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Former featured article candidateMany-worlds interpretation is a former featured article candidate. Please view the links under Article milestones below to see why the nomination failed. For older candidates, please check the archive.
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Theory not mentioned here[edit]

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.

Literature and alternate histories[edit]

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)[reply]

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)[reply]
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)[reply]
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:
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)[reply]
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)[reply]
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)[reply]
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)[reply]
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)[reply]
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)[reply]
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)[reply]
I changed the paragraph to attribute this point of view to Deutsch. Johnjbarton (talk) 22:32, 30 November 2023 (UTC)[reply]
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)[reply]
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)[reply]
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)[reply]
Within the MWI community it is consensus. cheers, Michael C. Price talk 23:09, 30 November 2023 (UTC)[reply]
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)[reply]
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)[reply]
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)[reply]
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)[reply]
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)[reply]
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)[reply]
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)[reply]
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)[reply]
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)[reply]
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)[reply]
https://tvtropes.org/pmwiki/pmwiki.php/Main/TheButterflyEffect cheers, Michael C. Price talk 17:14, 1 December 2023 (UTC)[reply]
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)[reply]
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)[reply]
The untestable claim is old and hackneyed, and dealt with elsewhere. cheers, Michael C. Price talk 19:31, 30 November 2023 (UTC)[reply]
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)[reply]
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)[reply]
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)[reply]
Good discussion and I agree. Johnjbarton (talk) 01:27, 19 February 2024 (UTC)[reply]

The butterfly effect claim is WP:OR[edit]

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)[reply]

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)[reply]
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)[reply]
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)[reply]

Feynman: equivocal or disinterested?[edit]

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)[reply]

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)[reply]

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Many-worlds interpretation

The many-worlds interpretation (MWI) is a philosophical position about how the mathematics used in quantum mechanics relates to physical reality. It asserts that the universal wavefunction is objectively real, and that there is no wave function collapse. This implies that all possible outcomes of quantum measurements are physically realized in some "world" or universe. In contrast to some other interpretations of quantum mechanics, the evolution of reality as a whole in MWI is rigidly deterministic  and local. Many-worlds is also called the relative state formulation or the Everett interpretation, after physicist Hugh Everett, who first proposed it in 1957. Bryce DeWitt popularized the formulation and named it many-worlds in the 1970s. According to this interpretation: in the "Schrödinger's cat" paradox, every quantum event is a branch point; the cat is both alive and dead, even before the box is opened, but the "alive" and "dead" cats are in different branches of the multiverse, both of which are equally real, but which do not interact with each other

Illustration credit: Christian Schirm

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