Talk:Many-worlds interpretation/Archive 1

message: The article currently says:
:However, many physicists dislike the implication that there are an infinite number of non-observable alternate universes, on the basis of Occam's Razor. (Note that that both sides claim to be using Occam's Razor, but are applying it to different things.)
I don't think that this objection should be presented as a valid alternative viewpoint because, as far as I can tell, it's untenable. Consider the following two explanations for the lights we see in the night sky:
# The Universe is billions of light years across at least (possibly much larger), and contains (at least) billions of galaxies, each with billions of stars, each containing something like 10^60 fermions and untold numbers of bosons. The photons we observe were produced by all that stuff over a period of billions of years.
# The Universe is a few light years in diameter, with the solar system at the center, and at the edge are machines which produce the photons that we see.
The second explanation is just as consistent with observations as the first, and it's far more "economical in its use of natural resources," so to speak. But it's absurd to argue that Occam's razor favors it over the first explanation because it has "fewer entities." This appears to be the sort of argument that the "many physicists" referred to above are making. If it is, then they're wrong, and the description should reflect that.
If there are no objections within a week or two I'll rewrite the paragraph.
-- BenRG 05:05, 20 Sep 2003 (UTC)
replies: text: Actually (2) doesn't fit observations at all, as it would clearly not lead to differing parallax measurements. Nor can I understand why one would claim that an infinity of invisible unknown seemingly complex machines has "fewer entities" than a system that can be summed up as "the universe is made up of many stars similar to ours". Personally I think this is a crappy example. Likewise, any attempt to wiggle out of the problem that MWI by claiming Occam doesn't apply is likewise unjustified. Everett never offered a mechanism by which "you" only see the histories down one path, which makes the wavefunction collapse re-appear IMHO. Nor does there seem to be any reason why two people would agree on the past, considering re-merging histories (the relative state of two people with differing distant pasts would seem to be degenerate). Later authors have added their take on this, but none of them seem particularily convincing either. So in the end MWI "hides" wavefunction collapse in an infinite number of unseen devices, and applying Occam seems perfectly relivant and nessesary. Maury 15:19, 19 Jun 2005 (UTC)
thread_title: Occam's razor

message: Could we leave Schrodinger's cat out of this one? Or at least combine Schrodinger's cat with the next "presidential election" example, which maybe we could more meaningfully rework as "Dick Cheney's heart" (he does have doesn't he?) where there is a pacemaker sensitive to gamma radiation?  CSTAR 15:15, 15 Jul 2004 (UTC)
thread_title:  Schrodinger's cat 

message: Are there any resources on WP or WikiBooks that will help me figure out the nasty math in the "simple example"? I know what a Hilbert Space is, what bra and ket vectors are, etc... but do we have "intro to quantum mechanics" or something? (probably belongs in WikiBooks rather than here...) and if so could we link to it? (And if not could we start it? :-]) Glenn Willen (Talk)  21:40, 4 Aug 2004 (UTC)
replies: text: Well you can start reading quantum mechanics.  Now this article on MWI has a wide range in what it requires. Some of it is at the graduate-level physics course, so don't be discouraged if you're not at that level.  Hopefully, you can get something right away from the beginning.  Feedback is appreciated!! CSTAR 21:44, 4 Aug 2004 (UTC)
thread_title:  Nasty math 

message: Many worlds is quite different from Possible worlds.  CSTAR 23:30, 4 Aug 2004 (UTC)
replies: text: I don't object to putting a link to holomovement; but discussing this in the introductory section to the article is totally misleading. CSTAR 23:45, 4 Aug 2004 (UTC)
replies: text: Allright we got this one solved :-) Now open your mind slowly and see ! If you were to touch holomovement Togo 23:51, 4 Aug 2004 (UTC)
replies: text: By the way I am still confident that the possible worlds and the multiple worlds are differnt views of the same issue. After all As you go down your path you may be producing many worlds but they are only so long possible and you stay united with your consciousness. From what I've read about Leibnitz thats what he was visualizing too! Togo 22:23, 5 Aug 2004 (UTC)
replies: text:  Not surprisingly, we don't agree on this either :(  But we probably do agree that the difference between possible worlds and many worlds needs to be elucidated more than is done in the (generally quite good) article on possible worlds. I intend to get to that sometime soon. That article does correctly point out that possible worlds are used in models of modal logic, but does not really explain at any length what a model of modal logic is. (Fortunately, this isn't too hard).  A possible world is essentially a valuation of all atomic assertions in a specific formal language that allows for "modal" operators. Possible worlds do not have an intrinsic of branching, which is one of the characteristics of many worlds.  The real difference between the two is that the notion of entanglement or relative state plays no role in possible worlds.  We disagree, but hopefully we're not at each other's throats!!  I do agree that Bohm (who seems to be a hero of yours) is an interesting "character".  CSTAR 22:37, 5 Aug 2004 (UTC)

text: The two are by no means identical, but they are at least somewhat related. I've just changed some self-contradictory wording in the article on this point. Ben Finn 20:29, 11 May 2006 (UTC)
thread_title:  Possible worlds 

message: I removed this for now, although it should go back in somewhere towards the top of the article after "as simple example" and before the mathematics of reduced state.  Nevertheless, it should be reworked, because perhaps it tries to deal with too many issues at once. (The cat, the radioctive emission, the observer and the rest of the universe). CSTAR 21:56, 5 Aug 2004 (UTC)
thread_title:  Schrodinger's cat 

message: Is the article about the relative-states formalism or the many-worlds interpretation?  The article claims they're different and that it's bad to confuse them, then seems to go off and talk about relative states (only?).  Perhaps relative states formalism should have a separate article? --Andrew 07:03, Dec 2, 2004 (UTC)
:: They're really the same; that was the point of the mathematics that follows.  Doesn't the article say they are the same right at the top? I wasn't aware the article said they're different somewhere else, although that statement may be in some legacy paragraph; who knows, I'll have a look (although later my connection is very slow now).
:: I also don't like the annotation on the graphic.  It refers to decision; QM has nothing to do with decisions by anybody. Such language seems to suggest there is a connection between consciuousness and QM and I think I am in good company when I assert there isn't.  I will make a new graphic to replace it. CSTAR 14:41, 2 Dec 2004 (UTC)
thread_title:  Relative states 

