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"Calculating probabilities" ff with no header, inserted out of sequence

Calculating probabilities? Basis problem?1Z 20:13, 9 February 2007 (UTC)

• What's the problem with calculating probabilities? Everett and deWitt both showed how probabilities emerged from within the MWI scheme.

• Since no measureable quantities (such as eigenvalues or transition probabilities) are basis dependent there is no basis problem.

--Michael C. Price ^talk 20:45, 30 May 2007 (UTC)

Not in a generally satisfactory way. Derivation of the Born rule is still being hotly disputed. Even MWI proponents are still disagreing about how to do it.

Preserving probability (in the form of the Born Rule) is critical for the acceptance of the Everett method. The Born Rule defines how to determine the probability that we will see various outcomes when we observe a system that is in a particular quantum state. For example, it may indicate we have a 99% chance of seeing an electron at location A and only a 1% chance of seeing it at location B. But what does it mean for location A to be 99 times more likely than location B when each outcome has a branch of the universe in which it occurs? Our hold on the mathematics of quantum mechanics depends upon being able to assign probability measures to events occurring inside the universe we experience, and as well as to events inside the universes we do not see! (And exactly who "we" are in this scheme that contains vast but indeterminate numbers of fractured selves is an ontological question related to the probability problem.)

Wayne C. Myrvold of the University of Western Ontario and Hilary Greaves of Rutgers University made a presentation backing up previous work by Deutsch, Saunders, and Wallace delineating a "decision-theoretic" statistical method that purports to preserve the Born Rule, i.e. probability, throughout Everett's multiverse. David Z. Albert of Columbia University objected to this argument: "Talk about the probability of this or that future event would seem to make no sense unless there is something about the future of which we are uncertain, and there seems to be no room for any such uncertainty in the context of anything along the lines of an Everettian picture." Albert critiqued the Everettians for trying to prove that their theory allows for the Born Rule to function by assuming the belief that the Everett theory is true (they should rather show how a non-believer could come to believe it to be true). Albert, who is sympathetic to the "pilot wave" or "non-local hidden variables" interpretations of quantum mechanics originally made by Louis de Broglie and David Bohm, described the Everettian's explanation of probability as at best explaining our betting behavior, which as an explanation of physical evidence is "sheer madness."

Many Worlds in Oxford -- 1Z

(I took the liberty of signing and indenting your comment.)

It's impossible to make sense, in any physical theory, of the statement that something happens with 99% probability. The only way you can describe this as a weakness of MWI is if you've noticed the problem in MWI and failed to notice it in other theories. I realize that many people, some of them well-known experts, have made this error, but it's still an error. Probabilities are only well defined in an unphysical limit (infinitely many experiments), or circularly (a self-consistent probability calculus with no reference to the real world). You can derive the Born rule in MWI if you take the limit, and you can derive it circularly (by introducing a prior measure on worlds). Otherwise you can't, which is hardly surprising since the rule you're supposed to derive doesn't even have a well-defined meaning otherwise. If you look at proofs of the Born rule in other versions of quantum mechanics, they're all either circular or take the limit. A proof in the context of Bohmian mechanics will probably assume that the system is initially in quantum equilibrium; that's circular. If the equilibrium state is justified, it will be by a limit. There's just no avoiding it; nobody knows any other way of talking about probability. This work by Deutsch and company is more about explaining classical probability in terms of quantum probability than the other way around, not that I think they've succeeded in doing that either. -- BenRG 15:48, 23 October 2007 (UTC)

MW probability theorists face a problem that classical probability theorists do not face. The latter are able to explain (if such a trivial statement can be considered an explanation) that improbable events are rarely observed because they rarely occur. MW theorists have to face the implication that all events, however improbable, occur, and that we might be inside such an event as observers. 1Z 20:09, 23 October 2007 (UTC)

In order to make this something other than a tautology, I'll take "improbable" to mean "theoretically improbable according to quantum mechanics". Then "improbable events are rarely observed" is another way of saying "our observations confirm quantum mechanics at a high confidence level", and "improbable events rarely occur" is another way of saying "the behavior of the real world conforms to quantum mechanics at a high confidence level". So you're saying, in short, that we see strong evidence for quantum mechanics because such evidence exists in the real world. Do you agree with that rephrasing? If so, this has nothing to do with the issue at hand. Events in the real world could have been inconsistent with quantum mechanics at high confidence. You've stated correctly that they aren't, but haven't explained why. Any such explanation could be repurposed to explain why we find ourselves in this world branch and not another. If you want to argue, for example, that quantum mechanics does not permit a world that's inconsistent with itself, then you'll have to be specific about how inconsistent it needs to be before it's not allowed. Once you've decided on a rule, you can translate it into the language of amplitudes and declare that the corresponding MWI worlds don't exist, thereby answering (by fiat) the same question in MWI. It makes no difference whether the worlds exist or not; the problem derives from the fact that the theory permits other experimental outcomes in the first place.

In any case, your objection has nothing to do with quantum mechanics; it's solely about the existence versus mere possibility of other worlds, regardless of what empirical or logical considerations lead one to imagine them. I have no problem adding to the article a statement like "Objections to modal realism apply to MWI", and foisting the debate off on whoever edits that article. -- BenRG 15:46, 24 October 2007 (UTC)

Your paraphrasing is wrong in almost every regard. I am addressing the claim that all possibilities occur, whether in the context of QM or otherwise. That claim has he implication that all events occur, improbable or otherwise. The contrary claim, that only some possible events actually occur has the implication that improbable events rarely occur. Modal realism has implications about what an observer would expect to see; so the interpetational claim that all branches of the WF exist is empirically testable as an issue distinct from the "shut up and calculate" considerations common to all interpretations of QM. 1Z 18:13, 24 October 2007 (UTC)

That only some possible events actually occur does not have the implication that improbable events rarely occur. Your belief that it does is either circular (if your definition of "rarely" is probabilistic) or a form of the gambler's fallacy (if it isn't). Some form of the gambler's fallacy may hold in the real world; I have no problem with taking this as a hypothesis, but to do so you must be more specific about what "rarely" means. That's what I was talking about in my last response. At this point I don't know what you mean by either "rarely" or "improbable". I proposed an operational definition of "improbable" above (improbable according to current theory), but you rejected it. My best guess is that you are relying on your common-sense understanding of these terms. In that case the problem is that your common-sense understanding is wrong, and the easiest way to see this is to sit down and try to convert it into an operational definition. -- BenRG 16:10, 27 October 2007 (UTC)

Opinions

I cut this rather POV stuff from the Opinions section:

Moreover, several books that could be considered scientific popularizations of quantum mechanics have often used many-worlds to justify claims about the relationship between consciousness and the material world. However, some of these claims are spurious quantum theory generally has attracted junk and pseudoscience spin-offs (e.g. "Quantum Healing"), so it hardly seems fair to tar MWI in particular with this brush. Apart from these new-age interpretations,

Yes, I've no doubt there are bogus New-Agey books with spurious discussion of consciousness and many worlds (note though this claim is unsourced). However it's not true to tar all such discussion with the same brush. E.g. possible worlds is a closely-related subject in philosophy with ramifications both for mind and physics. (And which also incidentally raises serious problems for the many-worlds interpretation - it is far from clear that this interpretation makes metaphysical sense.) Ben Finn 16:46, 30 May 2007 (UTC)

World-splitting objection

I'm moving the objection by Terse and response by MichaelCPrice here for the moment:

The many worlds interpretation is very vague about the ways to determine when splitting happens, and nowadays usually the criterion is that the two branches have decohered. However, present day understanding of decoherence does not allow a completely precise, self contained way to say when the two branches have decohered/"do not interact", and hence many worlds interpretation remains arbitrary. This is the main objection opponents of this interpretation rise, saying that it is not clear what is precisely meant by branching, and point to lack of self contained criterion specifying branching to be described. MWI response: the decoherence or "splitting" or "branching" is complete when the measurement is complete. In Dirac notation a measurement is complete when: $\langle O[i]|O[j]\rangle =\delta _{ij}$ where O[i] represents the observer having detected the object system in the ith state. Before the measurement has started the observer states are identical, after the measurement is complete the observer states are orthonormal. Thus a measurement defines the branching process; the branching is complete when the measurement is complete. The branching is only ill-defined where the interaction is not described as a measurement; in such circumstances the universal wavefunction is still available to give a complete description.

This objection doesn't make sense, and neither, in my opinion, does MichaelCPrice's response. The objection is like saying that universal gravitation is incomplete because it doesn't define exactly what a heavenly sphere is. That was the point. Previous cosmological models had to be more specific about what a heavenly sphere was, because they had different laws for heavenly spheres; if you got it wrong, you ended up with wrong predictions. It's the same with the "many worlds interpretation" and worlds. You can define world-splitting in whatever way is convenient for you, just as you can choose a convenient standard of rest or a convenient definition of "planet" that includes or excludes Pluto. That's the whole strength of the idea, the only reason it's interesting in the first place: it avoids the need to commit to some specific notion of world-splitting (aka measurement) in the postulates. So I think that the "MWI response" above misses the point by inventing an arbitrary definition of splitting out of nowhere. Even if this convinces the critics, it's for the wrong reasons: instead of disagreeing with something they think is MWI but isn't, they now agree with something they think is MWI but isn't.

I think the real problem here is just that "many worlds interpretation" is a misleading name. People would reasonably object to a theory of heavenly spheres that made no mention of heavenly spheres, even if it was just universal gravitation under a new name. -- BenRG 23:15, 2 August 2007 (UTC)

Nevertheless the objection cited is found in the literature and deserves mention -- whether it is a flawed objection is another matter. Everett uses the term "branching", ergo a criticism of the vagueness of the term is, prima facia, valid and needs to be addressed. --Michael C. Price ^talk 23:38, 2 August 2007 (UTC)

I suppose you're right. Don't get me wrong, I'd love to see a long list of common and not-so-common objections in the article, including the one above and the Occam's razor objection and the world-measure objection and the basis objection and the aether objection (MWI postulates various things that it then predicts can't be observed) and the other aether objection (how do you add GR?) and whatever I've forgotten. I think they're all interesting whether or not they're flawed. But I'm leery of writing anything along these lines because it all feels uncomfortably political. There seems to be a general dislike in Wikipedia of objections sections that end up looking like back-and-forth debates. -- BenRG 00:25, 3 August 2007 (UTC)

BenRG, I think you misunderstand the objection. The question when does the measurement take place is exactly the main issue for the interpretation, and it should be given from within the theory. Any interpretation should assign real world properties to the thing that is interpreted. So, just from the wavefunction and hamiltonian, it ought to be possible to tell what the universal wavefuction means. For instance, given a wavefunction of a Schroedinger cat, |alive>+|dead>, MWI should, just looking at the function and hamiltonian, be able to say - this is really a split function, it is really sum of these two vectors, which do not interfere. First vector is really an alive cat, and second a dead cat, and it is a wavefunction of a many-world in which there is an alive cat in one world, and dead cat in the other. This is what MWI is supposed to do, splitting is by no means arbitrary, it is something which depends on the meaning of the wavefunction and it is conceptually a way to determine properties - to interpret the universal wavefunction. Unlike Everett who was completely vague about the point, modern decoherence does indeed provide the way to say when splitting appears, and the criterion is RELATIVE to the position measurements in the future - the criterion is that, wrt these measurements, there is no interference. However, this has the following problem - it is only approximate for most functions, a vector |alive>+|dead>+|small vector> cannot be split EXACTLY.

The way the article is now, it provides little information about the main points of interpretation - recovering real world properties and probabilities - for instance, it just says that there is some way to recover probabilities, without saying anything about HOW they appear from within the MWI. It ponders repeatedly about general points of QM (partial trace relation to the measurement, really an issue of QM proper, not interpretation, though Everett thesis had lot about that), without adressing main points of interpretation. An article should adress in NPOV, balanced way all main points of INTERPRETATION, give more information about them, give objections to the interpretation and answers of MWI proponents to them. The way it is now, it just waves hands when it comes to main issues, praising MWI in vain, and not adressing the substantial things of QM interpretations. It appears as if there are no problems in MWI, which is misleading to the utmost, to say the least.

The main objections should be mentioned in introduction, and also, the main issues should be discussed more in the article, problems, objections and answers to them included. Terse 01:06, 3 August 2007 (UTC)

MWI response: the decoherence or "splitting" or "branching" is complete when the measurement is complete. In Dirac notation a measurement is complete when: where O[i] represents the observer having detected the object system in the ith state. Before the measurement has started the observer states are identical, after the measurement is complete the observer states are orthonormal.[5][1] Thus a measurement defines the branching process; the branching is complete when the measurement is complete. The branching is only ill-defined where the interaction is not described as a measurement; in such circumstances the universal wavefunction is still available to give a complete description.

This really does not adress the issue at all. You cannot refer to a measurement, if it is not defined from WITHIN the theory. Vagueness about splitting is just shifted to the vagueness about measurement. This is indeed the main issue - when does the measurement (splitting) take place? How to tell that JUST from the theory (hamiltonian and wavefunction), and nothing else - this is a problem for interpretation. I believe the answer that MWI now offers is better than this, and indeed has to do with decoherence (which involves definition of interference in the future, and this is relative to some basis in the future, like position basis - in this respect, MWI is selecting some basis just as Bohm interpretation is, though it is more easy to get rid of this dependence in MWI). Terse 01:25, 3 August 2007 (UTC)

Since lot of people seem not to get this, I will try to explain why this is so vague. Take any system, a hilbert space and a hamiltonian/unitary evolution. Then, if H=H1xH2, it is always the case that you can express any vector in H as a sum c_i|o_i>|s_i>, where |o_i> and |s_i> are orthonormal frames - it is just the Scmidt basis theorem. So, without telling what H1 and H2 are, you cannot tell when splitting/measurement happens. Everett did not tell anything about determining H1 and H2 (indeed, only some cases are consistent with decoherence, in present day understanding which is much better that that 50 years ago), but decoherence, as explained, has also problems for MWI. Terse 01:36, 3 August 2007 (UTC)

Yes, I understand all of this; it's getting into basis-objection territory now. But the purpose of the interpretations is not to say when measurement happens or to assign probabilities to things. The purpose of the interpretations (not counting Copenhagen as an interpretation) is to provide some sort of ontic world-picture which is consistent with what we observe. There is no interpretation of MWI's universal wavefunction; it's just the objective state of the world. The people doing the experiments are themselves encoded into the wavefunction in a nonseparable way, in the same sense that a chair is not cleanly separable from the floor and the atmosphere surrounding it. Asking for a definition of a measurement in this context is as sensible as asking for a definition of a chair—you're never going to get a clean answer, just various heuristics. There's no reason to expect more than this; stock quantum mechanics is the only theory that's ever singled out measurement for special treatment, and MWI is just one of the other theories. -- BenRG 03:15, 3 August 2007 (UTC)

Yes, that exactly right. MWI is a classical theory which treats the wf as a real entity; as such it doesn't have to define "measurement", any more than people ever worried about this in Newtonian physics.--Michael C. Price ^talk 06:54, 3 August 2007 (UTC)

Terse, maybe you were satisfied by what I wrote above, but if not let me expand on it a bit. With respect to the non-uniqueness of the decomposition of the wave function, what you're looking for is a physical principle that will locate measurements and consequent splitting given a wave function. I claim there's no such principle, but that doesn't mean you can't find the measurements; it just means you have to do a heuristic search. The lack of a preferred basis might make the search space larger, but doesn't make the search inherently more difficult. In practice I think you can choose the right basis a priori because the symmetry of bases is dramatically broken by the form of the Hamiltonian. The other possible form of the basis objection is that searches with respect to different bases might yield different sets of measurements, with nothing to say which set is the real one; but I don't think that can happen and I assume you don't either. Certainly 1/√2 (|scientist seeing X> + |scientist seeing Y>) is not the same as |scientist seeing 1/√2 (|X> + |Y>)>.

