Talk:Kramers' theorem

Wrong link

I think the link in the references to the original article goes to the right journal, but not the right issue? — Preceding unsigned comment added by 163.1.18.5 (talk) 12:10, 10 October 2022 (UTC)[reply]

Not completely correct

Have not read the original Kramers' work, but the "Kramers' theorem" I know is: In a system with time-reversal symmetry (TRS) all energy levels are even times degenerate.^[1] ^[2] (I have checked this statement for electrons.) Thus a system possessing TRS can not, for example, have a three-fold degenerate energy level. There is also a serious mistake in the article: an electric field can break the TRS (e.g., when I apply electric field to a metal, electric current starts to flow), and in this case Kramers' theorem is not valid. (Of course, a system without the TRS can still have degenerate energy levels, e.g., due to spatial symmetries.)

^ Петрашень, М. И. (2000). Применение теории групп в квантовой механике (in Russian) (4 ed.). Эдиториал УРСС. {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
^ Petrashen, M. I. (2009). Applications of Group Theory in Quantum Mechanics. Dover Books on Physics. {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)

--Shalaev (talk) 21:48, 17 December 2012 (UTC)[reply]

Thanks for the remark on the even times degeneracy issue. I reworded so that it points to this more general case. Megaleoo (talk) 06:33, 7 August 2022 (UTC)[reply]

Article name

I believe the name should be "Kramers' degeneracy theorem" (note the apostrophe). The current article name ("Kramers theorem") should just be a redirect to that name. Agreed ? StuRat 04:16, 27 October 2006 (UTC)[reply]

I don't think there is a reason why putting the apostrophe is necessarily better. There are some theorems that have them, such as Green's theorem, but many don't. For a discussion about this and many examples where there is no apostrophe after the name of a person after whom a theorem was named, see this discussion.

Hence, I think whether or not it should be Kramers or Kramers' should rest on which version is most commonly used. From what I could gather:

Google results for both spellings are almost the same number.
I could find four quantum mechanics textbooks that used the spelling Kramers degeneracy (without apostrophe): Sakurai, Le Bellac, Gottfried & Yan and Hal Tasaki.

So I think Kramers would be more appropriate as the main title. Megaleoo (talk) 06:32, 7 August 2022 (UTC)[reply]

I think we should use Kramers' theorem to keep up the style of theorem names in Wikipedia. See also Kramers' law --ReyHahn (talk) 15:43, 8 August 2022 (UTC)[reply]

There is an error in this brief explanation. In fact, the magnetic field (or induction) should be present in the Pauli's equation so that Kramers degeneracy can make sense. By the way, the spin-carrying charged particles always interact with the magnetic induction created by its movement, thus the necessity of the presence of the magnetic induction. —Preceding unsigned comment added by Ghjeung (talk • contribs) 16:57, 14 January 2009 (UTC)[reply]

[1] Петрашень, М. И. (2000). Применение теории групп в квантовой механике (in Russian) (4 ed.). Эдиториал УРСС. {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)

[PeTriEng-2] Petrashen, M. I. (2009). Applications of Group Theory in Quantum Mechanics. Dover Books on Physics. {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)

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