message: I think the section on fictional works could be a little less of an attack to science fiction. Calling fictional stories "misleading" and "deficient" because they don't conform to the details of quantum theory is asking too much from fiction. The stories are scientifically inaccurate or too fanciful, but you will be misled or deficiently informed only if you confuse fiction with fact. I was the one who added Borges, BTW. I've never implied that Borges got the idea of the MWI before the scientists, only that the literary concept and the scientific theory were similar, on the surface. --Pablo D. Flores 01:10, 16 Jan 2005 (UTC)
replies: text: I'm aware of that and the point I was trying to make was that Borges' story (as do others) are not illustrations of MWI because they don't involve superposition of states. I ceratinly didn't intend it to be an attack on Borges!CSTAR 03:52, 16 Jan 2005 (UTC)
thread_title: Fiction

message: The graphic of splitting is very misleading, not because there is an infinite branching tree, but because the origin of the tree has nothing to do (at least in any commonly accepted interpretation) with decisions being made.  his graphic belongs maybe in an article decision trees. I will be happy to compose a graphic of an infinite btanching tree but without reference to "decisions".CSTAR 04:55, 5 Feb 2005 (UTC)
thread_title:  Misleading graphic 

message: Consider a variation of the Schroedinger's Cat experiment where you only wait long enough for a 1/3 chance of the cat being dead.  There are only two possible outcomes for the experiment, so when you open the box, the universe only splits two ways, and it seems to me that that makes for a 50% chance that you'll be in the branch with the dead cat.  How does a probability of 1/3 come out of this?  I checked the FAQ linked from the article, and quickly got bogged down in tensor calculus -- and I never had classes in anything more complicated than basic vector calc. --Carnildo 23:15, 17 Mar 2005 (UTC)
replies: text: There is little point you trying to impose this on the article. Please try to edit in a collaborative way.  If you feel the article misses some essential point, please bring it up here. Charles Matthews 20:04, 18 Mar 2005 (UTC)
thread_title:  Non-50% probabilities 

message: Could you please explain this remark which you have seen fit to place in the main article? CSTAR 19:37, 18 Mar 2005 (UTC)
replies: text: In many-worlds, the different copies are correlated, so there isn't that sort of uncertainty in who you're talking to.  Of course you might never receive an answer from someone, since they could disappear in your world - but the possibility of death isn't anything new.
This is not the proper forum for discussing your new ideas regarding MWI, as interesting as they may be. Original research cannot be included in Wikipedia articles, and talk pages should not be used for discussing topics irrelevant to the content of the article. -- Schaefer 17:18, 19 Mar 2005 (UTC)

text: Wrong.  In MWI, you go through both doors.  And since the decisions that split universes are on the quantum level, the result is about a bajillion forks of the universe, in which you go through door A, go through door B, smack face-first into the barrier between the doors, say "to heck with it" and go through door C, remain befuddled with indecision until you starve to death, and many other futures, with the "go through door A"-type and "go through door B"-type futures being the most common. --Carnildo 06:05, 20 Mar 2005 (UTC)
replies: text: It is an issue in philosophy as to whether copies of yourself in other possible worlds can be you or are just copies of you (counterparts). I.e. whether you exist in other possible worlds. David Lewis (the main proponent of the real existence of possible worlds in philosophy) held the latter. Ben Finn 20:32, 11 May 2006 (UTC)
thread_title: "Life is just a bunch of quantum quackery."

message: If I understood this right, every measurement is an interactions which splits the universe into different relative cases. But what determines what case the observer (me, for example) is seeing? In Schrodinger's cat experiment - what determines whether I'm in a universe where the cat died or didn't? The universe "splits", but we still see a single result. What decides which universe we are "in"?
:You're part of the universe, too. You split. One of you sees one thing, another of you sees the other. The model doesn't give any special treatment to observers, and that's half its beauty. But anyway, a Wikipedia talk page isn't the place for this sort of dicussion. This page is for discussing the article, not its subject. If you want more explanation you can e-mail me (my address is on my user page). -- Schaefer 16:06, 24 Jun 2005 (UTC)
replies: text: Well that my friend, is the meat of the issue. No one can give you a "real answer" it's the quest for one that is the objective. DV8 2XL 21:07, 3 November 2005 (UTC)
thread_title:  So why do we see whatever we see? 

message: This part is extremely unfair towards the MWI:
:However, the physicist Asher Peres in his 1993 textbook expresses a great deal of skepticism towards MWI which is shared by many physicists. In fact, he questions whether many worlds is really an "interpretation" at all (particularly in a section with the title Everett's interpretation and other bizarre theories). Indeed, the many-worlds interpretation can be regarded as a purely formal transformation, which adds nothing to the instrumentalist (i.e. statistical) rules of the quantum mechanics. Perhaps more significantly, Peres seems to suggest that positing the existence of an infinite number of non-communicating parallel universes is worse than the problem it is supposed to solve.
:As such, because the interpretation results from an equivalence between two mathematical formalisms, and is considered unfalsifiable (because the multiple parallel universes are non-communicating), critics consider the many-worlds interpretation metaphysical rather than a testable scientific theory. Moreover, notwithstanding the personal opinions or speculation of individual physicists (or indeed even a statistical majority of physicists), subjective polls of "acceptance" such as the above cannot be interpreted as evidence of the correctness or incorrectness of a particular theory; as such, for example, the mere fact that any particular person or percentage of people "accept" the many-worlds interpretation should not be considered evidence of its accuracy.
If we assume that there is a empirically testable difference, then MWI and CI are scientifically valid theories, that are up to be tested against each other.
Or, if we assume that there is no mathematical difference between the MWI and the Copenhagen interpretations, then identical argument can be used to attack CI and support the MWI, or to attack the MWI and support the CI. For example we can replace "critics consider the MWI metaphysical" by "critics consider the CI metaphysical" and an argument of exactly identical validity.
The arguments listed in this section (and in some of the external links) start with completely unjustified supposition than MWI is worse than CI, and use it to prove that MWI is indeed worse than CI. 
The argument that support for a theory does not constitute an "evidence of its accuracy" is also flawed. If, as stated in the argument, the MWI gives exactly the same predictions as theory the CI, and accuracy is defined methamatically/empirically, then it's exactly as accurate as CI. So relative levels of acceptance of the CI and the MWI are completely moot, as accepting accuracy of either implies accepting accuracy of the other. Taw 21:36, 23 July 2005 (UTC)
replies: text:  One of the arguments you refer to this is Asher Peres' argument. I just made note of it as objectively as possible. David Deutsch has arguments in favor of it, however, I didn't put those in since the article spends a lot of time discussing the theory. The other material you quoted was put in by somebody else who insisted it ws too biaed in favor of MWI. --CSTAR 23:58, 23 July 2005 (UTC)

