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Copenhagen Interpretation vs Instrumentalism

  1. Dec 14, 2013 #1
    For 2 years now I have been reading posts at my university student forums about how the Copenhagen Interpretation is redundant because ensemble physics is the equivalence of CI and it is ensemble that is used in day to day physics. While I sympathize with applied physics and engineering I just see ensemble as an instrumentalist view that doesn't ask the sort of larger questions that where getting asked a Solvay. I just see instrumentalists as not wanting to make too much out of the metaphysical connections between maths and the physics.

    So anyway someone is trying to convince me that Quantum Physics is in a muddle. That we don't need to be going down the path of non-locality and can safely use almost classical type explanations. The paper they cite is Marcella on Quantum Inference Slits.
    http://arxiv.org/ftp/quant-ph/papers/0703/0703126.pdf

    I found a rebuttal quantum inference revisted by Rothman, Boughn.
    http://arxiv.org/abs/1009.2408

    I may have got something wrong on my understanding. I think the Marcella paper is a hidden variable and contradicts Bell inequality. I was told no it doesn't. ok. but I also pointed out that the paper contains problems with equation #5 and it appears Rothman has identified Marcella is saying nothing new and presents us with models that are well known and it turns out to be a case of normal problems in classical optics.

    I think Marcella can be rejected on the grounds put forward by Rothman. One argument they have made is that Rothman can't critic Marcella for using Dirac Formalism if Bell used it also. However I think Bell based his work on Bohms non-local hidden variable. Anyway I have been told that in textbooks Bell uses Dirac's formula and therefore the critic isn't valid.

    Now for some reason I think they don't understand Marcella's paper or the rebuttal but I could be wrong.

    I have always believed that CI as an interpretation is not equivalent to other interpretations but have been told that Bohms model is just as right but that ensemble is better. So I have a grasp of the interpretations, I just don't understand why ensemble is supposed to be better or even if it works at all!

    Also is ensemble saying the interference pattern on the screen in the double-slit experiment is just coincidentally like one waves would make, but its really just random scattering of particles and no waves are involved at all??? Yet isn't particles in oscillation waves?
     
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  3. Dec 14, 2013 #2

    ZapperZ

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    I don't get it. How is the Marcella paper an evidence that we do not have to go down the non-locality path? The Marcella paper is merely trying to show the derivation of the interference pattern without resorting to the classical wave picture. The fact that these are based on the same wave function as the standard Schrodinger equation means that it has the same non-locality consequences as that implied on the EPR-type experiment.

    Zz.
     
  4. Dec 14, 2013 #3
    ok, so is it correct? The rebuttal paper says no.
     
  5. Dec 14, 2013 #4

    ZapperZ

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    The rebuttal paper is arguing that Marcella wasn't completely kosher in employing no classical scenario in his derivation. However, the argument presented doesn't quite justify the premise, because what Marcella did was simply applying the various paths that photons can pass through the slits.

    In any case, neither paper makes ANY connection to the original premise of your thread. This is what I do not understand.

    Zz.
     
  6. Dec 14, 2013 #5
    Okay let me ask this. The Marcella paper, I was told this was ensemble and that ensemble is better than CI. That's it in a nutshell. However I don't see how given Bell's inequality and entanglement seem to suggest CI is correct.
     
  7. Dec 14, 2013 #6

    bhobba

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    The ensemble and CI are closely related. The difference is similar to the difference in the frequentest interpretation and Bayesian probability:
    http://en.wikipedia.org/wiki/Ensemble_interpretation
    http://en.wikipedia.org/wiki/Copenhagen_interpretation

    Ensemble is not better than CI, nor indeed is any interpretation better than another. There is no way to experimentally decide between any interpretations - that's why they are called interpretations. Any interpretation handles Bell and non locality equally as well as any other - of course in a different way - and you may prefer one way over another - but they all accommodate it. The choice is simply what appeals better - same with the choice between Frequentest and Bayesian probabilities.

    I personally hold to the ignorance ensemble interpretation with decoherence because it has features that appeal to how I view QM as simply the most reasonable probability model that incorporates entanglement, which I think is the rock bottom essence of QM. But that's just me - others do not view it that way - it doesn't make them wrong and me right or conversely.

    Thanks
    Bill
     
  8. Dec 15, 2013 #7
    Is ensemble science though?

    From what I can see instrumentalism has criticism in that it isn't addressing the questions of pure science (why) but those of applied science (how) and engineering (just use it).

    The problem I have with equivalence is parsimony.

