Talk:Many-worlds interpretation/Archive 6

Special Difficulty with Improving This Article - Harrassment
I'd like to call attention to a special difficulty with improving this article. As documented in the Reception discussion above, the reputable literature on this subject is largely critical and unfavorable, a view which is rather under-represented in this article. This is a large part of what needs to be fixed, to bring the article into line with Wikipedia policy. Unfortunately, whenever someone comes to this page (even the Discussion page, let alone the actual article) and begins to quote some of these sources and advocate fairly representing these published views in the article, they are immediately subjected to rather troubling harassment and hectoring, accused of using the Discussion page as a soapbox, have warning messages placed on their user pages, and so on. I don't think this harassment is helpful, and it certainly isn't justified. It would be better to assume good faith, and try to work towards improving the article, rather than trying to browbeat and intimidate any editors who dare to suggest that many (most) reputable sources in the literature express a very negative view of the subject of this article. This is a well-documented and fully verifiable fact, as I showed in citations in the Discussion of the Reception section above.

In my comments here on this discussion page I've included far more detailed references and citations of reputable published works than anyone else has, and I believe my comments have all been focused on the task of editing the article and explaining what I think needs to be changed, and why, all appropriate for a Discussion page. The edits I think are needed, in accord with Wikipedia policy, involve making the article more balanced and representative of the mainstream view of the subject, which happens to be not nearly as favorable as the view of the most enthusiastic proponents of MWI. This is to be expected. I don't question the good faith of any editors here. I firmly believe they are trying to make the article accurate as they see it. I'm just trying to bring some more well-sourced perspectives into the article, to make it more representative of the reputable sources in the literature. But if the harrassment continues, I'll just give up (as I suspect many have in the past). I don't think anyone should feel good about driving an editor like me away from this article, who has just surveyed the literature and tried to bring that perspective to the article. That would really be disgraceful. But at the very least, readers of the article can review the Discussion page, and see the tactics that have been employed to keep the article in its present form. They can draw their own conclusions. (Excuse me for being ticked off.) AIMW32 (talk) 16:00, 18 October 2011 (UTC)


 * (It might be better to keep your comments shorter - people don't want to read all that.) Note that harassment isn't considered acceptable behaviour on Wikipedia. As for the article content, you could ask on Wikipedia talk:WikiProject Physics to see what other people think. --Zundark (talk) 16:36, 18 October 2011 (UTC)


 * AIMW32, you complain that the "Common objections and misconceptions" sections always gives the last word to the MWI camp. But I think this is because adherents are more motivated to refute criticisms than critics are to refine their criticisms of a theory they find incomprehensible, hence the last published word usually goes with the adherents.  However, let's talk specifics, critique just one point in the section and let's hear your suggestions for improving it.-- cheers, Michael C. Price talk 16:59, 18 October 2011 (UTC)

AIMW32, in all this time, you have yet to improve the article or the encyclopedia in any way, unless you have a different edit history you'd like to share. You prefer to publish your POV here on the talk page, which you've clearly used as a WP:SOAPBOX. Needless to say, no one else has felt a need to post references here on the talk page, but actually, the lack of detail, selection bias and other problems with your sourcing is what's documented above.

By all means, please do engage in discussion rather than repeating yourself ad nauseum. However, talking about yourself in the third person, and thus indirectly accusing me of harassment, demonstrates who's harassing whom. Making those false accusations was a violation of WP:CIVIL/WP:NPA.

Yes, I put a WP:CHAT warning on your page yesterday, and rather than taking that advice on board, you've done the opposite. There is no “and so on”, your fabrications are paper thin, as usual, and no I don't imagine you find it helpful when I point that out. There is nothing preventing you from editing, but in lieu of that, you post increasingly deceptive screeds.—Machine Elf 1735  19:03, 18 October 2011 (UTC)

The Criticisms Section (Presently called "Common Objections and Misconceptions")
AIM32, you complain that the "Common objections and misconceptions" sections always gives the last word to the MWI camp. But I think this is because adherents are more motivated to refute criticisms than critics are to refine their criticisms of a theory they find incomprehensible, hence the last published word usually goes with the adherents. Michael C. Price talk 16:59, 18 October 2011 (UTC)


 * The critics of MWI don't say it is incomprehensible, they say it is self-contradictory, incoherent, vacuous, etc. Also, the mainstream view of a subject isn't decided based on "who published last" - if it was, it would change each time another book or paper is published.  So your defense of why the article always gives the last word to the "MWI camp" is not valid.

However, let's talk specifics, critique just one point in the section and let's hear your suggestions for improving it.-- cheers, Michael C. Price talk 16:59, 18 October 2011 (UTC)


 * Let's start at the beginning: The title of the section is absurd.  Do I really have to point this out?  Calling the Criticism section by the name of "Common Objections and Misconceptions" is laughable.  It should be called something like "Criticisms", or perhaps, to reflect the argumentative content, "Criticisms and Counter-Arguments".  Then look at the very first item:


 * * MWI states that there is no special role nor need for precise definition of measurement in MWI, yet uses the word "measurement" repeatedly throughout its exposition.


 * *MWI response: "measurements" are treated as a subclass of interactions, which induce subject-object correlations in the combined wavefunction. There is nothing special about measurements (such as the ability to trigger a wave function collapse), that cannot be found in the unitary time development process.[2] This is why there is no precise definition of measurement in Everett's formulation, although some other formulations emphasise that measurements must be effectively irreversible or create classical information.


 * The problem here is that the objection has not been stated fully. The Schrodinger equation is time-symmetrical, whereas the concept of a measurement (or any kind of interaction) leading to a splitting into multiple outcomes into the future is explicitly NOT time-symmetrical.  Take a look at the illustrated cat in the figure at the beginning of this article.  It splits into the future.  But how does unitary evolution of the wave function under a time symmetrical equation lead to a proliferating set of self-consistent worlds in one time direction but not the other?  Note that this is NOT just the same old arrow-of-time problem, because a trajectory in classical phase space doesn't "split" in either time direction. The splitting or differentiating into multiple self-consistent worlds in the future is a unique feature of MWI, and it is unintelligible without an explanation of the temporal asymmetry.  Of course, some MWI advocates actually agree with this objection, and they contend that MWI actually must entail the re-coalescing of worlds, anti-measurements, splicing as well as splitting, a constant total number of "worlds", etc., but this is controversial even within the MWI camp, and leads to an empirically falsifiable theory different from QM.  One could also mention the arguments of John Bell against the role of measurement in MWI.


 * Look, I'm mindful of the fact that this Discussion page isn't the place to discuss the topic. My only point is that the "misconception and correction" format of the existing article is not at all representative of the mainstream view of the subject.  The original (unsourced) criticisms in the article need to be stated more fully, explaining (for example) why the concept of "measurement" and the alleged associated "splitting" is problematic.  Once the criticism has been stated fully, we will find that there is no coherent "MWI response", although we could mention the speculative ideas about new theories with anti-measurements, by which some MWI'ers hope to salvage their interpretation.  Treating each of the criticisms this way, the section will eventually reflect the actual mainstream view of the subject.AIMW32 (talk) 18:38, 18 October 2011 (UTC)


 * First, it used to be called Criticisms, and I was happy with that, but some folks felt it wasn't NPOV enough, so we have present PC title.
 * Onto the substantive part: yes, a trajectory in classical phase space doesn't "split" in either time direction. So what?  We are talking about a quantum system here.  And you are correct, that The splitting or differentiating into multiple self-consistent worlds in the future is a unique feature of MWI, and it is unintelligible without an explanation of the temporal asymmetry.   The temporal asymmetry comes from the boundary conditions, i.e. the big bang / inflation left the universe with a low entropy density, which is the source of the arrow-of-time and why worlds predominately split into the future, and measurements and memories of measurements are possible. However this is a red herring w.r.t. to the "MWI measurement problem", which is why this is not mentioned.
 * I hope that clears things up. -- cheers, Michael C. Price talk 23:22, 18 October 2011 (UTC)
 * Addendum: I have added the temporal asymmetry objection, with sourcing, to the article. -- cheers, Michael C. Price talk 06:58, 20 October 2011 (UTC)

