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Many Worlds Theory

  1. Mar 25, 2012 #1
    Hello,

    I am new to this forum. This is an excellent, informative forum; therefore, I felt compelled to join.

    I would be interested to engage in dialogue with individuals who support the Many-Worlds interpretation of Quantum Theory. Personally, I despise this interpretation as I believe it is preposterous. I much prefer the Copenhagen interpretation.
     
    Last edited: Mar 25, 2012
  2. jcsd
  3. Mar 25, 2012 #2
    Stuff like"many worlds"? Descriptions such as codswallop come to mind.
     
  4. Mar 25, 2012 #3
    Well I am a supporter of the many-worlds theory :P

    And terms like 'codswallop' and 'preposterous' sound a little bit harsh, and not very technical, let's avoid the use of them, shall we?

    So, let's start with the basics by dissolving the ideas behind 'codswallop' and 'preposterous' into their meaning. Why would you say that they are as you described?
     
  5. Mar 26, 2012 #4

    Ken G

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    I am neither a proponent nor a critic of "many worlds", I think all interpretations of QM are simply pictures to have in your mind as you do the calculations implied by the theory. Isn't that what an "interpretation" always is? From whence comes the erroneous idea that an interpretation of a theory is ever a claim on how reality actually operates? If the history of physics tells us anything, it is that physics never gives us that.
     
  6. Mar 26, 2012 #5

    Hurkyl

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    The main thing about MWI is that ideas need to be translated. Nearly everything I've heard someone say is "preposterous" about MWI is the result of a failure to translate: someone takes a statement meant to be interpreted by one interpretation, and instead interprets it by a different one.
     
  7. Mar 26, 2012 #6
    This seems to me to be a decidedly sensible and reasonable approach/assessment. I also don't think that doing calculations using standard QM necessarily entails having any pictures about the way the deep reality is.

    MWI is one approach to interpreting the deep meaning of QM. Not a very good one, imho.

    For the OP, there have been lots of threads at PF on this. And some fairly recent ones that might be informative for you. A most recent one involving, primarily, the views of Hurkyl and Ken G. Check the archives. Read ... read ... read ...
     
  8. Mar 26, 2012 #7
    "Codswallop"....nonsense...of little or no use or importance.

    Physics is informed by observations and must conform to observations.If a theory or interpretation is to be of any use it must be possible,even if only in principle,to make the relevant observations.How can we make the observations on interpretations such as many worlds?
     
  9. Mar 26, 2012 #8
    I probably should not have used "preposterous" to describe my disdain for MWI; I agree that it is not technical, nor helpful.

    Hugh Everett was clearly an extremely gifted mathematician; however, I believe that he was probably slightly arrogant, and somewhat delusional, to assume that he could explain the entirety of quantum theory in his PhD thesis. MWI is just a fancy mathematical philosophy that can never be tested and is, therefore, worthless in my opinion. The assertion that Daffy Duck collapsed the wave function is just as valid as MWI, in my opinion (LOL).

    At least with the Copenhagen Interpretation (CI), it is sensible and useful. I have a lot of respect for Bohr and Heisenberg because they had "quantum humility." It is likely that they understood that the mind of the human species is not capable of understanding the "big picture" of quantum mechanics.

    Off Topic: I also strongly dislike quantum mysticism; it irritates me greatly. Particularly the "quantum consciousness" variety.
     
    Last edited: Mar 26, 2012
  10. Mar 26, 2012 #9

    Hurkyl

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    You know, this sounds an awful lot like "I can't understand something, therefore nobody else can either."
     
  11. Mar 26, 2012 #10
    While that is somewhat true right now, looking at the practical "shut up and calculate" side of it, I do think that eventually we will find evidence for one interpretation or the other. On the other hand, I'm pretty sure the whole point of physics is explaining about the operation of reality, and what is our search for the sadly named TOE if not the search for something to describe how reality works at its most fundamental level?

    Now this is probably just a personal opinion, but I think that physics should try to explain reality's actual field of operation. The fact that the outside view differs strongly from the inside view (and thus may be called weird by our merely human intuitions) doesn't make it any less right or describable by physics.

    Furthermore, I do think Hawking supports the theory that wormholes could connect two different Everett-branches, but that is... well, very weird to me, and sounds a little bit codswallop-y. Unless, of course, he can find a way to prove it (even if in principle - I haven't the faintest clue how he got to that idea).

    Now that is definitely true. I do seem to read a lot of people talking about for instance "splitting of worlds" like some collapse-type process, which is not even a part of the theory.

