Talk:Relational quantum mechanics

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The three conditions listed under Structure do not display properly. I don't know how to fix them. Anville 22:26, 26 September 2006 (UTC)

Look now. --GangofOne 22:45, 26 September 2006 (UTC)

Much nicer! Where in the documentation does it explain how to do that? (LaTeX I can generally handle pretty darn well, but TeX markup in wiki-world is a different matter.) Anville 01:03, 27 September 2006 (UTC)

I never saw it in the docs, I learned it from someone else when this issue came up before. --GangofOne 01:17, 27 September 2006 (UTC)

I have noticed people putting what seemed to me to be a superfluous backslash at the end of TeX bits, but never really understood what it was for. To be honest, I still don't quite know what it is for, because the equations were showing quite fine on my end...what do they look like without the slash? Byrgenwulf 09:08, 27 September 2006 (UTC)

I took a screenshot of the old version and cropped it to illustrate the problem, as shown at stage right. Anville 18:36, 27 September 2006 (UTC)

Ah, thanks. That does look unseemly. So I should remember, then, to include the superfluous backslashes. Byrgenwulf 00:16, 28 September 2006 (UTC)

Sorry, I was half asleep and without thinking went to add paragraphs between the 3 bullets, as it was difficult to tell whether the i was supposed to be on point 2 or 3. My bad, i need some caffiene. —Preceding unsigned comment added by 93.96.18.207 (talk) 13:59, 15 August 2009 (UTC)

"Coherence"

The sentence here and solution hereafter does not seem to make sense to me : "But, let us imagine that {\displaystyle O'}O' measures the spin of {\displaystyle S}S, and finds it to have spin down (and note that nothing in the analysis above precludes this from happening). What happens if he talks to {\displaystyle O}O, and they compare the results of their experiments? {\displaystyle O}O, it will be remembered, measured a spin up on the particle. This would appear to be paradoxical: the two observers, surely, will realise that they have disparate results."

In effect, the operator M forbids that any projection of O' own measurement of S can be in a different state than O(up), since O measured up. This would make the interpretation coherent. The tower of observers looks necessary only to reconcile unitarity. Please, authors of this section, can you either comment or modify? — Preceding unsigned comment added by 2A01:E0A:168:1C30:D580:FDEE:1A6B:773E (talk) 12:45, 1 September 2020 (UTC)

"Relational solution"

I am adding another comment: The solution proposed in this section is obviously flawed and wrong. Specifically, the singlet state is exactly what creates an illusion of spooky action at a distance. It is mentioned that Alice "knows" that Bob's spin will be down when hers is up, but this is exactly a hidden variable theory, and does not tell us why and how Bob's measurement returns accordingly. Besides, EPR paradox is more stringent at angles. — Preceding unsigned comment added by 2A01:E0A:168:1C30:D580:FDEE:1A6B:773E (talk) 13:11, 1 September 2020 (UTC)

As it stands, the "Relational solution" to the EPR/Bell problem is described as solving a non-problem. The stated "problem" is equivalent to mailing Alice and Bob letters containing the numbers 1 and -1, and then asking how Alice's envelope can "know" that the other has the opposite value. In other words, as stated, it is easily explained by hidden variables. This section needs to begin with a sketch of the actual problem, rather than a full explanation of a non-problem. The nature of the proposed solution is no different.

As it stands, this is not a valid objection. The EPR problem is well known, and needn't be recounted here. What's more, in any statement of the problem, hidden variables is offered as a solution (this was, in fact, the goal in composing the problem to begin with). Its status as a "non-problem" is contingent upon the acceptance of hidden variables as a solution, and this has not been done. At worst, it may be that the summary of the EPR problem given in this article is not consistent with the original statement of the problem. If you do not believe that it is, please give me some specific examples of why you think so. Finally, please sign your posts. --Auspex1729 (talk) 23:04, 23 August 2008 (UTC)

I was pointed to this article by an astute friend, but upon initial reading I couldn't immediately decide if this was a hoax article. On second reading I'm still not sure if it's not a hoax article.

For example, the approach taken in the section "Relational solution" is exceedingly odd, to say the least. I agree that the EPR problem is well known, but I'm unaware that "in any statement of the problem, hidden variables is offered as a solution."

More to the point, consider the statement that "So, at time t2, Alice knows the value of MA(α): the spin of her particle, relative to herself. But, since the particles are in a singlet state, she knows that MA(α) + MA(β) = 0, ..."

How exactly does she know that? And don't such statements signify an "absolute state" of the entangled pair (of photons).

MA(α) + MA(β) = 0 infers a nonlocal relationship that is independent of any observer - after all, how else could you denote the relationship on a piece of paper or this website, if it had no independent, objective validity. Furthermore, when the spins are checked by whatever means, they're really only confirming the original validity of the nonlocal relationship.

I sense that, despite all the mathematics, some basic principles are being ignored in this article. It reminds of those who argue "everything is an illusion" to which I respond by offering to lead them onto a busy highway, and for them (not me) to ignore the 20 ton truck about to hit them. Just an illusion, it won't hurt.

