Talk:Many-worlds interpretation

Theory not mentioned here

Some scientists claim that when a solution results to many answers, all occur at the quantum level of the same universe, and when the first generation of these parallel solutions of a single wavefunction become involved in a new interaction, all the wavefunction collapses to the new point of least energy, and the secondary wavefunction expands from there, and it repeats the process again and again. So we have one universe with scouting wavefunctions (Feynmanism).

This is an extremely mainstream idea and we must analyze it better.

The word observation is erroneous, silly and romantic.

Matematically only percentages of strength of interactions exist. I compose poetry but it's a result of the memoremotional ( < memory + emotional ) limbic system, not of the analytical frontal lobe, neither a result of the mathematical parietal lobe.

Key sources defining "Many-worlds interpretation"?

The current article uses lots historical references outside of the history section. It seems like, outside of the history, one sentence on Everett and one on DeWitt should be enough (even one for both). That would shift the focus of the overview to the MWI. But what would be an agreed core definition?

Tegmark summarizes MWI in a few paragraphs. Is that an adequate definition? Is there another key source better or in addition? (I'm saying to exclude any other refs or points of view, just to have a sourced definition of MWI as a base). Johnjbarton (talk) 22:24, 16 September 2023 (UTC)

Kent's 1990 criticism encompassed the variations as follows: Many-worlds interpretations share two essential characteristics. First, they suppose that there exists a definite physical reality, which can be put into correspondence with parts of a mathematical formalism. This assumption is necessary if an MWI is to have any useful content. [...] There seems to be no dispute in the literature on this point: if a theory is not mathematically realist then it is not an MWI. Second, they base the mathematical formalism on a state-vector $|\psi \rangle$ which belongs to a Hilbert space $V$ and has a purely hamiltonian evolution. Vaidman's pro-MWI entry in the Stanford Encyclopedia of Philosophy says that his MWI has two conceptual parts. Part (i) states that the ontology of the universe is a quantum state, which evolves according to the Schrödinger equation or its relativistic generalization. The other half is A prescription which sets up a correspondence between the quantum state of the Universe and our experiences. XOR'easter (talk) 00:06, 17 September 2023 (UTC)

Tegmark is seriously outdated. A better reference is Wallace's book (currently ref 14). Tercer (talk) 08:49, 18 September 2023 (UTC)

Just to avoid future confusion,currently 14 is Wallace, David (2012). The Emergent Multiverse: Quantum Theory According to the Everett Interpretation. Oxford University Press. ISBN 978-0-19-954696-1 Johnjbarton (talk) 17:28, 18 September 2023 (UTC)

Article already opens with coincise definition: MWI = real wavefunction and no collapse. So why are we discussing this??? cheers, Michael C. Price ^talk 18:51, 18 September 2023 (UTC)

The definition in the lead references a historical source, which we've agreed is not our goal in the article. The source which contains several articles not all of which are agreed to define MWI according to previous discussions (Wheeler, and the Cooper/van Vechten article). The source includes DeWitt's 1970 article which calls the theory EWG, for Everett-Wheeler-Graham. So this source seems like a poor choice for defining MWI.

In addition two sources challenge the idea that MWI is one consistent thing:

• Marchildon, Louis. "Multiplicity in Everett׳ s interpretation of quantum mechanics." Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics 52 (2015): 274-284.
• Kent, Adrian. "One world versus many: the inadequacy of Everettian accounts of evolution, probability, and scientific confirmation." Many worlds (2010): 307-354. Quote from the abstract: "Many different and incompatible attempts to define a coherent Everettian quantum theory have been made over the past 50 years."

I think your short definition is pretty good, but mixes up "real" and "wavefunction". To me the only thing that really unites all of the variants is insisting that the implications of Schrodinger's postulated wave equation be completely explored without additions. That naturally eliminates the collapse postulate. The variants take different tracks to explore the consequences of "without additions". Personally I think summarizing some of the different tracks would make a more interesting article than insisting that MWI is only one thing (reality as real multiple worlds which we can't ever check or see). But in any case agreeing on a defining reference or two would help set up the core of the article. Johnjbarton (talk) 23:07, 18 September 2023 (UTC)

local splitting

DeWitt later rowed back on his extreme splitting view, in line with the modern view that splitting can be viewed as a softer more local process. cheers, Michael C. Price ^talk 03:25, 20 September 2023 (UTC)

Please don't put such a weird back-and-forth in the footnote. The Wikipedia way is to present the consensus position, not the details of the position of one particular person.