    I know the meaning of the word 'codswallop,' what I meant was that it wasn't a helpful word in describing what your thoughts were on the interpretation.

    Also, I'm not a physicist (yet), nor do I know a lot of the meat behind the theory, but I have read about ideas to try to test the validity of Many-Worlds. As I mentioned above, I believe Hawking was thinking something along those lines (but he does seem to have a soft spot for wormholes, doesn't he?), and also Tegmark claims that there is evidence for Many-Worlds, somewhere.

    Two points, though: one, Many-Worlds (or, as its original name says, relative state) does seem to fall right out of the full and simple application of the Schrödinger Equation. It is a very simple idea, formally speaking, in that you don't need collapse as an actual fact about nature (mind projection fallacy, anyone?), but merely its appearance as a consequence of decoherence. Of course in your calculations you have to suppose something that's like collapse happened, because that's the inside view of the world, but it doesn't affect at all the outside view.
    The second point is actually a double point. The first part is that I do think every detail of a theory (up to and including its interpretation) has to be provable and falsifiable, somehow, for it to be valid. About that we agree. On the other hand, that principle should not be applied exclusively to Many-Worlds, but to Copenhagen, too. As I described above, the relative state interpretation merely makes the assumption that everything is described by a wavefunction, including the measuring apparatus (seems pretty trivial to me, the distinction between system and apparatus is a human one not a physical one), and that it evolves according to the Schrödinger Equation at all times. The Copenhagen one seems to introduce an ad hoc tool to describe our the experimental results called 'wavefunction collapse,' but doesn't seem to try to make any sense of it. In my humble opinion, I believe that what I need is evidence in favour of collapse to be swayed away from relative state, and not any evidence to do the opposite.

    There is an article by Tegmark that discusses the misconceptions about the Relative State interpretation, about what it says and does not say. It's a very interesting read.

    I think that you are a victim of the MWI misconceptions I mentioned above. You should read Tegmark's paper on it. Also, I do not think he was trying at any point to describe the entirety of quantum theory; he was merely irked by the seemingly random collapse postulate (that does not exist in his Relative State interpretation, as neither does any 'world splitting' postulate, it's all decoherence).

    I also claimed above that every detail of a theory should be able to be tested, and the fact that we haven't been able to test it yet does not mean it is untestable.

    Furthermore, I also disagree with you that we are incapable of understanding anything. (It's only in trying the impossible that one can truly grow as a human being...) It is very much true that our savannah-optimised brain isn't the best tool to analyse such deep details about reality, but I think you're underestimating the human brain's power and ability to grow.

    I agree with your first sentence, but I have no idea what "quantum consciousness" is or would be. Where did you hear that?
     
  12. Mar 26, 2012 #11
    You might be correct; maybe I do impose my beliefs on other people to a certain extent. However, I would disagree with you regarding terminology. I would replace the word "understand" with the following: "come to any firm conclusions on." Even if you're a proponent of MWI, it is simply an untestable belief and hypothesis, in which case you cannot come to any firm conclusions either.

    The human being is, for the most part, an exceptionally intelligent mammal. However, I agree with Lawrence Krauss' assertion that we need to have "cosmic humility." Although we like to think of ourselves as omniscient, our brains have only a finite capacity. Take the size of the human brain in comparison with earth (an infinitesimally small speck in the universe), let alone the cosmos. We're tiny organisms with egos larger than the universe itself. I believe even a mathematical genius with an IQ of 230 who develops a "Theory of Eveything" would be able to perceive the universe only in a limited manner (inside the limits of mathematics, logic and reason). We should continue to utilise quantum theory to our scientific and technological advantage, but it is a pointless endeavour to try and fully understand it.

    In conclusion, the entire universe is far (FAR) more complex than anybody is capable of ever fully understanding, this is obviously arguable, but it is my opinion nevertheless.
     
    Last edited: Mar 26, 2012
  13. Mar 26, 2012 #12
    All of the "quantum garbage" that Stuart Hameroff rants about; he believes that human consciousness is a fundamental property of the universe, and endeavours to appear intelligent by using quantum mechanics to explain the origin of consciousness. Again, another pretty and non-falsifiable, egotistical philosophy. He appears on the annoying quantum mystical documentaries, such as "What the Bleep Do We Know!?".
     