Sorry guys, but there is an objective reality that is quite real, while being an illusion. All systems are quantum systems while being relativistic and deterministic.

There are independent observers, while in deeper terms there aren't.

The universe complies to mathematical representations, while also being beyond modelling or representation. I.e it is also "immathematical."

I think this article highlights how representations (e.g. by using mathematics) can help people lose sight of the basic reality of life, and of timeless principles that remain true independent of circumstances.

Steaphen (talk) 14:54, 12 August 2009 (UTC)

>MA(α) + MA(β) = 0 infers a nonlocal relationship that is independent of any observer -

Yes but the particles only have this (nonlocal) relationship with each other when in a state independent of any 3rd party interacting with them. When Bob or Alice is added, the spin of that observer's particle takes an actual value from the perspective of that observer. So in a sense, the entangled particles are in an "absolute state" before 3rd-party interaction; it's just that no 3rd party has any additional information about them. The only thing a 3rd party knows is that MA(α) + MA(β) = 0, a general statement about any pair of such particles (based on past experiments). But as soon as you introduce yourself into the system to take a measurement, you will get a real value.

Nobody is implying that RQM says getting run over by a truck is an illusion that wouldn't hurt. In that case you are in a relationship with the truck / you are measuring the truck (or perhaps it's more correct to say the truck is measuring you). And that measurement/interaction results in real values of momentum, etc, that lead to pain and/or death.

In other words I don't see any difficulty with this article's treatment of EPR.

Jordgette (talk) 22:57, 17 August 2009 (UTC)

I will not delve into the philosophical quibble ("timeless truths"—and so on and so forth ad nauseam—is something on which a great deal of philosophical guerrilla warfare is now being conducted these days, and quite successfully, I sense, for something to be "timeless" really makes no sense, particularly insofar as sense is fundamentally time-based) in which you are engaged just now, because that (being a discussion beyond the scope of an encyclopedia) would not aid the development of the article using independent sources to reach a level of tertiary significance like that expected on Wikipedia (see WP:NOR, etc.). That said, well, what is there more to say? It is your opinion; and I find little much that would constitute a problem with this article except that it has a horrendous lack of—drum-roll, please—sources for the claims and statements made therein. This is not to be blunt, because I'm frank.—argumzio ϝ 21:41, 19 August 2009 (UTC)

I must admit I am confused by this solution to EPR and feel I am just not getting something. The mystery with EPR refers to the case of what the article calls subtle correlations that vary according to decisions ( measurement axes) made by Bob and Alice. Yes -these correlations can only be observed after the observers or their measurement records are brought together. Nevertheless the corrrelations certainly existed prior to this comparison because they could for example be recorded as marks on a piece of paper and the correlation depends on remote choices made by Alice and Bob. Also, what has a third observer got to do with this? — Preceding unsigned comment added by Confusdius (talk • contribs) 10:09, 4 October 2012 (UTC)

Ontology and Epistemology

The section on ontology and epistemology contains numerous statements which are unsourced and seem to be original research. What's more, some of the claims flatly contradict explicit statements made by Rovelli in his papers. The most blatant example is:

Epistemologically, RQM differs fundamentally from Bohr's understanding of the role of quantum mechanics as a theory: Bohr felt that quantum mechanics is not a theory about the world as it is, but a theory about what we (humans) can say about the world. On the other hand, while RQM is very much a theory about what can be said about the world (where "said" refers to any correlation of state between any two relata), it claims to be exhaustive in its description. There is nothing more to the world than the net of relational descriptions.

On the second page of "Relational EPR", this statement is flatly contradicted by an explicit reference to Bohr's account of knowledge in physics as a motivation for the relational programme. The statement also seems to contradict itself ("Bohr felt that quantum mechanics is a theory about what we can say about the world" is followed by "while RQM is very much a theory about what can be said about the world").

The remainder of the section is gratuitious name dropping and unsourced claims of correlation to the writings of other philosophers.

I suggest that the entire section should be removed. --Auspex1729 (talk) 22:04, 22 August 2008 (UTC)

I'm adding a request for a citation on the claims of nominalism. This has not been advocated by Rovelli (I may see if he is interested in weighing in on this). I have removed the incorrect paragraph on the contrast between Bohr's philosophy and RQM. --Auspex1729 (talk) 22:17, 22 August 2008 (UTC)

I axed the whole thing as there haven't been any citations added. -Jordgette (talk) 23:33, 17 November 2009 (UTC)

Citations, References and Footnotes

The citations, references and footnotes of this article are a disaster. I'm going to flag them for cleanup and attempt to do so when I have more time.--Auspex1729 (talk) 22:39, 23 August 2008 (UTC)

Gravity?