Moreover, that's quite overkill for the cat example. Tercer (talk) 06:57, 20 September 2023 (UTC)

I have moved it from the cat example. At the moment it sits as a footnote, but can change this later. cheers, Michael C. Price ^talk 09:30, 20 September 2023 (UTC)

@Tercer Could you explain which "details of the position of one particular person" you are referring to? Johnjbarton (talk) 14:44, 20 September 2023 (UTC)

The going back-and-forth about what exactly DeWitt thought about splitting. Tercer (talk) 16:03, 20 September 2023 (UTC)

I agree with you and I have exactly the same opinion about Wheeler's almost identical "change". Both changed their points of view regarding branching based on new ideas. Neither one "disavowed" the core MWI focus on pure wave equation. Physicist change their point of view based on models all of the time. It's not a religion where people take vows then disavow.

I tried several times to remove ", and in 1980, Wheeler disavowed the theory." from the article. Each time @Michael C Price reverted it. Would you agree to remove this phrase? If not, how can we not include almost the same comment about DeWitt at the same point in the article?

IMO the article does not present Wheeler with a Wikipedia:Neutral point of view. Wheeler went way beyond his role as PhD advisor to advocate for Everett's thesis. It has been argued that this historical information is not needed in an article on MWI. Fine, then surely a negative comment about Wheeler is also not needed.

I'm asking for consensus to remove the Wheeler phrase. Johnjbarton (talk) 16:45, 20 September 2023 (UTC)

As several others already told you, Wheeler did disavow the theory. DeWitt didn't. Moreover, the sentence about DeWitt was in the lead. It does not belong there. In the lead we should describe what the interpretation is, not what specific people think about it. The sentence about Wheeler is in the reception section, it does make sense there. Tercer (talk) 17:35, 20 September 2023 (UTC)

Literature and alternate histories

I am minded to restore a trimmed down version of the literature section. It was culled with the comment that worlds split with quantum events, not human decisions - which is false since human decisions are quantum events, along with all other events. I have seen, on other platforms, people question whether alternate histories are actualized in MWI, even after reading this article. Clearly the point needs to be emphasized for the lay reader. cheers, Michael C. Price ^talk 10:41, 30 November 2023 (UTC)

I am not convinced that mainstream references actually support the following statement: All of the historical speculations entertained within the alternate history genre are realized in parallel universes[6], which seems very speculative. With quick reading, I did not find this in Refs.[6] either. The figure about a fictional history of the US also undermines the credibility of the article (and the theory). Jähmefyysikko (talk) 15:19, 30 November 2023 (UTC)

True, ref 97 is a better source for the claim. I'll move the ref. See also Tegmark quote in the preceding section, which supports this.

The point about the "fictional" history of the US, is that it is not fictional in some Everett worlds, if we take the MWI seriously . cheers, Michael C. Price ^talk 16:34, 30 November 2023 (UTC)

I don't understand the phrase "genre are realized in parallel universes" in this sentence. I assume that what is meant is "genre occur in at least one of the infinite number of parallel universes."

The sentence, as it currently reads, is inappropriate. It states a fantasy as a fact, exactly the same as claims about religious miracles. Compare these sentences:

• "The miracles of Jesus are miraculous deeds attributed to Jesus in Christian and Islamic texts."
• "All of the historical speculations entertained within the alternate history genre are realized in parallel universes."

In the first sentence the encyclopedia carefully connects the extraordinary claim to the sources which make the claim. In the second sentence the miracles are stated a fact.

Similarly "Fictional histories which break the laws of physics (e.g. have magic) are not realised." makes an unverifiable claim as a fact.

The fact that such fictions exist and the nature of their content are notable. Statements claiming that such fictions are "realized" is WP:EXTRAORDINARY. Johnjbarton (talk) 17:08, 30 November 2023 (UTC)

Some "fantasy " as fact is exactly what Deutsch (and Tegmark) are claiming. Check out the Beginning of Infinity ref. cheers, Michael C. Price ^talk 17:11, 30 November 2023 (UTC)

I agree with WP:EXTRAORDINARY. Tegmark quote is under 'speculative implications'. This should be placed there also, and attributed to Deutsch and Tegmark, not presented as an absolute truth.

