Talk:Wigner's friend

message: Can someone link this word in the article to what it means? Eg is it Quantum_superposition. I am trying to understand this page but am stuck on superposition. Crackerlacken
----  —Preceding unsigned comment added by Crackerlacken (talk • contribs) 03:48, 9 January 2008 (UTC)
thread_title: Superposition

message: There is the line "alive cat/happy friend,". Was the term "alive cat" actually used in any source material? Typically English treats "alive" as a predicate adjective which may not precede a noun; we would rather say "the living cat" or "the cat is alive", but not "the alive cat". samwaltz 19:18, 18 January 2007 (UTC)
thread_title: "Alive cat" as direct quote?

message: The following par was the 2nd one of this article. I have replaced it with the one below it, for reasons given at the end. 
It posits a friend of Wigner who performs the Schrödinger's cat experiment while Wigner is out of the room. Only when Wigner comes into the room does he himself know the result of the experiment: until this point, was the state of the system a superposition of "dead cat/sad friend" and "alive cat/happy friend," or was it determined at some previous point?
 
It posits a friend of Wigner who performs the Schrödinger's cat experiment after Wigner leaves the laboratory. Only when he returns does Wigner learn the result of the experiment from his friend, that is, whether the cat is alive or dead.  The question is raised: was the state of the system a superposition of "dead cat/sad friend" and "live cat/happy friend," that was only determined when Wigner learnt the result of the experiment, or was it determined at some previous point?
1.“he himself” is confusing. It is not immediately apparent whether the pronoun refers to Wigner or his friend. I have made “he” unambiguously refer to Wigner. 
2. I have made it manifest that Wigner learns the result of the experiment from his friend, not from direct observation. 
3.I have remedied stylistic awkwardness of last part of sentence. 
4.I have substituted “live cat” for “alive cat”. Myles325a 02:29, 17 August 2007 (UTC)
thread_title:  Amend second par for clarity 

message: An element of this thought experiment that I found puzzling is that it is Wigner's friend who first learns of the result of the experiment. If thought experiment is designed to illustrate that consciousness has a privileged function in collapsing the wave function, then is it not Wigner who collapses it first? In that case, Wigner has come too late to collapse it himself. 
Otoh, suppose Wigner's friend had no idea of what the experiment involves. He only has to push a hutton, and tear off a print-out produced automatically by a printer attached to the box, upon the completion of the experiment. This printout contains a coded message detailing the result of the experiment. In such a case, we might posit that if Wigner's friend can read and understand the message, the act of reading collapses the wave function and the cat can be said to definitely dead or alive. But if he cannot, then it is Wigner himself who collapses the wave function when he returns and reads the printout himself. Myles325a 02:59, 17 August 2007 (UTC)
thread_title:  What about the consciousness of Wigner's friend? 

message: The recent re-write is not good. It is completely idiosyncratic and reads like a personal essay. 1Z (talk) 22:17, 10 January 2008 (UTC)
thread_title: Recent Rewrite

message: Um, I showed my brother (a high energy physicist currently doing a PHD) this page, and he said that it showed why you should be careful what you consider a measurement, nothing more, and that it in no way proves consciousness. I don't expect you guys to accept that, but maybe some deeper research should be done and someone with more authority should look at this page.
As physics student I concur.  This page says almost nothing about Wigner's Friend and what it says is rather misleading.
Olleicua (talk) 05:34, 8 December 2009 (UTC)
thread_title:  misunderstanding 

message: So.. there are a lot of interpretations of quantum physics.  Many worlds has its own page.  This page is about Wigner, not Everet.  Why then is the majority of the page (and the only reference) devoted to Everet and Many worlds.  This borders on an NPOV issue IMO because it makes it appear that there is only one major interpretation of QM.
216.158.163.188 (talk) 05:32, 8 December 2009 (UTC)
thread_title:  OTHER INTERPRETATIONS 

