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Local QM? MWI, RQM, QFT, LQM, + ?

  1. Jan 18, 2007 #1


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    I'm interested in studying LOCAL theories within QM. I have the impression that the following theories claim to be such:

    MWI (Everett)
    RQM (Rovelli's Relational QM?)
    QFT (Originated by ?)
    LQM (There's a book titled ''Local QM'' as I recall.)


    1. Are there any other LOCAL quantum theories?

    2. Does the definition of locality vary within the above schools?

    3. Given some unanimity on the meaning of locality, I guess each of the above differs in the conceptualisation of ''reality''. Where might I find a summary of such differences? OR: Might those differences be developed here?

    Thanks, wm
  2. jcsd
  3. Jan 19, 2007 #2


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  4. Jan 19, 2007 #3


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    QFT is not an interpretation of quantum theory, it is the application of quantum theory to a specific classical model (classical fields). As such, all interpretational issues remain with QFT in the same way as they remain with other applications of quantum theory.

    However, QFT people are often less concerned with this, because they usually only calculate S-matrix elements, which are transition probabilities from t = - infinity to +infinity, and they have already so many other technicalities to worry about that interpretational issues really only come in at low priority.
  5. Jan 19, 2007 #4
    Ah MWI, the new string theory. If I didn't think string theory was bad enough, with all it's extra dimensions no one could percieve, and strings no one could likely ever detect; someone comes along and suggests their are infinite realities we can't percieve too? Is anyone doing science these days or has physics turned into philosophy:wink: :smile:

    MWI is likely to remain unfalsifiable forever, as is string theory. I personally think as it says on the link it's metaphysics repackaged as science, but hey prove me wrong.

    IF MWI theory is right I'll eat my hat, and I have one too so you can hold me to it. It's a woolen one.

    Looking at all those you mentioned I'd go for QM and will probably learn about QFT at some stage anyway; I'd probably look into that too. If I had time I'd glance over the RQM, and if I was bored I'd look at LQM. If i wanted to read about MWI I'd probably go with A.C.Clarke or Asimov?:smile:
    Last edited: Jan 19, 2007
  6. Jan 19, 2007 #5
    Vanesch:” QFT is not an interpretation of quantum theory, it is the application of quantum theory to a specific classical model (classical fields). As such, all interpretational issues remain with QFT in the same way as they remain with other applications of quantum theory.”

    Allday:” One "law" that you can keep in mind is that quantum objects travel as waves and interact as particles”.

    It is follow deterministically from your discussion with me in the Particle-Wave duality and Hamilton-Jacobi equation session that

    There is no legitimation for M.Born statistical interpretation any more and it may be removed from the formalism of the Quantum Theory. Quantum Theory is the local field theory of the massive waves. No interpretation required.
  7. Jan 19, 2007 #6


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    That is true. However, a kind of locality is very manifest in QFT, much more than in QM of particles, which is why QFT is often mentioned in the context of "locality". Nevertheles, this kind of locality has almost nothing to do with locality inherent to some specific interpretations of QM.
  8. Jan 19, 2007 #7


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    Has nothing to do with it. MWI is just a rigorous application of the basic postulate of quantum theory applied to everything: the superposition principle. You have to *violate* that postulate in order NOT to obtain MWI. You have to say that there are things in the universe which do NOT obey the principles of quantum theory.

    Now, this can very well be the case ! I'm not saying that MWI is a correct description of nature. I'm usually just claiming that MWI is the most natural interpretation of a funny theory which we call quantum theory, and which starts with a totally crazy postulate: the superposition principle.

    The superposition principle says: if A is a possible state of nature, and B is a possible state of nature, then u A + v B is also.
    Well, if "me seeing the red bulb going on" (A) is a possible state of nature, and "me seeing a green bulb going on" (B) is another possible state of nature, then according to that superposition principle, any superposition of this is also a state of nature. Crazy ? Sure ! But that's a basic postulate of quantum theory. Doesn't apply to humans ? Why not ? Maybe it doesn't apply to humans. Could very well be. Because it is in contradiction to OBSERVATION ?

