Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Copenhagen interpretation of Quantum Theory

  1. Jun 12, 2006 #1
    I found a website that says:

    "The still-dominant "Copenhagen interpretation" of Quantum Theory developed by Niels Bohr, Werner Heisenberg, Wolfgang Pauli, and others says two basic things:

    1. Reality is identical with the totality of observed phenomena (which means reality does not exist in the absence of observation), and
    2. Quantum mechanics is a complete description of reality; no deeper understanding is possible."


    Is it true that the "Copenhagen interpretation" of Quantum Theory is the dominant theory?

    And is number 1 and 2 true?

    Is it also true that the 'rules' of the Universe seem to change reflect the 'maths'.

    Is it also true that Non-Locality (defined as phenomenon that occurrences on one side of the Universe can instantly effect 'matter' on the other side of the Universe) happens? (Im not sure if 'happens' is the correct word to use here.
     
  2. jcsd
  3. Jun 12, 2006 #2
    the Copenhagen Interpretation hasn't been 'dominant' for many years -

    “Political scientist" L David Raub reports a poll of 72 of the "leading
    cosmologists and other quantum field theorists" about the "Many-Worlds
    Interpretation" and gives the following response breakdown [T].

    1) "Yes, I think MWI is true" 58%
    2) "No, I don't accept MWI" 18%
    3) "Maybe it's true but I'm not yet convinced" 13%
    4) "I have no opinion one way or the other" 11%

    Amongst the "Yes, I think MWI is true" crowd listed are Stephen Hawking
    and Nobel Laureates Murray Gell-Mann and Richard Feynman. Gell-Mann and
    Hawking recorded reservations with the name "many-worlds", but not with
    the theory's content. Nobel Laureate Steven Weinberg is also mentioned
    as a many-worlder, although the suggestion is not when the poll was
    conducted, presumably before 1988 (when Feynman died). The only "No,
    I don't accept MWI" named is Penrose.

    The findings of this poll are in accord with other polls, that many-
    worlds is most popular amongst scientists who may rather loosely be
    described as string theorists or quantum gravitists/cosmologists. It
    is less popular amongst the wider scientific community who mostly remain
    in ignorance of it.” http://www.anthropic-principle.com/preprints/manyworlds.html



    non-local interpretations of QM have been shown to be unphysical: http://arxiv.org/abs/quant-ph/9906007
     
    Last edited: Jun 12, 2006
  4. Jun 12, 2006 #3
    So what is the dominant quantum theory among the physicists? Can someone sum up the major conclusions of the dominant theory about quantum physics please?
     
  5. Jun 12, 2006 #4
    as the reference to the poll indicates- it is MWI- since this poll the MWI has been experimentally verified http://www.quiprocone.org/Protected/Lecture_2.htm - since around the year 2000 the Everett interpretation has been confirmed as the only EXPERIMENTALLY VALID interpretation of QM- all other [non multiverse[ interpretations no longer fit with observations- as a result we now have the field of quantum computers- which are only predicted and described by the Everettian MWI-
     
  6. Jun 12, 2006 #5

    DaveC426913

    User Avatar
    Gold Member

    Does MWI invalidate the outcome of Schrodinger's thought experiment - that the cat is both alive and dead until observed?

    Seems to me MWI says that we find ourselves in one of the two possible worlds (oversimplifying), either the 'alive cat' one or the 'dead cat' one.
     
  7. Jun 13, 2006 #6
    That makes no sense to me. Isn't it Quantum Mechanics itself which is verified, not any given interpretation. The interpretations are different ways of viewing and ranking the importance and reality of mathematical entities in Quantum Mechanics and this can't be tested in experiment.

    I also think, though I'm not sure, that Hawking believes that there is probably other universes, in the form of disconnected spacetimes, rather than in the sense of QM's many worlds view.
     
  8. Jun 13, 2006 #7

    ZapperZ

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    You have made this assertion many times on here, and I think it is about time you are challenged for it.

    1. The VERY FACT that one can conduct A POLL on this means that the acceptance of some form of interpretation of QM means it is still A MATTER OF TASTE! Real physics isn't done this way. You cannot simply adopt something and call it physics when all you can base it on is PREFERENCE! So by the very act that you are citing A POLL of OPINIONS shows CONCLUSIVELY that this is NOT a done deal! Don't you see this?

    If you don't believe me, show me any other part of accepted physics that is done via such a popularity contest. Did the acceptance of BCS Theory of Superconductivity done via such a similar poll? Or was it simply based on an astounding body of evidence?

    2. If you think MWI has already a slam-dunk case and is widely accepted, please open a QM text that is being taught to undergraduate physics students all over the world and show me where such a scenario is being used.

    3. If you think MWI is generally accepted to be the ONLY interpretation of QM, please look at, for example, Tony Leggett's paper[1] on the Schrodinger Cat-type states and point out to me where he has used such interpretation to derive the coherence energy gap in those SQUID experiments from Delft/Stony Brook.

    Zz.