Quote:
 * Will you be updating all the other interpretative QM articles also? Michael C. Price talk 17:23, 17 October 2011 (UTC)

Ah so because other interpretative QM articles aren't objective, this one hasn't got to be objective either. (while this one is much more subjective 'in my opinion'). That makes a lot of sense. (this was irony) — Preceding unsigned comment added by Willempramschot (talk • contribs) 14:58, 19 October 2011 (UTC)
 * No, my implied question was about, why you are focussed on "cleaning up" the MWI article? Do you have a thing about MWI? No matter.
 * However I will repeat what I said to another poster - please be specific and critique a point from the "objections" section and we'll take it from there. -- cheers, Michael C. Price talk 20:52, 19 October 2011 (UTC)

First of all I'm not the same person that you posted that quoted response to, secondly I mainly have a thing against supposedly objective sites, that aren't and suggest they are. I have posted a post with a poll, and criticism. — Preceding unsigned comment added by Willempramschot (talk • contribs) 07:54, 20 October 2011 (UTC)
 * And how are we meant to know who posted those comments when you can't even be bothered to sign them? -- cheers, Michael C. Price talk 08:19, 20 October 2011 (UTC)

Somehow I can't see my poll that I posted with the results and a lot of extra information about it anymore. I'm not implying you deleted it, but I don't see a good reason why this couldn't be on the discussion site. So I'm posting it again without the background information, and if someone wants to have more information about the poll he/she can contact me on — Preceding unsigned comment added by Willempramschot (talk • contribs) 08:01, 20 October 2011 (UTC)
 * Please if you insist on posting stuff that isn't useful (it can't cited since it is unpublished) then at least learn some basic rules such as SIGNING your comments. And read your talk page. Thank you. -- cheers, Michael C. Price talk 08:10, 20 October 2011 (UTC)
 * Willempramschot, please stop. How many times is that now, five? Soliciting people to email your single purpose hotmail account is not ok, it's crossed the line into WP:SPAM. The removals were explained above, in your “preferred” section. No one can post this to the article for you and it seems unlikely it would ever be published by an WP:RS. On http://www.physicsforums.com you said the participates were given the impression it was anonymous… I'm not sure if you copied that particular remark here, but presumably they're not endorsing this poll. You decided to promote it using their names, seemingly without their knowledge, and it's not clear you acquired permission to use comments from their email either.—Machine Elf 1735  11:37, 20 October 2011 (UTC)

Sorry to put some questions on your beautifull dreams about eternal life and your infinite twin brothers. You are really really good at quoting wikipedia and fallacy's. It's such a shame you don't understand what they mean, and don't have a clue about how to apply them with sense. This is deleted, because I probably insult you, but if that's the case then well you got insulted by the truth. And the fact that everyone's vote is anonynomous, and the quotes are to, seems enough to have no objections don't you think? Or is this really hard to grasp? Shall I find out if they endorse this poll? I could... (though my energy is a little bit wasted). Why the hell did they vote if they didn't. I send them an email and I didn't get any negative reactions. You are so obvious biased, that it hurts. I'm really serious, with all the good faith in the world. — Preceding unsigned comment added by 145.18.226.113 (talk) 14:05, 20 October 2011 (UTC)

By the way I don't really care about getting it published, I care about the truth and so should you (and it was 3, wich I explained). I don't know if you're aware that wikipedia has influence on the opinion of people, and if you have any ethical standars what so ever. Or that you are just completely blinded by your heroes, or a idea that's not generally accepted by any scientific community what so ever (unless you call the subscribers to tegmark, and david deutsch's mail a scientific community). But please be honest to yourself. Look in the mirror, and think really hard. And ask yourself the question 'Did I do good'? — Preceding unsigned comment added by 145.18.226.113 (talk) 14:19, 20 October 2011 (UTC)

I'm affraid I speak to a conscience and a rationality you just don't posses. So I will leave you to delete all the criticism and posts by me and others you so kindly call harassment. With the information that there is a certain person with a psychosis (not me, if you might want to interpret it that way) that tried to commit suicide because of sources like this, that give dishonest information. And with a song that captures your attributions on this site perfectly, sleep tight (which I'm sure you will)! — Preceding unsigned comment added by 213.10.212.48 (talk) 17:48, 20 October 2011 (UTC)

I'm on the brake of being banned here, so let's just make it happen. This is a site that is not Wikipedia worthy (or it is, but that would be really sad). It is a propaganda page, for an idea which has very very very few people who subscribe to it, and very very active people who defend it. It's unethical, it's dangerous, it's false. I think the most active person on this site wants to live forever (judging on the 'we can live forever' marketing he does besides this). All the evidence we currently have is against this, and be glad (if I would imagine the doctor would say to me that I would only live another 30 years I would be sad, If he said I would live forever I would completely freak out). This can be seen as a personal attack, but then again it also can't because it's against your ideas, and not to you personally. It just seem you base your identity on this bull so you can still interpret it that way. There are plenty enough good arguments that you are aware off that the reception page is one-sided, and thus misleading. I won't use the word 'lying' now, but what you do is just the hypocritical version of the word. The arguments given by two users here against al criticism usually consists of a pile of fallacies and ironically they delete all the criticism on the basis of those very same fallacy's. It's a little bit said in my opinion, but that I leave to you dear reader. For the time being this is on the talk page. But I'm sure according to Price you will split in to a copy and so 'you' can still enjoy this comment. (koekoe) — Preceding unsigned comment added by Willempramschot (talk • contribs) 12:24, 25 October 2011 (UTC)


 * You habitually use the word "lying"… what "version of the word" is that, confession? As perfectly well know, your are right were you left them. Thank you for the ample demonstration, once again you've personally attacked those two users with impunity (WP:Administrators' noticeboard/Incidents).—Machine Elf 1735   02:14, 27 October 2011 (UTC)

I don't really use the word lying a lot I think, but I don't mean the version of the word 'confession' (?!) I will illustrate the version of the word I mean by the use of an example: A boy saw a cake in the fridge, he ate 3/4 of the cake, and threw the rest away. Then his mother sees a fridge without the cake, see says to the Boy: The cake is gone... Did you eat the whole cake? The boy says: No I swear I didn't. We all know the boy is telling the truth in a literary sense. But we also know the boy actually consciously leaves out crucial information, making it seem he didn't have anything to do with the dissapearing of the cake. Thus clearly suggestion a false reality. I will leave the rest of the anology up to you. That's why I thought the song of the arctic monkeys was pretty apropriate. But delete it if you want (sorry if this sounds 'blasé').--Willempramschot (talk) 08:16, 27 October 2011 (UTC)

By the way I don't know what impunity means (I'm dutch. I tried to look it up but I still don't know what it means in this context). And I surely didn't know that the ones I 'attacked' had impunitý.--Willempramschot (talk) 08:19, 27 October 2011 (UTC)
 * Hi Willempramschot, glad to see you're signing your posts - that does make the conversation much easier. (Impunity is a funny word - in this context it means attacking without fear or regard of the consequences.)  As for MWI being "dishonest", I think you're reading too much into it.  It is just a scientific theory for which there is evidence (good evidence in my opinion and some others, bad evidence in the views of others), and if the evidence points that way we just have to accept that that's the way the universe operates.  If people don't like the consequences, well that is another matter.  (People didn't like Darwinism, but that had no bearing on its scientific credibility and eventual acceptance.)-- cheers, Michael C. Price talk 10:14, 27 October 2011 (UTC)

Dear Michael Price, No you're suggesting again that people don't like it because of the consequenses. That's an assumption you make, but I regard the scientists I contacted higher then that. You can always site a well established theory, and then say first it wasn't well established, but look at it now. The fact is people got arguments against it, based on inconsistie and lack of observational evidence. You cannot really compare that to the objections people had against Darwinism. And the fact is (I think I did enough research to conclude this). Currently the mwi isn't well established in any sense (to put it stronger, most 'relevant' scientists are against it). And this is what the reception page should reflect. If in the first moments of Darwinism, people had made a book with the reception wich reflected a good reception of the theory (while it wasn't so), it also would be false. Then again Darwinism has much more evidence for it, then MWI has. In fact, right now real evidence (in my humble opinion) is actually pretty much absent, and I suspect even more scientists disliking MWI then in the early days of Darwinism. This while since Darwinism sciense has progressed a lot in it's methods.--Willempramschot (talk) 10:37, 27 October 2011 (UTC)