    At first sight, you would think so ! But when you work out what would be observed *if this postulate applied also to humans and everything else*, well, to your surprise you'd find that there is no observable consequence of this statement which is in blunt contradiction with what is actually observed.

    In other words, imagine for a moment the toy universe which is that "crazy world of MWI". What would its inhabitants observe ? Answer: they would observe exactly a universe as if "standard quantum theory" were valid. They wouldn't "observe their twins (that is, the other states in superposition)" most of the time (except in EPR experiments!).

    So, MWI is *not* in any observational contradiction with what is observed. You do NOT see your "doubles" in other branches (if you would, then you could do things differently depending on these observations, and this would then mean that the evolution equation would be non-linear and non-unitary), thanks to the strict unitarity of time evolution.

    So this indicates that there is *no observational indication* to assume that the basic postulates of quantum theory do NOT apply to macroscopic systems. Maybe they don't, but in absence of any evidence, there is no reason to assume this. Usually we assume that a physical law is valid until cases are found where it is clearly in contradiction with observation. Well, the superposition principle for macroscopic objects is NOT in contradiction with observation.

    Moreover, there are almost incomprehensible things going on in quantum theory, UNLESS you look upon them from an MWI viewpoint: locality is preserved in EPR business, there is no dichotomy between two different evolution laws (unitary and projection), things such as delayed quantum erasers find natural explanations in an MWI setting... everything looks formally much smoother in an MWI setting than in a projection scenario. This shouldn't surprise us, because in an MWI setting, the dynamical laws are not violated, and the kinematical descriptions remain the same.

    The only problem with MWI - which makes it unacceptable for many - is that it has a strange ontology: there COME OUT of the theory that there seem to exist "parallel worlds". This is not - as is sometimes assumed - PUT IN BY HAND. This comes out of it, and is actually very evidently seen, from the basic postulates: the superposition principle, and the postulate of unitary time evolution. It's the fault of these crazy postulates that we end up with such a crazy view ! If it weren't for their experimental success, we'd never consider such a crazy idea in the first place.

    I think that the MWI debate is a bit like the debate of whether the spacetime manifold "exists" or whether "the EM field exists".
    I think that if you work with a theory, such as GR, which cries out that the spacetime manifold exist, then it is easier to work with when you keep that in mind. In the same way, when you work with electromagnetism, it is easier to assume that there exists such a thing as the EM field. In the same way, when working with quantum theory, things come out much easier, conceptually, when you assume that the state vector of the entire system exists.

    Again, it is a metaphysical discussion of whether "the spacetime manifold exists for real" or whether "the EM field exists". You can do GR and say that this is just a mathematical trick that helps you calculate the effects of gravity, but that the whole BS of bending spacetime is forever unfalsifiable. You can say the same about the existance of an EM field. And you can say the same about MWI.

    I think you can start with some very good articles by Vaidman on the arxiv.
  9. Jan 19, 2007 #8
    Thanks Vanesch that's a very neat summation of the idea.

    I still can't help thinking though that MWI is making an assumption based on assumption. Using Occam's razor I would say it's too complex and invoking properties that it need not, my personal view is that we're not quite their yet, we haven't quite got how it works, so therefore anything based on the extension of what we know at the moment is subject to being based on faulty suppositions to begin with.

    Not that I think QM is wrong, I haven't seen anything that would suggest that, just that when you read a discussion about what a wave function describes, you tend to get the impression that it's pretty much a matter of mathematical interpritation, and obviously that's because we cannot observe directly a superposition.

    Sometimes when I'm floating around discussions, I often have to ask myself, how do you make that out? I could as easilly say x alot, it's all a little to grey to start making hypothesis based in incomplete theory, in other words let's get the foundation right first before we start invoking strings and many worlds. I have a bit of an issue with Hawking radiation as well, but that's a whole 'nother topic.

    I guess it's just a matter of what your interested in and what you think will pan out though. I don't see any problem with this hypothesis, but if like string theory it's ultimately going to prove philosophical I'd rather see top scientists discussing something a little more this world interpritation.