message: I have the book cited above, Times's Arrow, and it says very clearly on page 200, "I think it is fair to say that the measurement problem is an unsolved one, despite heroic efforts."
Further, hidden variable theories, which are those that present the most credible alternative to the Copenhagen interpretation, have been cast in doubt by experiments that prove that Bell's inequalities do not hold (up to 242 standard deviations). See the wikipedia article Hidden variable theory.  — Preceding unsigned comment added by Cliffberg (talk • contribs) 04:52, 2 February 2011 (UTC)
replies: text: I think that claim is overly broad. Read the Hidden variable theory article more carefully and you'll see that Bell's theorem and Aspect's experiments argued only against theories in which all hidden variables are local, not against all theories of hidden variables. Stating this in Einstein's terms: God might not play dice but He sometimes does things spookily at a distance. SEppley (talk) 15:50, 27 November 2011 (UTC)
replies: text: Okay, but those spooky things at a distance cannot transport information. Therefore, they must be illusions, just as much as stars appearing from Earth to move faster than c, or the point of closing of a scissors being able to move faster than c. That's an important point to remember. There is strangeness in QM, but nothing that results in miracles in the sense of violation of natural laws. QM has the potential to produce wonderful things (room temperature superconductors, room temperature superfluidity, and probably very fast quantum parallel computers), but not physical miracles like time travel of humans, time travel for human senses, time speedup or slowdown, antigravity devices, instant communication over long distances (even of one bit of information), perpetual motion, or teleportation of humans. David Spector (talk) 20:54, 18 December 2011 (UTC)
thread_title:  Hidden variable theories 

message: What if there are N friends in the chain? Why would the collapse not happen at the first friend who observes? why should it happen at the 2nd in the chain, or the last in the chain? More to my reductio ad absurdum point, is it sensible to ask if a tree makes a sound if it falls in an unpopulated forest?
It seems to me that observation does not require consciousness, it just requires injecting energy into a system. Push in a little energy and you can observe the interference known as the Uncertainty Principle. Push in enough energy and you can generate new kinds of fundamental particles!
If observation (perturbing with energy then measuring the new state) collapses wave functions, then, by Occam's/Parsimony, we don't need to invoke consciousness. David Spector (talk) 02:12, 29 November 2011 (UTC)
thread_title:  Seems like nonsense to me; what am I missing here? 

message: I strongly object to this addition. The experiment has yet to be peer-reviewed, and moreover, the coverage is almost pure hype. We cannot build an encyclopedia upon unreliable sources. Nor is the description of the experiment accurate: the test was done on photons, making it not an example of the defining feature of the Wigner's-friend idea, which is placing an actual observer in a quantum superposition. In no way should the Proietti et al. paper be presented as a real implementation of Wigner's friend, or any extension thereof. Reading the paper beyond their grandiose abstract makes this absolutely clear. We cannot even argue that it is a notable un-peer-reviewed experiment, since the coverage derives entirely by cloning from a single, awful blog post at Technology Review. Echoing the blithering of the hype machine is not our job here. The text in question is simply unacceptable. XOR'easter (talk) 20:30, 16 March 2019 (UTC)
replies: text: And even if you take the (ludicrous) step of regarding a photon as an "observer", the experiment didn't implement Wigner's Friend, but a variation of it due to Časlav Brukner, so the text can't even get that much right. The sentence  is wrong on both points, since it wasn't Wigner's proposal, and so the outcomes couldn't have been what Wigner predicted. With half the text being wrong, and the other half an admission the work is not yet published in a reliable source, we can't make the case for including it. The edit summary compares this case to that of FTL neutrinos, but there is really no analogy to be made. That was a report by a major collaboration which immediately attracted not just fawning press reports, but careful investigation by actual physicists (together with all kinds of speculation in the range between). This ... isn't that. Maybe it will be eventually, but Wikipedia is neither a rumor mill nor a prophecy service. We lose nothing by waiting for the formal cycle of physicist (and, in this case, potentially also philosopher) commentary and critique. XOR'easter (talk) 21:34, 16 March 2019 (UTC)
replies: text: I second everything XOR'easter says above. This is nothing like FTL neutrinos and the experiment in question is a far cry from any sort of experimental verification of the Wigner's friend scenario. --Patchworld (talk) 00:08, 17 March 2019 (UTC)