The image caption includes too much WP:SYNTHESIS, and should be removed. The image is very rasterized and gaudy anyway. Jähmefyysikko (talk) 17:33, 30 November 2023 (UTC)

The whole point of the MWI is that a seemingly extraordinary fact (existence of parallel worlds or timelines) is true. This is why many people find the MWI absurd or incredible - but that can't be helped, it comes with the theory. Which is precisely why the article needs to be explicit on this point. cheers, Michael C. Price ^talk 17:37, 30 November 2023 (UTC)

It does not follow from the existence of parallel universes that for each fictional universe there would exists some microscopic realization, even if there are no imnediately apparent violations of physical laws. There might be more constraints on the realized universes than there are on the imagination of the writers. But it is all speculation, and if you claim otherwise, there should be stronger refs than Deutsch's semi-pop science book. Jähmefyysikko (talk) 18:00, 30 November 2023 (UTC)

In have given three strong references, all from professors of physics (Deutsch, Tegmark, DeWitt), so dismissing the idea as "semi-pop science" is not justified. cheers, Michael C. Price ^talk 19:28, 30 November 2023 (UTC)

The Beginning of Infinity is undeniably popular science. And as far as I can tell (the references aren't very specific), Tegmark and DeWitt do not talk about fictional universes, so using them as references is misleading. Jähmefyysikko (talk) 20:07, 30 November 2023 (UTC)

I changed the paragraph to attribute this point of view to Deutsch. Johnjbarton (talk) 22:32, 30 November 2023 (UTC)

Tegmark explicitly agrees with Deutsch, so this is not helpful. I shall restore the additional refs. cheers, Michael C. Price ^talk 23:13, 30 November 2023 (UTC)

John Gribbin uses the example of Harry Potter as a magical work in fiction which is not realised, in his Royal Society award-winning book, Six Impossible Things. cheers, Michael C. Price ^talk 23:44, 30 November 2023 (UTC)

Besides, Deutsch is an advocate of MWI, and often makes very bold claims about it. Those cannot be taken to represent any kind of scientific consensus about the interpretation. Jähmefyysikko (talk) 20:15, 30 November 2023 (UTC)

Within the MWI community it is consensus. cheers, Michael C. Price ^talk 23:09, 30 November 2023 (UTC)

So far, we have only heard this claim from Deutsch. A slightly longer quote from Gribbin: Deutsch has pointed out that according to the MWI, any world described in a work of fiction, provided it obeys the laws of physics, really does exist somewhere in the Multiverse. There really is, for example, a Wuthering Heights world (but not a Harry Potter world).. Jähmefyysikko (talk) 07:55, 1 December 2023 (UTC)

No, the Wutherheights and Harry Potter is Gribbin's own synthesis. He is agreeing with Deutsch, but it is his own example.

Please don't use a topic merge as an excuse to delete such content again. It was in the article for years. I get that you think it "gaudy" - well let's try to improve it, not delete it. cheers, Michael C. Price ^talk 10:38, 1 December 2023 (UTC)

Gribbin devotes only half a paragraph of his popular science book for fictional universes. For the extreme interpretation that all alternative universes are realized in some branch, he cites Deutsch. The way I read it, he merely illustrates Deutsch's idea with Wuthering Heights and Harry Potter, and neither agrees or disagrees with him. In fact, since he says so little about the issue, citing him in support is WP:UNDUE weight.

And again, how are Refs. [6] (DeWitt) and [95] (Tegmark) relevant for the fictional universes? It seems incorrect to attribute such ideas to DeWitt and Tegmark, if they never explicitly articulated them. Please point out a specific place in the reference if I am wrong.