    For example, Bohm's model requires extra explanations than CI because it has to explain the hidden variable pilot wave. So its more complex. But CI claims to be complete.

    Is CI a complete description of QM? Does ensemble/instrumentation answer the questions put forward at Solvay?
     
  9. Dec 15, 2013 #8

    ZapperZ

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    This is now veering into philosophy, which is a banned topic. Unless it comes back to actual physics discussion, this thread will be closed.

    Zz.
     
  10. Dec 15, 2013 #9

    bhobba

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    Of course it is in exactly the same way the frequentest view of probability (which the ensemble view is related to) is science, which any book on probability with a proof of the law of large numbers from the Kolmogorov axioms will attest to.

    If you want the gory detail for the Ensemble interpretation one associates the concept of probability in the axioms of QM with the Kolmogorov Axioms and derive the ensembles from the law of large numbers.

    Errrrr. It's purely an honorific title indicating it required a significant amount of research and a thesis as opposed to say a Dr of Physiotherapy. Science divorced itself from philosophy ages ago, and by forum rules is not what we are concerned with here.

    If this thread isn't closed I am happy to discuss the issue of exactly what a state is in CI and ensemble. But its simple really. Its got to do with how each views probability - CI takes the Bayesian view that its a subjective state of knowledge and a quantum state that encodes such applies to a single system. The Ensemble interpretation takes the frequentest view and relates the state to a conceptual large number of similarly prepared systems, just like the frequentest view of probability relates it to how a large number of trials behave.

    QM has come a LONG way since Einsteins and Bohr's debates at the Solvay conference. Einstein said to Bohr is the Moon there when you are not looking to which Bohr replied - in relation to that and other questions - stop telling God what to do. The joke is we now know both were wrong - the Moon is being observed all the time by the environment and that's how the classical world emerges.

    If you really want to understand the modern view get a modern book on QM like Ballentine - QM - A Modern Development.

    The following by Weinberg may help (see the section Contra Quantum Mechanics):
    http://scitation.aip.org/content/aip/magazine/physicstoday/article/58/11/10.1063/1.2155755 [Broken]

    Thanks
    Bill
     
    Last edited by a moderator: May 6, 2017
  11. Dec 15, 2013 #10

    ZapperZ

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    You are stuck with historical semantics! That's the same as asking why there is nothing spinning when we use the term "spin angular momentum quantum number"! The "philosophy" in PhD has nothing to do with formal philosophy. It shows you don't know anything about a physics curriculum.

    I don't "threaten" a ban. The topic IS already on the banned list of the PF Rules that you had agreed to upon joining this forum! I can turn around and question your word of promise as well! If you want to know why philosophical discussion with very little science content is prohibited in PF, read the relevant threads in the Feedback forum. We have already heard all that argument you are giving. You are late to the party.

    Again, unless this has physics content and not simply based on philosophy or a matter of personal tastes, it will be closed.

    Zz.
     
    Last edited: Dec 15, 2013
  12. Dec 15, 2013 #11
    Frequentest view of probability is science? Wait. This is maths. I have done stats. How do you link the frequentest view of probability with physics?

    The core concept of probability, in QM, as far as I can understand it, is a probability amplitude from Born's rule. So are you saying the axioms upon which a probability amplitude is based upon is somehow used in conjunction with Kolmogorov to build the ensemble model? So what exactly is it that ensemble does that CI doesnt? Are you reverse engineering CI models and throwing out all the stuff you think is subjective 'baggage' or what?



    I think we all take it that we use some philosophy here in making our deductions etc. That was the point I was making and I bet most PhD dissertations have plenty of that... at least I HOPE!

    Thanks for the book link. I will check it out but need to get to the bottom of this ensemble business first. Maybe you have answered something here in the last part though I need to look into more.
     
  13. Dec 15, 2013 #12

    Nugatory

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    Ensemble and Copenhagen make the same predictions for the results of any imaginable experiment and therefore cannot be experimentally distinguished; we cannot say that one is more "right" than the other. Thus, your choice of interpretation is to some extent a matter of personal taste (and even the problem you're working on at the moment - I find Copenhagen helpful for reasoning about local photon polarization experiments, but not so helpful for reasoning about spacelike-separated measurements of entangled particles).

    The statistical interpretation pleases by not introducing the unnecessary and sometimes problematic notion of wave function collapse; annoys by obstinately refusing to speak to what's "really" happening; pleases by standing on a fairly rigorous axiomatic base; annoys by promising little and still claiming sufficiency; and pleases by delivering everything that it promises. Obviously "pleasing" and "annoying" are subjective terms, but as long as both interpretations work, that's all we have to go on and you are free to assign these values any weight you want.
     