    [1] A.J. Leggett, J. Phys.: Cond. Matt v.14, p.415 (2002).
     
    Last edited: Jun 13, 2006
  9. Jun 13, 2006 #8

    vanesch

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    This has even an interesting note (which I have from Penrose's book "The road to reality"). In fact, Penrose argues that a MODIFICATION of quantum theory is in order, for he doesn't see how ONE CAN ESCAPE the MWI picture if the current quantum formalism is to hold universally (including Penrose's last refuge, which is gravity).

    So Penrose's reasoning is rather: current quantum formalism LEADS automatically to MWI, and because that's a view I cannot accept, a *modification* of the formalism is probably due.
     
  10. Jun 13, 2006 #9

    vanesch

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member


    I don't think the point was that MWI is *the* accepted view on quantum theory. But whenever it is mentioned (I can testify about that), it provokes vivid reactions by some, as if it were some totally crazy fringe view one shouldn't really consider. And this, it isn't either.

    As you point out, the interpretation doesn't really matter it you really want to do physics: one should pick one's interpretation with which one can devellop ones intuition best. As you know, I prefer MWI for that - for me, it eliminates a lot of "bogus" questions IMO. You have your own view, which probably satisfies you also most.
     
  11. Jun 13, 2006 #10

    ZapperZ

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    But vanesch, I'm rebutting the claim that ".... as the reference to the poll indicates- it is MWI- since this poll the MWI has been experimentally verified...."!

    This is bogus, and I'm surprised you didn't address this. I have seen no experimental evidence that validates MWI and invalidates others. Have you?

    Note that nowhere in my criticism was there any denegration of MWI.

    It is, however, ethically dubious that, while in support of MWI, one also turns a blind eye when there are outrageous claims being made such as what setAI was doing. I would like to see this "experimental" evidence that singly verified MWI and nothing else.

    Zz.
     
  12. Jun 13, 2006 #11

    vanesch

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    I started a post on it, and then I killed it because I didn't like the way I wrote it :-)

    Of course, at the point we are now, all interpretations being empirically equivalent, there' s no way to prove one over another.

    However, there's - at least in principle - a way to distinguish views where there is a genuine, irreversible collapse and views - such as MWI, but also such as Bohmian mechanics for instance - where the superposition remains forever, by trying to observe quantum interference phenomena at "macroscopic" scales.
    In this sense, the "superposition for ever" views are in fact more falsifiable than the "I put my Heisenberg cut somewhere, but I can pick were I want" views, because if the quantum interference is not observed, then the first class of views is ruled out, while the second class has always enough wiggle room to wiggle out.
     
  13. Jun 13, 2006 #12
    the only interpretation of QM that succesfully predicts quantum computing is the MWI- Deutsch has DEFINED quantum computation as computation accross parallel universes-

    the experimental evidence of quantum computation- specifically independant CNOT operations carried out in parallel on single photons- physically demonstrates the MWI- and demonstrates that non-multiverse interpretations are unphysical- according to the leaders of the field-

    as I have said before- this is all rather recent- but I guarantee you within 5-10 years the physical verification of the MWI will be in all the texbooks- from that point Copenhagen and Hidden Variable interpretations will only be historical footnotes-

    Qunatum Mechanics IS the physics of parallel universes
     
  14. Jun 13, 2006 #13

    ZapperZ

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    Sorry, but you should know by now that on here, such statements are empty. Please provide me the exact citation of this experiment.

    Zz.
     
  15. Jun 13, 2006 #14

    ZapperZ

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    But really, this is irrelevant to MY point. I'm not debating the validity of ANY of the interpretations of QM. I'm debating the erroneous conclusion here that MWI has hit a home run with some "experimental" observation. I'm just disappointed that you didn't come in any sooner than you did and corrected such dubious statements, and you had to wait till *I* come in. Even then, you simply restated why you "prefer" MWI and not to debunk what setAI has said.

    One could adopt the Winnie the Pooh interpretation of QM, for all I care. Until there are experimental evidence to distinguish all of them, such a discussion is strictly philosophical and a matter of TASTES, not physics.

    Zz.
     
  16. Jun 13, 2006 #15
    I'm sorry guys. You lost me ages ago. Are there major conclusions about QM that all the interpretations agree on?
     
  17. Jun 13, 2006 #16
    you are obviously skimming the thread and not actually looking at the evidence already presented- but here it is again- a video demonstration and detailed lecture of the soon-to-be-famous experiment where a single photon is split and CNOT computations are performed in parallel universes then rejoined- http://www.quiprocone.org/Protected/Lecture_2.htm
     
  18. Jun 13, 2006 #17

    ZapperZ

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    Sorry, but you obviously haven't been following any of my postings, because if you have, you would have realized that such things are not considered to be 'evidence', at least not a valid citation.

    I will ask this for the very last time. Please give me the citation for the evidence that you have so claimed.

    Failure to do so will imply that you are basing your argument on speculative, non-peer reviewed sources which are not acceptable per our Guidelines. I will have no choice but to have remove your posts and have you submit your arguments to the IR forum for evaluation.