The other objection you might have been alluding to above is that every set of experimental outcomes is realized in some world, which gives no basis for assigning probabilities or doing science. That's true, but classical probability has the same problem. Classical probabilities can be shown to satisfy some internal consistency properties which suggest that they make some sort of sense, but quantum amplitudes satisfy all of the same properties. There's no reason not to take the position that quantum amplitudes are the only real kind of probability and reformulate all of science in terms of them, with classical probabilities showing up only as a derived notion. It's impossible to make sense of science that way, but it's also impossible to make sense of the way we do it now. -- BenRG 17:27, 3 August 2007 (UTC)

Update to this MWI story?

http://www.telegraph.co.uk/earth/main.jhtml?xml=/earth/2007/09/21/sciuni121.xml

"This work will go down as one of the most important developments in the history of science."

I hope the editors of this page can use this info

203.214.5.244 14:39, 23 September 2007 (UTC)multi

Thanks, a nice link. I see it is an outcome of a conference going on at the moment in Canada celebrating 50 years of many-worlds. [1] --Michael C. Price ^talk 20:51, 23 September 2007 (UTC)

Not so fast there. Dr. Deutsch is one of MWI's biggest supporters, so it's no surprise he'd make a claim like MWs really do exist, much like many of his previous papers suggest. His research is not without criticism (e.g. [2]). If this news article is based on new research we should wait a while so that the scientific community can adequately evaluate his research. ~ UBeR 02:04, 25 September 2007 (UTC)

Simply report the news without judging it. --Michael C. Price ^talk 07:41, 25 September 2007 (UTC)

The Telegraph article doesn't qualify as news. It's press coverage, which isn't the same thing. It's very badly written, and even after slogging through the whole thing I had no idea what the supposed breakthrough actually was. After looking through the talks from the conference, the best match seems to be Probability in the Everett interpretation: state of play. From looking at the PDF (I haven't watched the video), I gather that the big breakthrough is that they think the principle of indifference makes more sense in the context of many-worlds than in the classical context, because it can be expressed directly as a symmetry of the wave function. That's somewhat interesting, but I can't say I'm terribly impressed by it -- especially since Wallace seems not to understand the corresponding classical argument. He says you can't talk about the same symmetry in the classical phase space because it would be "circular" to introduce the classical phase space in the first place. But it's only circular if you introduce it as a phase space. It's not circular if you just construct it mathematically and then assert that it represents reality -- which is exactly what MWI does, for better or worse. The fact that Wallace seems to misunderstand this makes me wonder about the accuracy of his main claim. In any case, giving a talk isn't news either, nor is publishing a paper; it seems too early to mention this in an encyclopedia.

While I'm in the mood, let me complain about everyone else that's been mentioned in this thread. What I've never understood about Deutsch is that he says he's a proponent of MWI, but his use of the word "world" is totally incompatible with what everyone else uses it for in this context. He keeps saying that a quantum computer does its calculations in parallel worlds, and building a working quantum computer would prove that the other worlds exist. In terms of the usual definition of "world" that's dead wrong. So I have to wonder about Deutsch's understanding of this subject too. As for David Baker -- it drives me crazy that there are so many people publishing papers that say in effect that MWI is bad because it fails to solve some problem that no other interpretation, or theory of physics, solves either. Wallace makes the same point in his slides. Nobody knows what classical probability means, so there's no point in assigning classical probabilities to worlds. What's even worse is the people who think Occam's razor argues against the existence of the other worlds. It's a good thing Occam's razor doesn't work that way, or we'd all still be sitting in caves trying to decide if rocks are edible. (Dilbert.) -- BenRG 11:40, 25 September 2007 (UTC)

1. Many-worlds is not difficult to understand given a basic knowledge of quantum mechanics (which Deutsch has) -- but the way such people express themselves can be very frustrating. Also even people who understand MW don't always believe in MW (Deutsch used to say he believed in a version of many-minds that was an extension of Everett's, in that it required an extra axiom; not sure if this is his current position). However, I agree that people who think Occam's razor is a count against Everett clearly don't understand it.
2. Whatever we think about the individual contributions at the conference (and I haven't read them yet) I thought (from a New Scientist article) the main claim was a new and better derivation of Born probabilities within the Everett scheme. Either way, the conference as a whole can (and should) be reported. It is news. --Michael C. Price ^talk 14:28, 25 September 2007 (UTC)

Incidentally, should Wallace have his own page? He appears to satisfy the notability criteria. But there's already a David Wallace (physicist), so what should it be called? What about David Wallace (theoretical physicist)? Eve 12:21, 25 September 2007 (UTC)

I suggest David Wallace (Philosopher of Physics) since he says "I am a philosopher of physics at Oxford University" on his website. Plexos 01:52, 24 October 2007 (UTC)

"I thought (from a New Scientist article) the main claim was a new and better derivation of Born probabilities within the Everett scheme." So there really isn't much new in the New Scientist article? Just more hype? (I don't have a subscription, but was able to read it by searching blogs) Godspeed John Glenn! Will 14:54, 1 October 2007 (UTC)

So why would that be "hype"? --Michael C. Price ^talk 06:44, 8 October 2007 (UTC)

According to the Wiki article the probabilites were already derived from the Everett scheme. So what is the big hoopla about?Godspeed John Glenn! Will 19:39, 9 October 2007 (UTC)

I don't think the article makes this clear but Hartle and DeWitt extended Everett's derivation of probabilities -- none of which has ever been accepted by the MWI critics as fully satisfactory. Sounds like Wallace/Deutsch have come up with a new approach, which be may more acceptable to the wider audience. Haven't read the details yet. --Michael C. Price ^talk 23:41, 9 October 2007 (UTC)

There was a very interesting update to the section & I cleaned it up a bit. In electrical engineering we of course used complex numbers because they were natural to represent alternating current cirucits. The sinusoidal current is just the projection of the rotating vector. Well, opamps and electrontic circuits can be used to solve qm equations. And I guess "Z-transforms" could be used to provide digital signal processing equivalents.Godspeed John Glenn! Will 16:35, 11 October 2007 (UTC)

Could the probabilities thing be cleared up a bit more? I don't see how probabilities arise at all in MWI. Price's FAQ has some explanation which could be added, though it doesn't answer my questions. "Maverick" (Price's terminology) worlds go away "at infinity", but Born's law applies in finite time. After a large but finite number of observations, the norm of maverick worlds is of course much smaller than that of normal worlds. But why am I more likely to find myself in a world with larger norm? If this is an unsolved problem, or a problem whose proposed solutions are not genreally accepted, it should be noted as such, instead of claiming it was solved 40 years ago, and then solved again a few months ago. --192.75.48.150 (talk) 20:49, 18 January 2008 (UTC)

"Maverick worlds" is DeWitt's terminology. Born's law applies at finite time for finite sequences, but the verification of Born's law takes infinite time. Whether this is an unsolved problem is very much a matter of opinion and depends how you define probability, even for classical systems.--Michael C. Price ^talk 08:17, 25 July 2008 (UTC)

Not much criticism is there?

Should there be thread like comments to the points in the Objections section? After all the section is about objections rather than objections to objections and so forth. If the latter is allowed then why not the same for all sections of the article and have a threaded debate everywhere. Plexos 23:18, 18 October 2007 (UTC)

There should not be threaded debates in the Objections section, but it can't just be a list of objections either. The objections currently listed are only objections in the sense that the twin paradox and barn-and-pole paradox are objections to special relativity. They're worthy of mention and pedagogically useful and interesting, but they're not problems with the theory. They need to be described together with their resolutions. -- BenRG 21:09, 19 October 2007 (UTC)

There could be a "Responses to Objections" section below the Objections section. That way the threaded look would be avoided.

I find your statement dogmatic since you can't be certain the objections are not problems with MWI but you say they are not problems. David J Baker of Princeton University is a qualified critic as far as I know and he thinks there are problems (cicularity objection). There are other qualified critics too, Penrose for example, so I wouldn't be so sure about those problems. The article should take a neutral position but it looks biased to me. If you want to be neutral then maybe as much effort should go into the Objections section as elsewhere, especially since there is no physical evidence for MWI and it's all just opinion. Plexos 02:06, 21 October 2007 (UTC)

I'm certain that they aren't problems with MWI in the same way I'm certain that the twin paradox isn't a problem with special relativity. This is not such a strange thing to say, surely. I understand both special relativity and MWI well enough to see how to resolve these apparent paradoxes. Many metaphysical debates can never be resolved because there's no way to tell who's right, but these particular objections aren't in that category, at least as I read them. (One can read the twin paradox in such a way that it's an unresolvable metaphysical question, but it's more useful to read it as a solvable exercise.)

Re David Baker and company: You might know the story of Herbert Dingle, a respectable physicist who decided late in his career that special relativity was logically inconsistent. He even wrote a book about it. There's an interesting essay What happened to Dingle? which argues plausibly that Dingle never understood special relativity at any point in his career; what changed was not his understanding but his confidence in his own misgivings. Normally for every person who writes a book there are many who feel the same way but remain silent, so I suspect that many professional physicists misunderstand special relativity in the same way as Dingle. (There are certainly hints of this in a lot of writing about relativity.) With many-worlds the situation is probably similar, except that the social and peer-review barriers to publishing your misgivings are much lower. It could have been that way with special relativity too. Special relativity, quite aside from any experimental support, is an elegant theory that unifies a lot of unrelated concepts in Newtonian physics. Sylvester investigated quadratic forms and discovered the law of inertia back in 1850; he could have discovered MinkowskiSylvester space and noticed the physics connection decades before there was any experimental evidence for it. Undoubtedly the same objections would have been raised then as in 1905, but I bet they would have had a much easier time getting published. The barn-and-pole paradox probably would have been taken seriously as a flaw in the theory, even though you don't need any experimental support to see that it's wrong. Again, the barn-and-pole objection is wrong even if the theory is itself wrong. I'm not saying that MWI is correct; I don't believe that it is (nor that it isn't).

I notice that you've added a third objection saying that according to Penrose MWI is not correct on scales above the size of a dust mote. Penrose makes that claim because that's what his theory predicts. His theory is nonunitary and hence disagrees with all variants of ordinary linear quantum mechanics, including MWI. He argues against MWI because he's defending his idea against the competition. This is normal, healthy scientific debate. Eventually, one hopes, it will be possible to determine experimentally who's right. Until then, there's nothing wrong with either many-worlds or Penrose's hypothesis. They are not objections to each other, but alternatives. -- BenRG 14:45, 21 October 2007 (UTC)

Actually I only found Penrose to say that quantum theory (QT) falls short at scales above dust motes due to failure to incorporate gravity, rather than him saying MWI wasn't correct at such scales. I imagine he would say that though since he is against MWI that much I did find. Aside from Penrose wanting to sell his own theory, his objection to QT does seem common sense since gravity is an important force and isn't in the theory. One could even suggest it is in fact seriously defective in this omission. If QT has problems then MWI likely has too since it is QT based. So I don't think this objection is anything much to do with Penrose competing, it seems a common sense objection that others could come up with too. Plexos 15:18, 22 October 2007 (UTC)

Penrose's twistor thory is taken seriously by others, in particular top string expert Edward Witten, who uses it in 5 of his recent papers, 2003-2004. Plexos 15:47, 22 October 2007 (UTC)

You're probably right; I haven't read Penrose's stuff in a while. But my point remains. It might be, when a theory of quantum gravity is worked out, that other worlds don't arise naturally in it as they do in QM. Penrose's ideas might be right, or not. MWI might be wrong, or not. Nobody knows. "It might be wrong" is not a sensible objection to any scientific hypothesis, nor is disagreement with another hypothesis in the absence of any evidence to decide the question. Even disagreement with the evidence doesn't necessarily qualify as an objection unless it renders the theory worthless, which often isn't the case. NASA still uses Newton's law. -- BenRG 16:02, 23 October 2007 (UTC)

The objection is not "it might be wrong", but a "statement of how it might be wrong" and so by definition it is an objection. MWI hinges on QM applying to all reality as Deutsch and Hawking have said, but gravity is a huge part of reality and QM does not apply to it. That looks more like half a proof rather than just an objection. Plexos 01:43, 24 October 2007 (UTC)

It sounds like you're not talking about MWI being wrong so much as QM itself being wrong. That might happen because quantum gravity isn't quantum mechanical, or for various other reasons. How about something like this: "MWI depends on the correctness of quantum mechanics, and in particular on the unitarity of time evolution. There have been proposals to solve the measurement problem by adding nonlinear terms to Schroedinger's equation; experimental confirmation of such a theory would falsify MWI. It is also quite possible that quantum gravity will not be a quantum theory, in which case it would be incompatible with MWI. (It might, or might not, contain some other form of world-splitting.)" -- BenRG 15:46, 24 October 2007 (UTC)

I don't think many say QM is wrong at the small scale, but Penrose is suggesting it may be wrong at the larger scale of dust motes, due to gravity effects. MWI however seems to depend on QM being true at all scales and so is likely wrong if the gravity argument is true. In short, if QM is half wrong then MWI is likely completely wrong. Whether MWI could be right even if QM is half wrong I don't know. Plexos 19:06, 24 October 2007 (UTC)

Eh? MWI only requires that the theory of everything be linear, and there is a not a shred of evidence for non-linearity. In fact very rigorous empirical limits have been placed on non-linearity.--Michael C. Price ^talk 06:21, 25 October 2007 (UTC)

MWI is just QM with the collapse rule 4b removed so if gravity invalidates QM at higher scales then MWI is wrong seems to follow. Whether any "correct" theory for larger scales would be linear or non-linear I have no idea. What is the evidence that linearity is required at higher scales? --- Plexos | Talk 14:02, 27 October 2007 (UTC)

Whether linearity is required on general principles I have no idea -- my point is that there is no evidence for non-linearity. --Michael C. Price ^talk 16:45, 27 October 2007 (UTC)

