Talk:Spin-1/2

Page title

Should'nt this be named spin operator? Karol 19:40, 28 October 2005 (UTC)

Fermions

Recent edits seem to suggest that all fermions have spin of 1/2. However, I was under the impression that fermions have half-integer spin (not necessarily 1/2).--GregRM 02:51, 16 March 2006 (UTC)

You are right. What I really meant is that all fundamental particles that are fermions have spin 1/2. Of course, composite particles can have any integer or half integer spin. I have changed the article accordingly. Thanks for the catch. Grokmoo 03:51, 16 March 2006 (UTC)

It is still slightly unclear. The definition says

Fermions have half-integer spin.
Spin-½ particles constitute an important subset of such fermions.

Assuming that an important subset is strictly a subset, one derives that while having half-integer spin implies being a spin-½ particle, the opposite is not necessarily true. That, in turn, reveals the difference between half-integer and ½, after possibly excluding that the dash should be interpreted as a minus. Would it be overwhelmingly pedantic to state that Spin-½ is the property of particles whose spin is ½? Hmm... I'll do it. ale (talk) 13:41, 3 May 2009 (UTC)

Unclear use of dash

After reading this article, some people may be confused by the expression 'spin-1/2' - in that does it mean a spin of negative half, or positive half (with a dash just for linkage)? This should probably be redefined or at least explained in the article. Harabanar (talk) 11:21, 15 September 2009 (UTC)

I am confused, because the dash is omitted in some instances, and included in other instances. Is there such a thing as an unsigned spin? The article title implies only negative spins exist. Comfr (talk) 19:11, 27 June 2022 (UTC)

Heisenberg picture

How does the spin operator look in the Heisenberg picture?

Etymology

How should Spin-½ be pronounced..? "half-spin", "spin minus a ½"..? For outsiders it is not obvious. --Harabanar (talk) 11:21, 15 September 2009 (UTC)—Preceding unsigned comment added by Harabanar (talk • contribs) 08:06, 15 September 2009 (UTC)

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In the CRC Handbook, the spin of 4Be8 is given as zero. Then the spin of 4Be9 is given as -3/2. And the spin of 5B10 is given as +3. What is that supposed to tell me? WFPM (talk) 03:06, 14 November 2008 (UTC)

That nuclei are composite particles. Eutactic (talk) 02:47, 12 October 2010 (UTC)

Wave function

Can we put the wave function of the electron in the article? Jackzhp (talk) 16:36, 23 October 2013 (UTC)

Spin as consequence of ...

This claim seems not true, spin 1/2 seems to be explained by Heisenberg by the 1st time. Jackzhp (talk) 20:17, 23 October 2013 (UTC)

Mathematical Description Section

This sections sounds as if it was written by a non-native English speaker, so I'll try to clean it up. It could also use some fleshing out as it's rather sparse at the moment but covers a topic that's critical for undergraduate studies in physics. — Preceding unsigned comment added by ArchetypeRyan (talk • contribs) 04:36, 7 November 2013 (UTC)

Also, I would be very careful of citing McMahon's book QFTD. His publisher McGraw-Hill Education is notorious for farming out much of the production work on its books to Conveo, and the proof-reading tends to be abysmal, with dozens of errors. We removed McMahon's book Quantum Mechanics Demystified from the References in the article Angular momentum operator for just this reason: hundreds of typos.Edgeorge (talk) 00:01, 1 February 2014 (UTC) Duncan

There is a problem with this section that someone should really look into. There is a difference between the ket-notation and the spinors. They are NOT equal as written in the article, there is rather a correspondence between the two notations. For e.g. the state $\left|\psi \right\rangle =\alpha \left|\uparrow \right\rangle +\beta \left|\downarrow \right\rangle$ would correspond to the spinor

$\left|\psi \right\rangle \leftrightarrow \chi =\left[{\begin{array}{c}\alpha \\\beta \end{array}}\right]=\left[{\begin{array}{c}\left\langle \uparrow \right.\left|\psi \right\rangle \\\left\langle \downarrow \right.\left|\psi \right\rangle \end{array}}\right].$

To say that $\left|\psi \right\rangle =\chi$ is hence not strictly correct. Many authors tend to make the association, but I think it is important to clearly separate these two ways of denoting the spin state. JezuzStardust (talk) 13:10, 10 October 2018 (UTC)

Complex Phase

Hope i haven't annoyed anyone, but I just added the following para

In terms of more direct evidence, physical effects of the difference between the rotation of a spin-half particle by 360° as compared with 720° have been experimentally observed in classic experiments [5] in neutron interferometry. In particular, if a beam of spin-oriented spin-half particles is split, and just one of the beams is rotated about the axis of its direction of motion and then recombined with the original beam, different interference effects are observed depending on the angle. In the case of rotation by 360°, cancellation effects are observed, whereas in the case of rotation by 720°, the beams are mutually reinforcing.

- as this section seemed misleading or murky without something like that. Doubtless folk will correct me if I slipped up. Reflection (talk) 21:07, 9 December 2016 (UTC)

Requested move 11 September 2021

The following is a closed discussion of a requested move. Please do not modify it. Subsequent comments should be made in a new section on the talk page. Editors desiring to contest the closing decision should consider a move review after discussing it on the closer's talk page. No further edits should be made to this discussion.

The result of the move request was: moved. (closed by non-admin page mover) Lennart97 (talk) 17:20, 18 September 2021 (UTC)

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Spin-½ → Spin-1/2 – After some discussion on Wikipedia talk:Manual of Style/Dates and numbers#Fractions in article and category titles, it's been suggested that we bring science and math article titles into alignment with the MOS:FRAC guidance for that genre, which means avoiding precomposed fraction characters. Starting a discussion here to make sure that's a consensus that includes local editors. -- Beland (talk) 06:23, 11 September 2021 (UTC) Beland (talk) 06:23, 11 September 2021 (UTC)

• Support per (1) MOS:FRAC guidance not to use lifted⁄lowered fractions in mathematics and science articles, (2) the technical inability to use ${\tfrac {1}{2}}$ in article titles, (3) the fact that for this topic it's the meaning that matters rather than the typography of the name, and "spin-${\tfrac {1}{2}}$", "spin-1/2", and "spin-½" all have the same meaning, and (4) my not-very-thorough survey of Google Scholar in the linked discussion, from which it appeared to be the case that, although all three formats are in common use in titles of articles in the scientific literature, "spin-1/2" appears to be more frequent. —David Eppstein (talk) 08:18, 11 September 2021 (UTC)
• Support per the comment above. It's the meaning that matters, and we might as well go with the simplest and most portable encoding of that meaning. XOR'easter (talk) 16:48, 11 September 2021 (UTC)
• Support. I'd even go further and restrict article titles to ASCII characters. It is the meaning in English that is important, and as more and more platforms and devices provide web access this will become more and more of a problem, and the solution is very, very simple and has no downside other than for the purists. Andrewa (talk) 08:12, 18 September 2021 (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.