 * MWI is the most popular interpration of QM among the quantum phycisists (I do have a source later)Kartasto (talk) 10:54, 27 October 2011 (UTC)

Ok i'm waiting for it. It would be really hard to convince me of that I must say, since I conducted a poll which says that isn't the case. Unless you have a very narrow description of 'quantum phycisist' (that only applies to quantum computing, but then again I don't know of a poll that gives a majority of those people supporting MWI in a majority either. There is a poll of tegmark including people that finished a workshop that doesn't give a majority for mwi (but for the copenhagen interpretation). If you count 'shut up and calculate' it was third. I personally think this is an interpretation itself that just says 'we don't know yet' but you can have your own opinion on that. Also this poll has people voting more then once. And has 8 people voting for mwi. Even Tegmark (who strangely uses it besides this remark) says it's highly unscientific. To use this poll as an evidence for a good reception of mwi, let alone a majority would be a a little bit strange to say the least. Then there is a informal poll that tegmark cites with people at a quantum computation meeting. That doesn't have a majority for mwi. And strangely doesn't even have a single option for mwi. Consistent histories/many-worlds, or Copenhagen interpretation/many-worlds are the options given with many-worlds in it. Since they are both making very different clames then MWI, I think the poll in itself is useless. And even if you take the poll seriously you cannot conclude that mwi has the majority view. As if that isn't enough, it is held at a conference of a very controversial topic in quantum interpretation itself. Then there is the David Raub poll that's published in 1995, that's so at odds with every poll that's being held about MWI that it is really hard to take seriously. In fact it is so clearly at odds with my poll (which I know is honest, and is entirely open about everything, so can easily be refuted if it wasn't honest), that I have every reason to believe it's false. And so I do.

I suggest that we will wait with making a reception page that suggests a positive reception till the time is there and it is actually in accordance with the facts. If the time will ever be there. This still isn't the case (unless your source for some mysterious reason can object to all the evidence I have gathered). To make the anology with evolution theory (I will go along with this because of Michael Price's post), this had a considerable better (to put it mildly) reception after 55 years, then MWI.--145.18.244.40 (talk) 11:06, 27 October 2011 (UTC)--145.18.244.40 (talk) 11:07, 27 October 2011 (UTC)--Willempramschot (talk) 11:26, 27 October 2011 (UTC)


 * It was Esko Valtaoja who told in his book that there was an inquiry in Scotland among the quantum phycisists regarding the interpratation. "I dont know" was the top answer. MWI was second Kartasto (talk) 12:48, 27 October 2011 (UTC)
 * Which of his books was that? I can see that we'll need a precise ref here to satisfy the malcontents. -- cheers, Michael C. Price talk 13:56, 28 October 2011 (UTC)

Ok I'm not really convinced sorry(and you might see yourself why) I want to quote something about the evolution theory (to make you see that the anologyh with mwi, if it makes sense at all, is only in disfafor of mwi). The well-known theory that was extremely against common knowledge, cleary rejecting creation: source: http://darwin200istanbul.org/resources/topost/Brooke.pdf

Within fifteen years of Darwin’s publication, the success of his theory was greater than his critics thought possible. This is an important marker because it means that after about fifteen years the theory was so well respected among fellow scientists that it could not be ignored by the public. — Preceding unsigned comment added by Willempramschot (talk • contribs) 13:08, 27 October 2011 (UTC)

Retread
Look, I think we can all agree that MWI is not unanimously accepted by physicists, right? So, ignoring how aesthetically appalling the section is, it makes no sense that the Criticism section be written as if the debate is between "people who just don't get it", and the "enlightened defenders of MWI".

The section should be rewritten by someone who has a good understanding of both views to represent each topic separately, with the arguments and current consensus on each point, and specifically naming various physicists or interpretations behind the arguments instead of relying on unfalsifiable weasel words.

Also, especially for the section on falsifiability, someone should actually put up information on what the proposed methods of testing MWI are, rather than just statements that "it totally is, bromigo."192.249.47.177 (talk) 22:23, 14 September 2012 (UTC)

Yeah, I think the criticisms section should be called "Criticisms" and list only criticisms. This a wiki article and should expose the theory interpretation briefly and list the main criticisms to it (which all interpretations have). It should not be a forum for a debate on the merits and flaws of the MWI. As it is, that section is clearly biased towards MWI (I'd never really read about MWI before and noticed this).

178.199.171.234 (talk) 18:11, 6 November 2012 (UTC)

MWI *is* a mainstream interpretation
I agree with Michael C Price that MWI has currency with serious physicists, making his revert somewhat puzzling. It is by no means the dominant view, though, making contrast with Copenhagen appropriate. There were several changes in my edit earlier, and I would like to see the simple obvious ones restored; please detail your objections below. Please indicate points of disagreement, as some of these are quite obvious and could have been allowed to stand or incrementally improved instead of resorting to wholesale reversion. Thank you, FiveColourMap (talk) 14:52, 28 October 2011 (UTC)
 * 1) first line - changed a link to avoid a redirect. Might as well take a load off the servers when updating anyway.
 * 2) hyphenate many-worlds at end of first paragraph for the sake of consistency.
 * 3) remove bold from relative state at the beginning of the second paragraph. The term was already introduced at the end of the first paragraph.
 * 4) "apostrophe 70s" is ugly. As a matter of style, "1970s" is preferable.
 * 5) "Prior to" indicates that MWI is the only view with serious proponents, which is incorrect. My phrasing neatly and concisely introduces Copenhagen, compensating somewhat for the lack of discrimination in the table to the right of the table of contents. The old phrasing with two mostly redundant sentences really is atrocious.
 * 6) "reality" is out of place here as non-standard phrasing. Prefer "history", "time", or "the universe".
 * 7) "so called multiverse" - so called is unnecessary in this context.
 * 8) First sentence of the fourth paragraph (In many-worlds, the subjective ...) is fifty one (51) words long and long sentences tend to inhibit reading comprehension in the general public for whom we theoretically are writing this encyclopedia article and whom we strive to serve.
 * 9) Why is event linked to spacetime?
 * 10) "There is a number of spherical cows" is grammatically incorrect unless number is the collective noun for a group of universes.
 * 11) "and everything that could possibly have happened ..." is more atrocious phrasing. Each universe in MWI is only slightly different from the "neighboring" universes, but I agree that my wording could be improved upon to emphasize that these changes accumulate. The second sentence of the first paragraph seems to cover the point adequately, though.
 * 12) "The decoherence approach ... as a class overall" is again grammatically incorrect. We could use "decoherence approaches, taken as a class" or "MWI is a decoherence approach" or something like that. Thinking about it, it would be nice to give a sentence about decoherence.
 * 13) Multiverse was capitalized in the middle of a sentence. It was already linked in the third paragraph
 * 14) final sentence - Copenhagen interpretation was already linked, and the two links to Interpretations of quantum mechanics were likewise redundant.
 * Hi, some of the changes you made are still implemented (e.g. 1. and 4.)- it was not a total revert (please note this WMC, who called my edit summary dishonest). 9. was probably a mistake - I thought you had linked event.  I do not see why 11. is "atrocious phrasing".
 * My main concerns are with
 * the "Prior to..." removal - "prior too" indicates that MWI was the first credible theory to introduce the notion of parallel universe/worlds/timeslines. Just comparing it with the CI here does not seem enough, since that implies that there are other interpretations of QM or other theories of physics that also proposed branching realities, and I am not aware of any.  Classical physics is a non-branching theory, as are all the other interpretations of QM (with possible exception of many-minds).
 * the removal of the mainstream / decoherence class statement. I suspect we are getting our wires crossed over this.  But my intent in restoring this is because MWI is widely viewed as bizarre, hence it needs to be stressed that, despite its bizarreness, it is an interpretation that is taken seriously by many leading physicists.
 * -- cheers, Michael C. Price talk 15:28, 28 October 2011 (UTC)
 * Your first edit was a total revert, though I see now that there was some activity while I was writing this explanation.
 * I do not see this implication. How would you feel about: Many-worlds views time not as a as a single unfolding history but as a many-branched tree wherein every possible quantum outcome is realized. to replace the first two sentences of the third paragraph? Copenhagen is kind of the "gold standard" here, so I think it should be mentioned. Just linking to Interpretations may be enough, though.
 * Probably. I see it as basically redundant after my other changes; to quote Strunk'n'White: omit needless words. The old version also twice links to interpretations of quantum mechanics; we already appropriately link to that article in the first sentence, so the links are redundant (not to mention not very well labeled). "Mainstream" is not really a good word here, as quantum mechanics is itself a somewhat arcane topic. Besides, it is all intuitively a bit bizarre for us poor humans whose intuition is mainly informed by an apparently classical world. What if we merge the whole fifth paragraph into the second, leaving the introduction to end with the lay explanation? FiveColourMap (talk) 16:37, 28 October 2011 (UTC)


