth's rotation is independent of the interval over which the rotation is measured? Ditto “annal motion around the Sun”. A classical body does not have to make complete 360 degree rotations to have angular momentum. —Preceding unsigned comment added by 86.134.61.255 (talk) 14:50, 11 September 2008 (UTC)

I suppose so. But do note that the angular momentum of the earth must be a multiple of hbar/2. Gah4 (talk) 07:06, 13 June 2023 (UTC)

I'm not sure that's true. If Earth were in a single quantum state (all its particles being entangled), then that is obviously so. Anyway, whether it's true or not, it currently can't be measured because the energy of the Earth is way too large to measure with enough precision. David Spector (talk) 11:14, 15 June 2023 (UTC)

Are we sure the Daily Spin is a reliable source? Certes (talk) 12:33, 15 June 2023 (UTC)

"diagonal Detwiler matrices" ?!

In subsection "Spin and rotations", it says "Detwiler matrices". My research on what that could be was unsuccessful... so what is it? (As of now, I tend to think that such a thing simply does not exist.)85.166.232.86 (talk) 22:56, 1 January 2011 (UTC)

I can't find these mathematical objects either. I also tried spelling "detweiler". There's a Dwyer Matrix, but that has nothing to do with spin. David Spector (talk) 13:28, 15 June 2023 (UTC)

Edit requests

Peace and sorry I didn;t where to put the following feedback. Please remove after reading.

Can you please remove the following from the first paragraph: " it does not have a counterpart in classical mechanics (despite the term spin being reminiscent of classical phenomena such as a planet spinning on its axis).[2]"

It actually does have a real spin and the spin direction is what is called +1/2 or -1/2, and combinations thereof for the hadrons!

Please consider that electrical fields are merely photon fields helicating clockwise or counter-clockwise to give us what we call positive or negative polarity, and magnetic fields are CURLed electrical fields as the source particle physically spins around itself and therefore curling the electric field they are emitting.

Also worth noting is that an anti-matter of a particle is simply the same particle but with opposite helical photon fields emitted from it and when a particle meets its anti-particle their fields wrap around each other and hence don't radiate electric and by extension magnetic fields outside their local system (mistakenly called annihilation) but actually this what dark matter is. Random external gamma rays can knock such couplets off their "invisible hug and dance" back into particle and anti-particle.

Finally, please consider that neutrons are not neutral but rapidly alternating charged particle at such a frequency as to keep the positive protons from flying away. When a neutron is negative the protons around it starts moving towards it only for the neutron to change polarity (helication direction of its emitted photon field) to negative to prevent them from coming too close. This way the protons are constantly dancing around the spinning neutrons while being attracted and repelled constantly. This is what is called the strong nuclear force and required no magical glouns or any force carriers. The force carries are always the electromagnetic photon field (helicating and curling at the same time).

Please see http://heliwave.com/Helical.Particle.Waves.pdf

God > infinity — Preceding unsigned comment added by 100.1.90.243 (talk) 23:57, 26 March 2013 (UTC)

...the hell? Spin does not have a classical analogue at all - all apparent "spins" of macroscopic objects are really just orbital angular momenta of all particles, but then you go back to the quantum statement that "spin in classical mechanics is ±1/2 for hadrons"? Hadrons can have any allowed quantized values of spin. I'm sorry, but the rest of what you say is apparently plain nonsense... That pdf is nonsense and far from a reliable source. M∧Ŝc²ħεИ_τlk 06:56, 27 March 2013 (UTC)

Some of this comment sounds like bad physics. What is "real spin"? If you mean classical spin, this is contradicted by quantization. How can particles and antiparticles be the same except for emitted fields? Electrons and positrons don't emit fields unless they move. If neutrons had an alternating charge, where does the energy come from to power the alternation, and how come it doesn't emit radio waves? and how can the charge on a particle ever vary, when that has never been observed? The very idea isn't compatible with the "quantum" part of QM. David Spector (talk) 13:39, 15 June 2023 (UTC)

Comment on notation

The notation when specifying actual spin numbers is inconsistent. Sometimes the article uses spin 0, spin 1/2, ..., and sometimes it uses spin-0, spin-1/2, ...

To a casual reader, it may look like the spin can be negative. — Preceding unsigned comment added by 132.3.29.80 (talk) 20:33, 2 October 2013 (UTC)

In fact it is perfectly consistent and grammatically proper English syntax to hyphenate compound attributive adjectives immediately preceding their objects; i.e., we can speak of "a spin-1/2 particle having spin 1/2" and be perfectly consistent (and moreover, grammatically correct). However, your objection is certainly correct in that adjectival use in the article sometimes does NOT carry a hyphen, while nominal use often does carry hyphen.