If there is no evidence for linearity nor non-linearity at higher scales I can't see what point you are making. It's a level playing field. --- Plexos | Talk 18:12, 27 October 2007 (UTC)

There is evidence for linearity. --Michael C. Price ^talk 21:29, 27 October 2007 (UTC)

I did ask you about that a few steps back. Could you please say what it is at higher scales? --- Plexos | Talk 22:51, 27 October 2007 (UTC)

You did not "ask you about that a few steps back". --Michael C. Price ^talk 23:25, 27 October 2007 (UTC)

In reply to my point about linearity at higher scales you said there was evidence for linearity. What then is the evidence? --- Plexos | Talk 07:16, 28 October 2007 (UTC)

All accepted theories of fundamental physics are linear (with respect to the wavefunction). Start with Schrodinger's equation and work your way up.--Michael C. Price ^talk 09:24, 28 October 2007 (UTC)

From the thread, the evidence you refer to is related to the wavefunction and Schrodinger's equation, and any such evidence regarding those is so far only at small scales. The point here is the larger scales not the small. It may easily be that QM is just a linear approximation for small scales, of the complete (undiscovered) nonlinear theory of everything for all scales. You also say all accepted fundamental physics theories are linear but General Relativity is nonlinear, see The Einstein Field Equations. --- Plexos | Talk 17:13, 28 October 2007 (UTC)

I repeat, all accepted theories of fundamental physics are linear (with respect to the wavefunction). GR, like many theories, is nonlinear with respect to its component fields which says nothing about whether it is linear with respect to the wavefunction (for which we have to await a theory of quantum gravity to judge; GR is not a quantum theory).--Michael C. Price ^talk 17:40, 28 October 2007 (UTC)

You say "all accepted theories of fundamental physics are linear (with respect to the wavefunction)". This is a false statement because nobody yet knows how the wavefunction relates to GR. GR not being quantum has nothing to do with it since GR is still a fundamental theory. The fact is as Penrose has stated that QM does not take account of gravity, and as such is likely useless at large scales together with MWI. --- Plexos | Talk 19:01, 28 October 2007 (UTC)

GR is not regarded as a fundamental theory, which is why people are trying to construct a theory of quantum gravity. Every physicist understands that classical theories (such as GR) are not fundamental. --Michael C. Price ^talk 19:09, 28 October 2007 (UTC)

You better change the text on the General Relativity page then where it says "Quantum mechanics is viewed as a fundamental theory of physics along with general relativity". There are also sources and a paper saying GR is fundamental: 1, 2, 3, 4. All fundamental means is a foundation on which other things have been derived, and I believe GR qualifies for that. That GR cannot be quanitized is disputed. --- Plexos | Talk 21:36, 28 October 2007 (UTC)

We can quibble about what "fundamental" means (but I note you are quoting the GR article out of context, which was the merging of QM with GR to produce quantum gravity; so your point falls completely flat), but it won't alter the fact that the non-linearity of GR has nothing to do with the linearity of QM and MWI. --Michael C. Price ^talk 22:51, 28 October 2007 (UTC)

GR is a fundamental theory, but you said it wasn't, perhaps we better just leave it at that. --- Plexos | Talk 23:52, 29 October 2007 (UTC)

It is not regarded as fundamental, which is why people work on quantum gravity. --Michael C. Price ^talk 14:15, 30 October 2007 (UTC)

False. In fact it may be even more fundamental than quantum theory since at least it operates to the very boundary of the high size scale, whereas current quantum mechanics is "mid range" and doesn't go high nor low down to the Planck length $1.6x10^{-35}$m at which quantum gravity is thought operate. There's "plenty of room at the bottom" but current quantum theory doesn't go there. --- Plexos | Talk 22:37, 1 November 2007 (UTC)

No, true. String/M theory/QLG is a quantum theory and is conjectured to operate at all scales.--Michael C. Price ^talk 01:27, 2 November 2007 (UTC)

Quite false. Quantum Theory generally refers to the works of Heisenberg, Schrodinger, Dirac and the like. QLG etc comes a lot later and isn't part of established QT, for one thing there's no evidence for it. --- Plexos | Talk 07:27, 2 November 2007 (UTC)

Thanks for once again demonstrating your combination of arrogance and ignorance. Try looking at Quantum theory, instead of Quantum mechanics.

I'm amused that you condemn QLG for the lack of evidence. Just like non-linear QT. --Michael C. Price ^talk 12:27, 2 November 2007 (UTC)

Neither arrogant nor ignorant but based on sources taken in good faith. Do not slander me further unless you can prove it. Here are some examples: here it says Quantum mechanics is the final mathematical formulation of the quantum theory developed during the 1920s, and here it confirms quantum theory refers to developments up to 1927. This appears to be the usual meaning of QT. Your quoted QT wikipedia page is only a page of links, that's why I used the quantum mechanics page as my ref, as there is not a proper wikipedia page for QT. --- Plexos | Talk 15:00, 2 November 2007 (UTC)

The quantum theory page (which is not just a page of links) is there precisely to help people who are not aware of the correct usage of the term. --Michael C. Price ^talk 15:09, 2 November 2007 (UTC)

Nothing to say about the sources I mention then? --- Plexos | Talk 15:14, 2 November 2007 (UTC)

Nothing except go and debate it at quantum theory's talk page, where the subject has been done to death many times.--Michael C. Price ^talk 15:17, 2 November 2007 (UTC)

The meaning is obviously a matter of opinion then. Some boffins want it to mean all quantum theories. However, it will completely confuse the readers if you are using QT to mean all quantum theories, since the layman would imagine it to be the 1927 QT. What a mess. When I refer to QT I mean 1927 QT just for future reference. I will also assume QM presumably is unambiguous and refers to 1927 QM unless corrected. Hopefully I can now get on with fixing the QM objection having got this sorted. --- Plexos | Talk 15:38, 2 November 2007 (UTC)

This back-and-forth seems to have spiraled out of control. Is it accomplishing anything? I can hardly understand what you're debating about. Is there any chance we could agree on some variation of the paragraph I proposed in my last post umpteen levels up?-- BenRG 19:18, 2 November 2007 (UTC)

Actually the above QT definition thing now being clarified will allow me to correct the QM objection which has a citation required request in it. It may be better to combine my corrected version with Michael's if that is possible. Not quite sure what your variation was? --- Plexos | Talk 20:15, 2 November 2007 (UTC)

The basic rules of quantum mechanics have been essentially unchanged since the 1920s, so in that sense "quantum mechanics" and "quantum theory" refer to the theories of that time. But since then many quantum theories have been developed within the basic framework, such as the quantum theory of fields and the quantum theory of electromagnetism. "Quantum mechanics" is like "classical mechanics" -- it's a collective term for the whole area of study, but often excludes field theory (Maxwell's equations or QFT, depending). Is this related to your debate about those terms? I'm not sure.-- BenRG 19:18, 2 November 2007 (UTC)

Yes it is very related. Firstly, let me say I think it is confusing for the layman if QM means several things, namely 1920's QM, or any linear QM, or any linear/nonlinear QM. That point aside I needed a citation for the objection where it says if "the very rules of quantum theory" need modifying then MWI is obviously called into question[citation needed] since MWI is just quantum theory with collapse Rule 4b removed. Michael agreed the last part but I took "quantum theory" to mean 1920's quantum theory but in this context it should read as any linear quantum theory. I'll have a go at re-doing this bit of the objection. --- Plexos | Talk 20:15, 2 November 2007 (UTC)

I think it's worth clarifying what Michael C. Price means by "linear with respect to the wave function". You can take any classical theory and reinterpret it as a theory of ensembles of systems represented by a probability function over a phase space. Regardless of the linearity of the underlying theory, the ensemble theory will always be linear in the phase space because classical probability is linear. Classical probability is linear for very deep reasons; the linearity expresses the fact that the evolution of the actual world is independent of what else might have happened. Quantum probability is also linear, and I think (and Michael C. Price probably thinks) that it's linear for a similarly deep reason. The Standard Model is linear in the phase space, but as a field theory it's dramatically nonlinear; in that respect it's no different from the gravitational field. -- BenRG 19:18, 2 November 2007 (UTC)

Is there any physical evidence that a theory working down to the Planck length should be linear? Could there ever be such physical evidence at those small scales? If not then MWI will always be pure speculation and we can all stop worrying. Couldn't the basic building blocks of space, time, gravity be non-linear? I am interested in your answer but here's mine in advance: I don't think any of this science is going anywhere ultimately since there will never be any physical evidence at Planck length scales. It will always be just guesswork and countless different theories of everything. MWI will only ever be as valid as astrology. The readers need to be told. That's what I don't like about this page, it encourages readers to believe in a dream and so is absolutely not neutral and will do damage. --- Plexos | Talk 21:19, 2 November 2007 (UTC)

Just to clarify: that's an interesting point that BenRG makes about classical theory having to be linear with respect to the probability measure. Whether quantum theory has to be linear is unclear (Weinberg has some interesting observations on this in his Dreams of a Final Theory), since in the Everettian approach the probability measure is derived from the equations. Presumably with a non-linear QT then the probability measure would not be equal to the modulus of the wavefunction. All very interesting to be discussed elsewhere. However here, all we need to know is that there is no evidence for non-linearity. --Michael C. Price ^talk 22:25, 2 November 2007 (UTC)

Please see the top of the QM objection section below. --- Plexos | Talk 15:45, 3 November 2007 (UTC)

I would be also interested to hear BenRG's reply. --- Plexos | Talk 13:32, 3 November 2007 (UTC)

The QM objection

Linearity issue: Michael C. Price has said above "all we need to know is that there is no evidence for non-linearity". The evidence for linearity is apparently that all fundamental quantum theories are linear. At this stage my question is does this evidence for linearity imply or even suggest in any way that linearity is universal? --- Plexos | Talk 15:45, 3 November 2007 (UTC)

It suggests it by induction only. --Michael C. Price ^talk 13:50, 4 November 2007 (UTC)

Induction has several meanings. Do you mean mathematical induction? If so, for an infinite sequence, 1) this would require the first statement be true, and 2) that any one true implies the next true. How are those two conditions suggested as true from the proposed evidence? Indeed what is the first statement? --- Plexos | Talk 16:12, 4 November 2007 (UTC)

I refer to induction as in induction vs deduction. As in Bertrand Russell's turkey, who gets beheaded at Christmas, despite surviving all the previous days with increasing inductive confidence.--Michael C. Price ^talk 19:14, 4 November 2007 (UTC)

I may as well state my view of this: I don't think fundamental quantum theories being linear suggests universal linearity at all, in the same way that evidence from any place on earth for a flat (linear) earth should not have suggested the whole earth was flat. It turned out to be non-linear of course and the suggestions imaginary. --- Plexos | Talk 16:12, 4 November 2007 (UTC)

I could point out that even the Ancient Greeks knew the Earth was round from local observations (e.g. the disappearance the of bottom of departing ships as viewed from the coast had been noted from time immemorial). But this is irrelevant. We are all agreed that there is no evidence for non-linearity. That's all the article says as a well. Any further inference (deductive or inductive) made is purely on the part of the reader.--Michael C. Price ^talk 19:14, 4 November 2007 (UTC)

I propose merging the two objections as follows below. I didn't include the terms "theory of everything" and "quantum multiverse" since they weren't in the Penrose reference and don't seem to be necessary to mention really as the non-linearity point is sufficient on it's own. Any MWI rebuttal (response) of the objection should say how the objection might be wrong. Comments welcome.

• Penrose objects to the co-existent states of objects like Schrödinger's cat as proposed by MWI because the correct quantum gravity theory will involve a change in "the very rules of quantum theory". Roughly speaking the change will only become important above the scale of the Planck mass (10^-5 gram) i.e. objects slightly bigger than a grain of dust. According to Penrose the gravitational field interactions between all the cat's particles need accounting for in standard quantum theory, yet are not.Another way of looking at this objection is if "the very rules of quantum theory" need modifying then MWI may be wrong since it is just any linear quantum theory with collapse Rule 4b removed. More specifically, John C. Baez reports Penrose thinking the changes may need to be non-linear, so invalidating MWI. To date there is no evidence for non-linearity, nor for the universal linearity that MWI requires. The average string of string theory is about 10^-20 the size of a proton, so future evidence of linearity at the smallest scales is unlikely to say the least because of the massive energies needed to probe that scale. This could keep MWI permanently in the realm of science fiction. --- Plexos | Talk 02:22, 6 November 2007 (UTC)

All but the first sentence is superfluous or misguided. Penrose only mentions MWI in passing (that it applies to the universe if QM applies to the universe) - the rest is synthesis, and pretty much irrelevant (the details of Penrose's pet QG scheme are not relevant) or just wrong. To say that "To date there is no evidence .... for the universal linearity that MWI requires." is hopelessly prejudicial. We have already seen that there is inductive evidence. Perhaps you find that evidence unconvincing? It is still evidence. The crack about SF at the end is blatant POV pushing. --Michael C. Price ^talk 10:59, 6 November 2007 (UTC)

There is superfluous info in there and it could be condensed however I thought that a bit more background on why Penrose thinks the rules need changing makes more interesting reading. Readers are curious. Those points are from the reference so what exactly are the wrong parts? On the induction point I thought we were done with that. It can't be right to say that evidence for some is evidence for the whole, as the turkey and flat earth examples prove. If there was scientific evidence for universal linearity then there would be evidence for MWI and many sources have stated there is none for MWI. On another point I am unsure why you appear so in favour of MWI when it clearly has no basis in fact. --- Plexos | Talk 11:35, 6 November 2007 (UTC)

Cluttering up article with superfluous information is contrary to Wikipedia; irrelevant details of Penrose's QG schemes can be found at his (and related) articles and can easily be navigated to by curious readers. Induction and inductive logic is a well established mode of scientific reasoning (which I have no idea why you "thought we were done with that") I am not going to waste time debating that further here: there is no evidence for non-linearity and I am content just to report that. Are you? If you think MWI "clearly has no basis in fact" then you don't understand MWI. Tell that to Hawking. --Michael C. Price ^talk 13:44, 6 November 2007 (UTC)

If you are not prepared to debate the induction point then this can go no further and will be referred to an administrator. Please let me know. The "no evidence for universal linearity" bit should go in with the no evidence for non-linearity bit. Evidence in the context of this page means scientific evidence since the topic is scientific. See Inductive reasoning where it says Popper disputes it's existence, therefore it is not relevant to the scientific method. --- Plexos | Talk 09:27, 7 November 2007 (UTC)

If you wish to debate about inductive reasoning then debate it at the inductive reasoning page. I note you avoided answering "there is no evidence for non-linearity and I am content just to report that. Are you?" --Michael C. Price ^talk 09:45, 7 November 2007 (UTC)

Your question was already answered negatively from the start and above by including the "no evidence for universal linearity" bit in the rewording. So obviously I am not content to report just what you say, and the question was never necessary. Popper disputes the existence of induction, therefore there is no evidence for universal linearity. You should answer this point or accept the "no evidence for universal linearity" part in the wording. This is not a discussion about induction, which you introduced by the way, and only appears here subordinate to the evidence issue. As you likely know Deutsch includes Popper as one of his "Four Strands". —Preceding unsigned comment added by Plexos (talk • contribs) 11:46, 8 November 2007 (UTC)

The QM objection (older thread)

This was removed (now reinstated) on the grounds it is not an objection, however I already covered this point above. To recap, an objection by definition is a "statement of how MWI might be wrong". Penrose thinks QM might be wrong at higher scales, due to gravity, and since MWI is QM with collapse rule 4b removed, then it follows how MWI might be wrong too. This is a firm objection by definition and cites sources. Please do not remove again without discussion here first. --- Plexos | Talk 22:10, 28 October 2007 (UTC)

Okay let's discuss it here. First point: It says:

Quantum mechanics (QM) needs modifying for objects slightly bigger than a grain of dust and above[12] according to Penrose. This is the scale of the Plank Mass (10-5 gram) at which gravitational effects become important.[12] MWI is just QM with collapse Rule 4b removed,[25] so if QM doesn't hold at all scales then MWI is wrong.