    There is no reason to assume God exists, their is no reason to assume he doesn't scientifically either. But logic and proof are very different beasts.
    Last edited: Jan 19, 2007
  10. Jan 19, 2007 #9


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    MWI is hardly "new", it's been around since 1957. You may be confusing it with the landscape proposal that grew out of string theory, which postulates a huge number of different universes with different values of various physical constants.
  11. Jan 20, 2007 #10
    Well I was comparing it to the faddy nature of string theory it's kind of like the latest fashion in the physics world.
  12. Jan 20, 2007 #11
    That's not strictly true. The Stony Brook and Delft groups observed a superposition of current flowing both ways (in a SQUID) by detecting the energy gap between the two states. The energy measurement did not disturb the superposition as the respective observables commute.
  13. Jan 21, 2007 #12


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    We will ALWAYS be in that case, as long as we (and our descendants, or another species which thinks about physics) will be around. We will always have a finite knowledge, and we will always have to "extrapolate" if we are going to pose grand visions of the meaning of life, the universe and everything. So "waiting until we finally find out" is Waiting for Godot.

    My point is simply this: *IF* we insist on having a world picture, then it seems more reasonable to do this by extrapolating currently well-established theories than to postulate half-baked and not-yet-completely-worked-out dreams of theories of what "ought" to be (this sounds like string theory :biggrin:). So, totally aware of the extrapolation and its hypothetical character, I think it is more conservative to stick to the principles of established theories than to invent properties of principles of unestablished theories, and it is based upon that attitude that I think that an MWI view is more natural with quantum theory than a Copenhagen based view. But I'm well aware of the extrapolation this contains. I would even say (with Penrose), that there is probably a serious problem, which is gravity. But, or unitary quantum theory can cope with gravity (in which case the serious problem disappears), or unitary quantum theory will undergo a modification in order to deal with gravity, in which case we will not need an interpretation of unitary quantum theory anymore (and maybe we can do away with MWI, depending on how the new, and unknown, theory will be put together). However, given that at this moment, the only thing we have, is unitary quantum theory, we extrapolate to its universal applicability, and then you end up with MWI in one way or another.

    In this light, MWI is rather favored by Occam's rasor. Because what is "cut away" is all the extra hypotheses needed for the NON-applicability of unitary quantum theory (somehow the EXTRA rules that say that the superposition principle is NOT applicable to humans or so).
    There are two ways to consider Occam: one can try to simplify the RULES of the game (that is, cut away all extra rules which don't bring in anything), or one can cut in the acceptable solutions: that is, by adding rules, we can limit the kind of solutions we like to see. Usually, with Occam's razor, one means the first kind of simplification: one likes to limit the number of RULES, and wants to apply them as universally as possible. If this leads to a more involved set of solutions, then so be it. In this light, applying the superposition principle universally is a simpler view (preferred by Occam) than specifying extra rules of when it applies, and when not, and what to do when not (projection).

    Now, I can accept very well that people "shut up and calculate", because strictly speaking, that's what science is about: building models which make predictions and falsify them. It is when people start to talk about the weirdness of quantum theory (and more specifically about its confrontation with logic, or its lack of sensibility or the like) that I like to bring up an MWI view. In those "paradoxial" situations, like EPR-Bell, or delayed quantum erasers and so on, this view really helps "understanding" the quantum-mechanical machinery (in the same way as imagining that a spacetime manifold is curved helps you understand general relativity), and avoids all these "impossibilities" which are displayed. But if you are happy with saying "hey, that's what comes out of the calculation, and that's also what we find experimentally", then that's also fine. It is when one starts saying "uh, this must be wrong, this doesn't make any sense, although we calculate it, and we measure it all the same", that it helps to consider exactly what we assumed as a starting point and how these very same assumptions are also the key to the "understanding" of the "paradox".

    Well, it is part of the superposition principle that we can't observe it directly ! However, we can observe its consequences indirectly (each time this happens, we talk about a "quantum effect" or something of the kind).