The implication of spin "negativity" is not really objectionable, in that particles with nonzero spin can certainly take negative values of the vector quantity. But the inconsistent and ungrammatical usage (or lack!) of hyphenation is hardy of encyclopaedic standard. Perhaps you yourself would like to edit the article to conform to standard English usage? No technical knowledge should be required.72.179.38.56 (talk) 11:24, 21 October 2013 (UTC)

I agree. There would be a conflict between using "-" as a hyphen, since spin can be positive (up) or negative (down). David Spector (talk) 13:43, 15 June 2023 (UTC)

Quantum spin is a classical rotation

Spin has been considered as a purely quantum entity. However, it can be shown by using the Schrodinger wave equation in two dimensional multiply-connected space that spin angular momentum can take half-integral values. From these results, it can infer that elementary particles may have the topological structure of a gyroscope. Please refer to an article entitled ON THE SPIN ANGULAR MOMENTUM OF ELEMENTARY PARTICLES posted on ResearchGate by Vu B Ho for more details.101.182.40.21 (talk) 06:23, 24 May 2017 (UTC)

This just sounds like bad physics. The word spin is ambiguous and refers to two similar but different phenomena. One is classical, and really means angular momentum, which can be measured in theory to arbitrary precision. The other is quantum, and only occurs in certain fixed measurements (up or down), such as 0, +- 1/2, and +- 1. David Spector (talk) 13:49, 15 June 2023 (UTC)

Elementary particles are not points

Elementary particles are not points (which don't exist in nature anyway), so their intrinsic spin is well-defined. I suggest removing the text that suggests otherwise, starting "Since elementary particles are point-like".

The experimental proof is simple: particle beams of all kinds we can generate can collide with targets made of matter. For collisions to occur, the particles must have a collisional cross-section (see [[1]]). Although elementary particles are too tiny to have a well-defined size, their cross-section can do nicely to distinguish them from points, which cannot interact with anything else. All particles we can generate are capable of interaction. David Spector (talk) 17:49, 15 June 2023 (UTC)

The nature of the effective size of elementary particles is sufficiently unclear that any statement like "Since elementary particles are point-like" needs a citation. The sentence can be deleted.

The rest of the paragraph is an incomplete attempt to explain how the quantization of action connects classical angular momentum to spin quantization. In the quantum version of Hamilton's optico-mechanical analogy level surfaces (contours) of action become matter wave phases. The paragraph attempts to show the similarity of spin and orbital quantization by the similarity of spin and orbital action. I think.

Also not referenced and I think much more would need to be invested to make the content understandable. You make the call. Johnjbarton (talk) 22:59, 15 June 2023 (UTC)

Elementary particles are pointlike in the Standard Model. This is well established, and uncontroversial. See [2] for a low level explanation. Headbomb {t · c · p · b} 00:18, 16 June 2023 (UTC)

Thanks! However I do not believe that the sentence in the article is correct:

Since elementary particles are point-like, self-rotation is not well-defined for them.

The page by Don Lincoln ends with

"But even zero-size particles have an extended effect, due to the effect of the field surrounding them."

If a point-like particle can transfer linear momentum in a collision it seems to me it can have angular momentum as well. If not, then we need a reference for "self-rotation not well defined".

I also don't understand why that sentence even exists. As far as I can tell it is equivalent to "I'm about to tell you a lie". Following with "However," does not alter that in my mind.

I vote we deep six the paragraph.

I used your reference in the "Relation to classical rotation" section please check. Johnjbarton (talk) 01:36, 16 June 2023 (UTC)

The answer on this page aligns with the main content of the paragraph we are discussing:

https://physics.stackexchange.com/questions/73994/quantization-of-electron-spin/74050#74050

It also provides no reference and IMO it is too complex and incomplete for this place in this article. Johnjbarton (talk) 01:55, 16 June 2023 (UTC)

Revision of Relation to classical rotation

The last sentence of the current lead paragraph ends thus:

for electrons, the spin has no classical counterpart.[citation needed]

This claim can be shown to be incorrect with at least two citations.