So gravitation is not important below the planck mass? It is wrong. Gravitation is important at all scales. The paragraph is just nonsense, an attempt at parroting by a non-physicist that has failed. Penrose is actually talking about how quantum gravity will fit within a TOE. And this is covered by the following objection/response.

--Michael C. Price ^talk 22:49, 28 October 2007 (UTC)

Wikipedia should report the opinions of respected and published scientists which Penrose is. It should also take a neutral position which you don't in my opinion so some/all of your input to this page may be in question. In the system of a dust mote or Schrodinger's cat all the atoms are affecting each other with their own gravity so there are trillions of cross effects. If you consider a system of just a single atom or particle then it's gravity is only affecting itself (if that is possible). So gravity effects tend to zero for smaller system size and could be taken as unimportant for electrons and the like. Quantum theory is usually applied to small atomic systems so gravity effects would be virtually zero for QM.

Your TOE objection appeared during the above "Not much criticism" thread after I posted the QM objection, indeed you replaced my QM objection with your TOE one and you are now using my Penrose reference. It would have been nice if you had discussed the removal first. So how come you are using a Penrose reference if you think he is a non-physicist? I am not attempting anything except a fair and balanced account of many worlds. The TOE objection seems similar to the QM one but I am not yet convinced that it is a replacement especially due to lack of references when you first posted it. I couldn't see the TOE explicitly mentioned anywhere in the Penrose reference so I question your use of that reference in your TOE objection.

We are supposed to "parrot" respected sources. You are not supposed to state your opinion in Wikipedia (NOR policy) but you state yours frequently and without references. Penrose's twistor thory is taken seriously by others, in particular top string expert Edward Witten, who uses it in 5 of his recent papers, 2003-2004. Witten is also quoted as saying twistor theory is "undoubtably one of the most remarkable developments in mathematical physics in modern times" Are you a greater man than Witten to deride Penrose as a "non-physicist". Have you got any journal papers that would give credence to your critique of Penrose?

Off for a cup of tea before attempting the second point. --- Plexos | Talk 23:38, 29 October 2007 (UTC)

You have a talent for flying off on irrelevant tangents. The status of twistor theory is irrelevant to issues being discussed. I did not say we shouldn't parrot the sources -- what I criticised was the failed attempt at parroting. Penrose does not say that modifying QM will invalidate the MWI.--Michael C. Price ^talk 14:28, 30 October 2007 (UTC)

So you meant me rather than Penrose as a non-physicist, I guess I read "by" as "of". That makes sense now, I thought you were crazy at the time. Sorry about that. I believe I parroted mostly correctly so most of it can't be a failed attempt since parroting of experts can't fail if accurate. In the reference Penrose objects to the MWI cat in two states and then goes on to say QT needs it's very rules changing. It is clear he thinks MWI is invalid and there are other references to confirm that. You say Penrose does not say modifying QM invalidates MWI, so what reason has he been reported as giving? I suppose it would be possible that the new rules would still allow MWI but it can't surely be the same MWI that is based on incomplete QT. MWI = QT - Rule 4b = QTm say. The rules penrose is referring to do not include Rule 4b I believe, so if QTm rules need modifying then MWI needs modifying since MWI=QTm. If MWI needs modifying then MWI is wrong. Isn't that concrete? Just basically what is wrong with the seemingly obvious logic here. If you are talking about MWI under the new rules you would have to say MWInew = QTnew - Rule 4b, where QTnew is the Penrose modified QT incorporating quantum gravity. It couldn't be that MWI = QTnew - Rule 4b otherwise QTnew = QT. But we are not talking about MWInew on this page but rather just MWI (old) based on Everett. Indeed MWInew is completely undefined just like QTnew. Linearity appears to have nothing to do with it. If QTm needs the rules modifying then MWI (old) is wrong. If not, then please explain exactly and properly why not. --- Plexos | Talk 05:23, 31 October 2007 (UTC)

Linearity (with respect to wavefunctions) has everything to do with it. Any quantum theory that is linear and doesn't have an explicit collapse postulate implies many-worlds. Since most people recognise the problems with having an explicit collapse postulate they seek to avoid many-worlds by constructing a non-linear quantum theory. And since the only area of physics that remains to be quantised is gravity they usually propose that it is quantum gravity that is non-linear. (Penrose also proposes that quantum gravity be time-asymmetric, but that is another story.) Modifying quantum theory per se is simply irrelevant; what is important is whether the proposed modifications are linear or not. Penrose is proposing non-linear mods. But there is no evidence to support this. String/M theory (which contains quantum gravity) is, as far as I know, linear (with respect to wavefunctions).--Michael C. Price ^talk 09:44, 31 October 2007 (UTC)

The page intro says MWI is an interpretation of quantum mechanics (QM). This MWI is due to Everett/DeWitt and refers to the linear QM we have now doesn't it? So the page topic is Everett/DeWitt MWI. The objection is only against this MWI which is based on current QM and nothing else. The page topic does not appear to include any MWI based on a proposed or modified QT either linear or non-linear as far as I can see. Wouldn't that be a non-Everettian/DeWitt type of MWI? If so it may be best treated as a new page don't you think, to simplify things for the reader? --- Plexos | Talk 16:03, 1 November 2007 (UTC)

An answer on the above point would be nice. You skipped it before. --- Plexos | Talk 21:16, 1 November 2007 (UTC)

I did not skip it, it was already answered by my highlighted point Any quantum theory that is linear and doesn't have an explicit collapse postulate implies many-worlds. I have since provided you with an online ref for Everett on linearity.--Michael C. Price ^talk 00:50, 2 November 2007 (UTC)

Thanks for the online ref, that has really cleared things up. Before, you agreed MWI is just QM with collapse Rule 4b (aka Process 1 I believe) removed. I took QM to mean the common definition of QM i.e. 1927 QM, but it appears you (and others) may consider QM to mean any possible QM that is linear, say QM*. Therefore MWI is not just 1927 QM with collapse Rule 4b removed, and so the supposedly obvious conclusion is wrong. From the Everett paper it appears MWI postulates that any wave function universally obeying a linear wave equation is a complete physical system, this being Process 2, i.e. QM* without Process 1. I will now open a new section above. --- Plexos | Talk 19:34, 2 November 2007 (UTC)

Regarding Penrose, he doesn't mention linearity/non-linearity in the reference, which presumably he would if it was such an important point. It reads like he is objecting to many worlds only because the very rules of QT need changing, and with linearity not mentioned or not a factor. --- Plexos | Talk 16:03, 1 November 2007 (UTC)

Once again theorizing and getting it wrong. A quick google will show you that Penrose is talking about a non-linear theory, but quite frankly I don't think you're listening. --Michael C. Price ^talk 19:24, 1 November 2007 (UTC)

In the reference he doesn't mention it. Why should I listen to you any more than you should to me? Are you somebody important? Do you know what my qualifications are? A "quick google" doesn't do it for me I am afraid, I tried, if you know another online reference relating to the current Penrose one then please quote it. We cannot just take your word for it!! Stop the personal insults and the bold text. Much more of that and we will have to escalate this to involve the administrators and that would be very tiresome indeed. There is no place in wikipedia for people who insult others. However, I would prefer if you just answered without insults and we can just draw this to a close quickly by discussion. The insults just delay things, and put you in a bad light. I have other non-wiki things to do and want to get this sorted and finished. --- Plexos | Talk 21:16, 1 November 2007 (UTC)

And while it's true that a quantum state evolves linearly according to the Schrödinger equation, highly nonlinear events occur in Penrose's...--Michael C. Price ^talk 00:33, 2 November 2007 (UTC)

Would you agree with this: If QT without rule 4b needs modifying, then Everettian MWI needs modifying? A yes or no would be nice, to start with anyway. --- Plexos | Talk 16:03, 1 November 2007 (UTC)

No. MWI does not need modifying everytime we modify QM. Go away and study QM, I am bored and frustrated with having to explain elementary physics to someone who does not seem inclined to listen to anything. I don't have to do and I won't. There are other Wikipages for understanding such things. Go to them. --Michael C. Price ^talk 19:12, 1 November 2007 (UTC)

No is your answer, then MWI is not just QT with rule 4b removed as you said earlier - quote "'MWI is just unmodified QM with collapse Rule 4b removed' is correct -- although the adjective 'unmodified' is superfluous". So if they are equal then a modification to one must require a modification to the other. How do you get round that? You have contadicted yourself. You really must answer this point since it is the crux of it. I too am very tired going over the same ground over and over (this crux point) and this question may occur to some readers. It is up to wikipedia to try and cover such points. It is of no importance if you are bored or not. The readers are what matter, not your frustration. Sometimes patience is required on tricky issues. You also seem uninclined to listen to me, your criticism of me is mine of you. In any case you shouldn't personally criticise since that is against wikipedia policy. Now let's get this sorted out without personalising it. It shouldn't take long if you cut out the insults. As I repeatedly keep saying the whole point is to produce a balanced and fair article for the benefit of the reader and nothing more. --- Plexos | Talk 21:18, 1 November 2007 (UTC)

As the article says, MWI is a metatheory about quantum theory. It remains true no matter how you change QM, provided QM remains linear. --Michael C. Price ^talk 00:36, 2 November 2007 (UTC)

Regarding Hawking, he is not widely recognized as an MWI expert so I think it is not right to class him as such together with Deutsch and DeWitt. This is misleading to the readers. I have added him back as a supporter of unreal MWI together with Weinberg since that is what the online Gardner ref says. In addition your offline Tv ref needs confirming. Gardner seems quite sure that Hawking is of the unreal camp since he says he is "not sure of Gell-Mann's current belief" but doesn't for Hawking. Maybe he has actually spoken to some of them, I don't know. Please don't edit my addition until discussed here. --- Plexos | Talk 16:01, 1 November 2007 (UTC)

Actually it is clear that he hasn't spoken to at least Hawking about it, since the "trivially true" comment (which Gardner misrepresents or misunderstands) comes via Tipler. --Michael C. Price ^talk 01:13, 2 November 2007 (UTC)

The article is a not a scribbling board for someone to study QM at, which is how you are using it. You don't know what you're talking about, so stop altering the article first and asking questions second. Please stop issuing edicts about how we can't change your work, whilst you feel free to change the work of others -- others who understand physics a lot more than you do.

Stick to the point and stop the personal insults. I quoted Gardner, a respected source, so I am not scribbling. Stop deleting official quotes. I am allowed to demand a discussion before your removals over disputed points, and in this case it is a Gardner quote with only your unconfirmed Tv reference to the contrary! You reference one thing, someone else references another contrary, so it has to be discussed. If you don't like the wikipedia system then your website would be the best place for you to express your views. --- Plexos | Talk 21:18, 1 November 2007 (UTC)

Gardner is not reliable on this subject. Note how Gardner cites Hawking's "trivially true" as evidence that Hawking believes that the other worlds are unreal, whereas in fact if you read the fuller Tipler quote of what Hawking said it is clear that Hawking implies the opposite by this "trivially true" comment. Gardner is either being deceitful, is deluded or doesn't understand what "trivially true" means to a scientist/mathematician. Either way, unreliable. --Michael C. Price ^talk 00:44, 2 November 2007 (UTC)

Hawking said trivially true if QM holds universally, which is nothing to do with MWI being trivial and so doesn't support the unreal camp as Gardner seems to imply. So I agree with you there, however one slip doesn't make the whole lot wrong - even Hawking makes mistakes too remember. Gardner is responding to DeWitt (no less) who wrote to him, so why would DeWitt even bother with him if he wasn't worthy? Gardner must be a fair source. Anyway, first off, do you agree that there are two camps of MWI, real and unreal? If so there ought to be a mention of such an important point in the intro and the Gardner ref will do for that. --- Plexos | Talk 01:43, 2 November 2007 (UTC)

Anyway, first off, do you agree that there are two camps of MWI, real and unreal? - no. MWI is the real camp. Gardner is wrong (and arguing with DeWitt doesn't make him right or reliable, BTW). You may think that the "trivial" issue is itself trivial, but I think it shows how far Gardner is out of touch (well, he is old; perhaps going senile as well, sadly). Further evidence of Gardner's unreliability is given by his simplistic "determinism does not allow free-will" stance. Clearly he has some agenda here which is biasing him. --Michael C. Price ^talk 06:29, 2 November 2007 (UTC)

I have read in another reference that Everett himself was not of the opinion the worlds were actually real. I may look into it further. Obviously there would need to be another firm reference. It seems reasonable that some would think the worlds theoretical only. --- Plexos | Talk 14:18, 2 November 2007 (UTC)

Everett regarded the universal wavefunction as objectively real and the fundamental object of existence. Without a collapse postulate then the others worlds (which exist as components of the wavefunction in a quantum superposition) are automatically real. Read the footnote in his online article. People who reject wavefunction collapse but think the other worlds are not real (or are agnostic on the issue) are adherents of consistent histories or the lesser known existential interpretation of Wojciech H. Zurek. The article already acknowledges that some people are unclear as to Everett's beliefs. Michael C. Price ^talk 15:05, 2 November 2007 (UTC)

Everett uses "in the theory", "From the viewpoint of the theory" and "presented by this theory" in the footnote, so it appears he is only talking about what the theory predicts rather than his actual belief of whether the branches exist in reality. Could the theory be true yet the branches still not exist in reality(s). What is truth, what is reality.... etc, etc. Are there other missing pieces of the jigsaw. Possibly the realms of philosophy. Anyway, in the footnote, Everett doesn't say he believes all the branches actually exist in reality(s). The question many readers will be interested in is the "actually exist in reality(s)" one. --- Plexos | Talk 18:21, 2 November 2007 (UTC)

Read Everett's bio' (linked at the Hugh Everett page) and you will see that he does believe in the truth of the MWI.--Michael C. Price ^talk 23:00, 2 November 2007 (UTC)

Gardener is clearly mistaken and can't be regarded as a reliable source since he contradicts what Hawking himself says about Hawking's beliefs. Just because what he says is online does not make him more reliable.--Michael C. Price ^talk 19:12, 1 November 2007 (UTC)

So you say with your unconfirmed offline Tv ref. Gardner is a very respected source. It is a quote and you shouldn't delete it without discussion. Who knows what your Tv reference says since we haven't got the script. --- Plexos | Talk 21:16, 1 November 2007 (UTC)

It hasn't been deleted -- it's been moved to a more appropriate area of the article and both sides of the issue have been presented: Gardner's POV and the sources that contradict what Gardner says.--Michael C. Price ^talk 00:33, 2 November 2007 (UTC)

Second point: how does the fact that QM needs "modifying" invalidate MWI? You have jumped from "modifying" QM to saying QM doesn't "hold", which is rubbish. And OR, since it isn't what Penrose says. --Michael C. Price ^talk 22:49, 28 October 2007 (UTC)

You have to leave something for the reader. Maybe you would prefer I wrote "if unmodified QM doesn't hold at all scales then MWI is wrong" and also "MWI is just unmodified QM with collapse Rule 4b removed", but they don't read very well. The whole Penrose premise is that unmodified QM doesn't hold at higher scales due to gravity. What part of 1 + 1 = 2 is rubbish then? It is exactly what Penrose says. Your criticism is invalid. --- Plexos | Talk 01:50, 30 October 2007 (UTC)

You don't have the slightest idea what you're talking about. Penrose (like most physicists) says that QM needs modifying with quantum gravity. Whether or not quantum gravity will invalidate MWI depends on whether quantum gravity (or a TOE in general) is linear (wrt to the wf) or not, and nothing else.

