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Interpretation of Q.M. (with more options!)

  1. Copenhagen

    6 vote(s)
    14.6%
  2. Many-Worlds, a.k.a. Many-Histories, a.k.a. Relative State

    6 vote(s)
    14.6%
  3. Ensemble

    4 vote(s)
    9.8%
  4. de Broglie/Bohm

    8 vote(s)
    19.5%
  5. von Neumann

    0 vote(s)
    0.0%
  6. Quantum Logic

    0 vote(s)
    0.0%
  7. Time-symmetric theories

    1 vote(s)
    2.4%
  8. Stochastic

    0 vote(s)
    0.0%
  9. Many-Minds

    0 vote(s)
    0.0%
  10. Consistent histories

    0 vote(s)
    0.0%
  11. Objective Collapse

    0 vote(s)
    0.0%
  12. Transactional

    0 vote(s)
    0.0%
  13. Relational

    0 vote(s)
    0.0%
  14. Other (do post which one!)

    4 vote(s)
    9.8%
  15. Don't know / Agnostic / "Shut up and calculate"

    12 vote(s)
    29.3%
  1. Mar 31, 2012 #1
    I know, I know, it might be a little bit spam-y to post another poll, but since the option 'Other' was gaining so much attention, I decided to create a new poll with more options so that people could be more accurate in their description.

    Since I support the MWI, I will post a few links with more information about it for people who are undecided and interested in knowing more about the different interpretations. Everyone else should feel free to do so, too!


    I should also note that I got the list of interpretations from Wikipedia and so if you have any doubts about the contents of an interpretation and no one has posted anything about it, you can check the article there.

    --EDIT:

    And I apparently forgot to put Popper's Interpretation there, too. Oh, well :/
     
    Last edited: Mar 31, 2012
  2. jcsd
  3. Apr 1, 2012 #2
    I'm feeling bad for doing this but whatever, bump! /\
     
  4. Apr 1, 2012 #3

    HallsofIvy

    User Avatar
    Staff Emeritus
    Science Advisor

    What is your point? You didn't like the other polls that asked exactly the same thing?
     
  5. Apr 1, 2012 #4
    Well for one I didn't find any (other than the last one, which I started).

    And it has been suggested in it that I should make another one, with more options, since so many people there were voting for the option 'Other (which?)', so I did, and posted the link there. It's pretty much dead, but I'm still curious about what interpretation all the people who voted for 'Other' were really thinking about.

    --EDIT:

    And now that I did look further, the last one was in April of 2011, and it did mention 'annual poll,' so maybe I contributed to a starting trend somehow? XD It's always good to know more, even if it's something as silly as how many people like this or that view of the world.
     
    Last edited: Apr 1, 2012
  6. Apr 2, 2012 #5
    Voted de Broglie/Bohm because I know it is deterministic, but I'm curious... which of the other ones are also deterministic?

    Your MWI seems to have a delusion of being deterministic, on some grand objective level, but that determinism is completely lost for any subjective observer.
    On one side, I realise that asking "why am I in this world and not another" may be too philosophical, maybe even downright pointless, a bit like "why am I myself and not, for example, you", or "why am I now instead of, for example, yesterday or next year".
    On the other hand, without being able to answer "which world will I end up in upon this split", it seems completely stupid to me. Rolling dice for chosing a world is completely equivalent to rolling dice for a wavefunction collapse, and I don't like either.
    And actually, on a third hand :p even if it were able to answer the above question, it would still seem completely stupid to me. The "other worlds" are in either case completely unobservable, redundand entities, that should obviously be dealt away with by Occam's razor.

    Also, are all of the options actually interpretations? Time-symmetric theories in particular seem like an interesting alternate mathematics that may be usable and compatible with all other interpretations. It is not an interpretation in and of itself, it doesn't tell you what the meaning of the math is. Or I have misunderstood it with the whole 10 minutes that I dedicated to checking it out :p
     
  7. Apr 2, 2012 #6
    Well, no, it should not be dealt away with by Occam's Razor. Occam's Razor deals with the complexity of a theory, it says nothing about entities or universes, and since the Universe is already infinite, flat and ergodic, Nature doesn't seem to mind spending more energy and doing more stuff. And in a Universe that is already infinite, flat and ergodic, there are other 'yous' out there, in galaxies far far away, so there is nothing qualitatively new about the many-worlds approach.