Furthermore the section Relation to classical rotation seems off base. Except for the photon-polarization paragraph, its is about purely quantum ideas, defeating the purpose of classical analogs altogether. As is evident by the inconsistencies noted in that text assigning spin to rotation of distributed mass fails. I left these bits rebranded as "relation to orbital angular momentum". In my opinion the work "On the energy-momentum tensor" BY LÉON ROSENFELD demonstrates that much of this is also not quite correct. Johnjbarton (talk) 03:34, 15 June 2023 (UTC)

I'm not following you. If classical analogs have no purpose in QM, which I mostly agree with, then what, exactly, is wrong with the statement, "the spin has no classical counterpart"? It emphasizes that QM spin has different behavior than angular momentum (although formally similar). David Spector (talk) 13:56, 15 June 2023 (UTC)

I agree that we should emphasize the differences between subatomic spin angular momentum and macroscopic angular momentum due to rotating distributed mass. However there are "classical" models for subatomic spin so the statement is not correct. I have included a paragraph in "Relation to classical rotation", pointing to the wave circulation models with citations in the article. Please review.

The connection between spin and orbital angular momentum in the wave circulation model (Rosenfled paper) shows that both effects have related interpretations. But saying more than that seems impractical in the article. Johnjbarton (talk) 15:43, 15 June 2023 (UTC)

If I'm understanding your statement "there are "classical" models for subatomic spin", you are referring to Bohr's early model of the atom as a solar system. Besides being incorrect, such classical models are not in current use, so they could easily confuse a reader. I'm opposed to using classical mechanics to try to explain QM in any way. QM is simpler than classical mechanics, and by scaling up it gives rise to all of classical mechanics, so it should be presented that way. David Spector (talk) 15:58, 15 June 2023 (UTC)

I agree: we should not promote Bohr model concepts. They are history.

I agree that straight QM for spin is simpler. Some physical phenomena that are intrinsically quantum in nature, eg the relationship of spectral lines, are much simpler when explained with QM from the beginning. So approaching "spin" from QM to start rather than classical is fine by me. Ideally I would like to find a suitable reference that advocates just that approach and put a statement to this effect in the article. Do you know of one?

I don't agree with the idea that QM is simpler in general. Simple QM models for spin basically only address quantization and superposition. Awesome: these are very important concepts. But still you have a long road to cover QM and along the way the Correspondence principle is vital. Classical models are how we think about most of QM because we are classical.

I encourage you to read the opening paragraphs in the Ohanian paper I cited in Spin_(physics)#Relation_to_classical_rotation. It explains why the appropriate classical model is based on waves not particles. Quantum mechanics is wave mechanics, so this is no accident. Johnjbarton (talk) 17:09, 15 June 2023 (UTC)

I'm not interested in reading a paper, because papers frequently contain conjectures rather than facts. I suggest you read WP:RS, which explains what kinds of references are encouraged in WP. David Spector (talk) 17:36, 15 June 2023 (UTC)

Ohanian's paper is a WP:SECONDARY source with 319 direct citations clearly passing WP:SCHOLARSHIP. Johnjbarton (talk) 18:14, 15 June 2023 (UTC)

About "I would like to find a suitable reference that advocates just that approach": Me, too! But I think so long as Bohm's interpretation of QM remains little-known and even littler-believed, such an educational approach is not likely to happen. We are still in the infancy of QM; I feel sure that physics education will routinely start with QM hundreds of years from now, if not before. David Spector (talk) 18:07, 15 June 2023 (UTC)

I have a different perception. Bohm's interpretation is very well known. I've read about it in almost all modern QM books. Since interpretations don't make predictions it really is just one way of many to think about QM. Johnjbarton (talk) 18:28, 15 June 2023 (UTC)

I agree that right now, my statement that QM is simpler than classical physics is only an ideal. Since we, human beings, live in a classical world, a world some of whose laws may be tedious to derive from QM principles, I suspect that classical mechanics will always be taught. But it might be that someday soon, a student could query their computer about Newton's Laws, or even Reynolds number, and learn exactly how these concepts can be derived from QM, possibly with added stages between QM and the classical laws for easier comprehension. Perhaps someday we will have handheld or builtin tools that allow us to zoom into any object, and see how its molecules and bound particles interact, in some sort of standard symbolic rendering.

Quantum mechanics is not just based on waves; waves and particles have an equal footing, and under the Bohm interpretation, particles are more natural, since they have deterministic paths. I believe that waves, as discussed in QM, have finite extent and other complexities, so that there will always be an important place for particles. David Spector (talk) 18:07, 15 June 2023 (UTC)

I agree that waves and particles have equal footing. However there is no particle dynamics in QM, only wave dynamics. Particles can't be "more natural" since we agree that waves are on equal footing; I think you mean "easier to visualize".