text: Calm down.  Yes, it is not notable (but notability applies to article topics, not to their content), it is not peer-reviewed, and it is a primary source.  I do not think that your objection that photons are not observers is sensible in the context.  In all, I think that a mention of this does not belong in the lead, but that it does merit a mention alongside the equally shaky  (which seems like it could do with severe trimming).  The article is not at the quality level where every mention of non-notable research must be excluded.  I would suggest that both these should be reduced to subsections of a section "Published papers", or suchlike.  —Quondum 01:10, 17 March 2019 (UTC)
replies: text: I agree that the long section on extensions could stand trimming. It is rather, well, over-extended. In addition, it focuses excessively upon a single version of the idea, and not necessarily the first or the clearest. The first was, I believe, the version by Brukner, originally posted in 2015. The variant by Jeffrey Bub from 2018 might be less notationally demanding than what the article is currently trying to explain. (My use of the word "notable" merely echoed the edit summary to which I was responding. If I were in the mood to be a stickler for the peculiarities of Wikipedia's internal jargon, which I am sometimes, I'd call its inclusion in the lead a "violation of WP:UNDUE" instead.) Cheers, XOR'easter (talk) 03:58, 17 March 2019 (UTC)
thread_title:  "Experimental recreation" 

message: This edit introduces an error. The point of the "consciousness causes collapse" dodge is to ensure that the so-called paradox of inconsistent state assignments does not arise, because the friend is a conscious being so Wigner would not treat him as an ordinary quantum-mechanical system. It is not that , but that consciousness causing "collapse" (however that is supposed to work) escapes the contradiction. The contradiction is not specific to the "consciousness causes collapse" interpretation.
The article is already fantastically unclear; let's not make it worse, please. XOR'easter (talk) 01:28, 18 November 2019 (UTC)
replies: text: Fun fact maybe worth noting: at least in his later years, Wigner himself didn't actually hold to the "consciousness causes collapse" idea. He regarded that as the logical conclusion of the premises he had originally set out, but instead found the conclusion sufficiently absurd to be grounds to question the validity of those premises . XOR'easter (talk) 01:38, 18 November 2019 (UTC)

text: Reading that whole section from the top again, it needs more thorough revision to tell apart the wavefunction-collapse-is-change-of-information way of thinking (Peierls, Zeilinger, Fuchs, Mermin, etc.) with wavefunction-collapse-is-a-physical-event-caused-by-consciousness (like in the Greg Egan novel Quarantine). XOR'easter (talk) 22:09, 18 November 2019 (UTC)
thread_title:  Contradictory addition 

message: Paper summary might be usable in article. 67.164.113.165 (talk) 08:39, 18 November 2019 (UTC)
replies: text: Thank you for those links. The summary is by the authors themselves, which is both good and bad: it presents what they think without an intermediary, but it's not an evaluation by a secondary source. The copy at phys.org is a reprint of the original posting at The Conversation, here. XOR'easter (talk) 17:57, 18 November 2019 (UTC)
thread_title:  recent experiment 

message: Have none of the contributors of this article actually read what Wigner wrote? He doesn't once mention anything about cats, Schrodinger's or otherwise.
Look, here is Wigner's article: http://www.informationphilosopher.com/solutions/scientists/wigner/Wigner_Remarks.pdf
This article needs a total rewrite from somebody who knows what they're talking about. I don't know where all this talk of "dead cat/sad friend" came from, but it wasn't Wigner.
This article is a total shambles. Embarrassing.
No such thing as friend or amusing or not, laugh any.  — Preceding unsigned comment added by Viwkls (talk • contribs) 01:04, 15 December 2019 (UTC)
thread_title: Wigner's friend has nothing to do with Schrodinger's cat