    We will never be sure that we have the foundations "right", and we will always have an "incomplete theory". There may be moments when we will be deluded in thinking that we have it all right. Happily right now that's not the case: we KNOW we don't know everything. The day we think we do, we are deluding ourselves.

    Again, MWI is just a conceptual tool to help you understand quantum theory, as we have it right now, in the same way as the spacetime manifold is a tool to understand general relativity, or Euclidean space is a tool to understand our visual impressions.

    True, but there's a difference. It is a common misunderstanding of MWI that one has *introduced* the idea of "several worlds". As I tried to point out: this is a *consequence* of applying a basic postulate strictly and universally. If we used a theory in which there was a fundamental postulate that introduced a deity for the behavior of electrons in an atom, then wouldn't it be natural to assume that that deity also existed for us ?
    THIS is what is done in MWI: we APPLY an *already existing postulate* of the theory universally, beyond where it is "really needed". We don't introduce a totally new concept (such as a deity). It also indicates the weakness of an MWI view: it might be that the postulate is *not* universally true, and then of course, the view based upon it doesn't make any sense. But that day, we will also know WHAT is then applicable. Up to today, we haven't gotten any indication of a limitation to the applicability of the superposition principle (but gravity might be a spoiler - we simply don't know). As such, we can only GUESS at what might eventually replace it, IF it even needs replacement. So all non-MWI views are in fact based upon a *guess* of new physics - usually to bring it in agreement with intuitively more acceptable macroviews.
    And WHEN we do so, we run into a lot of paradoxes. So why do this ? Clearly, the day that we DO KNOW whether or not the superposition principle has limitations of its applicability, and we DO KNOW what replaces it eventually, we will also know what are the solutions to eventual "paradoxes". So we shouldn't worry about that. But right now we don't. So let us not worry about paradoxes that might not even be there, and which aren't there when we extrapolate our current theory's principles.
  14. Jan 23, 2007 #13
    Of Course though Vanesch, this is precisely the sort of discussion I could say: but I could just as easilly say X. In other words all the other myriad of theories are equally as viable, and since yours has no proof except in some logical theory, it's phillosophy, essentially your saying that because a is more logically consistant, it must be more viable, I don't personally see it that way, I find it mind numbingly overcomplicating the deal but then I guess it's a matter of interpritation?:smile:

    There is no real reason to believe it stands on it's own as viable and until there is, isn't it is as guilty of speculation as string theory, more consistant? Is this hypothetically more consistent, or really more consistent?

    Since also it is unlikely to ever get proof then what is the point of speculating about the existence of the Invisible Pink Unicorn? How does this advance science?

    I think at heart that is my biggest question to resolve before I accept that faries exist at the bottom of my garden if you see what I mean. Shut up and calculate. Or at the very least show me the money :smile:

    The only difference between many worlds and string theory is the philosophy is worded differently, both are as guilty of putting the cart before the horse.

    Speculation is good, healthy even, but be sure to make sure you bear in mind that is all it is atm, and if that's all it's likely to be, I don't personally see why I should indulge in speculation for the sake of speculation.

    Wake up with a hypothesis disprove it over breakfast, then you're ready to work.

    Last edited: Jan 23, 2007
  15. Jan 23, 2007 #14


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    It is of course partly philosophical, but then every consideration of the foundations of a theory is partly philosophical. So I don't see the qualifier "it is philosophical" as a counter argument !

    What we know of quantum theory, is that no matter what will come next, if anything, it can't be good old classical physics, in the good old way we used to do it, unless quantum theory makes entirely wrong predictions in some aspects. There is still a crowd of people hoping for exactly that: empirical falsification of quantum theory, not in an entirely eccentric part of the universe, but in a lab, using rather daily stuff. However, it hasn't happened yet, and as such, I still stick to quantum predictions as quantum theory makes them. Any empirical falsification of quantum theory would of course shine a totally new light on the issue. But we aren't there for the moment.

