Talk:Expectation value (quantum physics)

Stub?
The article was classified as a stub. However, I am not sure what additional information would be expeceted?

In my opinion, two alternatives would make sense:


 * Leave the article as it is, maybe with a bit rephrasing, and link it to quantum state for more information;
 * Merge with quantum state

What would be the preferred option?

--B. Wolterding 16:06, 6 May 2007 (UTC)

This article can definately be expanded as the concept of the expectation value is more diverse than what has been written. You can talk about expectation values and what they mean physically - i.e. observables and non-observables. This article would certainly benefit from a merger with expectation value (quantum mechanics) as they are really the same. I suggest NOT merging with quantum state however, as the quantum state is well, a state or parameter, while the expectation value is an operation on the state.

Renji07 00:15, 14 August 2007 (UTC)

Merger
User:Frostlion has proposed to merge this article with Expectation value (quantum mechanics). Please add your comments below. --B. Wolterding 10:25, 3 July 2007 (UTC)


 * Merge. I agree with the merger, the articles cover the same topic. The concept of "expectation value" is not restricted to quantum mechanics, it is used in all areas of quantum physics (relativistic and non-relativistic). The title of the merged article should be Expectation value (quantum physics). --B. Wolterding 10:25, 3 July 2007 (UTC)


 * Merge. Yes please merge these pages. I don't see any real point of difference between the expectation value of quantum physics or quantum mechanics. Renji07 23:50, 13 August 2007 (UTC)
 * If no one else has any objections to this, can the merger be performed within two weeks? Also I suggest that this article be merged into expectation value (quantum mechanics) seeing as its usage is really in the application of quantum mechanics.
 * The proposal has been around for quite a while, so you can just go ahead. (Or I could also do that within the next two weeks.) However, I do not agree with you that the usage of the concept is really in quantum mechanics. The expectation value is used just as well in quantum statistical mechanics and quantum field theory. That's why I said the target article should be Expectation value (quantum physics). --B. Wolterding 08:30, 16 August 2007 (UTC)
 * I see your point... but I think in general the field is simply quantum mechanics and subjects like quantum field theory is simply a sub-field if you like of quantum mechanics. This is also reflected if you look at the quantum mechanics entry. --Renji07 22:31, 16 August 2007 (UTC)
 * No, that is a misconception; and if it's in the quantum mechanics article, it needs to be corrected. Quantum mechanics is generally understood to be the "quantum version" of classical mechanics, that is, the theory of finitely many, non-relativistic particles (or "finitely many degrees of freedom", in the usual jargon). Quantum field theory, on the other hand, is the analogue of special relativistic classical field theory, that is, it describes systems with infinitely many particles and incorporates special relativity. The umbrella term is "quantum physics" or "quantum theory". You may check this in any textbook of your choice, or see this excerpt from the Encyclopedia Britannica (best online link I could find in short time). --B. Wolterding 08:30, 17 August 2007 (UTC)
 * That link doesn't really constitute a real proof in my opinion, it's just a google link with a very short sentence saying quantum physics (ie quantum mechanics and quantum field theory) and for that one link I can give another |(from Stanford Encyclopedia of Philosophy). I agree that QM and QFT are known under "Quantum Physics", however I still think that placing this under Quantum Mechanics is more relevant. (Most of the textbooks I have used btw have no problem listing it under QM and I think you'll find the two terms are almost interchangeable in literature.) Well, I think that this is an almost minor point whether the article is quantum physics or quantum mechanics, however if you look on Wikipedia for articles on the subject that expectation values are on ie: operators, observables, etc. you'll find they all explicitly state a relation to quantum mechanics. I admit an ignorance of quantum field theory but if there are entries to how an expectation value corresponds to quantum field theory, please let me know. - JT 23:41, 18 August 2007 (UTC)


 * To help solve this minor dispute, I've posted a request at the Physics Portal Talk Page and hopefully someone else will have an opinion on this. In the meantime, I'll be attempting to fill in some details on expectation value itself on this page. - JT 23:41, 18 August 2007 (UTC)


 * So here's a response triggered from that. In my experience (I've been teaching it at university level for over a decade), quantum mechanics and quantum physics are almost exact synonyms, both standing for the whole field. I would distinguish QFT from non-relativistic quantum mechanics. Historically, a slight difference emerges: quantum mechanics definitely describes the post-1925 theory and not the "old" quantum theory of Bohr etc, but quantum physics clearly covers both. The other thing to take account of is that quantum mechanics is the more common phrase: slightly more google hits (2.1M vs 1.6M), but dramatically more on google scholar. On this basis I'd go for QM over QP, but it doesn't really matter. PaddyLeahy 23:58, 18 August 2007 (UTC)


 * I agree with the view of PaddyLeahy. (Although I was going to suggest QP as that is the older article on Wikipedia; since 2005.) There will be a redirect so it really doesn't matter. I suggest you plow ahead with the merge and use whichever title seems to get the most well informed support in the next day or two. &mdash;Duae Quartunciae (talk · cont)  00:34, 19 August 2007 (UTC)


 * It's rather a minor question, but for the "almost exact synonyms", I think I have to provide a citation (just picking a book from my desk):


 * Rudolf Haag, "Local Quantum Physics" (Springer, 1996), page 3: 'In quantum mechanics in contrast to quantum field theory the "system" is characterized by its material content i.e. typically it is a certain number of electrons, protons or other particles.' (Emphasis as in the original.)


 * I have merged the articles, we can still change the title. --B. Wolterding 07:53, 20 August 2007 (UTC)


 * For the article: I have merged it into Expectation value (quantum mechanics) on your request, and expanded it at the same time. Feel free to change it, or comment on the talk page. --B. Wolterding 07:46, 20 August 2007 (UTC)