    Furthermore, the Many-Worlds seems, to me, to be the simples one, Occam's Razor-wise. It does not state other worlds, that's not an axiom of the theory. It has one major proposition, that every closed system evolves according to the Schrödinger Equation; and two corollaries, which seem to directly follow from the proposition:
    1. The Universe evolves according to the Schrödinger Equation, since it is by definition a closed system;
    2. There can be no real wavefunction collapse, because that would violate the postulate.

    That is everything that's said by the Relative State Interpretation (its original name). It says nothing else. The multiple worlds just follow naturally from that, because otherwise, well... you would have to assume that conscious observers are somehow treated differently by physics. I mean, if viruses can be in superpositions, why can't you? Why would you be that special?

    And that last part is also a criticism to one of your arguments. 'Seem completely stupid to me' sounds like a very human observation, and when dealing with the Universe in its true colours, you really, really should avoid using human intuition at all costs.

    Also, the whole is simpler than its parts. Tegmark uses Einstein's Field Equations to exemplify this: any general solution to the Equations is much simpler than a specific one, because the specific one needs the general plus a multitude of initial conditions and extra variables that define it. Same goes for the Universe. A Universe that includes all states is much simpler than one that contains only one of them.

    And since all those worlds are specifically real, and no 'you' is 'youer' than the other 'you', the question of why you are here and not there is really pointless. You are there, too. And you are here.

    Furthermore, there are a few people (Tegmark and Hawking included) that think it will be possible to detect the other Everett-branches in the future, somehow. I won't get into details here, because I myself have never really looked into it. In my head, Relative State seems to be the simplest, most natural one to follow, given the basic assumptions of the Quantum Theory.

    Finally, from your answer, I think you have not read the paper I suggested above (Tegmark's) :P Even if you disagree completely with the theory, you really should read it, to have a better idea of what it is you disagree with.

    The answer to your question is I do not know. In the other poll I made about this someone told me I should make a new one, with more options, and sent me a link to the Wikipedia article about the interpretations, and I just vomited them here.
     
  8. Apr 2, 2012 #7
    Sorry, I didn't mean to derail the thread and turn it into a discussion of the merits of one particular interpretation. Also, I apologize for calling it "stupid", that was just my subjective feeling about it, but could just as well be indicative of the amount of information and understanding I have about it.

    To me it seems a model with some unobservable, affecting nothing, i.e. entirely redundant entities, is made simpler by removing them from the model.
    But I will be the first to admit, I do not know enough about the theory and wether other worlds are really unobservable and redundant. If a way to detect or interact with them is ever found, then this theory will be worth considering. Until then, it is not for me. Feel free to prefer it for yourself though.

    I will read the things you linked later, if there isn't much math in them :p
     
  9. Apr 2, 2012 #8
    My personal opinion on this matter is to shut up and calculate. It suffices for me to see that in Quantum mechanics when looking at curves that are predicted by classic Lagrangian Mechanics the possible Quantum Mechanical paths are smeared out around the path predicted by Lagrangian Mechanics. Lagrangian Mechanics assume that the principle of minimized action holds true and thus we would only have one possible path predicted by the minimized action. In quantum mechanics it is easy to see that the paths closer to the path of minimized action are just more likely than one's stray from this path. So essentially quantum mechanics works better because it softens out a classical assumption. One could easily say that then energy what is used to make qm predictions(as the Hamiltonian operator in the Schrödinger equation or dirac equation or also Klein Gordon equation) might not be sufficient to describe a whole system. However then we would reach hidden variable theories that in my opinion seem quite unlikely for some experiments were done in quantum optics based on Bell's Inequalities. Also one should take a look at mathematical physics and how the dirac equation can essentially only be dirived from assuming that particles have mass and that the universe(at least to approximation) has Lorentz-Symmetry. You look for representations of the Lorentz-group on a Hilbert Space. One gets even better equations when trying to look for representations of the Poincare-group. Those representations have to be either unitary or anti-unitary so that when doing a transformation from one system of reference to another one gets the same probabilities for a measurement. If A is a representation of the Poincare group on a hilbert space and |ψ> and |ψ'> are vectors on that hilbert space then <ψ|ψ'>=<Aψ|Aψ'>=:<∏|∏'> has to be true(∏ and ∏' are the vectors ψ in a transformed frame of reference). So for this to be true only unitary representations of the Poincare-group are interesting. With these ideas you can pretty easily kill major parts of quantum field theory.