text: I have reworded some text that had been reverted.  The conclusion now reads However others note that science is a group activity (e.g. peer review) and that polls that indicate shifts in belief of scientists can't be dismissed lightly.  Remember no one is claiming that many worlds is true just because of poll results, but the numbers do have a bearing on its credibility.  Indeed amongst scientists it quite relevant; how often is a theory dismissed by a scientist with the phrase "Oh no one takes that seriously!"--Michael C Price 17:35, 17 May 2006 (UTC)
replies: text:  [Edit conflict] I reworded your rewording. I have specific reasons (see edit summary) but I can explain the change here in more detail if you think it is necessary.--CSTAR 17:42, 17 May 2006 (UTC)
replies: text:  No need to explain, it looks OK.  --Michael C Price 18:09, 17 May 2006 (UTC)
thread_title:  Acceptance of the many-worlds interpretation 

message: There should be some mention, a tie-in & link if you will, with Leibnitz's philosophical stance that we are currently in the best of all possible worlds, and, more in line with the theory, that all possible universes exist in a pyramid below our current universe of every different possible permutation on into infinity of alternate past possibilities, but that our 'current' one is the top of this pyramid. Not exactly the same as MWI theory, as each universe is its own 'top of the pyramid', and Leibnitz has a much more 'hard deterministic' rather than random quantum effect, view-point. Though the similarity remains nonetheless. Nagelfar 21:10, 13 November 2005 (UTC)
replies: text: See Possible worlds and multiverse.--CSTAR 21:23, 13 November 2005 (UTC)
replies: text: Do you mean to insinuate that the reference would be more suited at one of those articles? I visually scanned and then searched 'Leibnitz' with my browser and found no mention of him either place. What my intention for aiming a possible reference to this particular article was a linking of the exact concept, i.e. bifurcation of a separate cohesive universe(s) from a single universe. Which implies more than possiblity of or alternate stand alone 'universes.' Being that this is so particular an idea, one metaphysic the other quantum mechanic, I thought it fitting enough here. Nagelfar 01:56, 14 November 2005 (UTC)
replies: text:  MWI is discussed in this article is a very specific formulation involving quantum superpositions of alternate histories. Though it does fit better into the  multiverse article, the Leibnizian idea may deserve an article in its own right. It is sufficiently different from the concept discussed here, that other than a brief mention amd a link, I don't thik it should not be put here.--CSTAR 05:18, 14 November 2005 (UTC)
replies: text:  A link is all I meant, to Monadism and a brief discription, though it may be difficult due to the complexity of the concept, it bears similarity here particularly, was all I had meant. Nagelfar 22:08, 14 November 2005 (UTC)

text: *nevertheless the link should go in Possible worlds or Modal realism as it is more related to those than to MWI. DV8 2XL 22:48, 14 November 2005 (UTC)
replies: text: Not necessarily. It depends on if you mean "world" as whole 'universe/multiverse' or not (the original etymology, "ver-alt", means 'through time/history', or "time worn progression"). The terminology contradicts if you think of an isolated world in MWI, but at the same time the concept is the same for an individual 'world' within the whole uni/multiverse under MWI. For example, if in MWI every particle must exist in every possible combination by means of every different possible world/universe, then any individual universe must have its particular arrangement to not duplicate any other universe, so that the particles can be in every potential position and in every combination / permutation possible. Putting any individual universe in the most perfect position it is capable of having as to not repeat any other; making it 'the best of all possible "permutations" or worlds', for the very fact that, it is one instance necessary to the completion of every particle being in every possible place at every given time. Maybe associating it to his concept of "Monadism" would be incorrect, I don't mean to misdirect my point. His assertion that this is "the best all of worlds" seems not to be directly related (His Monadism may relate to Chaos Theory though this is not the place for such discussion) Nagelfar 23:53, 18 November 2005 (UTC)
thread_title:  Similarity to Leibnitz's 
Monadism
 'best of all possible worlds' 

message: I was wondering, what new things can MWI tell us about the world and universe we live in? I am comvinced that CI tells us things that noone else could say (when it was formed), but I fail to see what MWI can contribute with. To me, it sounds too much like a religious argument.
: I think there's no known alternative to the many-worlds interpretation if you are looking for an intuitive and physical understanding of what's going on in quantum superpositions and entangled states. In addition, the problem of the measurement in quantum mechanics is easily solved without postulating any unknown and unphysical mechanism as the collapse of the wave packet (see the Copenhagen interpretation -- before the collapse it also involves quantum superpositions) or the consistent-history requirement (see consistent histories) or some backwards-in-time information flow (see the transactional interpretation). All other known interpretations need additional axioms. Thus, according to the principle of Occam's razor I consider the many-worlds interpretation the best one. By the many-worlds interpretation, the universe grows in a similar way as it did when scientists realized that the stars are just distant suns. This may look like an additional assumption, but in both cases it is a consequence of a better theory requiring fewer assumptions than the old one. --DenisDiderot 18:29, 21 December 2005 (UTC)
thread_title:  What good does it do? 