  14. Mar 26, 2012 #13
    Untested, not untestable. One is reminded of Lord Kelvin's statement that the movement of muscles was infinitely beyond science. The fact that no tests have been able to discern between Copenhagen and Many-Worlds doesn't mean none will ever be developed - and because of that, Copenhagen and Many-Worlds are equally valid because what we observe is predicted by both theories, so currently favouring one theory over the other is a matter of mathematical taste. And it does look more tasteful (one could say elegant) to throw away unnecessary ad hoc postulates such as the wavefunction collapse. Which is what I mean when I say that I would need evidence to sway me towards Copenhagen.

    I again disagree. I also adhere to Tegmark's idea of a purely mathematical universe, so mathematics, logic and reason are nothing less than what you need to understand the universe. And while it may be that our egos are rather inflated, there is no evidence whatsoever so far that what we currently know is the limit of what is knowable to a human being, since almost everything that has been found so far was eventually met with a physical/mathematical theory that explains it, sometimes elaborates on it, and even makes novel predictions, and all those theories were created by human beings.

    More than that, to think that the limit on a human brain is something that cannot be changed also seems to me rather silly. Our IQs on average grow as time passes, and what was once considered an IQ of 170 nowadays might be called a 110. What I mean is that we as a species grow more intelligent as time passes, and I, as a transhumanist, think that if we ever do reach a biological limit to our processing power, we will be able to break even that limit with the technology we create.

    It is just not correct to think that anything that has been thought so far is the limit of what is thinkable. I myself have never studied deeply the mathematics behind Q.M., my knowledge there is sorely missing (the closest I came to that was one-dimensional Schrödinger Equation), but the theory to me seems, however counterintuitive, understandable.

    AH. That. I do think it is falsifiable, though, once we develop AI. If consciousness is ontologically basic, one should never be able to create it from other, smaller parts, right? Like electrons, we can't make electrons out of other stuff. So if we manage to make consciousness out of electrons and all that, I do think his theory falls apart.

    And this may be out of place in a forum such as this, but I detest that movie.
     
  15. Mar 26, 2012 #14
    James,

    Thank you for your articulate and interesting response.

    Fundamentally, what we're disagreeing about here is purely subjective philosophy; there are obviously no firm absolutes. As I am a scientist by nature, I do not dogmatically hold a belief if the evidence points to another direction; I always follow the evidence. However, science, mathematics and pure logic have limits.

    For me, there is a point in reality where mathematics and pure logic appear to be inadequate tools in terms of providing a ground of explanation for certain concepts. For instance, subjective consciousness, love and luck are very difficult to explain from a reductionist perspective. Yes, with love we can analyse the neural correlates of the monoamine system in the brain and develop mathematical models, but can the subjective experience of love ever be explained by mathematics? I very much doubt it! Artificial Intelligence is not even remotely close to human-esque consciousness, and I doubt that it ever will be.

    To reiterate, philosophy is always arguable; however, it is a personal belief that mathematics and logic are too limited in scope to explain the entirety of the universe. I have come to accept that certain things are simply inexplicable.
     
  16. Mar 26, 2012 #15
    Hmm, yes, indeed, that is where we differ.

    I believe everything, including subjective consciousness, love and luck, is explainable by mathematics, and is in fact a direct cause of mathematics (Tegmark's Ultimate Ensemble theory), and in fact, Tegmark does mention the mathematical model of subjective experiences in his exposition about SAS (Self-Aware Subsystems). That is, I think everything that exists is, in principle, explicable, and I don't see any evidence on the contrary.

    And I also think eventually we will be able to build Artificial Intelligence that mimics human intelligence perfectly (and perhaps even surpasses it, with its potential ability of being a perfect Bayesian), and probably will use that knowledge to advance humanity itself beyond the boundaries of mortality. Yes, it does sound like the plot of a sci-fi story, but one can dream (and work to make that dream come true, too).
     
  17. Mar 26, 2012 #16
    Tegmark's mathematical universe hypothesis is an elegant theory; I am fond of it. I would say, though, that this is ultimately a "faith" position. I would actually prefer it if I could believe that mathematics explains everything, but I cannot force myself to believe something that I do not. If you haven't already done so, I suggest that you read about the limitations of mathematics, so that you can view both sides of the argument.
     
  18. Mar 26, 2012 #17
    Tegmark himself claimed that even his MUH (the Level IV Multiverse) was provable and falsifiable, but I am a bit sceptical about that, at least in the foreseeable future. Then again, I am sceptical about scepticism itself, so :P

    Nice, confirmation bias avoidance :)
    But I would ask you to recommend me books and/or articles on that subject, because the closest I've ever seen to a true limitation of math was Gödel's theorem.
     