In the case of this Spin article, particle visualization does not pan out. A wave visualization, while not as simple to visualize is more correct. That is the point of Ohanian's paper. Johnjbarton (talk) 18:35, 15 June 2023 (UTC)

I can't find a link to it, just the Journal reference. Do I need to look it up there?

You are incorrect that QM interpretations don't make predictions. The standard interpretation doesn't make predictions because it Bohr preferred to state a set of axioms.

Bohm indicated precisely how to calculate the paths of particles through QM experiments such as the double slit. An experiment to validate or disprove Bohm was designed in 2003 (using Weak measurement) and was done and published by another group in 2011. So there is experimental confirmation, plus the famous recommendation of John Bell. There also was one refutation published, but it was retracted due to an incorrect understanding of the proposed experiment.

So why isn't David Bohm accepted as yet? It is a big mystery, possibly due to a blacklist from Robert Oppenheimer, or possibly due to his being a victim of the Communist witch hunt of the 1950s and his inability to find work in physics as a result. David Spector (talk) 20:04, 15 June 2023 (UTC)

"I can't find a link to it, just the Journal reference."

Thanks! I fixed the link. Please try again. Johnjbarton (talk) 22:34, 15 June 2023 (UTC)

Can't find the link. Please put it here, thanks. David Spector (talk) 11:11, 16 June 2023 (UTC)

The problem is that the link first shows an irrelevant article, AND THEN the correct article further down the journal page. Go to the References section near the end of the article. Ohanian's paper is reference 3. Click on the words "What is spin?" which is the link you need. You will first see a paragraph starting with the words "IX. The importance of calculating with numbers", but this is the journal article which precedes the one you want. Move further down the journal page and you will see Ohanian's paper "What is spin?" Dirac66 (talk) 21:45, 16 June 2023 (UTC)

Wow thanks I would never have guessed that could be the explanation. Johnjbarton (talk) 21:51, 16 June 2023 (UTC)

No, that isn't the real problem. The real problem is that you keep writing about a link without giving the link. I still can't find it from your clues. David Spector (talk) 21:54, 16 June 2023 (UTC)

I set the link in the article. I gave it to you in my reply to your question on my talk page. And here:

The link is: https://physics.mcmaster.ca/phys3mm3/notes/whatisspin.pdf

I hope it works out finally. Johnjbarton (talk) 22:14, 16 June 2023 (UTC)

To users Johnjbarton and Dirac66: I have finally had time to read the paper, "What is Spin?" by Hans C. Ohanian, publshed in 1985. I find it to be very well-written, clear, and compelling, although I must admit that I do not have sufficient physics background to follow any of the equations and other formalism. I used ChatGPT to investigate some of my questions about the paper and got reasonable confirmations: treating spin and orbital rotation together as resulting from the circulation of energy in an electric field does indeed tie together elementary particle spin as revealed by QM with spin as revealed by classical physics, and therefore it is justified to say that these two kinds of spin are in a real sense the same, even though QM spin is quantized and only fully measurable in two opposite directions along a laboratory axis, so that classical spin depends (similar to gas pressure) on a statistical ensemble of QM spins.

However, that being said, the reasoning for making this connection, and hence for justifying its inclusion in this WP article, depends currently and fully on advanced mathematics for its validity, not on common sense or high school physics. Therefore, assuming a reliable publication reference can be found for Ohanian's ideas (to avoid WP:OR), I would favor their inclusion, but only in an advanced section of this WP article, and certainly not in the lead or early paragraphs. I welcome continued discussion, if any. David Spector (talk) 12:50, 19 June 2023 (UTC)

Thank you for taking the time to read the paper and report your conclusions.

I agree that this article should not delve any further into the mathematical details discussed by Ohanian. My purpose in adding the citation is to justify the content added to describe the nature of subatomic "spin", to you and to other, future wikipedia editors. In addition, a curious or skeptical reader can look up the resource to learn more you did.

If we had a tertiary reference for the subject that would be great to add. Finding readable, accurate descriptions of complex physical phenomena for non-physicists is -- as you may know -- very difficult. I hope to visit some libraries soon and I will be on the look out.