message: I'm no physicists but this smells like pseudo-science to me. Why is it called an "interpretation" and not a hypothesis? Could it be that if it were to be called a hypothesis, then it would need to be either falsifiable or admitedly an unscientific belief? Neurodivergent 16:19, 21 December 2005 (UTC)
replies: text: Everett's Many-worlds interpretation doesn't add any new hypothesis to quantum mechanics, it even manages to do away with two of the axioms (assumptions) of the standard formulation of quantum mechanics, see the section about axiomatics in the article. The concept of quantum superpositions is common to all formulations of quantum mechanics, though they are usually argued away as something purely mathematical. But physical understanding of the EPR paradox and entangled states requires acknowledging them as something real and physical, and that's exactly what the Many-worlds interpretation does, no more, no less. If there are real quantum superpositions, then there's no reason why macroscopic objects shouldn't rest in superpositions of states or even entangled states as well. This is an implication, not an assumption. --DenisDiderot 18:09, 21 December 2005 (UTC)
thread_title:  Pseudo-science? 

message: Excuse me, how does the phrase "taking superposition at face value" used in the intro avoid misconceptions? --CSTAR 15:08, 28 January 2006 (UTC)
replies: text: PS In case there is any doubt, I earlier made the edit which removed the phrase.--15:11, 28 January 2006 (UTC)

text: Fine. But please get rid of or replace "at face value" and be more specific. --CSTAR 22:43, 28 January 2006 (UTC)
thread_title:  Irrelevent (IMO) phrase 

message: Hey guys.  I tried to join in and pick sides in the argument going on above, and simply couldn't pick up the thread.  So I won't.
But I will say this: this article has problems.  The very first sentence, many worlds considers superposition a real phenomenon instead of a mathematical construct, is perfectly meaningless at best, misleading at worst.  Perfectly meaningless because the terms "real phenomenon" and "mathematical construct" are pretty useless (though I would argue that they actually apply quite nicely to virtual particles).  It's misleading because superposition of states has observable consequences, it is the foundation of all quantum mechanics.  Any flavor of quantum mechanics worth its spit treats superpositions as real phenomena, where "real phenomenon" means something with measurable  predictions.
Here's my suggestion for an intro:
:In physics, the many worlds interpretation is a formalism for doing quantum mechanics in which one views the space of states of outcomes of the measurement of a system as a subspace of the space of entangled states of the system and the measurement apparatus together.  The advantage of this is that states always evolve unitarily; there is no nonunitary collapse of the wavefunction as in the Copenhagen interpretation.  It is called "many worlds" because it involves viewing the outcome state as being in a space which includes other possible outcomes of the system entangled with corresponding states of the observer, thus viewing the observer as being in one world of many, one for each of the possible outcomes.
OK, that was pretty hard to write, and I don't really like the outcome, and don't want to suggest swapping it in.  But this bit about superposition being a "real phenomenon" leaves a bad taste in my mouth.  I don't like the mentioning of a "multiverse" in the intro either.  I haven't followed that link, but I have a deep horror that it is going to take me to a D&D or Marvel comics page. -lethe talk [ +] 02:14, 6 February 2006 (UTC)
replies: text: The Many-worlds interpretation considers the superposition components to be literally present (in different worlds, universes etc.), which is not the case in other interpretations. Don't you think that therefore there is a difference in how superposition is treated in the interpretations? Shouldn't we stress this? --DenisDiderot 08:57, 6 February 2006 (UTC)
replies: text: literally present?  I don't know what that phrase means, but I can't think of any sense in which the Copenhagen thinks superpositions are not present.  I definitely think we should not stress this. -lethe talk [ +] 09:30, 6 February 2006 (UTC)

text: Why do you think the words "many worlds", "multiverse", "parallel universes" are used if the superposition components are not considered to be literally present? Why are they said to exist then? The Copenhagen interpretation definitely denies the existence of many worlds, since they are considered to be somehow cut off by the wavefunction collapse. Above, you are talking about a mathematical space, but the universe is a real space. --DenisDiderot 09:41, 6 February 2006 (UTC)
replies: text: As far as I know, parallel universes and multiverses are only used in pop sci books.  So you ask why do I think they are used, and the answer is, I think they are not used.  For your second question, Copenhagen has unitary evolution and linear superpositions, which can be interrupted by collapse, but that doesn't mean they're not there.  Of course they are there.  Once again, linear superposition is the foundation of all QM.  Any theory which doesn't have superposition isn't QM.  -lethe talk [ +] 09:49, 6 February 2006 (UTC)

text: Hmm. What about the name of the article (many-worlds) then? Is it a misnomer? What do you think is literally present before the measurement? Please don't answer by "Shut up and calculate". The many-worlds interpretation is capable of providing a perfectly consistent real picture of what's going on. You may censor yourself in thinking about reality, but aren't you nevertheless interested in it? --DenisDiderot 12:46, 6 February 2006 (UTC)
replies: text: First, yes, "many-worlds" isn't a great name.  Everett himself never called it that.  I don't know if I would call it a misnomer, but it does tend to make people believe that it is a theory about multiverses, when in fact it is a theory about subspace and projections.  But we can't change the name.  Second, why would I answer "shut up and calculate"?  That's not an interpretation of quantum mechanics.  As far as I know, that's a phrase used by David Griffiths to suggest that one doesn't need an interpretation to do quantum mechanics.  That's not relevant here, so let's leave it.  Third, I can't answer what is "literally there", because I don't know what that phrase means.  Quantum mechanics is about systems (things you can measure) which act a certain way and are modelled a certain way.  I can tell you what measurements in QM look like, and I can tell you what the models look like.  You take your pick whether you consider one or both of those things to be "literally there".  Finally, why are you suggesting that I censor myself?  Because I won't answer questions about what is "literally there"?  Let's not get melodramatic. -lethe talk [ +] 13:09, 6 February 2006 (UTC)