  14. Dec 15, 2013 #13
    I read Weinberg before on his criticism. I have kept it in mind, yet doesn't the classical also touch on the quantum in the same way. Like for example using quantum processes in classical models. :)

    It seems to me though that you have said something here I have been considering. You said the moon is being observed all the time by the environment. This is pretty much the position of empiricism that rejects idealism interpretations right? So if this is the case, what do we say is going on? That the universe is one big experiment and that in a deterministic way it has a definite history but the future is probabilistic because of QP? Well that would be wrong of me. There is determinism in nature. In the human zygote, sex is determined for example, but on the quantum scale, it isn't like this. So what mechanism is going on in this environmental/moon interaction. I am interested.
     
    Last edited by a moderator: May 6, 2017
  15. Dec 15, 2013 #14

    bhobba

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    Easy - conceptually, or if you are a glutton for punishment actually do it, conduct an experiment, observation, whatever a number of times.

    As you mention, this involves the Born rule which says given a state P and an observable O the expected value of the observation is Trace (PO). Expected value is a concept of probability the underlying basis of which depends on your view of probability. For frequentests its the behavior of a large number of trials, for Bayesian's its an extension of propositional logic. You can look up Wikipedia for further details. Which view you ascribe to determines your view of the state P.

    BTW I need to mention something very important - Gleason's Theorem:
    http://en.wikipedia.org/wiki/Gleason's_theorem

    It shows Born's rule basically is determined by the properties of observables - the state P is simply a requirement derived from that.

    Read a few and make up you own mind - here is one:
    http://physics.lamar.edu/rafa/dissertation.htm [Broken]

    Here is another at Masters level on Gleason's theorem I mentioned previously:
    http://kof.physto.se/theses/helena-master.pdf [Broken]

    But most would say, except for those in philosophy itself its really got nothing to do with it.

    Ballentine's textbook explains the Ensemble interpretation carefully and completely - its considered THE book on it. You would be mostly interested in the first 3 chapters and Chapter 9.

    The most recent view however is QM is basically one of the two most reasonable probability models that can be used in describing physical systems:
    http://arxiv.org/pdf/quant-ph/0101012.pdf

    This is my view.

    Thanks
    Bill
     
    Last edited by a moderator: May 6, 2017
  16. Dec 15, 2013 #15

    bhobba

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    I cant comment on the philosophy stuff, but its got to do with decoherence and apparent collapse. Copenhagen, and Ensemble for that matter, partitions the world into classical and quantum and QM is a theory about 'marks' left in the classical world. But that cant be correct - everything is quantum, and QM is supposed to explain the classical world, so how can a theory be formulated in terms of that world explain it? This is the real quantum mystery - not what Einstein and Bohr debated - and what Weinberg correctly points out. Much progress has been made - but issues remain.

    You can read about it here:
    http://philsci-archive.pitt.edu/5439/1/Decoherence_Essay_arXiv_version.pdf

    The above is a fair and balanced view of the issue, but I need to mention I personally am not as pessimistic about if it solves the central issue. It doesn't - but I am happy with - for all practical purposes.

    Thanks
    Bill
     
    Last edited: Dec 15, 2013
  17. Dec 15, 2013 #16

    Nugatory

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    I think you're reading too much into that word "observed". We choose that particular wording only to suggest that the quantum mechanical notion of "observation" neither requires consciousness nor necessarily conflicts with macroscopic realism; that is, no one is seriously suggesting that the moon isn't there when nobody is watching.

    There is, but that macroscopic determinism is not inconsistent with microscopic randomness. Even in classical physics, we've always recognized that macroscopic determinism ("I apply a force of five newtons to a one kilogram mass and it WILL accelerate at five meters per second per second") can in principle be analyzed at a microscopic level ("Look at all those charged particles that make up the idealized one kilogram mass, work out their equations of motion, see what the center of mass does"). The success of statistical mechanics when it's infeasible to do that "can in principle" analysis just goes to show that we can accept randomness at the microscopic level yet still experience determinism in (macroscopic) nature.

    [As an aside for newcomers to this thread: In this context, a human zygote with 1015 or more atoms in it is a macroscopic system, even if you need a microscope to observer it directly]
     
  18. Dec 15, 2013 #17

    Dale

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    Even for an "interpretations" thread this one has gone downhill fast.
     
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