    So to sum it up how i would understand quantum mechanics:
    Space has some kind of symmetry and this symmetry predicts how particles/or fields behave on this space. As a field of course once you measure something you influence this field and so the field behaves differently. It is easy to compare it to a sheet of paper if you try to press the edges of the paper the paper ripples and you get to see something else than you would have otherwise. The problem with quantum mechanics is to do measurements you need to ripple the paper and so the theory behaves differently once measurement is involved.
     
  10. Apr 2, 2012 #9
    No, no math at all! (Well, except for the third one, there's math in it XD)
    But as I said, Many-Worlds does not propose the multiple parallel universes. They are just not there in the theory. They are an epiphenomenon of the theory. They are explicitly anywhere in the model. The model just states what I mentioned above, about the Schrödinger Equation governing the whole Universe.

    Also, I do believe we should discuss interpretations here. If not here, where? It's as good a thread as any, and by discussing, we can both review our own concepts and beliefs and throw away those that we no longer believe. Update our probabilities, that is.

    That is indeed an annoying problem. But I myself prefer to subscribe to an interpretation because I do think here's an universe "out there" behind the math. I want to make my inner map as close to the real territory as possible, within the limits of my understanding and knowledge.
     
  11. Apr 2, 2012 #10
    Maybe i should put it a bit differently essentially everything bahaves like the equations predict because they are direct consequence of fundamental symmetries of space. Imagine a sheet of paper doing wave motions or anything like it if you have no boundary conditions you can choose a phase rather arbitrarily. However once you do a measurement depending on the exact properties of that measurement it acts as if you press something at the sides of the paper(from within the paper) the sheet gets rippled at the place where you do the measurement. The exact properties at where you touched the paper will then depending on the state of the paper ripple in different ways. However the act of touching the paper cannot be part of the apparatus describing the sheet of paper itself(at least not if you want a easy theory). So what you get in the end is a probabilistic result on how the sheet of paper might ripple if you touch it(do a measurement).

    Maybe this is equivalent to the Copenhagen Interpretation afterall but at least it is in a lot easier to grasp terms(i think).
     
  12. Apr 2, 2012 #11
    Hm... except that is wrong. The Uncertainty Principles are not technical measurement problems, they are embedded into Nature itself. It's not because our measurement affects the system that it holds, because we can nowadays measure position or momentum with arbitrarily large certainty, but Nature forbids us to possess both pieces of information at the same time.

    The notion that such relations hold because it's impossible to measure without disturbing the system is an old one, but it's also a false one. Otherwise, the Uncertainty Principle would have to be revised whenever new measurement technology that influences *less* the results was invented, and that is just not the case.
     
  13. Apr 2, 2012 #12
    I wouldnt see where i implied that uncertainty is a measurement problem. This was just a comparison by picture why a wavefunction would behave differently after a measurement was done. Actually even this picture implies that the uncertainties are NOT results of the measurement. Rather it implies before the measurement is done the system behaves differently the unrippled sheet of paper and as thus already has uncertainties encoded because the properties you measure actually only come as a result once you do a measurement(by rippling it).

    So to sum it up the papersheet behaves according to the symmetries of the system. Then when you ripple it some of that symmetry is broken. Then you measure properties that are actually not well suited to describe the system. Depending on how you broke the symmetry the wavefunction will be differently projected onto a new wavefunction. You get your properties from that new wavefunction that has some uncertainty encoded that result from its origin.
     
    Last edited: Apr 2, 2012
  14. Apr 2, 2012 #13
    In that case... unless I'm misunderstanding your idea, I really don't see any specific interpretation there, just the mathematical core of Q.M. - that is, really, the shut up and calculate part.
     