    As such, Bell's argument shows us that any underlying mechanism, if any, will not be both relativistically invariant AND kind of to be dealt with the way we used to do classical physics. Some are prepared to sacrifice relativity in its inner bearings. That's what the Bohmians do. Who knows.
    But the principle of relativity has shown to be very powerful, and giving it up for no apparent reason then leaves us with more explanations to give than by keeping it. So I want to keep relativity too. I'm quite conservative. I want to keep those theories that worked well.

    So I have to have quantum theory AND relativity. And this is entirely possible. I only have to apply *strictly* the principles of quantum theory, and *strictly* the principles of relativity, and I find that there's no problem. So allow me to point this out to anyone who comes to the conclusion that there are very "impossible" things going on.

    What do you mean "no real reason to believe it stands on its own" ? All axioms are laid down ; they are simply the same axioms as those of special relativity and of quantum theory, with the "extra requirement" that they are universally valid - in other words, that they apply to everything. What *follows* from doing that, is that quantum theory as we know it, applies, and that relativity, as we know it, applies. It is not a "dream of a theory" of which the postulates still have to be written down (as is string theory), but of which we are already listing all the properties we hope we will derive once we find the right set of postulates. The postulates are known, and they are those of quantum theory!

    The invisible pink unicorn is not the result of verified postulates. As such, there's no reason to *INTRODUCE* it. But the superposition postulate has been at the basis of a lot of useful quantum theory. So instead of talking about a *totally new and useless* concept such as an invisible pink unicorn, it is like talking about the "back side of the Andromeda galaxy". It is very unlikely we ever get proof that there's light emitted from the backside (from our PoV) of the Andromeda galaxy into outer space. Now, do you have a reason to assume it "is there" or not ? Or is it more reasonable to *introduce* a new postulate which tells you that far away galaxies don't emit light away from earth ? And then find out that "paradoxes abound" because now it seems that there is an inbalance in the total energy output of those galaxies. And then start talking about "spooky actions" on remote galaxies, which change the physics in some yet-to-be-explained ways which can then explain why the radiant flux of remote galaxies is different from nearby stars ?

    So we have first a theory which tells us that stars and so on emit light in all directions. Now, for far-away galaxies, the only thing that matters for most observations, is that part of the light which comes our way. It wouldn't make a difference if we said that in those cases, the light emitted is ONLY in our direction. Except for certain observations (such as a kind of radiation balance), where we then get into trouble. We then start speculating about new physics that might happen to those remote galaxies, for which the light is only emitted in our direction, and get their radiation imbalance all wrong because of that.

    Because this is exactly what happens in quantum theory. We have the superposition postulate, which gives good results on microscopic scale. We also know that we could apply it on macroscale, and that this would, most of the time, not make any observational difference (decoherence). However, we decide that somehow, it doesn't apply on the macroscale. And then we have problems in those cases where it WOULD have made a difference. But we refuse to go back to the idea that we could apply it to macroscale.

    That said, I have nothing against "shut up and calculate", but I find it a bit "inspirationless".
    Last edited: Jan 23, 2007
  16. Jan 23, 2007 #15
    Partly or totally? is their any experimental evidence of MWI, I'd be keen to hear if their is?

    No because classical physics does not describe the quantum this is self evident.

    Agreed, ditching the baby with the bathwater is not a viable way of proceeding.

    Well it's a bit of a stretch to say that coming to a conclusion should from the basis of a theory no? Equally those who think their are possible things going on can come to any number of conclusions of the possible and that's what I mean by I could as easilly say X.

    No they aren't untill you prove they are they are hypothetical, and so is everything the MWI says untill it can show us something tangible in either experimentation or at least in inference, I can quite easilly conclude myself that the reason we cannot see what we are measurinbg is because we don't have the right sort of tools, and if we could it would be obvious how the Dirac equation works so beautifully, it is because it describes perfectly x. Whatever x is. But in mathematical form.