I understand that you don't find classical analogs helpful. You and similarly inclined readers are welcome to skip such sections and focus on the content that you do find helpful. For readers who do find them helpful or are curious about them I think we should provide accurate and referenced information.

HTH Johnjbarton (talk) 15:14, 19 June 2023 (UTC)

We seem in agreement to remove all analogies between quantum and classical spin, perhaps replacing them by a statement that such an analogy is possible but difficult to justify without advanced mathematics. It is a bit iffy even to include this statement without having a reference in a WP:RS. David Spector (talk) 15:20, 19 June 2023 (UTC)

Sorry we don't agree. I think the article is fine as is; I've defended the Ohanian reference as secondary, in a reputable journal, and well cited. The mathematical content of his article, while not to your taste, is not relevant to assessing its validity as a reliable reference. A very large number of lower quality reference in physics articles exist with as much math; it's in the nature of the field to be so.

Classical analogies appear in almost every quantum text book; they are an historical fact and continue to be valuable. If you don't find them useful just ignore them. They absolutely belong in any encyclopedia summary of quantum mechanics.

If you have or find references as solid as Ohanian with a different point of view then we should present both points of view without bias and with appropriate references. It's not appropriate to remove a point of view that you don't agree with.

(To be honest I'm unsure why you think this issue is important. As I understand it you prefer Bohm's quantum model whose main attraction as far as I can understand is the connection to classical models of particle motion and determinism. Furthermore, according to wikipedia, "De Broglie–Bohm theory deals with this by noting that spin is not a feature of the particle, but rather that of the wavefunction." suggesting some overlap with Ohanian's point of view.) Johnjbarton (talk) 01:42, 20 June 2023 (UTC)

Classical spin

There should be more discussion of spin in classical physics and astrophysics. For example, why does the moon show the same face to the earth all the time, implying that that its rate of rotation about its own axis is exactly the same as its rate of rotation about the earth, whereas the earth does not show the same face to the sun? Xxanthippe (talk) 00:44, 27 July 2023 (UTC).

I most strongly disagree with this proposal. The first few words of this article makes it clear that the article does not include any discussion of angular or orbital momentum. There is another article for those topics. This article refers only to quantum mechanical spin, which bears no resemblance whatsoever to the observation that the Moon never shows a certain part of its surface to Earth. David Spector (talk) 00:56, 27 July 2023 (UTC)

Agreed with the reply. Dhrm77 (talk) 10:48, 27 July 2023 (UTC)

The Moon/Earth rotation issue you are looking for is called tidal locking, the article is excellent, check it out.

The second line of this Spin article points out that this article is about quantum effects. For classical it points to Rotation. So we should improve that article to make the connection to tidal locking. Johnjbarton (talk) 14:32, 27 July 2023 (UTC)

I added a section to rotation under astronomy named spin and linked tidal locking in a paragraph.

Resolved

Johnjbarton (talk) 14:43, 27 July 2023 (UTC)

even and odd spin

When it turned up that spin 1/2 exists, one talks about half odd integral spin versus integral spin. This ugly language should be changed. In the unit of h-bar/2 the fermions have odd spin and the bosons have even spin. That is easier.

When it turned up that the quark charges are integer multiples of 1/3 proton charge, the decent thing is to introduce a new elementary unit so that the proton charge is 3 and the electron charge is −3. This is not what the physicists did, however, for they had grown accustomed to the Millikan unit, but for the teaching of young people it should be done right.

Am I wrong? Bo Jacoby 14:25, 19 July 2006 (UTC)

You are not wrong, however fixing notation is not within the purview of Wikipedia. The right approach is probably to write some physics textbooks. After a few decades, if your proposal has caught on in physics education, then Wikipedia may follow suit. -lethe ^{talk +} 17:17, 19 July 2006 (UTC)

Yes, I agree with your idea. 90.242.56.230 (talk) 19:34, 6 January 2024 (UTC)

Thanks for your respons. A short explanation might save future readers from some of the confusion which I felt by the mystery of half odd integer spin. The subject matter is sufficiently complicated already. This extra complication may be the straw that breaks the camel's back. Bo Jacoby 14:24, 20 July 2006 (UTC)

When writing your book, please also rename the concept of "atom" to "tom", for "a-tom" literally means "un-splittable", we now know they are in fact divisible, not only will it save them from years of confusion, it is also more concise in notation as it is 25% shorter.. — Preceding unsigned comment added by 213.211.139.49 (talk) 03:20, 10 September 2017 (UTC)