    Zz.
     
  19. Jun 13, 2006 #18

    PEER REVIEWED documentation has already been provided!

    here are some of the main papers and their citebase stats-

    http://xxx.lanl.gov/abs/quant-ph/9906007
    http://www.citebase.org/cgi-bin/citations?id=oai:arXiv.org:quant-ph/9906007

    http://xxx.lanl.gov/abs/quant-ph/0104033
    http://www.citebase.org/cgi-bin/citations?id=oai:arXiv.org:quant-ph/0104033


    http://www.arxiv.org/abs/quant-ph/0210204
    http://www.citebase.org/cgi-bin/citations?id=oai:arXiv.org:quant-ph/0210204


    here are some of the research programs that are using the observed behavior of this experiment for quantum computation research:
    http://www.vcpc.univie.ac.at/~ian/hotlist/qc/research.shtml

    this is quite unbelievable and you are abusing this forum with your empty claims that this is not rigorously peer reviewed science- this research has been at the forefront of mainstream quantum mechanics for nearly a decade now- any user of physicsforums claiming to be a mentor should know all of this already- it says in your profile that you are physicist zapper- I guess I am dissapointed that you are not giving us more information about this news and are instead actually arguing against it?!?

    I will report any abuses against this peer-reviewed research to Warren-
     
    Last edited: Jun 13, 2006
  20. Jun 13, 2006 #19

    vanesch

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Uh oh :grumpy:

    I made my first post (my time) in this thread when I first saw it at 5:25 PM concerning Penrose, my second at 5:29 PM replying to you, then I typed a long post which I finally didn't submit exactly addressing the issue you mentioned and you came in at the issue at 5:48 PM, when I was finding out whether I'd put myself in the traffic jam or whether I'd stay a bit longer in my office :redface:
     
  21. Jun 13, 2006 #20

    vanesch

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Well, I hate to disturbe a fellow MWI-er, but I fail to see how one can say that quantum computation proves MWI. Honestly, quantum computation is nothing else but the unitary evolution of states of a system, and it is sufficient to put the Heisenberg cut AFTER obtaining the final result to be in agreement with Copenhagen, no ?

    Imagine that the Heisenberg cut comes in for objects heavier than 200 tonnes. In other words, systems of more than 200 tonnes are classical systems and obey a superselection rule that only allows them to be in nearly classical states, and not in superpositions of these, and this is done by the projection postulate. How does quantum computing prove this statement wrong ? And if it does, if we now put the Heisenberg cut at 10^10 kg objects ?

    I fail to see how, for instance, Bohmian mechanics would give different observable results than MWI-QM. Now of course, I am also sensitive to the argument that Bohmian mechanics has some MWI flavor to it :smile:

    Well, I also find this the most obvious interpretation of the formalism, but on purely formal grounds. I don't see how one can experimentally PROVE this view, given that it is empirically equivalent to Copenhagen with the Heisenberg cut far enough away, or to Bohm. It is for formal ugliness that I don't like these interpretations, not for their empirical falsifiation.


    In fact, the experiment that "proves" to me MWI up to a point is an EPR experiment, but unfortunately, one needs another hypothesis for that, which was historically the first to be "tested" by these experiments.

    The reason is that in order to get an indication of the validity of MWI, that one needs to put in superposition, and show interference, of VERY MACROSCOPIC systems (ideally, say, a planet).
    Now, this is practically impossible to do because of environmental decoherence, which makes the interference invisible... unless one finds a way of making sure that the two branches that have to interfere cannot entangle with the same environment (and hence decohere).
    Well, if one takes locality for granted (that's the point of course!), then one can use spacelike separation as a way to avoid environmental decoherence of the overall system (there will be local environmental decoherence, but it will not be the same environment degrees of freedom, and hence preserve the possibility of interference).
    If one puts a macroscopic system in this way in a superposition (by having it observe one branch of an entangled system) in the basis of another macroscopic system (by having it observe the other branch of the entangled system in a rotated basis), and one brings then these two macroscopic systems together, one can try to find out if there is interference in their interaction, which would show up as correlations in their measurements. That's exactly what happens in an EPR experiment !

    But, caveat: the only "superpositions" have been tiny electronic signals yet, over relatively small distances (50 km or so -> 10s of microseconds). That doesn't have much "gravitational" weight. We haven't really put human beings, or planets or so in superposition that way, for say, an hour or so. And there is still the issue of detection efficiency and the fair sampling hypothesis. So the "proof" isn't there yet that planets and so on can be in superpositions.

    I'm focussing on the mass of the system in superposition, because I have to say that I'm sensitive to Penrose's argument. As long as we don't have a verified theory of quantum gravity, the possibility exists that superpositions of gravitationally important systems does not work, which would be the end of MWI. I fail to see how quantum computing proves this wrong.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Copenhagen interpretation of Quantum Theory
  1. Quantum interpretations (Replies: 125)

Loading...