BTW "if unmodified QM doesn't hold at all scales then MWI is wrong" is false, whereas "MWI is just unmodified QM with collapse Rule 4b removed" is correct -- although the adjective "unmodified" is superfluous.--Michael C. Price ^talk 14:28, 30 October 2007 (UTC)

The references you quote regarding the linearity argument are all offline and would take time to investigate. Are there any online references? --- Plexos | Talk 05:23, 31 October 2007 (UTC)

I did a google on "linearity" and "many-worlds" and my FAQ came up tops. Try Q27 at [3]. --Michael C. Price ^talk 09:29, 31 October 2007 (UTC)

I am trying to get to the bottom of this. Obviously I can't use your own site, and your refs are offline. The linearity point needs confirming I think so I will have to see how offline refs are confirmed in Wikipedia. There is no library near where I am so if there was an actual paper online you know of then it would really help. --- Plexos | Talk 13:48, 1 November 2007 (UTC)

Note the phrase that MWI "... postulates that a wave function that obeys a linear wave equation everywhere and at all times ...." in the online link I've copied from the Hugh Everett article. Some typos in it, though. --Michael C. Price ^talk 14:47, 1 November 2007 (UTC)

Wave function collapse and the problem of interpretation

"As with the other interpretations of quantum mechanics, the many-worlds interpretation is motivated by behavior that can be illustrated by the double-slit experiment. When particles of light (or anything else) are passed through the double slit, a calculation assuming wave-like behavior of light is needed to identify where the particles are likely to be observed. Yet when the particles are observed in this experiment, they appear as particles (i.e. at definite places) and not as non-localized waves."

Assuming for the moment we're talking about a single particle observation (detection) then such can be specified by a globally unique location in spacetime. This is because a particle detection is defined as being detected at only one location, ie. to the exclusion of all others. It needn't be, of course. We could define a "single" particle detection as capable of happening at multiple points in space and/or time, be it in single universe or in multiple universes (even if our semantics would become somewhat more complicated).

But normally we don't define a detection this way.

And we needn't change this definition for a multi world model either.

We could use five numbers rather than four, where the fifth is the world ID, and the remaining four are the conventional spacetime ones: x,y,z,t

Defined this way, (ie. all particle detections as a one off unique event - as is the typical case in single universe models) any specification of such a detection is unavoidably non-local, ie. a global specification. A globally unique identifier (see GUID http://en.wikipedia.org/wiki/GUID).

Any transform on a specified point, results in an equally global (non-local) re-specification of that point. The result, however, need not be another single point. A fourier transform of a single point yields a range of (non zero) points. But the transform is reversible, reconstituting the original single point again.

The point here (excuse the pun) is that the terms "local" and "global" are just the inverse transform of each other, ie. mathematically equivalent terms.

In simpler terms, a particle detection specified by where a detection didn't happen, is the same as one specified by where it did happen.

But in Ancient Philosophy - there is the concept of "Reality", in opposition to the concept of an observation - which many physicists find impossible to ignore (for some peculiar reason). There is an ancient opposition to the Superficial, the Surface, the Image, the Imaginary. It is as alive today as it ever was.

Thus, although we can talk of particle detections and transforms on such, which yield wave functions capable of partially predicting (reconstructing) an observation (an image), there is this competing concept of realism.

Classical realism produces the concept of a "particle" - as distinct from a particle detection. The particle (Real) is responsible for the particle detection (the Image). Or would be if we could agree on a definition of such.

The problem is that particles do not enjoy the same generally consensual definition as that enjoyed by particle detections.

In "old" quantum theory (ala Copenhagen) the wave function has nothing to do with the ancient concept of Reality or particles. It is simply an algorithm for "predicting" where a unique observation (particle detection) might occur. Or predicting what is exactly the same thing: where a particle detection might not occur. And it follows directly from how particle detections are defined in the first place - as globally (ie. non-locally) unique events in spacetime.

Nothing at all was formalised about any Reality behind such observations. Indeed there was a general consensus (ignoring Einstein) that whatever reality was behind observations it could not be the Ancient or even early modern concept of such.

The historical fact is that Reality remains as woolly a concept as it ever was, at best defined negatively: as the mythical opposite of images and information. The mysterious Cause of observations - not unlike, in many respects, the concept of Gods.

Carl —Preceding unsigned comment added by 203.214.133.173 (talk) 23:15, 9 November 2007 (UTC)

Clean up the Advantages/Objections section

Ok this is just a mess and strikes me as amateur wikipedia. First off, many of the advantages have already been included in the Outline section. If some 'advantages' need to find a home... find a place for them... The points in Objections belong in Acceptance Amongst Physicists along with relevant citations. That entire section reads like an argument on some forum. Also some of the objections seem to be directly addressed within http://www.hedweb.com/everett/everett.htm which includes references which may be useful. If the objections camp (as there clearly appears to be two communities in the writing of this article) wants to get their points in earlier, move the Acceptance section up to replace Advantages and Objections. It is going to get lost below all the heavy-duty ket functions when the people mostly interested in it will be hitting the back button way before they get to Acceptance. —Preceding unsigned comment added by 129.128.29.97 (talk) 06:07, 20 November 2007 (UTC)

A meaning of the many worlds interpretation,
in concrete terms and effects.

Are there any numerical issues arising, philosophically, and physically, about the idea of having a many worlds interpretation of QP? I cite the following calculation with some assumptions, to give a rough idea of what is involved to believe in this paradigm:

TimeSinceBigBang ~= 60*60*24*365*12*10^9 [sec],

RateAverageOfInteractionsPerSecondPerParticle ~= 1/10^10 [sec/(interaction*particle)],

UnitParticlesInUniverse ~= 3*10^52 [kg]* 6.02*10^26 [amu/kg]* 2 [particle/amu],

QuantumBranchFactorPerInteraction ~= 2 [branch / (interaction*particle)], where

UniversesSuperpositions = QBFPI ^ UPIU ^ (TSBB / RAOIPSPP) =

10^41147681254863400000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 [universe superpositions since Big Bang]

, or,

10^10^106.61435 [universe superpositions since Big Bang].

There can be reductions in scale for local light speed isolation of distant objects, but the numbers of parallel universe superpositions is still beyond astronomical, with reduction factors in the exponential equation. It sounds more like just a philosophy, than a real system, as matter and energy and universes, are not conserved in the MWI "hyperspace". Even counting just the Earth for 4 billion years, one gets numbers around 10^10^50 for earth superpositions, depending on the assumed numbers of particles, interaction rates, branch factors, and timespan over 4.5 billion years.

Of course, it makes interesting interpretation, of how such a large space operates if there are physical theories to substantiate *interpretation*, but sounds as grand and inaccessible to measurement as the often cited God.

For example, in MWI, what are the "fluctations of the quantum vacuum", vacuum virtual particles? What, a trans-dimensional particle pair temporarily crossing our plane of existence, and always crossing in a time limited particle anti-particle pair, to conserve matter-energy with creation and destruction in our plane? What physics is this? And if they are universe crossing particles, what do virtual particles tell us about so-called MWI bifurcations of other "planes"? Or is this all wrong?

LoneRubberDragon (talk) 04:52, 25 July 2008 (UTC)

"universe crossing particles" require non-linear physics, which is not observed (i.e. such particles are not observed). And before anyone says, note that there are universe crossing particles in string theory, but this a different sort of universe. Regarding large numbers, there seems to be no constraint on the number of universes that the theory can handle; if you want to see some really large numbers, look up Graham's number.--Michael C. Price ^talk 08:22, 25 July 2008 (UTC)

Ok, so there's no nonlinear operators in MWI at all, for virtual particle fluctuations of a vacuum say observed in Hawking Radiation caused by vitual particles at the event horizon of a black hole. It glibly doesn't explain why it is reasonable that there's no physical constraint on the number of universes, in that, any one universe conserves matter and energy, but there's no conservation of parallel universes. Schrodinger's equation is actually a continuous function in space, so the branching factor is infinitely higher than my calculation example of an abstract branch factor of 2 to illustrate the scope of branches. Also, there are also universes where the laws of physics don't appear to apply that are parallel universes, where the odds of a glass shattering backwards, for instance, however low, are part of a few rare paths of quantum wavefunction evolution, reaching numbers beyond Grahan's Number, since the branch factor is infinite in these improbable universes, with no constraints of universe conservation, with a statistical measurement operator at any scale occuring, in non-zero probability wave functions for interacting matter. LoneRubberDragon (talk) 02:32, 27 July 2008 (UTC)

So can you elaborate beyond the article, why it is reasonable to believe in infinite numbers of parallel universes, that are all unobseveable? A Bohmian hidden variable type of theory is a much more Ockham preferable conservative equivalent, as another isomorphic version of Copenhagen Interpretation, than a hidden but blatantly nonconservative Many Worlds quantum physics isomorphism universe, where MWI QP spawns infinite unobserveable universes, over an unobserveable pilot wave or hidden variables on one universe with conservative properties.

I agree, even Bohmian pilot waves are more reasonable than this MWI.IbleSnover (talk)

In other words you failed to address, is MWI merely to be taken as a philosophical interpretation for mathematical calculation convenience, in some instances, only, which is why there are no limitations on universes without issues. That is MWI is not an actual physical theory of how space operates, where Cophenhagen or Bohmian interpretations keep a more conservative local existential spirit, than MWI does when taken plysically-literally instead of only interpretation? LoneRubberDragon (talk) 02:32, 27 July 2008 (UTC)

And before anyone says, hidden variables are just epicycles, they do follow field equations isomorphic enough to Copenhagen QP, as much as Feynman Infinite Path Integrals also do for tractible problems. An epicycle theory of planetary orbits has no such isomorphism with gravity, as much as it does with approximating orbits with a nested series of harmonic functions that are unrelated to gravity, mass, energy, precession, mutual effects, etc.. And as Hidden Variable Theory are indistinguishable but isomorphic to Cophenhagen, Ockham may have a soft edge to pick, but rather, Ockham can take them as physics theories, over MWI as philosophical interpretation with mathematics applications, because of the literal physical space defined by infinite universes that abstractly don't interact at all. LoneRubberDragon (talk) 02:32, 27 July 2008 (UTC)

I believe most, perhaps all, of your concerns (e.g. conservation of energy, Ockham, etc) are covered either by the article or the FAQ (which I wrote) in the external links section. As for the number of worlds, there is no conservation law for the number of worlds. Loosely speaking the number of worlds follows

$\Omega =exp(S/k)\,$

which, since S is the entropy of a set of branches of the multi-verse, is an increasing and very large number by the 2nd law of thermodynamics. It is simply the inversion of Boltzmann's entropy formula. --Michael C. Price ^talk 08:43, 27 July 2008 (UTC)

I've read that FAQ, I'm not impressed, persuaded, or convinced at all. More appalled than anything else really.IbleSnover (talk)

PS By "increasing" I meant that since S (entropy) is a function of time, so is omega (the number of microstates = number of worlds). i.e.

$\Omega (t)=exp(S(t)/k)\,$

A more detailed calculation of omega (if possible) would have to also consider the Bekenstein bound and the infrared divergences.

(reindent down)--Michael C. Price ^talk 12:47, 3 August 2008 (UTC)

LoneRubberDragon (talk) 14:19, 2 August 2008 (UTC)

I've skimmed what I can from the article and the external links. I appreciate the balance of dissenting and ascribing links. I found amusing the external link saying many physicists use the MWI, but noone really likes to talk about it. With all that reading, though, I still find am left cold to know what is being conserved using the Many Worlds Interpretation method as anything more than a mathematical tool, and not a physical reality. Given the nature of defining a Hilbert space with continually branching points spreading in the infinite dimensional vector space, with each point representing the branching of whole universes, in ANOTHER universe that is separate and distinct from this material universe, as each point in this Hilbert hyperspace is a whole universe, in itself. I found one FAQ interesting saying that all of the MWI unvierses are supervenient to this plane of existence, and yet virtually none of them interact, and MWI supposedly doesn't show anything new that QP Copenhagen Interpretation, Bohmian Hidden Variables, or even Feynman Infinite Path Integrals show, other than maybe mathematical ease in some problems. I can conceptually understand this MWI idea of having a larger universe of Hilbert Space with universe points spreading throughout the Hilbert Space. But why consider that "real", a Hilbert Space universe of spreading diffusing point universes, which fails Ockham's razor of observeables, and thus the postulating of such an infinite dimensional Hilbert Space is not to be considered "reality", but just a mathematical tool?