text: Everett's theory was a relative state theory. And yes why are we discusing existence in a physics article? As I said earlier, that's ontology a perfectly legitimate endeavor (but not in this article), not physics.--CSTAR 15:06, 6 February 2006 (UTC)
replies: text: I agree totally.  Denis seems bent on making this about philosophy.  Interpretations of quantum mechanics are not a purely philosophical question (although they have an admittedly philosophical flavor).  What's "literally there" or what's "really true" have no place in this article.  By saying so, I'm not espousing a "shut-up and calculate" stance.  In summary, QM is about calculating matrix elements, interpretations is about deciding what happens in your model when measurements occur, and philosophy is about deciding "what's really there".  Only the middle one has a place in this article, therefore the claim that "many worlds treats superpositions as literally there" simply has to go.  I will now excise. -lethe talk [ +] 15:17, 6 February 2006 (UTC)

text: I agree. Generally, I get suspicious when Occam's razor is invoked. Particularly in this case, where though indeed MWI has fewer axioms, it proposes a universe with more things in it (many words versus many worlds as I believe Max Tegmark puts it). Is this really Occam's razor anyway?--CSTAR 18:02, 6 February 2006 (UTC)
replies: text: I vanished it. And no I don't think Occam applies here anyway, and in general I think it is high time that it is returned to the study of philosophy from whence it came; Nature has only a passing familiarity with the concept. --DV8 2XL 18:46, 6 February 2006 (UTC)

text: See my answer above. --DV8 2XL 18:48, 6 February 2006 (UTC)
thread_title:  the intro 

message: I am quite new to Wiki so pardon me if I make any breach of protocols by writing here. That said, I do have a PhD in quantum theory, so not a crank.
From reading the excellent article I am starting to believe that Everett has been discredited (by me, at least!). Like many others, I was familiar with the popular (and I might say sensationalist) descriptions of MWI which talk about multiple universes co-existing, which struck me as patent nonsense. Having read the article, it now seems to me that pehaps Everett had no such thing in mind.
Everett is right that there is, according to quantum theory, a single many-body wave-function that covers everything in the universe. Most of the examples and calculations found in text books or popular science books adopt the single-particle approximation, in which one particle is assumed to have an associated wave-function; but it is just that- an approximation, one in which the effect of the rest of the universe on the particle is treated as a potential field in the Hamiltonian. For non-physicists, what this means is that all of the other particles in the universe are replaced, for the purposes of trying to make the calculations simple, by their averaged-out background effect on the particle being studied (if anyone is interested I can provide a better explanation). So there is a tendency to talk about the collape of the single-particle wavefuntion as if it were a real effect, whereas it is only an approximation. What 'really' happens in a measurement is that the particle whose properties are being measured is intracting in a complex quantum mechanical way with the zillions of other particles that make up the measuring device. So when we talk about the collapse of the wavpacket, what we should really think is as follows: the particle was in a state in which the single-particle approximation could be sensibly applied, and in which we could view the particle as having its own wave-function; now there is'a measurement' which means that the degree of interaction between the particle and the rest of the measuring device is such that the single-particle approximation no longer applies; and now, after the measurement, the interaction has simplified and we can go back to a single particle approximation, but surprise surprise the wavefunction has changed. All clear so far??
Next, let's suppose that there is a wave-function which at a given instant describes the whole of the universe. One property of wave functions is that they can be expressed as linear expansions of other functions, each of which could also be a legitimate wave function. This means that it is technically correct to say that the quantum mechanical state of the universe (ie its wavefunction), is methematically equivalent to a super-imposition of other possible states of the universe (each of which would be multiplied by an expansion co-efficient), but that is quite different from saying that there are multiple universes each existing simultaneously. Let me see if I can give an analogy to illustrate this...
...well, a quick analogy (which is not exactly water-tight but nonetheless illustrates the issues) imagine that I put 1000 pounds into a bank account, and withdraw 999 pounds. As a result I have one pound. Mathematically this is indistinguishable, in terms of the overall result, from putting 1,000,000 pounds into my account and withdrawing 999,999. Both patterns of withdrawal and deposit yield the same overall 'state' of my bank account. More generally, in the same way that the number one can be expressed as the super-imposition of 1000 and -999, or as the super-imposition of 1,000,000 and -999,999, it can also be represented as the super-imposition of many other combinations of numbers. Taking the analogy with MWI, a bank balance of one pound could be treated as a sum over all possible states of my bank balance each with an appropriate expansion coefficient. While this would be mathematically correct, it does not mean that there are infinitely many simultaneous states of my bank balance each with its own independent existence. Given this, people need to be wary of attributing a physical significance the the individual multiple states considered by Everett.
Taking this as a starting off point, does anybody fancy trading ideas about how to derive a more sensible interetation of MWI?
---
Hi! generally add items to the bottom or people won't see them. And put four ~s at the end of your posts so people know where your post ends etc. Stephen B Streater 19:13, 25 March 2006 (UTC)
thread_title: Who would like to help develop an alternative view?

message: There are numerous problems with the recent changes to this article which I reverted and were re-reverted. I am sorry to say, the following added paragraphs are simply wrong (at best) or meaningless:
: Both sides in physics, are attempting to model (mathematically) the physical world and the various conservation laws fundamental to science, and the difficulty deals with what are known as singularities or mathematimatical discontinuities in the calculus equations (e.g. dividing by a quantity which goes to zero at some point in time) involving the law of conservation of energy taught in secondary school physics.
 	