    I think you can assert as many postualtes as you like and in fact if you gave me a couple of years I could come up with something very simmillar to MWI, call it many existence theory, meaning that every event takes place but only one is realised. So that reality itself is a quantum superposition? How is this less valid than your hypothesis? In fact it's simmilar? BUt I don't say there are infinite realities only infinite possibilities? Explain how this hypothesis is worse than yours or better? I hereby anounce the formalisation of a new theory: single world interpritation. SWI or Schrodingers World Interpritation :smile: Maths paper to follow, where I show how this all works beautifully with a series of thought experiments and a few tweaks of the math.

    Indeed alot of observation relies on the idea that our area of the universe is consistently how the universe works everywhere and although I can't prove that is true, it's probably the best way to proceed with theory for now.

    But what happens at the quantum scale is not what happens at the classical scale, this is a fundemental of QM? Why therefore do we assume that? What reason is there to make this assumption other than a philosophical one?

    Shut up and speculate then:smile:
    Last edited: Jan 23, 2007
  17. Jan 23, 2007 #16


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    What I personally consider as experimental evidence for MWI, are EPR-Bell situations. They are an "observable way" of putting macroscopic observers in superpositions of "observer states", and have them interfere.

    It is about the closest you could get to "showing MWI true". But it is not really an experimental *proof* of it ; it only shows that quantum-mechanical superpositions happen at scales which could easily be considered "macroscopic" (namely, several kilometers). Once we are there, and we have to consider quantum-mechanical superpositions for:
    - systems on the scale of kilometers
    - systems with 10^20 particles (like the currents in superconductors)
    then why would we consider that this principle does NOT apply to "macroscopic things" ? Especially when IF we do, we can keep both relativity and the EPR kind of results ?

    As I said: is the "resolution" of the Bell-EPR paradox not good enough ?
    It is about the only situation in which one can "demonstrate" the actuality of macroscopic superposition: take an entangled microsystem, get the parts far apart, and entangle them *in arbitrary ways* (= choice of angle) with two macrosystems (Alice and Bob). Then have Alice and Bob interfere. Remember that quantum interference is the difference between a superposition and a mixture. Now, if our Alice and Bob were in a kind of mixture, they wouldn't show the "singlet interference correlation pattern". So they were clearly in a quantum superposition.

    You should refine your definitions of "take place" and "is realised". Depending on how you do so, you end probably up with or a kind of collapse theory, or with just another flavor of MWI.
    In the first case, you run into Bell's theorem.

    You can play semantics only so far. At a certain moment, you have to tell me, whether yes or no, when Bob does a measurement, there *is* only a unique outcome, or whether the two outcomes somehow happen both.
    In the first case, you unavoidably run into Bell's theorem. From the moment you consider the second, you are in an MWI kind of frame.

    Many people have tried what you propose, you know. That's now about 80 years that this issue is with us.

    No, this is just a vision on QM (the Copenhagen school) which somehow is called the standard view, and it leads to all these interpretational problems. One should still show me what exactly is meant with "quantum scale" if it can encompass 10^20 particles, and and be of the size of several kilometers.

    Now, don't get me wrong, I don't want people to adhere to MWI as if it were a kind of dogmatic religion ! I'm only saying that, given that MWI respects the basic postulates of QM rigorously, and given that it gives quite a natural explanation for otherwise quite strange or even incomprehensible situations, it is IMO the natural view on the formalism of quantum theory - in as far as one is in the need of a view at all (hence also my respect for those who "shut up and calculate").

    You could use your arguments just as well against the idea that gravity is the bending of spacetime. You could call all those tensor equations just a mathematical tool, but gravity is, well, gravity, the thing that attracts stuff in an Euclidean space, and seems to also affect clocks, and those curvature things in spacetime is just a totally speculative view on things, taking the mathematics too seriously. This can very well be. Nevertheless, imagining that gravity actually IS the bending of spacetime makes the understanding of general relativity much more natural. "paradoxes" in relativity become naturally explained when you accept that spacetime is bend - even if you want to keep in your mind that this is just a trick to remember those pesky tensor equations, but that of course no-one in his healthy mind would take seriously the idea that there is something as a "bent spacetime", whatever that might mean.
    I take MWI versus quantum theory on the same level as imagining a bent spacetime is versus general relativity. Whether this has anything to do with "what is really out there" or not. In both cases.
  18. Jan 24, 2007 #17
    Here's a paper I read on RQM a while ago, I really like it, and I think trying to derive the QM formalism from a bunch of postulates sounds like a very good idea, as we would probably get a better understanding of QM.