There are many words that are literally incorrect due to knowledge gained since the word was first coined. We don't usually change our language to account for this very real effect, especially when the word or its components come from another language, as in this case. Sorry my reply was delayed by 5 years. And consider the famous pairs of words flammable and inflammable, which are two views of the same situation. David Spector (talk) 11:10, 16 June 2023 (UTC)

I agree with you as much etymology does not make sense, like atom (meaning unsplitable ( as mentioned was in another post) when you can split atoms.) 90.242.56.230 (talk) 19:39, 6 January 2024 (UTC)

Perhaps we should use the past tense: atom meanT unsplittable when the word was proposed, although now we understand that what we call atoms are not in fact unsplittable. Dirac66 (talk) 22:35, 6 January 2024 (UTC)

Helium atom

It is mentioned that the Helium atom in the ground state behaves like a boson. It should be mentioned that probably only some of its degrees of freedom behave like bosons. If we make the full parallel with elementary bosons such a statement would lead me to think that a liter of Helium would collapse into a small volume as a BE condensate, but this is not true as it just becomes a superfluid. Thus its wavefunction cannot be bosonic in spacetime. — Preceding unsigned comment added by Dragomang87 (talk • contribs) 07:40, 21 April 2020 (UTC)

Above absolute zero, not all will be in the ground state. At absolute zero, they will be, but I think it doesn't go to zero volume. Gah4 (talk) 04:25, 23 August 2023 (UTC)

Also, protons and neutrons in the nucleus pair up by spin, but the volume doesn't decrease. It is interesting, and I don't know the physics enough to say more about it. Except that they don't. Gah4 (talk) 18:45, 16 January 2024 (UTC)k

Ohanian

Do we need to start the article with a quote from some not-so-notable researcher? It is kind of weird, like who is Hans Ohanian? I know that he contributed to general relativity but it is unclear to me why is important to put this quote of him in the lead of the article about spin. Can we find a quote from one of the pioneers of spin research? Maybe we can just remove attribution or the quote altogether?

The phrase is not even that clear to produce a classical picture of spin. What is one supposed to think by reading energy flow of the wavefield of the electron ReyHahn (talk) 13:12, 16 January 2024 (UTC)

Please read Ohanian's work and look up the articles on Google Scholar. (I don't know why he has no wikipedia bio when so many obscure folks do).

• From the bio on his Gravitation book: Hans C. Ohanian received his BS from the University of California, Berkeley, and his PhD from Princeton University, where he worked with John A. Wheeler. He has taught at Rensselaer Polytechnic Institute, the University of Vermont, and in summer courses at UNED in Spain. He has published several textbooks in addition to Gravity and Spacetime, including Classical Electrodynamics and Principles of Quantum Mechanics, as well as articles on various aspects of relativity and quantum theory.
• From the bio on his Norton books: "He is also the author of dozens of articles dealing with gravitation, relativity, and quantum theory, including many articles on fundamental physics published in the American Journal of Physics, where he served as associate editor for some years."

The "What is spin?" is a peer reviewed secondary ref with 335 citations on Google Scholar. I assert that it would be difficult to find any other reference on spin with anything like this quality metrics.

As for energy flow of the wavefield, it seems clear to me, certainly as clear as any physics explanation, but maybe you can find better. Any description of a electrical fluid flow is difficult to describe.

The reason I believe this content is important is because it refutes two incorrect ideas about quantum spin: 1) tiny spinning hard ball and 2) "nothing, nothing, we can not think about it!". Both are incorrect. Johnjbarton (talk) 17:35, 16 January 2024 (UTC)

I am not saying that he is not notable, but it is unusual for physics concepts (specially high-priority) to start with a quote from somebody specially if he did not came up with the concept. Also I am not saying that we should not cite him, we should if it is useful, but the quote seems unecessary in the lead. The analogy makes me think of a fluid around the electron but a fluid of what? And how is that better than saying the electron is rotating?.--ReyHahn (talk) 18:59, 16 January 2024 (UTC)

The electron is not rotating, so we can't say that; the electron has no diameter. The quantum wavefield represents a probability and that wavefield has circulatory dynamics leading to angular momentum.

Another similar article by Sebens:

• Sebens, Charles T. "How electrons spin." Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics 68 (2019): 40-50.