 * Changing "reality" for "time" looks good to me - but can't "possible quantum outcome" be reduced to "possibility"? And I still think there should be some indication that MWI was the first physical theory ever (classical or quantum) to incorporate the branching idea.  (We shouldn't assume that the reader knows that classical physics was always non-branching.)
 * Merging the 2nd and 5th paragraphs looks like a good move.
 * -- cheers, Michael C. Price talk 16:54, 28 October 2011 (UTC)

Shouldn't it say "inter" instead of "intra"?
In the Weak coupling section, shouldn't it say inter instead of intra? Intra-world means within a world, while inter-world means between different worlds, no? --TiagoTiago (talk) 06:35, 31 October 2011 (UTC)

MWI doesn't have anything to do with the anthropic principle
In the double-slit experiment when the electrons exist in superposition the electrons all follow the same laws and constants. The double-slit experiment doesn't tell us that the electrons would follow different laws of physics under different constants. Instead if you only assume MWI (and don't assume other multiverses) all possible time-lines under the same constants and laws of physics would occur.

Only other multiverse theories would allow constants to change (like the chaotic inflation).

It's just a common misunderstanding in non-science circles. --96.255.71.254 (talk) 17:38, 8 September 2012 (UTC)

Misinterpretation ? Or "point of view" presented as fact ?
>> ''"The many-worlds interpretation leads to a deterministic view of nature in which there is no special role for the human mind".

The many-minds interpretation is just as deterministic (anyway, a wave function is deterministic, only the observations - wave collapses - for a given observer are not) as the many-words one, as they are just two ways to look at the same thing : inner and outer, so to say. Nothing in the "many-minds" suggests that the mind "plays a special role" (!) in observations, since on the contrary the observations define the observer, not the other way round. At least that is what I learned in my physics courses. Just my two cents. 82.226.27.88 (talk) 05:09, 10 January 2013 (UTC)

"all possible alternative histories" is imprecise
In the intro, the phrase, "Many-worlds implies that all possible alternative histories and futures are real," is used. This phrase lacks precision because it fails to define "possible". Looking at particles, for example, a branch point might be a radioactive decay. There might be a very small probability of a given atom decaying, producing two possible outcomes: decay or not decay. However, though it is certainly possible for there to be no nucleus, there is no branch available that would lead to the nucleus simply disappearing. To resolve this ambiguity, I would suggest, "Many-worlds implies that all possible chains of dependent events do play out, creating an extremely large number of alternative histories and futures, all of which are real." -Miskaton (talk) 18:32, 10 July 2013 (UTC)
 * Hello, Miskaton. The majority of the sources I have read about the many-worlds interpretation describe it very similarly to the way the current sentence, the one you dispute, does. For example, this source by MIT Technology Review (the website) states, "The many worlds interpretation of quantum mechanics is the idea that all possible alternate histories of the universe actually exist. At every point in time, the universe splits into a multitude of existences in which every possible outcome of each quantum process actually happens."


 * Also, with regard to this edit you made about "cannot" vs. "do not," many sources state "cannot" as well with regard to the many-worlds interpretation. They state this because, as you may know, quantum decoherence makes certain that the different outcomes have no interaction with each other; in fact, various sources state that once the subjects (I'll call them subjects in this case) are decoherent, they can never interact.


 * I'm not sure about changing the "Many-worlds implies" sentence to what you suggest, and I will wait a week or so to see if anyone else comments on that matter and/or the "cannot" vs. "do not" matter. I suggest "a week or so" because this article is not high-traffic with regard to editors editing it or its talk page. I'm also busy with other matters on and off Wikipedia. So don't think that I'm ignoring you if I don't reply to your followup comment before a week goes by. Flyer22 (talk) 19:15, 10 July 2013 (UTC)
 * I've come back to this discussion to state that I have not made an additional reply in it because you have not yet replied again, and no else has yet commented on the matters. Flyer22 (talk) 17:09, 1 August 2013 (UTC)

Raub's mysterious poll
There is enough doubt about Raub's poll that the article (currently) says that "The poll is controversial."

However, I would like to spell out just how dubious this poll is.

First, the only and original citation of the poll that I can find, is in the 1995 book The Physics of Immortality by Frank Tipler, pages 170-171. In the notes it is cited as "Raub 1991 (unpublished)", and there is no entry for Raub in the bibliography, so presumably this is a personal communication.

The Wikipedia article on MWI currently cites, as its source of information about the poll, an obscure recent (2008) book called "The Universe - Solved!", which promotes the idea that we are living in a computer simulation, and an "unauthorized guide" to What the Bleep Do We Know. The latter says the poll was published in "Sciences et Avenir" in January 1998. I have not located a copy of the journal, but this "fact" is also widely cited on the web, saying that Raub's survey was conducted in 1995 and that almost 60% of those surveyed endorsed MWI. Tipler's book was published in 1995, and Raub's survey then claimed 58% endorsement, so most likely "Sciences et Avenir" had an article which mentioned Tipler's book, and this has been garbled into the false claim that Raub's survey was "conducted... in 1995".

Tipler lists Feynman, Gell-Mann, and Hawking as among those who agree with MWI. Feynman died in 1988, so no-one ever had a chance to ask him for clarification. But did he ever verifiably say that he agrees with Everett? Can anyone produce a source for this, other than Raub? Feynman did invent the path integral or sum over histories formalism for quantum mechanics, and since we do not have access to any facts about how Raub conducted his poll, it is possible that he asked his respondents whether this is the most fundamental formulation of QM. But agreeing with that is not the same thing as agreeing with the existence of parallel worlds. For example, Gell-Mann recently coauthored a paper employing a many-histories formalism but arguing for "one 'real' history".

So I think it is fair to say that Raub's poll is not a credible source. It has apparently never been published; the only place where its results are directly reported is a work of many-worlds theology; we know nothing about how the poll was conducted; and its results are at odds with a number of other surveys. Independently of this, we can also say that the current sources for the survey, cited in the article, are not original sources, they are fringe publications even more dubious than Tipler's, and they are just repeating confused claims that they have heard somewhere else.

Perhaps it is reasonable to say that Raub's poll is widely cited on the web, but it's not just "controversial", it is unpublished, unverifiable, and cited only by fringe sources.

P.S. There is an earlier discussion of the poll in "Archive 5". Mporter (talk) 06:50, 2 August 2013 (UTC)

Branching vs Diverging
In recent years there has arisen a debate as to whether the 'worlds' branch or diverge. Ever since Everett introduced the term "branching" and DeWitt followed up with "splitting", almost all the litterature on Everettian QM has used the same terminology. However in the formalism of QM, there is noting that indicates that worlds branch, a more coherent view is that all worlds exist and are qualitatively identical up to a certain point and there they diverge.