:Certain facets of the necessary calculus lead to the Schrödinger equation (in all schools of interpretation) which involves the definition of energy (including matter, by Einstein's famous E=mC^2) in quantum system, and therefore it's conservation. It describes the time-dependence of quantum mechanical systems. It is of central importance to the theory of quantum mechanics, playing a role analogous to Newton's second law in classical mechanics.
MWI has nothing to do with singularities or with Einstein's E=mc^2. Quite frankly this sounds like gibberish. Unless something sensible replaces it soon, it should be reverted.--CSTAR 06:20, 11 May 2006 (UTC)
replies: text: Other problems with the new text:1. the first line is now a sentence fragment "the many worlds interpretation is how the equations."  2. what does HUP have to do with the measurement difficulties in the Copenhagen interpretation?  Fabartus, I can appreciate that you spent a lot of time on this, but please don't be so belligerent ("YOU DON'T THROW AWAY TWO HOURS of work and expect to avoid a fight CSTAR!!!").  Why don't you make a list of the problems with the current text, post them on the talk page, and suggest your revisions here.  With very long edits, if the new edit is not an improvement, it's a lot easier to revert it than to go through it and decide what should be kept and what should be excised, and then to incorporate the result smoothly into the text.  Therefore, if you're planning a long edit, make sure it's a good edit.  The way to do so is to take it to the talk page. -lethe talk [ +] 07:27, 11 May 2006 (UTC)
thread_title:  Recent edits 

message: If individual claims of Michael are unjustified, they should be deleted or edited sentence by sentence. It's very unpolite and aggressive to just revert the whole edit which does contain some interesting points. --DenisDiderot 09:59, 12 May 2006 (UTC)
replies: text: If you think there are interesting points, then please extract them.  The text is mostly wrong, and mostly badly written.  Restoring the whole text wholesale (including even Wolok's sig) is unacceptable. -lethe talk [ +] 10:01, 12 May 2006 (UTC)

text: Of course I agree with you that we should be tolerant to newbies.  In fact, that's a wikipedia policy (WP:BITE).  However, this does not mean that we have to accept every addition that every newbie (nor well-seasoned editor) wants to make to the article.  If you want to comb through Wolok's edits to find valuable points that could be added to the article, I invite you to do so.  But the text as it stands entails a degradation of the article.  We do not suffer degradations of the encyclopedia for the sake of comfort of newbies who want to flout consensus and process. -lethe talk [ +] 11:03, 12 May 2006 (UTC)
thread_title:  Michael D. Wolok's additions 

message: Ditto Schrödinger's cat -lethe talk + 
This is a paradox par excellence and it's exactly what MWI is about. 
On this matter I disagree with you. -lethe
 
How are we going to have an intelligent discussion when we can't even agree on something so basic as this??? Even Roger Penrose who disagrees with MW accepts this paradox, and admits MW would solves it. It is ridiculous to be arguing something so elementary. 
Michael D. Wolok 02:15, 15 May 2006 (UTC)
thread_title: =================================

message: Well, can you propose a definition of "classical" which allows MWI to be considered a classical theory? 
Yes. "Classical theory" is not my expression. When I first heard the expression "classical theory" I thought it meant "non-relativistic." I have conversed with dozens of PhD physicists who specialize in relativity, quantum mechanics or cosmology. I frequently hear them use the expression "classical theory." I always ask them what they mean, and they all give the exact same answer: a deterministic theory or a theory which is in general accordance with General Relativity. Now I know there is still a problem with quantum gravity and relativity, but that is not a direct assault on relativity. If quantum mechanics implied there was no such thing as quantum gravity, that might be a problem. But the search for quantum gravity is still on. Einstein had many objections to QM, quantum gravity was not one. The MWI answers all Einstein's objections.
Michael D. Wolok 02:33, 15 May 2006 (UTC)
thread_title: =================================

message: "restores causality" causality was never lost in QM (despite the EPR paradox) -lethe talk + 
"Causality" should be changed to "determinism". I think that's what Michael means. 
Michael Price is correct. For some stupid reason I always equate causality with determinism 
Michael D. Wolok 01:20, 15 May 2006 (UTC)
thread_title: =================================

message: FWIW, I'm with Lethe on this one. In general, any big sweeping additions to this article should be discussed here first. Stephen B Streater 17:22, 12 May 2006 (UTC)
thread_title: =================================

message: > The edits in question were just plain wrong. They were not supported, 
I can support every claim I made. I made a few claims that needed minor editing, but that is it. Michael Price understood what I meant.  Nobody asked me to support my claims.  Support for my claims do not belong in the article.  I would think there is near universal acceptance for my claims even from those who don't accept Hugh Everett's Many World's thesis.
Michael D. Wolok 01:08, 15 May 2006 (UTC)
thread_title: =================================

message: Greetings Michael,
I just spent five hours answering all Lethe's objections.
I then did some operation that inadvertantly caused my 
Wikipedia page to go to another website, and lost all my 
work. 
Sometime later this week I will try to rewrite what I 
wrote.
In the meantime, I would appreciate it if Michael Price 
would email me at:           MichaelDWolok@aol.com  
Michael, you might remember that I last emailed you a 
few days before 9/11.
:Aha, I knew I heard from you before....  Good to hear from you again.  I agree with your points about MWI.  We'll get them onto Wiki eventually, I'm sure.  Click on my sig and you should get my newly created user talk page --Michael C Price 09:13, 15 May 2006 (UTC)
replies: text:  What would help you would be some trustworthy independent sources which you can cite. See WP:OR. Stephen B Streater 09:34, 15 May 2006 (UTC)

text: I left some links on your talk page which might help explain how things work here. -lethe talk [ +] 01:18, 15 May 2006 (UTC)
thread_title:  Greetings. 