  15. Apr 2, 2012 #14
    I guess you could say that since exactly the way the calculation is done how understand that. The sheet of paper i gave as an example is just a way to visualize it in an intuitive way. I would not see why that is less intuitive than lagrangian mechanics(relativistic or not).
     
  16. Apr 3, 2012 #15
    Oh I wouldn't say Lagrangian mechanics is intuitive at all! XD The model you proposed seems to be a good intuitive overview of an approximation to Q.M. that could be used more or less as an introduction to newcomers to the theory.

    On the other hand, the different interpretations are theoretically supposed to be analysed by people who already have a firmer grasp on the theory and wouldn't really need the intuitive model to work with it.
     
  17. Apr 4, 2012 #16
    To me Lagrangian mechanics always seemed more intuitive than Newtonian mechanics in the sense that you are first forced to consider a system in the simplest way possible and then write down the properties you know about it. Everything else is done by the formalism that involves only one big assumption namely that action is getting minimized. This is very easy to translate into mathematical terms. Newtonian mechanics in contrast seems a lot less intuitive in the sense that a lot of guess-work is involved in the description of a system. Ussually the equations of motion have to be guessed. By that i mean one has to guess which differential equation approximates the system best. For somebody trying to understand what somebody else is doing Newtonian mechanics are harder to grasp since by nature it leaves gaps in the chain of thoughts. Lagrangian mechanics or Hamiltonian mechanics for that matter do not.

    I thought the model i gave very easily replicates what steps of calculations are needed to get average values. <A>=<ψ|A|ψ>=:<ψ|∏>. essentially you check how well the papersheet (a analogy to the wavefunction) before the measurement and after the measurement are aligned (the operator used on a wavefunction defines a new wavefunction). So maybe it is not much of an interpretation but a replica of the maths combined with a picture to imagine the maths involved.
     
  18. Apr 5, 2012 #17
    Pretty much, yes. I think that fits the "Shut up and calculate" idea :P

    But again, I, personally, like having a model in my head of what's behind the math on a "grand" scale, or whatever you want to call it. Why we get the results we do, especially on the subjects that are more controversial (like entanglement and collapse).
     
  19. Apr 5, 2012 #18
    I think Quantum Field Theory from the view of mathematical Physics gives a lot more answers than Quantum Mechanics. With that anything in space behaves according to fundamental symmetries and particles(as you measure them) and their properties are a consequence of those symmetries. The existance of only two types of statistics(Fermi-Dirac and Bose-Einstein) for particles in 4-space as an example can also be seen as direct consequence of that particles that are seperated in a spacelike manner cannot influence eachother's measurement results. In this way i find entanglement not to be too surprising. Maybe a too simplified analogy would be that if one were to throw a snowball of 1kg against a knife nobody would be surprised to find that if one half was 600g that the other is 400g. To be more general entangled particles were in contact once so why is it surprising that from the measurement of one of them one is able to predict the measurement values at the other one? Separated spacelike means they could not have been in contact with eachother (and yes the property that particles such as this could never have been in contact with eachother is used in axiomatic qft to derive what i said about statistics).
     
  20. Apr 5, 2012 #19
    I wouldn't place at the same level the "Don't know / Agnostic /" option with the "Shut up and calculate". These are very different categories.

    Anyhow, my option is any theory that abolishes completely the notion of particles, waves, even no strings or branes which I perceive as 'objects' which completely are at odds with QM, and where time and space are emergent properties.
     
  21. Apr 6, 2012 #20

    strangerep

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    Science Advisor

    If you demand invariance of probabilities, i.e.,
    $$
    \def\<{\langle}
    \def\>{\rangle}
    \frac{|\<ψ|ψ'\>|^2}{\<ψ|ψ\> \<ψ'|ψ'\>}
    $$
    then both unitary and antiunitary transformations are possible. But the antiunitaries usually only involve time reversal.

    Huh?? Weinberg (and others) develop modern QFT precisely by constructing causal field representations of the Poincare group.

    Actually, one only needs little more than the theory of good ol' unitary irreps of SO(3) to get that result.
     
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