As the notion of uncertainty has been under attack in the branching view, quite a few proponents of EQM have abandoned it, for instance Steven Weinberg and some others have adopted new views, for instance David Deutsch has proposed "fungible" worlds. Alastair Wilson and Simon Saunders has advocated for the divergent view in the last 4 years in a series of papers. 2 of Wilson's papers here: http://alastairwilson.org/files/opieqmweb.pdf and http://alastairwilson.org/files/moieqmweb.pdf Simon Saunders has a chapter dedicated to this in the 2010 oxford volume. — Preceding unsigned comment added by Quantumental (talk • contribs) 15:14, 29 April 2012 (UTC)

- I take the branching vs divergence issue to be an important one, and would welcome an addition to the MWI entry mentioning it. Is the appropriate metaphor for MWI 'parallel worlds' or 'splitting worlds'? It has to be one or the other! Modalizer (talk) 15:51, 22 June 2012 (UTC)

Hawking tacitly accepts MWI as the straight forward interpretation of QM. When asked if the universe is deterministic, he replied, "There are many parallel worlds. In one of those world's Hitler may have won WWII. But since we don't know our future, for all practical purposes we live our lives as if universe were not deterministic." Without interpretation, theories in physics are meaningless symbols. Wheeler and Penrose claimed they rejected the MWI because it carries too much metaphysical baggage. Since when did carrying too much metaphysical baggage become a valid objection to a scientific theory. That is the very same objection raised by the Roman Catholic Church to discredit Galileo's claim that the sun is the center of our solar system. Does the MWI of QM really carry more metaphysical baggage than SR, GR, and the Coppenhagen version of QM? How do you measure just how much metaphysical baggage a physics theory carries before you deem it not valid because it carries too much metaphysical baggage? The article fails to mention that the MWI justifies the anthropic principle, and eliminates the need for the silly concept of complimentarity. Another advantage is it gives a realist view of the universe between measurements. Finally, the Capornican principle favors the MWI. The worlds we can't observe directly are the same as the inside of black hole, or seconds after the Big Bang. Since we will never be able to see the inside of a black hole, or go back in time to Big Bang, we can say whatever physics says about the inside of black holes or the Big Bang is not falsifiable. The distant past, the other side of an event horizon is off limits just like other worlds in Hugh Everett's MWI. — Preceding unsigned comment added by 98.254.210.8 (talk) 11:07, 15 August 2012 (UTC)

I have an argument in favour of branching over diverging.

Branching or splitting requires the creation of energy, BUT the CoE is not assured to apply outside of each universe.

But if all universes already exist and only diverge, then we must eventually bump into a failure of quantum physics if times goes on as more and more universes are required.

And diverging really requires that existence started off with an exact and limited number of universe's, once things diverge too much we run out of other universes that share a common history.

Additionally some improbably world lines that have longshots occur would run out of common history universes very fast, if something happened with a very long shot of occurring rather few universes would end up with that fate, and even fewer of that same longshot happening again.

Such an outlier universe could run out of neighbouring universes very quickly.

Indeed a universe (or multi-verse) doomsday machine could be built that would create lots of quantum events with millions or billions of outcomes every second, this could potentially exhaust a universe of universes with which to interfere with causing the collapse of quantum physics and presumably the end of too many processes for existence to carry on in that or any other universe that ran the machine long enough. — Preceding unsigned comment added by 121.99.188.97 (talk) 05:10, 23 January 2014 (UTC)

How is "world" defined in MWI?
I always wondered how the MWI defines a "world". I can't seem to get this knowledge out of the article. Yeah, you can write down Schrödinger's equation and explain the possible states that a state can collapse to with the sentence "all of these states are in another world". But this does not explain what a "world" is.

So, how exactly does MWI define a "world"? What exactly is it that exists after "splitting up"? --2003:63:2F5A:1600:8C0A:C643:6701:12CA (talk) 10:07, 19 February 2014 (UTC)

The Veilerian approach
the many worlds interpretation is not a testable realistic view but an artistic one, there is one optimum path. We know that because if we measure a spin and then remeasure it, it remains the same. So eternaly a spin is the same, and we might read it as different only is we twist at an angle our detector at a second measurement, or if we do not twist at all the spin detector but if we move it at a close fragment of the light speed faster than the first measurement.

The modern view is that we shape the spin during measurement, and we have proven statistically that the entangled spin is created during the measurement. This measurement either kills the pro detection spin, either coalesces with the pro-detected spin if we measure the particle at a very abstuct-low enegy level [also then we have reading spin noise]

so yes, the spin is produced during measurement, but that does not mean that a particle has no spin. Mathematically even the non collapsed wavefunction requires a spin, because that angular momentum is an oscillation of nothingness itself, so we have something called field of one particles energy level.

So if we knew all spins from big bang and after, and if we could calculate all Richard Feynman's diagrams, we could then predict all probable anwers, but that is against Heisenbergs uncertainty.

The Heisenbergs uncertainty does not kill spin before detection, it just make is uncertain to various beholders that have different personal time flow perception also called angular momentum also called spin/period duration for a particular beholder versus an external particle to interact. — Preceding unsigned comment added by 2.84.206.14 (talk) 02:41, 30 June 2014 (UTC)


 * The talk page of an article is not the place to discuss your view of the validity of the concept that the article presents. —Quondum 05:11, 30 June 2014 (UTC)

One of the assumptions made by the relative state formulation?
The article says "The first is that the wavefunction is not simply a description of the object's state, but that it actually is entirely equivalent to the object, a claim it has in common with some other interpretations." Is that actually stated in Everett's writing or did that come later? What's the significance of that assumption in the article? MazeHatter (talk) 13:27, 30 July 2014 (UTC)

"many interacting worlds" interpretation
There is apparently a new many-worlds interpretation of QM, called by the authors MIW, or "many interacting worlds". I don't know if this is too new to be included in this article, as the paper was only published on 23 October 2014.

Here's the paper: https://journals.aps.org/prx/pdf/10.1103/PhysRevX.4.041013. Here's a popular news article about it: http://www.sciencedaily.com/releases/2014/10/141030101654.htm.

A few neat things about this interpretation:

- There is no splitting of worlds at measurements. All the worlds are always there.

- The law of motion has a classical term and a quantum term. The classical term is just Newtonian motion within one world. The quantum term can be interpreted as a repulsive force between "close" universes. The paper shows how this force gives rise to quantum-mechanical behavior such as tunneling, the uncertainty principle, etc.

- This interpretation could enable easier predictions of QM behavior, because you can make good approximations by only considering a finite number of universes, sometimes as few as two.

Does anyone here believe this new interpretation should be added to this article, or is it too new? There hasn't been time yet, for example, for other papers to critique it or even reference it. It would be great if an actual quantum physicist could weigh in here. —Egamble928 (talk) 23:23, 10 November 2014 (UTC)


 * IMO, it should not be added to this article, as it is a fresh interpretation of QM. It would only be referenced/mentioned in this article.  But give it time: we should wait until secondary sources start commenting before creating an article on this new interpretation (just as a standard WP principle). —Quondum 23:32, 10 November 2014 (UTC)


 * That seems reasonable. Just to be clear, are you saying that a reference/mention of it should not be added until a separate WP article is made about it? —Egamble928 (talk) 00:20, 11 November 2014 (UTC)


 * To be fair, the bar for inclusion of mention of something into an article in WP is much lower than for creation of an article for that same something. Thus, I am not saying that creation of a separate article should precede mention of other specific interpretations in this article; I'd expect it to be the other way around. however, I'd nevertheless think that it would make sense to wait for further references before including anything, or at least someone knowledgeable who can digest the paper; WP is not newspaper.  I think others should comment here, especially those with more expertise than I have. —Quondum 01:38, 11 November 2014 (UTC)


 * I have been in communication with an author of the MIW paper, who told me of a review (opinion piece) of the paper by another physicist in Physical Review X: http://journals.aps.org/prx/abstract/10.1103/PhysRevX.4.040002. There are now at least three papers on arxiv that cite the arxiv version of the MIW paper  . Other physicists have also given their opinions of MIW in popular articles  . IMO, there are enough secondary sources now to warrant a short mention of MIW on this page, contrasting it with Everett MW. What do others think? —Egamble928 (talk) 00:46, 14 November 2014 (UTC)

Article contradicts itself
In the Common Objectives section, in response to the conservation of energy objection, it says:
 * the law of conservation of energy says that energy is conserved within each universe.

But in the Speculative implications section, under Weak coupling, it says:


 * This does not violate the fundamental principles of physics because these require energy conservation only for the whole universe and not for the single parallel branches.