  19. Mar 26, 2012 #18
    Hi Actuality,

    Remember, MWI is by far the most conservative approach to QM (obviously, disregarding Einstein's interpretation, which we know is wrong), it simply states that because the Schrodinger equation does not make wavefunction collapse necessary, it can be dealt away with. The "many worlds" part comes a side effect.

    It appears more and more likely that decoherance is a better explanation than wave function collapse. As Everett explained, wavefunction collapse is unnecessary, so, following Occam's Razor, it is best to deal away with it.

    To use the example from Everett's dissertation: Imagine two observers A, and B. A is locked within a laboratory, with a particular quantum system S, described by [itex] \psi [/itex]. B is outside the laboratory, and can describe the totality of A and S with [itex]\psi ^{A+S}[/itex]. Now B would say that [itex]\psi ^{A+S}[/itex] was evolving according to the Schrodinger equation as per usual. But what if A takes a measurement on S? What happens according to B?

    The idea of parallel universes comes from Everett's assertion that you can describe the universe as a quantum state. So, as this wavefunction evolves, we get the "splitting" of universes. (to use a terrible term)

    Though, I have to say this: the debate is really irrelevant, because as Ken G said, all that matters is the fact that we can use the equations of quantum mechanics to describe particles. No matter what the interpretations, the equations do not change, so even if somehow an interpretation was confirmed, quantum mechanics would not change. On top of that, almost no one says any interpretation can be confirmed, making it more of a philosophical question in some cases.
     
  20. Mar 27, 2012 #19

    Hurkyl

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    Don't discount pedagogy. The way a subject is presented can make it easier or harder to learn. The way knowledge is organized can emphasize and clarify certain aspects while at the same time being misleading or otherwise obscuring other aspects.



    As an aside, from what I've learned about the history of QM (and long before I had learned about other interpretations like MWI or deBB), I have the impression that the only reason collapse-based interpretations were ever embraced was simply because people thought it was the only choice.

    And, apparently, some people still think that way, because my early readings had informed me of a impossibility proof of alternative interpretations, which I now know to be flawed. (which roughly boils down to "collapse is not unitary, so you can't reproduce it by unitary evolution")
     
  21. Mar 27, 2012 #20
    Hi Mark,

    I do not have a problem with the concept of decoherence. There are a multitude of ways in which one can interpret the collapse of the wave function or, indeed, the "appearance" of collapse. It's all a matter of subjective interpretation of the evidence. Is there any evidence that the collapse of the wave function is an epiphenomenon? If so, could you point me to this?

    There is one main reason why I specifically dislike MWI and is as follows: it grafts on a set of extremely counter intuitive ideas, way beyond what is actually testable. I, for one, believe many of its components are unfalsifiable. Granted, "counter intuitive" does not automatically equate to erroneousness, but still.
     
  22. Mar 27, 2012 #21
    Yes, there is, and it's a simple mathematical principle that states that absence of evidence is evidence of absence. So far we have no evidence whatsoever that collapse itself exists, since we have had no methods of evaluating when it happens and extensive experiments like the Quantum Eraser seem to basically rule out any collapse-like postulates. So, because of such absence of evidence, one would be tempted to believe the absence of the effect.

    Furthermore, for the past many years there have been many discoveries in the field of physics about the way things seem to work in general. A few discoveries specifically about the latest years say that everything in Q.M. is local, linear and unitary. Except for collapse. And we have had a lot of experience with recognising patterns to know when one seems to be a general rule. It's just like conservation of energy: simply true. And so a non-linear, non-local, non-unitary (among other things) postulate, without a proper mathematical formulation, seems a little bit far-fetched to be believed.

    Let's be honest here: for the past hundred years (give or take), intuitive seems to automatically equate to erroneousness. And while this is a light-hearted joke-like statement, it does have a grain of truth in that both very fast and very small things behave in ways that are completely counter-intuitive. Based on that, I would say that being counter-intuitive, while not necessarily evidence for anything, is definitely not evidence against it. We must abandon our human ways if we wish to unravel the secrets of the universe.

    Now let me comment on your first sentence: it is wrong. MWI - or Relative State - starts with one postulate: all isolated systems evolve according to the Schrödinger Equation, and then goes on to state exactly and only two things:
    • The entire Universe evolves according to the Schrödinger Equation, since it is by definition an isolated system.
    • There can be no definite outcome of quantum measurements (collapse) since this would violate the basic postulate above.
    So, if you accept the postulate, that all isolated systems evolve according to the SE, and accept the corollaries, which seem to basically come out of the postulate, you have MWI. As simple as that. So I believe you may be a victim of the misunderstandings of MWI, because the interpretation states nothing else. The postulate and the two corollaries are all MWI says at all. What is counter-intuitive about that? Seems pretty basic and logical to me, at least when you take into account all observations so far.