message: "Paradox puts objectivity on shaky footing"  George Musser  Science 369 Pages 889-890  28 August 2020 Charles Juvon (talk) 22:16, 30 August 2020 (UTC)
replies: text: - Already considered and added - see this edit and related - iac - Drbogdan (talk) 22:25, 30 August 2020 (UTC)
thread_title:  News article in Science 

message: I would like to consider reinstating the reference on this page to: -
Łukaszyk, Szymon (2018-01-25). "A No-go Theorem for Superposed Actions (Making Schrödinger's Cat Quantum Nonlocal)". New Frontiers in Physical Science Research. 3: 137–151. arXiv:1801.08537. doi:10.9734/bpi/nfpsr/v3/17106D
The reference was removed in November 2022 by Tercer as the author was considered self-promoting and B P International as a predatory publisher.  My understanding is that B P international https://www.bookpi.org/ is not predatory (but I am basing this on a browse of their site and consideration of the sorts of publications they produce), and that the reference could be allowed to stand.  — Preceding unsigned comment added by Travelkev (talk • contribs) 11:57, 28 November 2022 (UTC)
replies: text: It is a predatory publisher, as listed here under the name "Sciencedomain International". Also, the edit was clearly self-promotion, as the user who added it is the author of the paper. I'm very curious about how you even find out about the removal of this source, given that you haven't edited in 6 years, and never in physics articles. Tercer (talk) 17:33, 5 December 2022 (UTC)
thread_title:  Reinstate Reference? 

message: The section "An extension of the Wigner's friend experiment" should be changed to "Extended Wigner's friend thought experiments" to provide a summary of various extended Wigner's friend no-go theorems developed in the past 7~8 years, not just the Frauchiger-Renner theorem. For example, the Local Friendliness theorem is also a significant development in quantum foundations based on Wigner's friend https://www.quantamagazine.org/a-new-theorem-maps-out-the-limits-of-quantum-physics-20201203/). The content in the current section could be moved to a separate wiki page for the Frauchiger-Renner no-go theorem. Ggstddup (talk) 12:22, 6 August 2023 (UTC)
thread_title:  Extended Wigner's friend arguments 

message: This article includes the following: "On the other hand, one presentation of the experiment as a quantum circuit models the agents as single qubits and their reasoning as simple conditional operations. [21]"
where the citation is the following blog post, which itself appears to be blank: 
Watching the Watchmen: Demystifying the Frauchiger-Renner Experiment — musings from Lidia del Rio and more at the 6th FQXi Meeting
I looked through Lidia de Rio's publication list on Google scholar and found this paper: Thought experiments in a quantum computer, which introduces a software library for running Wigner's friend as a quantum circuit. I'm not certain if this is the first article to propose a formulation of this thought experiment as a quantum circuit, but it seems a more appropriate citation for the above quotation. I reached out to the author to confirm this, but haven't heard back. PlantainPhysics (talk) 17:35, 26 March 2024 (UTC)
replies: text: I would just remove that sentence. Modelling it as a quantum circuit is trivial and achieves nothing in the way of enlightenment. Tercer (talk) 20:55, 26 March 2024 (UTC)
replies: text: It may be trivial for experts, but it seems appropriate to include in an introductory article like this. Enlightenment is in the eye of the beholder, and personally speaking, I found it interesting that this formulation had been implemented. I accept that the above citation was likely not the first time it was introduced. Perhaps given that David Deutsch extended the Wigner's friend thought experiment in  as well as having a canonical quantum algorithm named after him, he may have connected these two at one point. I simply haven't read all the relevant papers from that era. 2601:602:8D00:3C70:CCCA:7D82:7ED:1BE9 (talk) 16:12, 27 March 2024 (UTC)
thread_title:  Wigner's friend as a quantum circuit