Also, while I can appreciate the terse Boltzman Equation for a uniform universe of indistinguishable particles with equal probabilities of states:

$\ S[NaturalUnit]=k*log_{e}(W)$

I would not see why that relates to the definition of MWI universe counts, where the particles have associated state QP wave functions with distingushable probability wave functions each particle of nonuniform information, also roughly stated here without a time factor in the Gibbs Equation (here converted to represent binary information count):

$\ S[bit]=-k\sum _{i=1}^{i=N}Prob(S_{i})*log_{2}(Prob(S_{i})$

Which, alone, has a strong correspondence to Shannon information of messages (lacking Boltzman Constant), here, with an example of 4 symbols of equal probability of 0.5 for this example, illustrating the calculation:

$\ entropy[bit]=-\sum _{i=1}^{i=N}Prob(symbol)log_{2}(Prob(symbol))$

$\ 4[bit]=-\sum _{i=1}^{i=4}Prob(1/2)log_{2}(Prob(1/2))$

Likewise, taking an equation transformation, one sees the relation of binary information entropy with states (or in this case universe splits):

$\ 2^{entropy[bit]}=2^{-\sum _{i=1}^{i=N}Prob(symbol)log_{2}(Prob(symbol))}$

$\ 2^{4[bit]}=2^{-\sum _{i=1}^{i=N}Prob(1/2)log_{2}(Prob(1/2))}$

Which is equivalent to a product form of the equation of state probability:

$\ state[count]=\prod _{i=1}^{i=N}{\frac {1}{Prob(symbol)}}$

$\ 16[count]=\prod _{i=1}^{i=4}{\frac {1}{Prob(1/2)}}$

And most simply shows a state count as symbol relationship of simple products:

$\ state[count]=\prod _{i=1}^{i=N}symbol[count]$

$\ 16[count]=\prod _{i=1}^{i=4}2[count]$

Your too-terse Boltzman Equation inversion, appears only "roughly" equivalent to a formal universe splitting equation definition without further clarification of the terse post, firstly, because it doesn't show time as a factor, where my equation is a function of time. My equation (reformulated from before, but equivalent) uses a simplified set of state space, defined for the universe of localized particles in the universe at the Big Bang, where each particle is counted as a symbol (universe split) generator. Each particle is considered a wave function with a symbol "universe" generating branch factor at each measurement, generating new symbols "universes" at a rate of a branch factor with each interaction:

$\ Universes[count](T[sec])=\prod _{t=0,1/10^{10}[sec/(inter*part)],...}^{t=T=3.78432*10^{17}[sec]}2[br/(inter*part)]^{3.612*10^{79}[part]}$

$\ Universes[count](3.78432*10^{17}[sec])=10^{10^{106.61435}}[count]$

I also include a feedback in the terms, because the universes would split at each interaction, and split again, from the former split state, which gives rise to the feedback of self scattering probability wave functions in each so-called "universe". For example, with 2 particles that have 7 branch factors, e.g. spin, momentum, position varieties in 7's for each interaction, one simply sees in an interaction sequence 1[universe], 49[universe], 2401[univese], ...; which reflects the originally formulated direct calculation (simplified):

$\ Universes[count](T[interaction])=QuantumBranchFactor^{Particles^{T[interaction]}}$

$\ 1[count](0[interaction])=7^{2^{0[interaction]}}$ (Big Bang)

$\ 49[count](1[interaction])=7^{2^{1[interaction]}}$ (one interaction)

$\ 2401[count](2[interaction])=7^{2^{2[interaction]}}$ (two interaction)

Which shows the potential for quantum chaos of entangled wavefunction, in an MWI which is supposed to never collapse, but always linearly evolve, and with splitting new Hilbert Space universe points at each still ill-defined measurement/decoherence "events".

And in actuallity, the wave function that is evolving linearly in every universe, is a continuous function at the resolution of quantized time, space, and momentum, so there is nearly an infinite number for quantized QuantumBranchFactor options for each universe.

So perhaps a more accurate equation of universes in this increasingly hypothetical Hilbert Space universe of universes is (roughly stated):

$\ Universes[count](T[sec])=\prod _{t=0,1/10^{10}[sec/(inter*part)],...}^{t=T=3.78432*10^{17}[sec]}10^{100}[br/(inter*part)]^{3.612*10^{79}[part]}$

$\ Universes[count](3.78432*10^{17}[sec])=10^{10^{109.13574}}[count]$

Where the quantum branch factor is arbitrarily selected at 10^100 symbol potentials, since measurement is in MWI still arbitrarily statistical, so the Hilbert Space universes can branch in a spreading universe cloud with every particle's probability wave function interaction creating "measurements" with distributed probabilities and amplified macroscopic effects from each quantized universe of potential. So the Hilbert Space is not just a cloud of universes, but possibly a cloud of universes with probabilistic weight on each universe following the probability wave function density of every particle wave function interaction. Unless you simply quantize even the least probable universes to whole universe existence, in which case the MWI universes have an almost plank-scale like density and flow, taking even the most QP improbable quantization universes (where glasses break backward, and gravity flows the wrong direction), and magnifying all of them to quantum full existence.

I dunno, MWI seems a good enough mathematical tool, but completely-unreal otherwise. Because mainly, despite your flawed article's mention of promoting Ockham's razor, it removes the measurement collapse of wavefunctions, at the expense of defining an axiom with an infinite size infinite dimensioned Hiblert Space Universe of quantized universe clouds branching and spreading through it (what was Ockham pared off, really). Instead, it appears to make a thoughouly unexploreable universe, that is thouroughly unreal as far as large scale observational science is concerned, "PROVED" with only 1 part in 10^10^106+ observations of universes being observed, it seems. Taking MWI as real and not explicitly stated as being pure math tools, is dishonest of an article, bordering on philosophy of mathematics as science. It definitely makes watching "Dr. Who" more interesting, I must admit!

LoneRubberDragon (talk) 11:01, 2 August 2008 (UTC)

Responding to your last point, surely it is dishonest to pretend that all these other worlds aren't real, since they appear in the maths? By what criterion are they judged non-real?--Michael C. Price ^talk 12:42, 3 August 2008 (UTC)

I/m sorry, I realize I wrote many words and equations that may make the criterion hard to detect without careful reading. The criterion giving a judgement as an honest math tool, and not assumed real, being: LoneRubberDragon (talk) 12:38, 4 August 2008 (UTC)

"PROVED" [observed] with only 1 part in 10^10^106+ [universe] observations of universes being observed. LoneRubberDragon (talk) 12:38, 4 August 2008 (UTC)

If humans can send probes that can diverge themselves INTO other universes and BACK, like a Dr. Who, then the MWI math-tool is promoted into tangible multiple-universe theory, as much real as can be measured beyond our current one universe "Hilbert Space" point of view. That is a more concrete criterion of testability. Or, perhaps, a "large scale" quantum computer with a carefully designed interface to the "larger" universe could be used to port data between universes close enough to inter-act. However, it seems any differences large enough to indicate another distinct universe, would be in different spots in "Hilbert space" and so such probes seem forever out of reach, and one is stuck with only 1 in 10^10^106+ part observation knowledge of multi-verses as real, which is a pretty high noise to signal ratio! QP, Feynman, and Bohm are all mostly local proofs in one universe of wavefunction and measurement uncertainty black boxes (not black universes). LoneRubberDragon (talk) 12:38, 4 August 2008 (UTC)

Just take the controversial qualia (tangibility of perception) in humans, at least, that have been observed in one in 7 billion people, and psychologically reported in 7 billion out of 7 billion (though without proveable communication of qualia between humans), but at least 7 billion reports in this one earth, the instances of living witnesses of qualia. LoneRubberDragon (talk) 12:35, 4 August 2008 (UTC)

For a computer with a color camera, does it *see* color in its memory and self referential analysis in a system, as a human with neurotransmitters in a system? How do three planes of black and white data become colors is a good question (not even recursively inspecting why light and dark are even observed in neurotransmitters distributed in a complex self referential system). Does the mathematical X,Y,Z coordinate system of space have colors too, that we just can't see, to be obscure? Do pigeons see 5 planar tangible dimensions, with 5 different spectral receptors in their consciousness (in one report I heard one bird type has 27 different receptors)? To be sure, they materially process the data, but do they see a psychedelic color world by-some-called "illusion" like all sighted people can see? As some argue, qualia are indication of transcendental or not-understood soul-self, while others say it is unreal illusion. But for me at least I can confirm a 1:7,000,000,000 observation, where three planes of black and white data become color. And maybe a computer does tangibly *see* colors too, of as many dimensions as data array depth. All of this is tentatively accessible to inspection today or someday, in this one universe, here. Likewise MWI is testable, if a measurement and processing probe can be diverged out of and back into this universe from a neighboring universe with measurement data supporting MWI as real versus creatively mathematical illusion, like human qualia, of even color vision. LoneRubberDragon (talk) 12:35, 4 August 2008 (UTC)

By your logic, if to be taken seriously, the Greek Epicyclic infinite harmonic function series approximation definition of planetary orbits is REAL ISOMORPHIC CORRESPONDENCE to reality, even though gravity plays no direct role in the all too REAL AS MATHEMATICAL TOOL use of Ancient Greek Epicycles. But where's the compact gravitational correspondence equation, or it isn't honest to discriminate against otherwise gravity less Greek Epicycles as UNREAL, or a fourier transform harmonic representation of planet orbits for that matter as UNREAL? Therefore all mathematical isomorphisms are REAL MATERIAL UNIVERSE COMPACT ISOMORPHISM DESCRIPTION, by your logic?!? I guess General Relativity and QP CI did as much to define another refined approximation, as much as Bohm type Hidden Variables formulations, by transforming dimensions and relations in formerly unseen ways, so MWI isn't on the cutting block, but isn't there either, otherwise it wouldn't be controversial right now. And similarly, a log base 2 of object [count] produces the real physical unit of quantized-data [bit], that can be stored moved and processed in computers. So maybe qualia as transcendental and unknown process are HONESTLY REAL too, and the other philosophers are being dishonest in calling them illusion. If anything honestly goes with isomorphisms, Platonic Realm is true, as Max Tegmark (alluding to Plato) is true and real too (and yet he dishonestly poo-poos Roger Penrose or John Wheeler type of structured processing matter extra-reality theories of macroscopic consciousness and measurement). And maybe Greek Epicycles, fourier transforms, and spatial ensemble entropy equations may have a correlatable effect on reality of the information of classical configuration effects on reality, with forces yet to be discovered or enumerated in those dimensions, as much as an MWI probe someday may leave and reenter our universe plane from another parallel universe diverged, but pre-synchonized to transmit a similar looking branched probe from that universe back into our universe, with grossly different measured data moving information between "Hilbert" universes? If anything isomorphic goes, really and honestly, virtually-mathematically equivalently. For you see, a Greek Epicyclic frame of reference can be used to perfectly polarize a measurement frame of reference to prove there are special forces that are otherwise smeared out in a conventional local General Relativity frame of reference with gravity wells and N bodies as the assumption. For example a planet circling a black hole with even relativistic epicycles on seconds timescale could realize a Greek Epicyclic force unrelated to the General Relativity frame of reference, in short fourier transform measurement order of years of close observation of those "crystal sphere's" effects not accounted for in the General Relativity equation ... or falsified finally and honestly after 2000 years since Claudius Ptolemaeus. Or test it with an elliptical cyclotron on electron Greek Epicycles in a few minutes, possibly. Then one can see that both General Relativity and Greek Epicycles are quite REAL with proveable observeables in their own dimension, increasing the numbers of basic forces in the universe, if proven, when taken in that PROPER frame of reference. Like you imply, anything goes for virtually identical isomorphisms, regarding reality. Even Morphogenic resonance, if taken in the right frame of reference to measure, leading to proving or falsifying telepathy and such ESP fields, even Chinese CHI lifeforce, in the right framework for isomorphic mathematical measurement to not smear out the effect in the wrong frame of reference. Anyhting honestly goes in virtually isomorphic reality is a nice concept, surely and honestly, as the non-linearities of one theory are picked up by another universal force that linearizes things in its space where the other theories all fail. Thanks for taking the time to talk! LoneRubberDragon (talk) 12:35, 4 August 2008 (UTC)

And maybe it is just a semantic pholosophical issue of what REAL and HONEST mean to you and me, like Clinton's what the definition of "IS" is. LoneRubberDragon (talk) 12:35, 4 August 2008 (UTC)

http://en.wikipedia.org/wiki/Max_Tegmark LoneRubberDragon (talk) 12:35, 4 August 2008 (UTC)

http://en.wikipedia.org/wiki/Ultimate_ensemble LoneRubberDragon (talk) 12:35, 4 August 2008 (UTC)

http://en.wikipedia.org/wiki/Platonic_realm LoneRubberDragon (talk) 12:35, 4 August 2008 (UTC)

http://en.wikipedia.org/wiki/Deferent_and_epicycle LoneRubberDragon (talk) 12:35, 4 August 2008 (UTC)

http://en.wikipedia.org/wiki/Pentachromat LoneRubberDragon (talk) 12:35, 4 August 2008 (UTC)

http://en.wikipedia.org/wiki/Rupert_Sheldrake LoneRubberDragon (talk) 12:35, 4 August 2008 (UTC)

http://en.wikipedia.org/wiki/Morphic_field LoneRubberDragon (talk) 12:35, 4 August 2008 (UTC)

I'm with you LoneRubberDragon. If this MWI isn't the most colossal example of a "viewpoint" in massive need of Occams Razor, then, well, I'm a peanut. And I mean that literally, because surely - in one of these many universes I sure as hell must be a real, literal, peanut. How can anyone possibly think there is anything to gain with this MWI? Its the most mind-bogglingly lazy theory in the history of physics. It essentially says: "Hello, I am a scientist, and a physicist, its my job to get to the bottom of the laws of the universe. But I can't be bothered looking into the mysteries of the universe any deeper than we already have. I prefer to believe the universe multiplies itself into unheard-of googolplexes upon googolplexes upon googolplexes of parallel universes in which every possible consequence of all the current unknowns of our physical theory are enumerated. And there is no point trying to work any harder to reduce those unknowns, and narrow the possible consequences of our current theory, because all the unknowns are fundamentally irreducible and all the possible consequences do in fact exist in one of the convenient multitude of many worlds that are out there. And this is all because I'm too lazy to stop eating donuts on my couch and refine our theory a bit more."
It just astounds me - why do people find it so hard to believe that gravity collapses the wavefunction? Its a tiny modification to the theory which instantly does away with a near-infinitude of universes. How economical and kewl is that? We may not know exactly how gravity does collapse the wavefunction (although there are proposals which sound like they're on the right track to me) - so, well, why don't we do some work and try to find out?
Considering the standard everyday QM doesnt incorporate gravity... why is it so hard to imagine that addition of gravity causes some kewl new behaviour? We know gravity works on large scales, and QM works on small scales where gravity can be neglected. Where the two scales meet, something in our current theory is going to break. Is it unreasonable to say wow, these wavefunctions are getting bigger and bigger, these various superpositions are starting to involve a lot of energy and mass. Will they really continue to exist simultaneously? If we start to consider the gravity we have optimistically neglected until now, we find wow, it should be becoming significant at these scales - the superpositions of different states in the wavefunction will have different gravitational fields, and the differences between the fields are even larger than the magnitudes of the fields themselves, and the difference between fields may be oscillating wildly in a highly unstable fashion. Might that not cause some new gravitational hocus pocus which simplifies things a bit by blipping some of that energy/field difference into some gravitons which interact with the differing gravitational fields and lessen the difference between fields by or thus collapsing the wavefunction a bit. For those who think its a bit cruel for the nasty ogre of gravity to impinge on the beauty and linearity of Schrodingers equations, well... if we include gravity into QM somehow, maybe we'll have something even nicer. The wavefunction collapse will be part of the improved QM theory instead of being imposed on it externally, and we'll see the resulting behaviour of wavefunction collapse is a thing of beauty too.
But the physicists in our universe will say: "No, we're all too lazy, we'd rather eat donuts and leave all that hard work to our thin clones in the those other alternate universes in which donuts weren't invented. Once the donut was invented in that ancestor universe of ours, we were all doomed to eternal laziness. But, take heart! Somewhere in the Multiverse is a universe in which donuts were never invented, and tv only shows the discovery channel. Let them solve everything in that universe, then they will surely go on to invent a sub-quantum multiverse-tunneling hyper-vortex so they can come and tell us all the answers, and we'll give them donuts and TV in return. Sounds like a fair deal to me."
I was interested to see someone's assertion that collapse of the wave-function is non-linear, and that is apparently bad so it can't be true. But why is non-linearity bad, if it explains what we see in our universe without postulating the absurd existence of a billion gazillion other universes? If so, it sounds good to me. A small price to pay. So why is it so hard for MWI proponents to deal with? A bit of non-linearity here, a bit of CP-violation there, and weeeeeee, suddenly we're starting to find explanations for aspects of the small and large scales of the universe that have hitherto been inexplicable. But MWI people want to close their eyes and plug their ears and say "umumumumumumumumumumumum not listening umumumumumumumumumum don't understand umumumumumumumumumumumumum ooooooh collapse is non-linear umumumumumum go away go away go away etc" IbleSnover (talk) 05:38, 12 August 2008 (UTC)