Which is it? The latter has a better source and makes more sense to me :) Maybe one response to the conservation of energy objection is enough and the statement that energy is conserved within each universe ('branch' would have been clearer than 'universe' anyway) should be removed. — Preceding unsigned comment added by 50.141.109.13 (talk • contribs) 2015-03-05T09:05:53‎


 * Well spotted. This would seem to me to be a problem arising from using a single primary source. The wording comes almost directly from the source, and seems to be a simple statement of the writer's preconceptions. My bet is that your second quote is making and utterly baseless and incorrect statement about physics; in any event, without corroboration from a secondary source (especially since it makes a big claim that would be a focus of such, as it seems to me that it violates Noether's theorem), it does not belong in the article at all. —Quondum 14:43, 5 March 2015 (UTC)

Sections re-arranged
I've re-arranged the order of the sections in this article, but the content remains unchanged.

Sections "Brief overview" and "Relative state" now appear after the section "Probability".

The section "Comparative properties and possible experimental tests" now appears after the section "Properties of the theory".

The result of moving these three sections (which describe the interpretation) up is that they now all precede the "Common objections" section. I hope this is uncontroversial. Peter Ells (talk) 00:39, 14 August 2015 (UTC)

Multiple histories
Many-worlds implies that all possible alternate histories...

"The only way to reconcile all the observations, Cotler says, is to conclude that the photon went through multiple histories in parallel." Kartasto (talk) 12:02, 13 April 2016 (UTC)

Origin
In Dublin in 1952 Erwin Schrödinger gave a lecture in which at on point he jocularly warned his audience that what he was about to say might "seem lunatic". It was that, when his Nobel equations seem to be describing several different histories, they are "not alternatives but all really happen simultaneously". This is the earliest known reference to the multiverse (David Deutsch. The Beginning of infinity. Page 310).

Here is an another source: "Gribbin’s coup is to trace the origins of what is now called the Many-Worlds Interpretation to a lecture delivered by Schrödinger in Dublin in 1952, some five years before a paper by Hugh Everett more usually credited with the idea." Kartasto (talk) 03:05, 19 April 2016 (UTC)

Many-Worlds vs. Relative-State
The Many-worlds interpretation article appears to try very hard to persuade the reader that there is no distinction between the Many-Worlds interpretation (MWI) and the Relative-State formalism or interpretation. It even tries to claim that the three sources (the Ph.D. Thesis, the published article, and DeWitt's "popularization") all have the same "content".

This is not true.

For one, DeWitt bases a great deal of his "popularization" upon a non-published, early version of Everett's Thesis. This, of course, correlates with Wheeler's short article that accompanies Everett's Relative State formalism article, wherein Wheeler points out that Everett actually wanted to publish a qualitatively different paper, but that Wheeler had persuaded Everett to produce the version that was published. (The published Relative-State paper is a shortened version of the Thesis, which, presumably, was also a modified version of Everett's ideas, as persuaded by Wheeler. After all, the unpublished, early version of the Thesis that DeWitt published is rather distinct from the actual, published Thesis.)

For instance, while the MWI reifies all possible outcomes, the Relative-State formalism never splits the Universal Wavefunction into multiple "realities", but, instead, each "reality" is simply a refactoring of the Universal Wavefuntion relative to the state of the "observer", which is also part of the Universal Wavefunction. (Incidentally, as Everett points out, said "observer" need have no "consciousness", but can even be an "automaton".)

Additionally, the Relative-State approach has no need, and makes no mention of "decoherence". — Preceding unsigned comment added by DWHalliday (talk • contribs) 01:23, 17 October 2016 (UTC)

So, I assert that the MWI and the Relative-State "interpretation" are just as much (if not more so) separate interpretations as is the MWI vs. the Many-Minds interpretation.

Yes, they use, in a sense, the same mathematics. However, that can be said for very nearly all interpretations of Quantum Mechanics. So that is insufficient to argue that the Relative-State interpretation—a qualitatively different interpretation vs. the MWI—should be "subsumed" into the MWI (and, effectively, repressed thereby).

For instance, I, as a Theoretical Physicist, can ascribe to the Relative-State interpretation, while I cannot do so for either the MWI or the Many-Minds interpretation. DWHalliday (talk) 01:07, 17 October 2016 (UTC)

One can, of course, argue that what DeWitt has "popularized" could be closer to Everett's original thinking than the papers he was persuaded to write by his thesis advisor, Wheeler.

I would not argue against that.

However, it further illustrates the distinction between the interpretations. DWHalliday (talk) 01:11, 17 October 2016 (UTC)

What about probabilities that are not rational numbers?
I've got one question that I really expect has been already answered by experts, but I have never read such an answer.

Say a quantum event has a probability $$\tfrac{a}{b}$$ with $$a$$ and $$b$$ integers. Then it's fine, create $$b$$ universes and have $$a$$ of those in which the event occurred. But what's going on when an event has a probability of $$\tfrac{1}{\sqrt{2}}$$ or even $$\tfrac{1}{\pi}$$? Do we spawn a non-integer amount of universes? Do we spawn an infinite amount so that the limit of the sum converges to this irrational probability? Do we say that real numbers are mathematical abstractions that don't actually exist in a reality that is fundamentally discrete?

Niriel (talk) 15:03, 15 December 2016 (UTC)

Of two minds on the subject
It occurs to me that proponents of MWI must agree that in some universes they are not proponents of MWI. Therefore, they can't even agree with themselves. Twang (talk) 08:35, 18 February 2015 (UTC)

I like your reasoning, so many fallacies /paradoxes can be stated with MWI; another thought, if one verse differs by a single particle, would the 2nd Verse appear different. Why cant C of E be applicable for the whole MV, not just each Verse? so many other ideas can be asserted to ridicule the theory. if other Verse cant conceive of MWI, why is its state not the correct one? If I have 100 Schrodinger cats, how many will appear as a 747 when door is opened? how illogical can the theory be with so many illogical permutations available. does logic not exist in some Verses? If physical laws could be different in a Verse based on initial state, then how many mathematical laws, would not even exist in one? why does each verse have to have same # of dimensions? Did the big bang result in a point Verse? or a 2D plane, of even 3d without time? Juror1 (talk) 09:20, 17 February 2016 (UTC)


 * The examples you provide are neither fallacious nor paradoxical. It is clear that you misunderstand MWI to a high degree. This is massively ironic considering those that think it is illogical mainly do so on the basis of fallacious and illogical thinking.


 * If you are going to disparage an interpretation, you should do so on the basis of its claims rather than an obvious straw man. &#124; &#124; skubb &#124; &#124; 22:31, 17 March 2017 (UTC)

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Proposed new lede
Hi all, thanks for the contributions!

I feel like this is an improvement. Thoughts? suggestions?

The many-worlds interpretation is an interpretation of quantum mechanics that asserts that for each simultaneous state exhibited by fundamental particles, as a result of their wave-like property, there exists a corresponding "real" macroscopic world. It denies the actuality of any wavefunction collapse and stands in contrast to other interpretations based on that principle.

Many-worlds implies that all possible alternate histories and futures are real, each representing an actual "world" (or "universe"). In layman's terms, the hypothesis states there is a very large—perhaps infinite —number of universes, and everything that could possibly have happened in our past, but did not, has occurred in the past of some other universe or universes. The theory is also referred to as MWI, the relative state formulation, the Everett interpretation, the theory of the universal wavefunction, many-universes interpretation, or just many-worlds.