I put the quote in because the summary I had previously kept being changed in ways that changed the meaning. Johnjbarton (talk) 19:15, 16 January 2024 (UTC)

Oh and it seems I failed to quote correctly, sorry. flow of charge, not energy. Johnjbarton (talk) 19:20, 16 January 2024 (UTC)

(edit conflict) Would you be ok with either one of this two possibilities: a) move Ohanian's quote somewhere else in the article b) leave the quote in the lead but move the discussion of the interpretation of spin to the bottom of the lead? --ReyHahn (talk) 19:22, 16 January 2024 (UTC)

What else will take the place of this material if it is moved? Generally the top of the intro is definitional.

In many applications, for example classifying particles by possible values of angular momentum, a very simple quantum concept is adequate. Maybe you can find a reference to that effect? That the spin is quantized does not alter the microscopic model any more than the quantization of orbital angular momentum alter the spatial character of hydrogenic orbitals. It just has turned out that orbitals are visually useful but flows of charge are not.

I think that the amount of misinformation about spin (tiny balls or "impossible") speaks to the need to place a reasonable summary of the complex issue early in the intro. The phenomenon is complex and I think it should be faced as such. Johnjbarton (talk) 19:45, 16 January 2024 (UTC)

Funny enough Griffiths' Introduction to Quantum Mechanics (book) says that Ohanian's "What is a spin" takes a "contrarian view".--ReyHahn (talk) 19:07, 16 January 2024 (UTC)

yes, Ohanian says as much in his introduction. Johnjbarton (talk) 19:16, 16 January 2024 (UTC)

Maybe we just need to add more to the article from the wave field model work? Johnjbarton (talk) 19:51, 16 January 2024 (UTC)

What do you suggest? I think the definition should be clearer from the start something along the lines:

• In physics, spin is an intrinsic form of angular momentum carried by elementary particles, and thus by composite particles such as hadrons, atomic nuclei, and atoms.  It behaves like angular momentum but it is not associated to spatial coordinates.
• To explain the electron magnetic moment, the electron was originally proposed as a small rigid particle rotating about an axis, as ordinary use of the word may suggest. However if one replaces the electron by a sphere with a radius equal to the classical electron radius, the sphere would rotate faster than light violating special relativity. The electron is a point particle and has no structure, the spin is thus an intrinsic property with no classical analogue.

Then we may include Ohanian, but if Ohanian is not explained in more detail in the article then I do not see the point of keeping it.--ReyHahn (talk) 09:09, 17 January 2024 (UTC)

"spin is an intrinsic form of angular momentum carried by elementary particles," We should start with a reference for this claim. I provided one for the electron case.

(The Ohanian article only discusses electron, so that is the strongest reason to move it out of the intro).

"The electron is a point particle and has no structure, the spin is thus an intrinsic property with no classical analogue."

This is synthesis. QM does not allow these kinds of statements. Certain kinds of high energy collision experiments attempting to determine the radius of the electron fail to detect any. There are a vast number of other experiments where the electron does not act localized. Experimental measurements of angular momentum are not done in the high-energy collision cases.

Please re-read the paragraph you wrote. You have two classical models for the electron that fail. Then you conclude that angular momentum must still be intrinsic! Why? Ohanian's review looks at QM models and shows that QM models provide a non-voodoo explanation. Complex? yes, complex like say QED. Would you dismiss QED with "dynamics with no classical analog?" Johnjbarton (talk) 17:34, 17 January 2024 (UTC)

Hmmm. could you explain the following:

• "spin is an intrinsic form of angular momentum carried by elementary particles," what is controversial about this? "Intrinsic angular momentum" is a common synonym for spin, or is it "elementary particle"?.
• This is synthesis. QM does not allow these kinds of statements. what kind of statements are not allowed?
• Certain kinds of high energy collision experiments attempting to determine the radius of the electron fail to detect any. I agree that it is a little bit more nuanced, however the radius cannot be larger than problematic classical electron radius, and even if it had a radius the "paradox" stil holds because spin is not related to rotation.
• Then you conclude that angular momentum must still be intrinsic! I am falling to see the contradiction.
• Sorry again, I am failing to see the analogy with QED. Some phenomena in QED have classical analogues some don't. The easiest way to look for them is to take semiclassical approximations and see what survives.