Your views about quantum gravity already appear in the article. --Michael C. Price ^talk 09:36, 12 August 2008 (UTC)

Well, I apologise for my little rant above. I spose I'm just appalled at statements in this article saying that MWI is a "mainstream interpretation" up the top, supposedly believed by 60% of physicists. Its enough to make one despair. And then, much later on we read that even those who supposedly regard MWI as "true" are divided into two camps, those who think its real or unreal. Ridiculous. We're not discussing an abstract mathematical theory which may be true in the sense that its logical and consistent, or illogical and inconsistent and untrue. Its about whether MWI is (mathematically consistent AND) a good model for the real universe. This is physics, not mathematics, there is a distinction.
And then there are passages like this: "Dr. David Deutsch along with Oxford colleagues have demonstrated mathematically that the bush-like branching structure created by the universe splitting into parallel versions of itself can explain the probabilistic nature of quantum outcomes". Surely thats depends on viewpoint. The whole basis of MWI is the bush-like branching is caused BY the probabilistic nature of quantum outcomes. All he's done is state the same argument in reverse. Now, hes saying the branching explains the quantum theory, instead of the reverse. I wish he would make up his mind. Or say something new.IbleSnover (talk) 11:34, 12 August 2008 (UTC)

But MWI is a mainstream interpretation nowadays...

I agree that the "real and unreal" camps stuff is rubbish (a figment of M Gardiner's biased imagination)-- unfortunately it seems to be published rubbish, hence its appearance here.

Finally about Deutsch and his branchings; it does not strike me as tautological -- the branching is a feature of quantum theory even before you add any probabilistic veneer, so if you can derive the probabilities from the branching then that is a highly non-trivial achievement. There seem to be a number of ways of doing his (Everett gave one, DeWitt another, Hartle a third, now Deutsch ....) -- and, I must confess, I doubt that they are dependent on MWI.--Michael C. Price ^talk 13:52, 12 August 2008 (UTC)

The point is that MWI holds only as far as linearity of QM holds. If QM is effectively linear below a certain scale, then MWI is going to hold below that scale. To a particle or wavefunction at these small QM scales, the MWI view is, I have no doubt, a perfectly valid viewpoint. One can look at these little particles and say, well, as far as that little packet of wavy particley Schrodingerness is concerned, its existence is bifurcating or trifurcating and so on, into mutliple little particle-verses which can be considered to really and objectively exist. But on the larger scale, it doesn't hold, because the linearity of QM doesn't hold when extended to larger scales. This is a critical point. You say there is no evidence for this, and I say that is absurd (and many would agree with me). Earlier in this discussion you yourself have shown you're happy to use inductive reasoning, but you dismiss the Occams razor argument. Now, when one considers the magnitude of the unnecessary multiverses which MWI (on the large scale) proposes - the Occams razor argument against MWI is an example of the most mind-bogglingly convincing inductive argument ever constructed. But you discard it because you don't want to believe the purity of the wavefunction can be tainted. I'm sure you'd be aware of D. Fival's paper saying all it needs is the addition of a tiny bit of stochastic random noise to the wave equations, and then we find the wave function IS non-linear enough that it begins to collapse by the time it involve mass near the Planck scale. Its a simple, and beautiful little modification, and does away completely with MWI on large scales, and its that sort of thing which is exactly what I'm talking about. I'm not saying Fival has found the final answer - no doubt this line of investigation can and is being pursued further. Perhaps merging gravity into QM will give us a better and even more beautiful explanation of where the additional noise term comes from and lead to the generation of general relativity on larger scales too. How kewl (and beautifully economical) would that be? Occam would be delighted.

I doubt you will convince me that it means anything at all to derive probabilities from branching. As I've explained, I'm sure MWI is a valid viewpoint at quantum scales. So depending on where you start your proof, I'm sure you can derive branches from probabilities, OR derive probabilities from branches. If, perchance it is slightly easier mathematically to start with MRI and derive probabilities than it is to go the other way, well, thats great. That'll be a useful consequence of MWI, the mathematicians will be happy, and it may make it easier to model or numerically evaulate some events at this level. And for this reason I'm all in favour of following the logic and mathematics of MWI through and seeing where it takes us and what we can get out of it. But, it doesn't really have any bearing on physics at larger scales and I don't think its likely anything much is going to come of doing so, beyond a temporary mathematical or numerical convenience or two.IbleSnover (talk) 01:48, 13 August 2008 (UTC)

Wow, long conversation.

Ignoring MWI for the moment, there are quite a few reasons to believe in the existence of things we can't empirically observe and never will be able to empirically observe. Here's one. We can see out into the universe to a distance of about 46 billion light years (comoving); that's as far as light has been able to travel since the universe became transparent. For as far as we can see the Universe is filled almost perfectly uniformly with matter. There are at least two possible conclusions: (1) this distribution of matter continues beyond the part we can see; (2) the Earth is at the center of a perfect sphere of uniform matter with a radius of 46 billion light years. Physicists prefer the first option for what should be obvious reasons; however your position on Ockham's razor would seem to require you to prefer the second. In fact there are other cosmologies that would be even more strongly favored by this version of Ockham's razor. For example, there's no logical inconsistency nor conflict with experiment in supposing that the universe is just a few thousand light years across with our solar system at the center, and at the edge are machines that emit patterns of light suggesting the existence of a Milky Way and other galaxies. This is a ridiculous idea, and it's worth thinking about why. It's ridiculous because light-generating machines could produce any pattern whatever, and most such patterns would not be consistent with the universe continuing uninterrupted beyond the machines. We reject this kind of cosmology out of hand because we don't believe in conspiracies.

I see your point, but even so, I'm sure you know its a naughty misrepresentation of Occams razor. Neary as bad as the claims of those who say the razor favours MWI because it proposes a simpler basic theory (with no "additional" collapse). They fail, because they miss the point that any sensible use of Occams razor favours a slightly more complex theory if it results in a vastly simpler physical universe which is still (or more) consistent with what we know. You start to go wrong when you say your sphere of lights doesn't necessarily conflict with experiment, and sure, I agree that might be the case in principle. But to postulate a simple shell a few light years across throwing a few photons at us in a way which is consistent with the evidence we see and (therefore) with our theories - well, it might look more acceptable to Occams razor because the shell-universe is small, but you must know its not. Look at the nature of the evidence and the theories we have, to fake all of that, this shell must have some amazing physical and (you admit) conspiratorial powers. You don't just stick a few light bulbs on the shell, you have to line the inside of the shell with particle accelerators to generate cosmic rays. You have to co-oordinate the bulbs and accelerators and on and on and on. You have to then postulate the existence of an intelligence controlling this shell, an intelligence so vast that it could actually decide to fake all this evidence AND be smart enough to make all that fake evidence point towards an astoundingly complex and yet amazingly mathematically consistent "fake" universe". That would be a truly stupendous and god-like feat if that universe is not actually there and this intelligence exists only in a shell a few light years across with nothing much in it which could even serve to inspire this being to come up with such a marvellous hoax.

If you follow all that through, in effect you have to give the shell some absolutely god-like powers, both in the physical and intellectual and supernatural realms. So even if, on the surface, the shell seems simpler, its got to be an even bigger Occam-istic blunder than postulating a relatively bloated physical universe. By comparison, wave function collapse doesn't have to be anywhere near as godlike or conspiratorial. You people would have to know D. Fival's nice little adjustment to the wavefunction model, in which all it takes is a tiny bit of stochastic noise in the wave equations - to bring about wavefunction collapse... how utterly simple is that? Much simpler than many-worlds :) IbleSnover (talk) 01:48, 13 August 2008 (UTC)

The Born rule is also a conspiracy. Years ago I came up with what seemed like an easy way to test whether human consciousness was involved in the collapse of the wave function. All you have to do is set up a double slit experiment with a detector at one slit, but then never look at the output of the detector; look only at the screen. If the interference pattern disappears then the detection at the slit collapsed the wave function without human awareness of its outcome. If the interference pattern doesn't disappear then there was no collapse. This experiment doesn't work because wave function collapse isn't the only thing that will make the interference pattern disappear. You can show using Schroedinger evolution alone that there is no interference if any information about the path the particle took is left behind at the slit. As a result you can't tell when the wave function collapses; virtually any triggering rule is consistent with every experimental result, as long as it doesn't get too close to the quantum regime. Like the light-generating machinery, it's hard to understand why the collapse would hide itself so effectively if it's really a physical phenomenon independent of Schroedinger evolution.

Consciousness causes collapse is a nutter-idea too. As you say, if information about the particle path is left at the slit, then effectively the slit has taken a measurement. Consciousness whatever it is, can come along later and look at the result. As you say, virtually any triggering rule is consistent with the result. That, is a very good indication that collapse ISNT hiding itself so effectively... and there are experiments which can be designed to make this clearer.IbleSnover (talk) 01:48, 13 August 2008 (UTC)

Of course, not believing in the Born rule is not the same as believing in MWI. But I'm not arguing that MWI is correct, only that you have no rational basis for rejecting it, which is a much weaker statement. Ockham's razor applied to current astronomical evidence favors a universe that continues uniformly beyond the part that we will ever be able to see, and applied to evidence in astronomy and high-energy physics it favors a "multiverse" of one kind or another. Ockham is not always right, but I hope this will help you understand why physicists think it's okay to believe in this stuff. -- BenRG (talk) 17:39, 12 August 2008 (UTC)

Thanks for your input. The shell idea was good :) But I still think its very clear Occam's razor does not favour a multiverse :) Perhaps it would be true to say if we look through our rose-coloured glasses in which all the massive effects of gravity are invisible - then occams razor favours a multiverse. But thats only true because a universe without gravity is a fantasy, its not reality. Gravity obviously permeates and governs the structure of our whole universe. The only place it can be ignore is at Planck-type scales, below which QM is a (very) good approximation. I don't think Occams razor makes so much sense in pure mathematics. If there is a long-winded way of reaching a result via some method, and a short way via a completely different method, they are both just as mathematically valid as each other. Sure occams razor and the law of the laziness of undergraduate students will favour teaching the simple method, and glossing over the long method. but they're both equally valid, and the long method if it comes from a different angle, may offer additional insight into the problem.

But Occam's razor has more applicability in physics... much more. In physics it says the simple explanation is much more likely to correspond to objective reality. And thats a useful guiding principle in physics, because if a theory corresponds more to objective reality, then its much more likely we can delve further into that theory and discover even deeper theories which explain more about our universe than the more approximate theory we started with. And that is what we need to do here!
MWI says ok there is no need to look any deeper, I can already explain everything at the expense of postulating these absurd multiple-universes plus a huge chunk of of blind hope that gravity and all of its many many consequences (eg wavefunction collapse, CP-violation, arrow of time etc), can be ignored. Never mind that these multiple-universes have poor Occam spinning in his grave.
Standard QM plus a basic model of wave function collapse says we don't need all these ridiculous many-universes. And it gives us a much better guide as to where to look deeper in order to resolve the things we can't quite fully explain yet, like gravity, symmetry violations, or indeed, the underlying reason and mechanism (ie reality) of waveform collapse.

MWI is an interesting theory to develop and see if it can provide any insights or mathematical ideas which might be powerful at or above the level of QM. But, its not particularly likely to help us go deeper, because it doesn't suggest (or even leave room) for anything new physically. Its actually a smug, self-satisfied and ignorant denial that there can even be any deeper theories which might explain the things MWI ignores.

Regarding this controversy over Hawking's opinion the most I've been able to find on the net is the quote: "It is wellknown that if the quantum formalism applies to all reality, both to atoms, to humans, to planets and to the universe itself then the Many Worlds Interpretation is trivially true." Going from this statement to conclude that Hawking believes in MWI is a pretty big leap. He says MWI is obviously true IF the quantum formalism applies to the whole universe. Thats a pretty big if. It leaves him an entire universe of room to have some doubts the quantum formalism applies to the whole of reality, and therefore, it leaves plenty of room for him to doubt MWI. So, I don't think anyone should misrepresent Hawkings views in this wikipedia article by claiming he believes MWI is "real". Unless they have a different quote. This quote via Tipler doesn't cut it. In my view it means Hawking was much more likely to think MWI is unreal.

I'm not trying to make this a personal attack, but, in M. Price's FAQ, he says: "Linearity (of the wavefunction) has been verified to hold true to better than 1 part in 10^27 [W]. If slight non-linear effects were ever discovered then the possibility of communication with, or travel to, the other worlds would be opened up. The existence of parallel Everett- worlds can be used to argue that physics must be exactly linear, that non-linear effects will never be detected." That is a very very weak series of assertions. Linear to better than 1 part in 10^27 isn't saying much more than the fact that QM is an amazingly accurate model. And noone would dispute that. But there is still plenty of room for non-linearity. Suppose we are trying to verify linearity over distances of a just metre. One part in 10^27 will be 10^-27m. The Planck length is 10^-35 metres. If we have only verified linearity down to 1 part in 10^27, then the wavefunction could have non-linearity 8 orders of magnitude less than 1 part in 10^27 - and the non-linearities would still be on the scale of the Planck length, So they could therefore easily be significant to QM, and therefore kill MWI. And if the Universe is 46 billion light-years across, then MWI relies on QM holding for another factor of 10^27 or something like that, on the larger scale. 1 part in 10^27 is nothing when you are talking about scales which span 54 or more orders of magnitude...