Informata ob Iniquitatum (talk) 08:35, 9 September 2017 (UTC)

Quantum theory of observation
I've been surprised that the link to my wikibook, Quantum theory of observation, has been suppressed. Quantum theory of observation is just another name for the many-worlds interpretation. This is exactly the same theory. We obtain a wave function which represents many worlds when we apply the Schrödinger equation to observation processes. TD (talk) 07:46, 4 July 2018 (UTC)
 * Do you have a peer-reviewed paper discussing this? If not it is not suitable content here. In addition, this type of self-promotion is not wanted here, and you are well aware of this. --mfb (talk) 08:13, 4 July 2018 (UTC)
 * "Although several versions of many-worlds have been proposed since Hugh Everett's original work,[4] they all contain one key idea: the equations of physics that model the time evolution of systems without embedded observers are sufficient for modelling systems which do contain observers" in the present article. Everett's original work is explicitly about solutions of the Schrödinger equation for observation processes.
 * Sorry for the COI rule. I remembered the discussion, but not its conclusion, which did not convince me completely. But the original discussion about the COI rule was about an explicit mention of the title of my book. Here it is only a link to a sister project. Is it really forbidden ? If my wikibook had been entitled Many-worlds interpretation, wouldn't it be automatically linked ? TD (talk) 08:35, 4 July 2018 (UTC)
 * It is still your work, and you try to promote it. It doesn't matter if you link to to a description of the book or mention the title. No it wouldn't be automatically linked with another title. A link could go to a list of books about MWI. Unless you have an external reference that your book is the standard textbook on the subject (it is not). --mfb (talk) 09:11, 4 July 2018 (UTC)
 * You're right. Surely not the standard textbook. But the only one on this subject on Wikibooks. And you're wrong about the automatic link. I tried with another book. If the title of a wikibook corresponds exactly to the title of a wikipedia article, it is automatically linked. TD (talk) 09:31, 4 July 2018 (UTC)
 * The link depends on how you fill the template. Anyway, "I wrote together some stuff" is far away from the quality criteria we have here, and it stays self-promotion. --mfb (talk) 12:06, 4 July 2018 (UTC)
 * Why do you judge what you do not know? You didn't even know that Everett's theory is a quantum theory of observation and you think you can judge my work. Why? TD (talk) 15:07, 4 July 2018 (UTC)
 * I know the MWI better than you think. You are inventing new descriptions here that are outside of what the literature uses. That is not my fault. --mfb (talk) 15:19, 4 July 2018 (UTC)


 * Please be precise. I like people who disagree with me when they know what they are talking about. If you know, please explain why my book should deserve your contempt. TD (talk) 15:35, 4 July 2018 (UTC)

See WP:SELFPUB, WP:COI, WP:OR. And Wikibooks do not qualify as reliable sources. Headbomb {t · c · p · b} 15:38, 4 July 2018 (UTC)
 * Do you mean that there shall not be links on Wikipedia to its sister project, Wikibooks? All wikibooks are original research works because an educational book is always a research work. We have to invent how to teach. I do not contest the COI rule, even if I am not completely convinced, because it is how Wikipedia works. Self-promotion is usual practice on Wikibooks. When we have written a book, we put a link on Wikipedia to make it known. Is it wrong ? TD (talk) 15:50, 4 July 2018 (UTC)


 * I never found any reason to link to Wikibooks any more than I would Lulu.com. Headbomb {t · c · p · b} 15:54, 4 July 2018 (UTC)
 * This is not the usual practice on Wikipedia. There are many links to Wikibooks and there should be more. This is a way to unify all Wikimedia projects. We are stronger when we are united. TD (talk) 16:01, 4 July 2018 (UTC)
 * I strongly feel we should not be linking to Wikibooks or Wikiversity, and I've raised this at Wikipedia talk:External links. Doug Weller  talk 16:54, 4 July 2018 (UTC)
 * hi and thanks for your contributions! I'm inclined to agree w/Headbomb and Doug.  That said, can you provide an example of such a Wikibooks link in another article? Informata ob Iniquitatum (talk) 02:11, 7 July 2018 (UTC)
 * FYI: They are all the same form in many articles: From my point of view, this discussion is finished.TD (talk) 06:57, 7 July 2018 (UTC)
 * I agree too. (Everybody wants his/her work cited and acknowledges, yet Wikipedia should adhere to the highest standards for its sources and this includes keeping promotion of own work at a minimum).Benjamin.friedrich (talk)

Evidence that Everett proposed branching of the universe?
Additionally, I would like to ask the experts where Everett actually introduces the existence of several worlds that co-exist in parallel? I did not find any such statement in his PhD thesis. Quite the contrary, his footnote 1 on page 68 uses the language of several co-existing observers only to account for several "observer states" that can co-exist in a superposition. I found a German article by Oliver Passon "Nicht-Kollaps-Interpretationen der Quantentheorie", published in the book "Philosophie der Quantenphysik", Springer. On page 201, footnote 22, the author expresses his doubts that the splitting of the universe into separate branches was actually intended by Everett. Instead, he cites references (Barrett, Eur. J. Phil. Science 2011; Saunders et al., in "Many worlds", Oxford University Press, 2010) that attribute this idea instead to the popularization of Everett's original idea by Bryce deWitt and Neil Graham (The many-worlds interpretation of quantum mechanics, 1973). Could someone comment? In any case, it could be useful to go back to the original publications (instead of citing popular science books). Benjamin.friedrich (talk)
 * How would these several observer states differ from what we now call worlds? --mfb (talk) 00:59, 25 July 2018 (UTC)
 * Maybe you are right. However, the terms used in the article as well as the figure can be understood in the way that each world represents one copy of the universe. At each interaction event, the universe really splits up into two copies of itself in this view (e.g. one copy of the universe where Schroedinger's cat is dead and one copy of the universe where the cat is alive). In contrary, from my reading of Everett's thesis, I understood that the branching is only a mere mathematical description of a single universe that evolves in time. Please comment. Benjamin.friedrich (talk)

Many Interacting Worlds
I'm surprised that there seems to be no mention in Wikipedia of Many Interacting Worlds, in which quantum mechanics is a side effect of world interactions.

https://journals.aps.org/prx/abstract/10.1103/PhysRevX.4.041013

"We introduce an approach to quantum phenomena in which all quantum effects are due to interactions between a large but finite number N of worlds, and probabilities arise from assigning an equal weighting to each world. A number of generic quantum effects, including wave packet spreading, tunneling, zero-point energies, and interference, are shown to be consequences of the mutual repulsion between worlds (Sec. IV). This alternative realistic interpretation of quantum phenomena is also of interest in not requiring the concept of a wave function." Scott McNay (talk) 21:36, 22 December 2017 (UTC)
 * Sorry, but I do not see the link (except for the similarities in the title). Everett's many-world interpretation stresses the universality of the wave function, whereas this PRX proposes the wave function as a secondary effect. Please clarify. Benjamin.friedrich (talk)


 * I agree. Actually "Many Interacting Worlds" should have it's own article on WikiPedia. https://arxiv.org/abs/1712.01918 https://en.wikipedia.org/wiki/Howard_M._Wiseman 23.240.1.247 (talk) 23:54, 8 June 2019 (UTC)

Improve first paragraph : Everett's thesis much more readable than this article
Sorry, but I find this article difficult to understand; often language is not as precise as it should be. In contrast, I found Everett's original PhD thesis a very accessible resource. I want to propose to follow more his exposition to make the article more accessible. Here is a rough suggestion, please improve:


 * The many-worlds interpretation is an interpretation of quantum mechanics that assumes that the wave function provides a complete description of reality. As a consequence, it does not have to assume a discontinuous collapse of the wavefunction of a quantum mechanical system if its state is measured by an observer. Instead, also the observer must be described by its wavefunction. The measurement process amounts to a non-trivial coupling between the wavefunction of the system and that of the observer. Benjamin.friedrich (talk)
 * Sounds good. --mfb (talk) 00:59, 25 July 2018 (UTC)


 * Thanks for raising this. The lead does need work.  It needs to be better written per MOS:JARGON. Alas, I feel the above proposal doesn't address that.
 * The many-worlds interpretation of quantum mechanics proposes that for each possible state in a quantum system, there exists a world in which that state is "real", including our own.
 * Something like this. Informata ob Iniquitatum (talk) 01:53, 25 July 2018 (UTC)
 * That is a consequence, but it is not the main concept of the interpretation I think. The wave function as key element is the main assumption, the rest follows from that. Also, what does "possible" mean in the context of MWI? We shouldn't use one interpretation to describe another. --mfb (talk) 02:13, 25 July 2018 (UTC)
 * It is a challenging topic. Opening with this seems right to me.  How would you introduce the wave function/collapse?  Informata ob Iniquitatum (talk) 02:27, 25 July 2018 (UTC)
 * Well, there is no collapse. I like the change proposed by Benjamin.friedrich. We can remove "if its state is measured by an observer" and add the many worlds as consequence in the following sentence. --mfb (talk) 02:31, 25 July 2018 (UTC)