The fact that the figure you added in 2009 was in the article for some years after its initial addition is not really an argument for it, as it had also been absent from the article for multiple years now. The caption is original research (WP:IMAGEOR), as there is no source which states that Sobel's universe is realized in some branch of the Multiverse without WP:SYNTHESIS. If we remove the original research from the caption, the figure is not connected to the article. Why should we have it, when it is also very ugly? To improve its appearance would require it to be completely redrawn. Jähmefyysikko (talk) 13:27, 1 December 2023 (UTC)

I suggest you re-read WP:IMAGEOR, because it is explicitly encouraging editors to introduce images. "Original images created by a Wikipedian are not considered original research, so long as they do not illustrate or introduce unpublished ideas or arguments". The idea here, of alternate histories being actualized, has been published, so that is really the end of the argument. Or are you going to argue that we can have an image based on Wuthering heights, but not for want of a nail? cheers, Michael C. Price ^talk 13:45, 1 December 2023 (UTC)

Yes, we could have Wuthering Heights, not as a fact, but as something attributed to Gribbin. For Sobel, we cannot do the same. Of course, neither is a good illustration of MWI. In the text, we would not invent our own example either. Jähmefyysikko (talk) 13:57, 1 December 2023 (UTC)

Also, following your suggestion, I reread WP:IMAGEOR. It says that captions are treated equally with the main text. Here the problem lies within the captions, not with the figure itself, which is fine to use in For Want of a Nail (novel), where it is not associated with MWI. Jähmefyysikko (talk) 14:50, 1 December 2023 (UTC)

And if you read the caption you will see that Sobel is not cited as an example of a MWI alternate history, but to illustrate the general point about the butterfly effect and branch points in history. It then goes on to say "everything" (explicitly following Tegmark and DeWitt) is covered by MWI, and it is left to the reader to connect the dots. cheers, Michael C. Price ^talk 15:05, 1 December 2023 (UTC)

If one takes two unrelated statements and juxtaposes them in order to imply a conclusion not present in the sources, then this constitutes WP:SYNTH, even if the logical connection is not explicitly stated (but is obvious enough). And butterfly effect is not discussed in the article, so introducing it requires some reference. Jähmefyysikko (talk) 15:27, 1 December 2023 (UTC)

Actually I think what matters is whether the butterfly effect has ever been mentioned in the context of for want of a nail.

BTW, a Deutsch uses the examples of Roma Eterna and Fatherland. cheers, Michael C. Price ^talk 15:51, 1 December 2023 (UTC)

The word "butterfly" appears once in "For want of a nail : if Burgoyne had won at Saratoga" by Sobel, Robert, 1931:

... Niles was “the best butterfly collector Mexico has ever seen, but this is no recommendation for the presidency.”

See https://archive.org/details/forwantofnailifb0000sobe/page/134/mode/2up?q=butterfly Johnjbarton (talk) 16:44, 1 December 2023 (UTC)

https://tvtropes.org/pmwiki/pmwiki.php/Main/TheButterflyEffect cheers, Michael C. Price ^talk 17:14, 1 December 2023 (UTC)

One may also use the Ladyman & Ross reference to argue against the idea that all fictional universes would necessarily be realized. They say: So although on the Everett interpretation, there is more to reality than the actuality that meets the eye, it is still the case that the actual (in the non-indexical sense) universal wave function rules out some possibilities, and hence that not all the modal structure of the world is realized. So, even if some fictional universe would be allowed by the laws of physics, it is not necessarily contained in the actual universal wavefunction. Jähmefyysikko (talk) 13:42, 1 December 2023 (UTC)

The claims of MWI are untestable and therefore equivalent to miracles. We should present them similarly, independent of our personal opinions. Johnjbarton (talk) 18:14, 30 November 2023 (UTC)

The untestable claim is old and hackneyed, and dealt with elsewhere. cheers, Michael C. Price ^talk 19:31, 30 November 2023 (UTC)

I made this series of edits. I concur with many of the criticisms above. Having content about a specific work of fiction/alternate history is WP:OR and WP:UNDUE, giving credence to an unscientific claim that it could be real. I also reorganized the section to not have so many (now overlapping) subheadings and tiny separate paragraphs, and, crucially for this matter, adding a source from Sean M. Carroll in which he debunks the common misconception that human decisions can be thought of as quantum events, with equally existing worlds for each outcome. Crossroads ^-talk- 01:43, 18 February 2024 (UTC)

The edit comment " Ugh, not this 'MWI means some fiction is real' silliness again " indicates you are pushing your own views of absurdity and not going with the sources. Both Deutsch and Gribbin are claiming exactly that, namely that some fiction is realised in MWI. The wholesale removal of the section without discussion is not justified. cheers, Michael C. Price ^talk 04:07, 18 February 2024 (UTC)