The assertion that non-linear effects opens up the possibility of communication to other worlds, is sadly mistaken. As long as the non-linearity is just a wee bit of nice stochastic noise, there are no such possibilities of communication or travel, and indeed, no such possibilities that the other worlds even exist, because such a small non-linearity is enough to collapse he wavefunction and eliminate all these other worlds. The last statement that existence of Everett worlds can be used to argue for exactly linear evolution is just completely fallacious and circular. Again... I ask.. in despair... how can any self-respecting physicist think this way?! Nothing personal, I'm not picking on anyone in particular. I just marvel that this MWI is such a widely accepted view among people who supposedly know anything about these subjects. I can't believe this is really the case.

IbleSnover (talk) 02:37, 13 August 2008 (UTC)

Is this appropriate? To have this outrageously long a conversation about (from what I can tell, I don't have time to read through the whole thing) MWI itself and not the article? I'd suggest someone archive it somewhere so the talk page is still readable. Cheers, General Epitaph (talk) 04:33, 13 August 2008 (UTC)

Probably not, feel free to archive away. Obviously people will continue to believe this silliness indefinitely, even when its proved QM is non-linear and some sort of wavefunction collapse does occur. Someone is sure to invent an even more nutty variant of MWI that claims to still work. I expect we'll never be rid of this mad theory. I just think this article should make it clear that it takes very little modification of QM to avoid the whole many-worlds mess, and there is good reason to believe those modifications are required, and they will improve quantum theory in other ways. But it seems to me this topic has been hijacked by people who have a distorted view of reality and who ignore the gaping holes and huge (and unlikely) assumptions upon which MWI hinges. I mean, I appreciate being able to come to this Wikipedia and read all this info on MWI, so thanks to all those who have contributed to this article. Its more than my lazy ass has done. But... unfortunately... I swear, this article, in terms of what sane quantum physicists really believe, vastly overestimates the mainstreaminess of MWI - and its chances of holding up under what will probably be a reasonably imminent onslaught of evidence against it. MWI adherents should prepare to be rather disappointed in coming years. Oh well, we will see. IbleSnover (talk) 05:46, 13 August 2008 (UTC)

I vote for archive, since we are only racapitulating points covered in the article. --Michael C. Price ^talk 08:01, 13 August 2008 (UTC)

Interesting. Well, as bits-quanta are cheap, and readers will read as they please or not, and the discussion page is "unoffical" to the main article, I'd never archive away a thing, myself, as it shows more magnified, the article's introduction to the debate of the math-real vs cosmic-real versus cosmic-unreal debate. It (MWI), is as good an idea, in reality, as the concept of luminiferous aether or general relativity, in potential, that for luminiferous aether crescendoed in a now-we-can-test-it event with Michaelson-Morely, leading to knowledge, and GR finally absorbed all concepts of the preceeding decades in the most encompassing, observeable, precisely verified framework. LE remains classical, and important ... if anything to remember what not to forget in analysis and pedagogy, whether to-be falsified or to-be verified, in the ultimate analysis. And I found out my hunch about branching Hilbert Space clouds has its precedent from "Dr. David Deutsch", here in discussion, so I learned something good and useful, from this very thread, even if I have archived it locally on my own HDD, but who can see that other than who I speak about it with, directly. I see it in the article now, but must have been eating a donought that section. Wiki is more powerful with an official front page and background discussions intact, both. As good as "upstairs downstairs". Like teachers and students in college or school, both indispensible and useful to status quo and dissent, both; when coherent, classified, and topically networked. LoneRubberDragon (talk) 06:54, 15 August 2008 (UTC)

http://en.wikipedia.org/wiki/Upstairs_Downstairs

And I would not call consiousness affecting reality a nutter-idea, because I reckon that human-consciousness, computers with senses, and amorphous ceramics all collapse wavefunctions, but in different ways, according to their structural entanglement and measurement characteristics. Even if, perhaps, Wheeler and Wigner may have overstated consciousness's centrality to reality, they were on to something good. I would analogously liken it to human-consciousness as light through a nonlinear optics thick film hologram, computers with senses as light through nonlinear optics diffraction gratings, and amorphous ceramics as light through nonlinear optics frosted glass. Each one has its affects on wavefunction collapses, and each according to the structure of the measurement apparatus structure. And consciousness really remains special, insofar that it has masssive coherently organized organizational channels, akin to "parallel-information=processing-loops", which itself is equivalent to "parallel=entangled-probability=measurement-network=structure". While a block of amorphous ceramic is just that, amorphous, so it processes wavefuncction in unstructured amorphous ways. LoneRubberDragon (talk) 06:54, 15 August 2008 (UTC)

Another comment I might add. If one considers that the macroscale universe is predominantly formed in classical forms, with exceedingly large masses, and with exceedingly small wavefunctions, overall, then one can assume that the largest volumes of multiple universes of the Hilbert-space exist in practically the same macrostate. If we also assume that there is a minor statistically signifignat amount of systematic crosstalk effects between all similar universes, instead of the perfectly 0.0-bar crosstalk defined for conventional MWI, then one may see that the classical universe is the product of all virtually identical MWI, with a nearly perfect unity of their statistically evolved macro-forms after billions of years of crosstalk mixing. Now consciousness (machine or human) is a different type of effect on the evolution of the macro-universe in that it can amplify a single quantum measurement up to macroscales, branching the universe strongly, especially on the thin gravitational skin of the active earth. Now if one were to find a lagrangian point in the solar system for a set of solar system bodies, for say an asteroid set, where consciousness of a process (a digital machine with quantum measurer and rockets under measurement control will suffice), can alter the path of the astronomical objects in concert to the quantum level magnified, for one distant configuration or another distant configuration, both being different from the natural solar system, controlling at the lagrangian points, which will, over time, exponentially changes the character of the solar system, from the purely passive statistical macroscopically classical orbits that would have invariably occured without any presence of humans, to the orbits that are grossly and systematically different because of the consciously machine-amplified effects on the macroscale bodies and thus the solar system as a whole system in infinite Hilbert-Branches. Now if 99.9-bar-X% of the natural solar systems go one way, and we have taken one small set of classical universes to go another two potential very different ways, are there now statistically different measurements of QP through to gravity, due to the influence of an active amplification process of a machine with a quantum measurement being magnified to move an asteroid one way or another, both away from the natural, with their accompanying solar system configuration differences. If the lagrangian points are all selected very carefully to even chain double bodies, and lagrangian control points, so that kinetic energy and macroscopic differences can be amplified to their greatest solar system effects, then one may observe irregularities in orbits through to quantum physics effects, altered from the natural-solar-system-evolution-without-human-consciousness, to the unnatural-solar-system-quantum-altered-by-human-consciousness states. Its one testable hypothesis on a strong scale of influences, and has the greatest effects observeable, if the solar system can be greatly affected with such chained "pinball" chain reaction alteration of the solar system from its, until now, virtually prestine untouched by human state. So this provides one testable method for MWI avenues, or puts upper limits on all of the amounts of crosstalks allowed in MWI that are part of the experiment, and what kinds of forces they belong to, for the observed effects between the hidden MWI's of the natural passive unconscious solar system, to the consciously affected one way or another solar system. LoneRubberDragon (talk) 11:06, 25 August 2008 (UTC)

Some additional comments I can make, are that the solar system is basically evolutionarily pristine, limited by solar system probes, some probe to comet and asteroid landings and impacts, and military experiments with asteroid / comet orbits. They are all likely only 50 years of selected and slight orbital effects on the current solar system's 99.9-bar-X% of currently natural states in Hilbert-Space, that have not evolved to exponentially different states. If several asteroids are selected, and displaced one way or the other with a delicate saddle set of kinetic energy paths, and its orbital effects are calculated out precisely for before and after, then one can compare the new orbits with the old for all solar system bodies, and also measure along the places where the asteroids would have gone with branching probes to follow the now empty spots in space where the asteroids would have been otherwise with manouevering, to see if a streaming quantum experiment and space measurement along the empty paths would register in time along the path to increase the SNR ratio of potential anomolies when the 99.9-bar-X% asteroid pass through their now empty spot in this space where the branch probes are now located. All of the asteroids will be aletered by the nonlinear-unnatural-consciousness effects on the natural evolution of the 99.9-bar-X% natural solar systems, that no longer exist, on the one measurement plane we inhabit collectively from earth. Likewise, to reiterate, no effects would indicate that the 99.9-bar-X% of the solar systems have no crosstalk effects en-masse in Hilbert-Space, approaching zero crosstalk. The good thing is that large masses and critical paths can be evolved with minor power control, to grossly alter the solar system to the maximum difference of possible mass distributions, in two sets of very different final solar system configurations, in comparison to the very different natural solar system without conscious effects on orbits. LoneRubberDragon (talk) 11:34, 25 August 2008 (UTC)

LoneRubberDragon, please be aware that the less you write the more likely you are get a response -- paragraphs would help as well! This is just too dense and unstructured for easy reading. Sorry. --Michael C. Price ^talk 17:57, 25 August 2008 (UTC)

Sorry, as it cannot be helped much at that level, even if it does keep it beyond simple AI bot and basic comprehension. Four paragraphs of text seemed adequate, unless you're asking for *more* paragraphs of smaller size. Plus to reduce the density would make the paragraphs *longer* as a fixed information content product of less information in more words. You can always pick out things to formulate refinement questions for yourself to me, from the corpus of the informal paragraphs. LoneRubberDragon (talk) 11:02, 29 August 2008 (UTC)

The last paragraphs describe a way to see if the crosstalk between amplified divergence universes (on a massive solar system scale) is proveable as virtually zero in practical measurements, in the massive/bulk divergence of solar system masses with continuing broadcasts and measurements on the asteroid(s) being probe-controlled, and on the paths where the asteroid(s) would have gone with measurement-probes only, on those other-paths. It is interesting to consider, too, because large masses are involved, in pretty natural states, to see if even gravity ghosts could be detected on the divergent paths, as part of the preceeding conversations, considers the relationship of gravity to the aspect of causing quantum measurements. LoneRubberDragon (talk) 11:02, 29 August 2008 (UTC)

Another interesting aspect of the experiment, if macroscale "consciousness"/great-amplification divergence crosstalk can be observed, then perhaps gravity-time-space curvature and quantum-measurement are potentially proveably two aspects of one unified thing. As most of the matter of the universe has little quantum critical and amplified effects on the cosmic scale, where matter, space, and gravity are the natural dominant forces of the macroscale cosmos. Consciousness is small scale, in very little of the universe, but it has the capacity these days on earth, to greatly amplify small things into the cosmic scale. If MWI has a real aspect, detectable in some macroscale crosstalk criteria, but it is all so close to being quantum cosmic scale unitary-macroscopic-classical in virtually all cosmic material evolution, because consciousness/great-amplification tends to have little cosmic scale effects, until today. Such MWI crosstalk may be a coherent self-forming aspect of the universe, as the measurement-gravity-time-space concept may rule most of the cosmos over consciousness-amplification-measurement effects. A human experiment to make cosmic level changes, along with an MWI measureable crosstalk, even if minute, opens the avenue to investigate the characterization of the relationship of MWI-mweasurement-gravity-time-space-consciousness differentials on the cosmos. LoneRubberDragon (talk) 11:31, 29 August 2008 (UTC)

Additionally, a low mass part of the experiment can even be tested on earth, if one setup a general calibrated characterized broad spectrum radiator, on a very long three way track, where the radiator can go into one of the two branches, based on a quantum measurement, to enter one of two thick lead faraday cages on the ends of the tracks, and measure both cages, one cage being the empty faraday cage. If the empty faraday cage has ANY signals not present in a "control" third faraday cage equidistant from the other two cages, then one has the capacity to show that an earth frame of reference MWI crosstalk may be true, as some of the branched universes are bleeding a crosstalk signal into this universe. If the second empty faraday cage matches the "control" third faraday cage, as only background noise, then MWI is still in that strange potentially useful mathematical tool, but hard-to-believe-otherwise googles-universe status in a criteria-based test with *zero* macroscale crosstalk of signals traveling between universes, even though "on the same relative inertial plane of existence", for all those googles of universes. It is also good, in that, if the radiators are periodic, then long term FFT fourier transforms can be performed, to *very* carefully measure for a frequency peak of MWI crosstalk in EM, particle, or quantum effects, in a contunuous-streaming measurement, in as many dimensions of signals possible. A kind of an earth based "MWI no-macroscopic-communications-crosstalk theorem" characterization, one way or the other, through definitive crosstalk tests, or an interesting transformation of MWI Schrodinger's Cat on a large scale. LoneRubberDragon (talk) 11:02, 29 August 2008 (UTC)

Another similar test, is to have a photon passing through a half silvered mirror, directed at two faraday cages with two radiators that are rapidly actuated on by a photon, and a control cage with no radiator. Where the immediate former setup measures slow or steady state crosstalk terms, if any, this one measures transients, in that if the this-universe radiator that didn't get a photon shows any rapidly decaying radiation-response, it shows a transient MWI crosstalk from other parallel branched universes. LoneRubberDragon (talk) 15:16, 29 August 2008 (UTC)

Likely, all these tests would show no crosstalk in a classical measurement sense (bad for MWI in the ways previously discussed), showing rapid measurement collapse of the whole universe with every measurement into perfectly isolated but in the test context, utterly un-inspectable universes. But QP can be strange, and it would be interesting to find an extant experiment that has tested some of these MWI crosstalk check tests, to show that the *macroscope-universe* has either exactly zero MWI crosstalk, or some measureable MWI crosstalk transient, or MWI crosstalk steady state. I've not literally seen such an article testing that, yet, nor seen one off hand in the Wiki references, or web, maybe I missed a key link or book. LoneRubberDragon (talk) 15:16, 29 August 2008 (UTC)

I have nothing much to add to this thread, right now, without additional more-specific clarification-questions, if you would like me to expand the harder to read parts of the, admittedly, conversation informal writing style of mine. I will grant you ahead of time, it is unverified or theoretical content outside of Wheeler, Wigner, Chalmers, Quantum-mind/consciousness, et cetera articles on Wiki and on the web, being theoretical considerations, for sure. LoneRubberDragon (talk) 03:30, 29 August 2008 (UTC)

There are more things in heaven and earth, Horatio, Than are dreamt of in your philosophy." WILLIAM SHAKESPEARE / Hamlet Act 1. Scene V abt. 1601

No better words sum up Hugh Everett't M-Ws.

There are more things in heaven and earth, Horatio, Than are dreamt of in your philosophy." WILLIAM SHAKESPEARE / Hamlet Act 1. Scene V abt. 1601 —Preceding unsigned comment added by 66.229.53.158 (talk) 19:02, 1 January 2009 (UTC)