Forgive me if I'm wrong, but I'm missing something major from this article. The article seems to suggest a relational + quantum description of reality. As far as I'm aware, for such a theory to be considered complete, it would need to embed a description of gravity. Clearly, this would have to be embedded in the relational model, however, it's not clear what the resultant model of quantum gravity is. Could the article at least hint at what the resulting gravitational theory might look like? 70.247.168.170 (talk) 04:28, 5 March 2012 (UTC)

Criticism

I see some discussion here in the talk section on the value of this interpretation. I don't think this is the right place for such discussion. On the other hand, I think it would be a good idea to add a section to the main article mentioning criticism that may have been expressed by other phycisists. This may be hard to find and I haven't searched for it. Anyway I am suggesting to those collaborating with this article to look for such criticism, which would make the article a little more balanced and contribute to a neutral point of view. Alex Pascual (talk) 18:56, 26 March 2014 (UTC)

duplication? independent development?

What's the deal with Relational quantum mechanics vs. Relational approach to quantum physics?

• As early as in 1985, S. Kochen suggested that the paradoxes of quantum physics could be overcome by developing a relational approach, which was needed at one time to solve the paradoxes of relativistic physics of space and time (S. Kochen, Symposium of the Foundations of Modern Physics: 50 Years of the Einstein-Podolsky-Rosen Gedankenexperiment, (World Scientific Publishing Co., Singapore, 1985), pp. 151-69.)
• Relational quantum mechanics: treats the state of a quantum system as being observer-dependent, that is, the state is the relation between the observer and the system. This interpretation was first delineated by Carlo Rovelli in 1994.
• Relational approach to quantum physics: asserts that the physical world can only be studied accurately in terms of relationships between systems, as all experimentally verifiable facts about the world result explicitly from interactions (such as the interaction between a light field and a detector). [...] The approach was adopted, in a time span of 1992-1996, by Q. Zheng, S. Hughes, and T. Kobayashi in the University of Tokyo.(Zheng et al. (1992, 1996)) [...] It is also hoped that this entry will serve as a complement to Rovelli's relational quantum mechanics (RQM).

So:

• Rovelli "the state is the relation between the observer and the system"
• Zheng et al. "all experimentally verifiable facts about the world result explicitly from interactions"

This appears to me to be one and the same basic idea. Then why are both articles basically disjunct in terms of the literature they cite? And why does the Zheng page say "It is also hoped that this entry will serve as a complement to Rovelli's RQM"? I can imagine that two groups came up with the same idea independently in the 1990s, but since then clearly there must have been some degree of collaboration or confluence, or at least third-party literature comparing the two approaches? Why does Wikipedia keep this in two separate articles?

Is the Relational approach to quantum physics page in essence about a single paper that happened to end up under-appreciated because the Rovelli paper was on the same topic and became the attractor for later work on the topic? --dab (𒁳) 13:24, 18 April 2015 (UTC)

You might be right. The articles should probably be combined at some point; since RQM has gotten much more traction, I’d vote for Relational approach to quantum physics to be rolled into this one. -Jordgette [talk] 01:02, 19 April 2015 (UTC)

I am not a physicist; however the two summaries (Rovelli vs Zheng et al.) do not appear to me to be one and the same idea at all. But then I maybe I am missing something: Rovelli states that the observation is meaningful only within the context of the observer's frame of reference, whereas Zheng et al. assert that physics can only be expressed in terms of interactions (aka observations), but they might not claim that observation is meaningful only within the context of the observer's frame of reference. It also seems to me that Rovelli equates causality with the role of the quantum observer, and even implies that the speed of light may correlate with the scope of interactions - which appears to be substantially distinct from Zheng et al. (20040302 (talk) 10:17, 10 October 2016 (UTC))

Closing merge proposal for lack of consensus over 2.5 years. Klbrain (talk) 04:21, 5 September 2017 (UTC)

Something wrong with Postulate 3

I'm unable to make sense of Postulate 3, which says that Ubc satisfies an equation that doesn't mention Ubc. How to read/fix this? Vaughan Pratt (talk) 00:11, 2 December 2018 (UTC)

Information and Correlation ... and Buses?

I may be stepping away from the serious intent here a little but, back in 1997, I was independently reaching what seems to be the same conclusion as Rovelli: that the problems of superposition reduce to statements that different observers have different information. For some pre-Wikipedia meanderings, please see the sci.physics thread, Schrodinger's Bus p.r.newman (talk) — Preceding undated comment added 12:18, 6 March 2021 (UTC)

I think that's broadly similar to what Rovelli is saying. Of course, there are experiments in which superpositions can be physically prepared, and subsequently destroyed through decoherence...so to me, it seems that if superposition is just about observers' information, then some very radical things about measurement and the Heisenberg cut are implied. But we aren't really improving the encyclopedia here are we :-) -Jordgette [talk] 19:36, 7 March 2021 (UTC)

Does the observer have to be conscious? From reading Rovelli's Helgoland it would seem so. Also https://medium.com/predict/carlo-rovellis-relational-quantum-mechanics-256cc264f394. This is crucial to understanding the idea of RQM.