    It's not too complicated or long, I could understand most of it and I'm only a 2nd year undergrad. Didn't understand any of the stuff on information though.

    Here's a paper on RQM-EPR


    It would be interesting to see what you all think. You probably all know a lot more about QM than me. :)
    Last edited: Jan 24, 2007
  19. Jan 24, 2007 #18
    To be honest we're both guilty of semantics here, your saying that an incomplete understanding of a leads to b,and I'm saying that an incomplete understanding of a might lead to b, but I think it doesn't because of occams razor? Who's right? I'm sticking with my SWI, I can explain all you can with MWI just by sticking to the three dimensions we know and time, I prefer the idea of infinite possibilities not dimensions, and until someone shows me something other than the bell theorem, I won't be leaping to any tangental conclusions, have you ever thought that an entangled particle may be in some sort of state we haven't accounted for? And that there may be no locality or non locality as such it's just an account of unobserved variables.? Probably. I'm more inclined to believe this than that it leads naturally to MWI.

    At the end of the day though provided you acknowledge it's speculation and don't take it seriously in the same way you would a theory, I don't have any problem with it. It's the faddiness that worries me, too many people with little or no understanding reading about it and then you get serious PhD students trying to find the fairies at the bottom of the garden, to rehash an old analogy. I personally jost don't think the answer is that bizzare, but of course that is just my own flavour of speculation.
    Last edited: Jan 24, 2007
  20. Jan 24, 2007 #19


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    Do a search here on Rovelli or relational quantum mechanics: there have been long discussions about that. I'm pretty convinced that RQM is some other wording of an MWI, but then some people don't agree with that.
  21. Jan 24, 2007 #20


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    I'm not claiming any "incomplete understanding", on the contrary. I'm just saying that, with the postulates we have, we can build an entirely coherent picture which doesn't lead to contradictory situations as some claim. That's rather the opposite than "claiming incomplete understanding", no ?
    However, I place the caveat, that our understanding *in general* of nature will always be incomplete, and as such, that the picture can change, when we learn more. It can also be correct if no such change is required. THAT is the point: it CAN also be correct. Many other views cannot claim that. They NEED vague, new, ununderstood postulates which must somehow fix the obvious problems. THAT's where I apply Occam's razor.

    I don't see why one should introduce the idea of vague, unspecified, ununderstood postulates which are needed to solve problems which don't even appear in the first place when you don't modify anything.

    What else do you think Bell's theorem does, than exactly inquire that possibility, and find out that it doesn't exist ?

    I take it exactly as seriously as the theory from which it follows: namely quantum theory, in its unitary form. That's why I don't take it 100% seriously, and leave open the possibility that quantum theory is in fact wrong or limited in its application. THIS is the kind of "incompleteness" I refer to: the possiblity that we discover one day an empirical falsification of unitary quantum theory. That day will probably also be the end of MWI.


    This is in fact the single and only objection to quantum theory and its natural consequence, which is MWI: 'I really don't think the answer is that bizarre'.
    Which is rather strange, because this "bizarreness" is a basic postulate of quantum theory!

    I'll admit that I ALSO find this very bizarre. That's why I leave open the possibility that this postulate (the superposition principle) may one day turn out to be wrong. But unfortunately, this day hasn't come yet, and may never come, and as such, I have no choice but to accept that, to the best of our knowledge today, this bizarreness is real.

    Now, many people also think that "one day one will find a reasonable explanation for all that" ; but that's nothing else but introducing our "vague, undetermined and ununderstood hopeful postulate that will solve it all". Until this is EXPLICITLY DONE (and many tried, only Bohm succeeded somehow), I don't think it is a fair application of Occam's razor to accept this unspecified postulate, and to reject the systematic application of known postulates, ONLY to satisfy the subjective desire for less bizarreness.
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