message: "The Copenhagen interpretation of quantum theory starts from a paradox."  --Heisenberg, Physics and Philosophy, pg. 44.   
Michael D. Wolok 19:25, 17 May 2006 (UTC)
replies: text: My view is that it is not a paradox. How can reality be a paradox? Stephen B Streater 08:25, 17 May 2006 (UTC)

text: "he"?  Where does it say light doesn't take every path?  I've had a quick look at the interpretation section of the PI entry and it seems balanced.--Michael C Price 13:52, 17 May 2006 (UTC)

text: Paradox is described here. The double slit experiment only appears to be a paradox to people with sub-standard intuition based on incorrect theories of physics. 
I guess that would include Heisenberg!!!! "The Copenhagen interpretation of quantum theory starts from a paradox." --Heisenberg, Physics and Philosophy, pg. 44.  Why don't you 
read the definition of PARADOX given by your link!!!!  
Einstein object to wave-particle duality.  Feynman claimed it could not be understood.  19:25, 17 May 2006 (UTC)
replies: text:  You mean, anyone who doesn't subscribe to MWI?  :-) --Michael C Price 13:52, 17 May 2006 (UTC)

text: I wouldn't base an encyclopaedia definition on the supposed lack of accurate intuition of some people. Stephen B Streater 13:37, 17 May 2006 (UTC)
thread_title:  Is the double-slit experiment a paradox? 

message: First, what would it mean to say wave-function collapse is unitary? Consider measurement of an observable A ehich has a basis of eigenvectors. There are at least two ways of describing wave function collapse associtaed to measuring A: (a) as a map from a pure state (described as a vector in a Hilbert space) to a discrte probability measure on pure states or (b) as a completely positive map (or quantum operation) on density matrices. How could this possibly be unitary? In either case, unitarity for such objects doesn't make sense a priori. Let us consider the description (b) as quantum operation.   
It is possible for a quantum operation P to be described by a unitary U (which is unique up to scalar) as follows: For any density matrix τ, 
: P(\tau) = U \tau U^\dagger
The quantum operations described in this way are those that describe reversible evolution. 
It is possible however to replace U with a (non-invertible) isometry on an infinite dimensional Hilbert space in which case it is certainly not possible to claim that P is described by a unitary. This descibes non-reversible non unitary "wave-function collpase".  Note that the most general quantum operation can be represented by Kraus matrices (for which see article).--CSTAR 14:23, 17 May 2006 (UTC)
replies: text: Paradox is described here. The double slit experiment only appears to be a paradox to people with sub-standard intuition based on incorrect theories of physics. 
I guess that would include Heisenberg!!!!
"The Copenhagen interpretation of quantum theory starts from a paradox." --Heisenberg, Physics and Philosophy, pg. 44.  Michael D. Wolok 19:11, 17 May 2006 (UTC)

text: Yes. Scientists at that time had limited intuition in sub-atomic affairs. Just as people who thought the Sun orbited the Earth thought the simple orbits described by a heliocentric model were paradoxical. Now our understanding has increased, these no longer appear paradoxical. The equations are consistent with the reality they describe. All these interpretations are attempts to find analogies using an impoverished language. Any paradoxes arise because of the paucity of the analogies, not the underlying theory. Stephen B Streater 18:50, 18 May 2006 (UTC)
thread_title:  Wave function collapse 

message: Feynman's sum-over-histories is true for MW interpretations of QM, but it is not automatically generated by the CI.  If you accept the CI, Feynman's sum-over-histories is just a mathematical quirk.  According to the CI light does not actually take every path.  According to MW it does.  See how Stephen Hawking and Hartle use Feynman's sum-over-histories to create Quantum Cosmology, their No Boundary Proposal which is completely analagous to Hugh Everett's M-Ws.
:Feynman's sum-over-histories or path integral approach to quantum mechanics/fields theory naturally lends itself to many-worlds, but you can't derive Feynman's approach from many-worlds.  MW is a metatheory whereas sum-over-histories or PI is a physical theory.  MW makes no pronouncement about the weighting of each path, whereas the novel thing about the path integral approach is the weighting is just (with some qualifications) an imaginary phase angle, where the angle is proportional to the classical action.--Michael C Price 11:18, 18 May 2006 (UTC)
thread_title:  Feynman's sum-over-histories 

message: This section currently reads:
From the point of view of quantum mechanics, these stories however are deficient for at least two reasons:
There is nothing inherently quantum mechanical about branching descriptions of historical events. In fact, this kind of case-based analysis is a common planning technique and it can be analysed quantitatively by classical probability. 
The use of historical events complicates matters by introduction of an issue which is generally believed to be completely extraneous to quantum theory, namely the question of the nature of individual choice
Surely both these deficiencies are incorrect?  All historical events are intrinsically quantum mechanical, since all events are quantum mechanical.  By the same token the question of free-will is not outside the domain of quantum mechanics, although I wonder why it is mentioned here.  
I suggest that this section is substantially rewritten, which I'm happy to do if no one else volunteers or objects.
--Michael C Price 21:10, 23 May 2006 (UTC)
replies: text:  Well it's my fault. In my defense, what was there before was a hodge-podge of stuff from science fiction stories etc., which are now (mostly) in the parallel universe page. Although I still would argue that some phenomena can be accounted for well without QM (for example, planning using an event tree or branching in stochastic processes) and some of the science fiction "examples" would fall into this class or involve modal realism. But please feel free to change it. If someone has a disagreement with what you write, it will surely be brought up and talked about here.--CSTAR 21:19, 23 May 2006 (UTC)
replies: text:  OK, replaced above text with According to many worlds most of the historical speculations entertained within the alternative history genre are realised in parallel universes.--Michael C Price 05:36, 24 May 2006 (UTC)
replies: text:  Looks good to me.--CSTAR 05:43, 24 May 2006 (UTC)

text: I believe that Wolok must have emailed Tegmark and Wales in an attempt to get support for his text.  I haven't been able to read Wolok's extensive and badly formatted posts here, so I haven't engaged in a discussion about his text. -lethe talk [ +] 13:46, 24 May 2006 (UTC)

text: Perhaps this is just where the action is on WP at the moment ;-) Stephen B Streater 13:56, 24 May 2006 (UTC)
thread_title:  Speculative Fiction 