ReyHahn (talk) 18:54, 17 January 2024 (UTC)

• "spin is..." I was just asking for a reference.
• In QM the "classical" behavior observed depends upon the experimental set up. EG wave-particle duality or many which-way experiments. One experiment that shows eg zero radius does not contradict another experiment that shows infinite plane waves.
• The entire concept of radius is classical.
• Holding to an infinitely small spherical model of a "particle" is what leads one to the conclusion that spin is a mysterious voodoo property. "Intrinsic" is a word that leads on to believe that a fictional isolated tiny spherical ball would have angular momentum. But there is no isolated spherical ball. QM models for isolated "particles" fill all of space.
• The analogy to QED: it seems to me that your complaint about the wavefield model boils down to "it's too complicated". But the microscopic phenomenon is complicated. Lucky for us the bound states are quantized so we can make a great deal of analysis without ever thinking about the microscopic model.

I proposed a section "Microscopic models" or similar to cover these issues. The intro can have one sentence summary which we can fight over after the section is complete. Johnjbarton (talk) 19:19, 17 January 2024 (UTC)

• Intrinsic angular momentum is an alternative name for spin, spin is intrinsic. Read the chapter of spin from Introduction to Quantum Mechanics (book) where it says basically the same stuff. The point is that in QM spin has no spatial extent. Even if the electron was a wave in a material, the spin is not associated with any set of points in space and it is not a function or "x" or "p" coordinates. Spin is only associated (intrinsic) to the electron and lives in its own tensor product space separate from position (particle or wave).
• Point particle in the sense that it has no internal structure, no shape to associate to it. Also its charge distribution is spherically symmetric.

Ohanian model makes me think that there is something else, that if I think of the electron as some wave in space, that there is some circulation within the wave. I think that is flawed.

As for the proposed section, I can agree on that. There one can expand more Ohanian model. ReyHahn (talk) 19:43, 17 January 2024 (UTC)

Well an electron is a wave in space, that has been established for over a hundred years now. QM is a wave theory. As we know, this does not preclude point-like quantum events. Such dichotomies are why the subject is famously difficult.

It will take me a few days before I can address a new section; I stepped in something over on International system of units that need to clean up first. Johnjbarton (talk) 00:22, 18 January 2024 (UTC)

My criticism has nothing to with the electron being a wave or a particle. The fact that the spin is associated to the electron but does not have any dependence in space-momentum coordinates is what makes me think that any analogy of sort where something orbits or rotates is going to be flawed.

Take your time, you are doing great work!--ReyHahn (talk) 19:19, 18 January 2024 (UTC)

Ok I've not forgotten. I'll start work now. Johnjbarton (talk) 17:09, 28 January 2024 (UTC)

• Comment. I do not think that Ohanian's book is a very reliable source; he is very much outside the mainstream of theorists. I think that references to Ohanian should only be used when supported by more authoritative sources. Xxanthippe (talk) 09:19, 17 January 2024 (UTC).

  Reliable source or not, it is a still well known and valid source. My probably is not the source but the quote at the beginning of this article. It is not a good way to start an article. It is unconventional and it says little. --ReyHahn (talk) 16:11, 17 January 2024 (UTC)

  Please read the article. The reference is not to his book. If you have sources supporting a claim that his review is unreliable, then both can be included. (Since the article quoted is peer reviewed in a well known journal with over 300 citations you will need a secondary reference with a hundred citations to make a credible claim in my opinion.) Johnjbarton (talk) 17:16, 17 January 2024 (UTC)

Motivation

I would like to start this article with a section like "Significance" or "Importance" or some such. I guess a typical reader may not realize the vast impact of the spin concept. I have a couple of good sources. By reviewing the impact of the idea readers may be motivated to read more; the impacts are likely to be easier for non-technical readers to appreciate.

This would necessarily include applications currently at the bottom of the article. I have seen this in other articles (roughly a bunch of math and a small section on applications). I think this "axiomatic" model for articles is off putting for many readers but before I make this change maybe other opinions will be offered. Johnjbarton (talk) 19:48, 1 February 2024 (UTC)

History section revamped.

I worked over the history section; please review. @ReyHahn Johnjbarton (talk) 02:24, 4 February 2024 (UTC)

Looking great!--ReyHahn (talk) 12:34, 4 February 2024 (UTC)

One question, the Thomas half mentioned here is about the fine structure of hydrogen right? Maybe it should be mentioned.--ReyHahn (talk) 12:39, 4 February 2024 (UTC)

Yes, thanks, done. Johnjbarton (talk) 23:16, 4 February 2024 (UTC)

Models

I have rebuilt the "Relation to classical rotation" in to a "Models" section. Just a start and needs some TLC. I have several references to build in still but this is the structure I'm going for. Johnjbarton (talk) 01:16, 5 February 2024 (UTC)