    I think you should read this to understand the metatheory a little bit better and, if you have any doubts about it, look for answers here.

    On a different topic, you haven't mentioned what limitations of mathematics you were talking about before :P
     
  23. Mar 27, 2012 #22
    Hi,

    Thanks for the reply!

    Wavefunction collapse according to CI is an instantaneous process, hence, decoherance makes it a epiphenomenon. Decoherance has been observed, see here:

    http://www.atomwave.org/otherarticles/gasd_PRL.pdf [Broken]

    I don't understand this. MWI takes only the basic assumptions, and goes from there. It doesn't stand on any "counter intuitive" ground. Let me refine my example from my previous post:

    Say an observer, A, is performing an experiment on a quantum system. Another observer, B, is in the next room. A and B both agree on the state of the system as [itex] \psi [/itex]. Then, A performs a measurement on S. Since B is unaware of A's result, and since the system is a quantum system, B can say A is in a superposition of having observed different quantities. This is the same thing as Schrodinger's cat, except I'm doing it with humans. Same idea though. Let's say A could have observed one of three results, which we'll designate as F, G, or H. So B will say A is in a state [tex] \psi = \frac {F+G+H} {\sqrt{3}} [/tex] So we could say there is a "blur" between three different possibilities of A, that of seeing F, G, or H.

    Now let's say B enters the room, and realizes A observed F. There is now no more superposition. So what happens to the two states where A observers G or H? MWI simply states that they continue to exist. I don't really see a way around this.
     
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  24. Mar 27, 2012 #23
    Okay, mathematical question: why √2?
     
  25. Mar 27, 2012 #24
    Hi James,

    I will peruse the material that you have provided before I respond to your MWI comments. It may very well be that I have misunderstood certain aspects of MWI, so I will take a look at the material and get back to you on that.

    Regarding the limitations of mathematics, did you not find Gödel's ideas persuasive? Analysing it from a different perspective, I am one of those individuals who believes that mathematics was invented rather than discovered. A good example of this is calculus; Newton (or Leibniz) invented calculus, which still has massive utility in theoretical physics. To reiterate from a previous thread, I believe that the universe is ultimately inexplicable to the human mind; we're just not smart enough to understand the entire picture. However, what we have discovered thus far is obviously extremely impressive.
     
  26. Mar 27, 2012 #25
    I find it rather hard to believe that mathematics was invented by humans. It works far too well for that. Even Calculus itself, which was a branch of mathematics invented so that we could describe our physical observations better, describes those observations so beautifully and perfectly it's hard to believe it's manmade. Man is flawed, and I don't mean in the deep, philosophical sense of the word. I am talking about biases, about flaws in rationality that plague man thought to this day, the kind of flaw that created witch-doctors and other superstitions. It would be rather uncanny that a model developed by man could fit the data so impressively.

    Furthermore, do you not think that, whichever notation they may use, other kinds of alien intelligence will have arrived in the same mathematics that we have? I find that rather unlikely, because there is just such a deep truth in mathematics. 2 + 2 = 4 wherever you are, and it always will.

    As a matter of fact, that is the main argument against that: everything man made can be corrected and changed (in the spirit of the topic, physical theories and interpretations are manmade, which is why they have so many problems). But math cannot be corrected and changed. Math itself cannot be wrong. It may be wrongly used, but it's not wrong. It simply is. I don't know where in the universe the deep truth that the perimetre of a circle divided by its diametre equals ∏ is, but it is true regardless of referential, regardless of what you do. It is literally unimaginable for the universe to behave otherwise.

    On Gödel's theorem, I don't think that is a true limitation of mathematics. Tegmark himself has commented that possibly the only MUHs that effectively exist are Gödel complete ones, which would explain why our universe is so simple.

    Now I have a personal question to ask, and it is the basic question of the rationalist. What do you know and how do you think you know it? Or otherwise formulated, why do you believe what you believe? Why do you think we're not smart enough to understand the entire picture, if we have understood every single picture so far?

    And even if we hadn't, what would make you think that the pictures we hypothetically don't understand aren't understandable? What's so special about them that makes them different from all the other explanations humanity has had to deal with before?
     
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