message: Zeno's paradoxes would still be paradoxes today even if they 
were all answered.  But as a matter of fact, many mathmematicians
today believe Zeno's paradoxes still have no 
completely satisfactory explanation.  See the Wikipedia
entry on "Zeno's Paradox."  I can also cite many 
article written on Zeno's Paradox by leading mathematicians.
Michael D. Wolok 23:20, 24 May 2006 (UTC)
replies: text: Well, maybe, but is this really an issue of major disgreement in this article? Is there something specific in the article you object to? Talk pages are mostly for discussions about writing the article. It doesn't seem to me there is major disagreement on anything currently written in the article.--CSTAR 23:26, 24 May 2006 (UTC)
replies: text:  PS I don't consider myself an MWI proponent but I think the article is NPOV.--CSTAR 23:28, 24 May 2006 (UTC)
thread_title:  Zeno's Paradoxes are still Paradoxes 

message: The word "purported" carries a negative connotation.  As such it runs contrary to Wikipedia's NPOV policy.  64.12.116.67 04:34, 25 May 2006 (UTC)
replies: text: I'm afraid you're imagining things here.--CSTAR 04:41, 25 May 2006 (UTC)
thread_title:  "Purported" carries a negative connotation 

message: Before you cite problems with the MWI, you should give the reasons why people favor it in the first place!!!  64.12.116.67 04:36, 25 May 2006 (UTC)
thread_title:  Pros must proceed Cons 

message: I am happy with Advantages of MW but . . . that seems to favor the MWI.  Some physicists may disagree with one or more of the items I enumerated saying they are not true.  A more objective heading is: "Reasons given by those who favor the theory."  I think all the reasons listed are valid reasons for favoring MW, but I make allowances for others who have an opposing viewpoint. Michael D. Wolok 05:28, 25 May 2006 (UTC)
replies: text: The text below the heading makes this very clear.--CSTAR 04:56, 25 May 2006 (UTC)
thread_title:  I am happy with "Advantages of MW" but . . . 

message: You should be at the forefront making changes to this article. —The preceding unsigned comment was added by 64.12.116.67 (talk • contribs) .
: I appreciate the sentiment, but comments like this, directed to a specific user and of no interest to the wider public, should be directed at my talk page, rather than clutter up the MWI discussion page.  Click on anyone's signature to get their user and thence talk page.  BTW Michael (Wolok), do you read your own talk page?  They're invalauble for everybody, including yourself.  Find "my talk" at the top of your WP page; go there and I can offer suggestions more easily there. When I hear from you I'll delete this section from the discussion page. --Michael C Price 07:48, 25 May 2006 (UTC)
replies: text:  Micheal C Price, if you want to access Wolok's talk page, it is at User talk:Michael D. Wolok.  It was in fact created quite some time ago.  You can't get there directly, since he doesn't include a link to it in his signature.  Instead, you have to click the redlink for his user page, then click the discusssion tab at the top.  But then, we have to do the same thing to access your own talk page since your signature also links to your userpage, not to your user talk page.  So remember: user talk page, if you want to talk.  -lethe talk [ +] 08:23, 25 May 2006 (UTC)
replies: text:  Thanks for the correction. I've amended my previous text to reflect this --Michael C Price 08:38, 25 May 2006 (UTC)
thread_title:  Michael Price 

message: "Quantum mechanics becomes a deterministic theory making it more compatible with the theory of relativity and all deterministic theories." 
I wish to make clear in this point that all other theories in physics are completely 100% deterministic, and contain no randomness. 
: Yes, but doesn't mean that MW is more compatible with "other theories" such as relativity.--Michael C Price 07:24, 25 May 2006 (UTC)
replies: text: Well, you added the section and posted it here afterwards.  Isn't C* just following the same MO?  --Michael C Price 07:24, 25 May 2006 (UTC)

text: This is not true AND far to partisan for WP.  First deterministic and indeterministic theories are not incompatible.  Second, other indeterministic theories had been proposed before (Newton proposed one such for light; I doubt he was the only one).  Third, given that indeterministic results appear in the lab, the idea that an indeterministic theory is required is quite natural.--Michael C Price 07:24, 25 May 2006 (UTC)
thread_title:  CSTAR quit this. 

message: Here is absolute proof of time travel!  Here is proof some people alive 
today are actually living in the past:
dancris wrote: "The modern explanation of this PARADOX—the wave/particle duality—is that both light and particles have BOTH a wave nature and a particle nature." 
Gee, and all this time, I thought this was Neils Bohr's "Principle of Complimentarity" which Richard Feynman found impossible to comprehend.  Could you possibly explain how the modern explanation differs from Neils Bohr explanation?  Or maybe it is as Hitler said, if you repeat a big lie often enough people will without questioning it accept its truth.
Richard Feynman said in his famous lectures: "You had to know which experiment you were analyzing in order to tell if light was waves or particles. This state of confusion was called the 'wave-particle duality' of light, and it was jokingly said by someone that light was waves on Mondays, Wednesdays, and Fridays; it was particles on Tuesdays, Thursdays, and Saturdays, and on Sundays, we think about it! . . . 'I think I can safely say that no-one understands quantum mechanics… Do not keep asking yourself, if you can possibly avoid it, 'but how can it be like that?'… Nobody knows how it can be like that."  
By the way, dancris, no one who knows anything about physics says particles have a wave nature.  Roger Penrose and many others explain that this is an incorrect way at looking at things.
[User:Michael D. Wolok|Michael D. Wolok]] 06:06, 25 May 2006 (UTC)
replies: text: Citing Roger Penrose is not a good idea.  Despite his contributions to physics many of his more philosophical pronouncements (especially on the mind and QM) are widely regarded as cranky.--Michael C Price 07:30, 25 May 2006 (UTC)
replies: text:  Here is a more humorous example. Stephen B Streater 08:32, 25 May 2006 (UTC)
replies: text:   "Penrose must err to believe this sentence."  :-) --Michael C Price 10:03, 25 May 2006 (UTC)
thread_title:  This Modern World