I'll grant that my edit summary, in shock over seeing that map return, was a bit much, but to be clear, I did not remove that section entirely. I retained this: David Deutsch speculates in his book The Beginning of Infinity that some fiction, such as alternate history, could occur somewhere in the multiverse, as long as it is consistent with the laws of physics.[92][93]. Anything more than this is undue weight - this idea exists solely as a rather brief mention in two popular-science works and both times is attributed to one man (Deutsch); it is not a scientific discovery or consensus in the peer-reviewed literature or even found there at all. It is those latter sources Wikipedia articles usually go by. Gribbin, as stated above by another editor, appears to simply be repeating and explaining Deutsch's idea without necessarily endorsing it - he specifically attributes the idea to him. In addition, as made clear by Ladyman and Ross, and Carroll (as mentioned above), just because humans can imagine something being plausible on a very coarse level doesn't mean it's actually consistent with the universal wavefunction. Given these factors, I think adding the one sentence I quoted is more than fair, but beyond that is undue (and relating the map to this topic remains OR in any case). Crossroads ^-talk- 23:57, 18 February 2024 (UTC)

Good discussion and I agree. Johnjbarton (talk) 01:27, 19 February 2024 (UTC)

The butterfly effect claim is WP:OR

The current article makes this claim in the caption for a figure:

A map from Robert Sobel's novel For Want of a Nail, an artistic illustration of how the butterfly effect – in this example the branching or point of divergence from our timeline's history is in October 1777 – can profoundly alter the course of history.

The connection between this classical effect in nonlinear systems and the branching in the many-worlds interpretation of quantum mechanics is not referenced.

Here is a contrary reference: “The Quantum Butterfly Noneffect” in SA Space & Physics Vol. 3 No. 6 (December 2020) "A familiar concept from chaos theory turns out to work differently in the quantum world."

Now there may be scientific work showing that MWI's model matches the butterfly effect, in which case both points of view could be represented. To me such a presentation of opposing points of view belong in quantum chaos or butterfly effect. Johnjbarton (talk) 03:47, 1 December 2023 (UTC)

Irrelevant to the effect on macroscopic, non-linear history. As they say, "To what extent the no-butterfly effect might apply in the macroscopic world of our lives is an open question," cheers, Michael C. Price ^talk 04:07, 1 December 2023 (UTC)

Ok let's check your reference. Oh, you don't have one. So we have no idea if there is any connection between the butterfly effect and MWI other than your personal assertion. Johnjbarton (talk) 16:46, 1 December 2023 (UTC)

I've re-removed the picture and caption; more explanation in the "Literature and alternate histories" section above. Crossroads ^-talk- 01:39, 18 February 2024 (UTC)

Feynman: equivocal or disinterested?

The "Equivocal" section begins with Ladyman and Ross weighing the pros and cons of MWI. This makes sense as an example of "equivocal". But the Feynman paragraph is not similar. It has two references. One is a pseudo-science book that cites an unpublished poll supposedly by a political scientist, L David Rabi. (The poll reports Gell-Mann as giving the same answer as Feynman, but Gell-Mann is not a Yes.) Two is an offhand remark by Feynman commenting on someone else's interest. The section quoted starts out: "In fact the physicists have no good point of view. Somebody mumbled something about a many-world picture, and that many-world picture says that the wave function ~ is what's real, ... It's possible, but I'm not very happy with it. So, I would like to see if there's some other way out,..." Does that sound like "yes" or even weighing the idea pro/con?

Richard Feynman publish many books on QM and discussed QM in many public lectures: he had plenty of opportunity to discuss MWI but did not. James Gleick never mentions Everett or MWI in "Genius: The Life and Science of Richard Feynman." Gleick mentions that Feynman rarely read other peoples work. Feynman was passionately interested in his own views of quantum mechanics. Rather than equivocal Feynman was disinterested. Johnjbarton (talk) 16:52, 3 December 2023 (UTC)

Feynman also at least once rejected the notion of 'universal wavefunction' when Wheeler brought up the Everett interpretation up in the 1957 Chapel Hill conference. (Chapel Hill report, p.270) But since it is just a single remark, I wouldn't use this to put him into the 'Rejection' bin either. I agree that we do not need to invoke Feynman here if he did not write anything about this topic. Jähmefyysikko (talk) 17:27, 3 December 2023 (UTC)