The problem is two-fold: It assumes too great a degree of knowledge on the part of a general audience, and while I understand your position, the contingent existence of different worlds is the most distinctive feature of the theory. That's why Dewitt's name is the one that caught on. I'm not saying that my proposal is the answer, it's just more in keeping with MOS:JARGON. Starting off with it "assumes the wave function is a complete description of reality" and then "it does not have to assume a discontinuous collapse of the wavefunction of a quantum mechanical system if its state is measured by an observer." is way too technical. The proposed paragraph doesn't even mention the titular "many worlds" that someone new to the topic will no doubt be curious about and will wonder why they aren't mentioned. Benjamin's proposed content has a place, but it should be somewhere after an easier-to-digest description. Informata ob Iniquitatum (talk) 03:03, 25 July 2018 (UTC)


 * I agree, and would like to point to a fundamental issue: more and more, I am gaining the impression that DeWitt misinterpreted and misrepresented the theory put forward in Everett's PhD thesis. Possibly, Everett never complained because this misinterpretation popularized his work (see also my comment below). For the introductory paragraph of this article, a decision is needed whether we want to follow Everett or DeWitt. We should be careful and cannot assume that both Everett and DeWitt are referring to the same interpretation only because they claim that they do. Benjamin.friedrich (talk)


 * I'm discovering this topic and have exactly the same impression. The posts Many-Worlds Interpretation of Quantum Mechanics and Everett’s Relative-State Formulation of Quantum Mechanics explain more clearly the distinctions. Maybe the article should reflect that Many-World is more of a general idea from which derives several interpretations (or not, maybe I just don't understand well enough). Kaylier (talk) 11:22, 20 February 2020 (UTC)

Tags
The "original research" tag in the "Overview of the interpretation" section is unhelpful. I'd like to address it, but I don't know to which statements it refers. The specific complaints are about "unsourced statements, interpretations of sourced statements, and statements made about a source that are themselves unsourced". Could the editor that added the tag please explain? Tercer (talk) 18:33, 6 March 2020 (UTC)
 * Yeah, that was me. That was before any work was being done to fix the article. I'll retag it on a statement by statement basis tomorrow. Crossroads -talk- 05:07, 7 March 2020 (UTC)

Everett's derivation of the Born rule
I don't really know what the article should say about Everett's derivation of the Born rule. The article was mentioning it before I edited it, and I left it there because I thought it is historically significant. I decided though to add criticism of his derivation, because nobody thinks that Everett solved the problem. The problem is that almost nobody even mentions his proof! I managed to find three mentions: one by DeWitt, who simply calls it "rather brief" (taken literally this could even be considered as praise, although from the context it is clear that DeWitt meant it as criticism. In any case it is not substantive enough), another by Graham, who spews a load of nonsense about frequentism, and another by Ballentine, which calls Everett's assumptions ill-motivated. I put the last reference in the article, because Ballentine's paper is also a historically significant criticism of Many-Worlds.

That's not really satisfactory, though, because the very fact that hardly anyone even mentions Everett's proof is strong evidence that everybody thinks it is garbage. But how can we put this kind of information in Wikipedia? Even if we went through the literature to demonstrate that almost nobody mentions Everett's proof, that would be WP:OR. I got curious then, and decided to look at what he did. It's embarrassing, his proof is just a circular argument (he assumes that quantum states are normalised via the 2-norm, and concludes that the probability rule is the mod square. Well, if you assume instead that quantum states are normalised via the p-norm, you conclude that the probability rule is the mod to the p). Argh. But we cannot put this information in the article either, it would be even more blatant WP:OR. The best solution would be if we could find a paper with this demonstration of circularity, but I searched a lot and didn't find anything. Tercer (talk) 17:40, 2 March 2020 (UTC)
 * When I was first trying to clean the article up a bit, I had a vague memory of somebody calling Everett's "proof" a circular argument, but I couldn't track it down. I will look again. XOR&#39;easter (talk) 17:54, 2 March 2020 (UTC)
 * I just searched again, and found several accusations of circularity levelled against the Deutsch-Wallace approach, some against the frequentist approach, but nothing about Everett's original proof. I hope you do find something, otherwise I'll have to write a paper myself demonstrating this point. Tercer (talk) 09:04, 3 March 2020 (UTC)
 * I might have been thinking of Barrett ("The upshot is that one can get the standard quantum probabilities by making an ad hoc choice for how branches are individuated and/or an ad hoc choice for one's probability measure over branches"). Kent says that there is "no way to deduce any statement connecting μ with real physics." Hemmo and Pitowsky say that Everett and DeWitt were "refuted by various authors essentially on pain of circularity", but the circularity they point to doesn't seem to be exactly what you had in mind. (They talk about "the identification of measure zero with probability zero", which I guess is related to deriving a norm by choosing a norm, but doesn't sound quite the same.) XOR&#39;easter (talk) 14:19, 3 March 2020 (UTC)
 * For that matter, why pick a norm at all? That is, why make the probability (or the typicality, or whatever you want to call it) a function of the magnitude alone? My sense was that, as Barrett says, the branch coefficients "can only be empirically determined up to an arbitrary phase factor" &mdash; but doesn't this presume the desired answer? If the probability rule were different, the theory would predict different statistics, and maybe different statistics could allow an inference of a phase factor. It seems like phases are declared empirically non-determinable without real justification. XOR&#39;easter (talk) 14:31, 3 March 2020 (UTC)
 * It is remarkable that all three authors attack Everett's proof only on philosophical grounds, and seem to take for granted that his mathematics work. Kent doesn't actually mention the derivation, only the result, so perhaps he thought it smelled fishy. Barrett, on the other hand, goes into detail about the demonstration, and waxes lyrical about Everett's additivity condition, as though it is what actually resulted in the Born rule. Hemmo and Pitowsky are not talking about Everett's proof, but rather about the frequentist derivations, which are of course wrong.
 * In any case, I agree with you, the assumption that the measure depends only on the norm of the branch is not well-motivated, it should be taken to depend on the whole vector, and we need physical arguments to restrict it. I also find it very strange this assertion that we cannot determine the phases. We do, they are relative phases! Using only the global phase freedom is not enough to set the phases of all branches to zero. I don't think your circularity argument is correct, though. For any relative phase we have, we can build an interferometer that will give a deterministic measurement result, so we can actually determine the phases independently of the probability rule. Tercer (talk) 14:58, 3 March 2020 (UTC)
 * Yes, it was interferometry and the distinction between global and relative phases that made the whole thing sound fishy when I first read it, whenever that was (undergrad?). I will make one more trip into the archives to see if I can find more commentary on Everett's "derivation" specifically. XOR&#39;easter (talk) 17:46, 3 March 2020 (UTC)
 * Another comment: Everett [EI57] proved that if a measure can be attributed to branches, and is preserved by further branchings, it equals the Born weights. And the total measure of branches with results deviating from the Born rule tends to 0, as the number of measurements tends to infinity. But for finite experiments this only means branches with frequencies deviating beyond a given error have small measure, which only makes them negligible if Born weights have a probabilistic interpretation, in a circular argument. XOR&#39;easter (talk) 18:36, 3 March 2020 (UTC)
 * Argh this quote is terrible. He misunderstands Everett's argument about the measure (there's nothing about the measure being preserved by further branches), seems to have a frequentist interpretation of probability, and misunderstands Everett's argument about typicality. Maybe leaving Ballentine's reference is good enough, as it is the text doesn't mislead people into believing Everett's argument was accepted by the community.
 * I wrote to Barrett, by the way. He said that my argument was correct, but was not so impressed, as he think the problems with Everett's argument are deeper than that. Tercer (talk) 20:24, 3 March 2020 (UTC)
 * Neill Graham's contribution to the 1973 book, where he tries his own frequentist derivation of the Born rule, has some criticism of Everett's specifically. I've heard that there might be more in Graham's PhD thesis, but I haven't been able to dig up an actual copy yet. (His thesis is also reputed to have a very thorough bibliography.) XOR&#39;easter (talk) 18:03, 7 March 2020 (UTC)
 * Yeah, I know. I'd rather avoid citing him, as not only his criticism of Everett is nonsensical, but also his own proof is nonsensical. If we must add another criticism beyond Ballentine's, I would go with Barrett's. Unlike Graham, who is universally derided, Barrett is in line with current thinking. Tercer (talk) 18:11, 7 March 2020 (UTC)