Talk:Leggett–Garg inequality

Hi, I found the link from Bell's theorem to Leggetts' inequality had a "this page does not exist yet", so I had the temerity to add one with what I knew. I was too hurried, but I shall review what I have done more patiently now I have edited something on wikipedia for the first time.

I expect to see some better contributors than I revise and extend it, so I shall look forward to learning more!

I am Chris Godsalve, (user=Tethys_sea).

Oh, and I have just noticed that "sign" means four tilde's

Tethys sea (talk) 13:19, 25 November 2008 (UTC)

Call for edits!
Well, I think I have made a substantial improvement to Monday's efforts, and I think I have it close to the best I can do.

I am hoping that someone working in the field out there can make major improvements or even rewrite it completely. I shall watch this space.

Tethys sea (talk) 11:55, 26 November 2008 (UTC)

The page on Leggett's inequality is not about Leggett's inequality
Let me start saying that I appreciate the attempt to deal with Leggett's work applying Bell's theorem to the quantum mechanics of macroscopic systems. However, I do not think it to be done in the right way. In the 1985 PRL paper (the first reference) on which the page is based there is no Leggett inequality. What is done in that paper is just discussing how the Bell inequalities could be tested on a macroscopic system. It is proposed by Leggett and Garg to do this by measuring one single observable at different times. The main problem with this is the invasiveness of quantum measurement, a problem that is not encountered in the usual tests of the Bell inequalities like the Aspect experiments.

An inequality derived by Leggett can be found in A. J. Leggett, Foundations of Physics 33 1469-1493 2003, Nonlocal Hidden-Variable Theories and Quantum Mechanics: An Incompatibility Theorem. This inequality holds for certain kinds of non-local hidden variables theories, and therefore transcends the Bell theory. Probably the link should be referring to this issue.WMdeMuynck (talk) 11:34, 28 November 2008 (UTC)

Thanks Willem!

It is clear I need a major rethink (or needed a major prethink!) here.

I hope to be able to make a big improvement here soon, but...

Would it be best to delete this wikipedia entry until I have done so?

I think that I flagged the expert help and work in progress stuff is sufficient for it not to appear at all authoritative, so I don't think it will do any harm to leave it as is for the time being.

If of course, I cannot manage to get it into good enough shape in a couple of weeks, I shall consider flagging it for deletion myself.

Meanwhile, any further comments and suggestions will be most welcome. Tethys sea (talk) 00:17, 30 November 2008 (UTC)

Revised this article. Best option: Rename it
Hi, I have just (Dec. 14th, 2008) revised the article. It had already nicely covered the Leggett-Garg inequality. Indeed, the Leggett inequality is something different and allows to test non-local realistic theories. I propose to rename this article (or shift its content) to an article named "Leggett-Garg inequality" (maybe somebody can do that, I do not know how that can be done in a simple way) and to reopen a new one with the current name "Leggett inequality". Both inequalities are very important in modern quantum information science and quantum foundations and deserve entries in Wikipedia. [Anonymous]

Is The Moon There?
"... Einstein's still more fundamental objection that the Moon is still there when nobody looks. If the violation of the Leggett–Garg inequality can be demonstrated on the macroscopic scale, this would challenge even this notion of realism."

I think this hyperbole has no place in the article, or it needs very throughout elaboration. If The Moon is *not* there when we don't observe it, then what there is to be observed in the first place? Moreover, The Moon can be observed every time where and *only* where classical physics predicts it to be. There is no indeterminism or any quantum weirdness here. It's just hyperbole. And it's harmful one. Quantum physics is already one of the most misunderstood field of science and all kind of fraudsters are taking use of it, in form of various kind of quantum woo. See https://en.wikipedia.org/wiki/Quantum_mysticism. Please consider this when editing these and similar articles.

I removed the sentence, please return it with proper elaboration, if you return it.

88.115.35.57 (talk) 22:51, 22 February 2019 (UTC)