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The measurement 'problem'

  1. Oct 16, 2004 #1
    Hi all,

    I'm preparing to write a critique on the issue of whether or not there is a measurement problem in QM. Ive been reading various things on the internet but id appreciate if anyone knows any good published papers related to the subject. Also some comments on the issue would be nice (since its a controversial issue, could you please be clear if you are stating either your personal opinion, or what is regarded as accepted 'fact' in the scientific community).

    The reason i ask is that its difficult to find a good (unbiased and objective) review of the subject, but maybe im not looking in the right places.

    Any comments etc are welcome.

  2. jcsd
  3. Oct 16, 2004 #2

    Kane O'Donnell

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    What do you mean by measurement problem?


  4. Oct 17, 2004 #3
    For the sake of clarity one must contend to the "Information Loss" paradox.

    Whilst reading some of Lee Smolins work, I became fascinated by the E-P-R paradox, this I followed up with some of Rovelli's workings on Loop Quantum Gravity.

    My own personal conclusion is this:If one can ask an infinite amount of questions, one can never get an infinite amount of answers, the price of asking an infinite amount of questions about a singular object, is the loss of the original Question!

    This is one reason that"ORIGINAL", the String Theory evolved into the complex confusion currently being brought to its knees.

    Any variation of Unique String theory is most definately not Unique, there are an infinite amount of Variations of every component within ST..dimensions..9..10..11...etc..etc Membranes..D..T..P..etc..etc

    I content that for String theory, the more one inputs..the less one outputs!.. just a simple Measure of a simple Vacuum cannot yeild a physical portion of reality, sorry :cool:
  5. Oct 17, 2004 #4


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    I think that the following is "standard knowledge". The measurement problem in QM comes from the confrontation of the two different behaviours of the system under, on one hand, "time evolution" (which is given by a unitary operator defined by the Schroedinger equation) and on the other hand, "measurement" which is an instantaneous, but random and irreversible projection, given by Born's rule. The fact that there are 2 different prescriptions for behaviour, together with the fact that what exactly constitutes a measurement is in principle not clear (although it is for all practical purposes) is considered as a problem.
    How to deal with it is not standard, but several main approaches have been proposed (with lots of subtle variations).

  6. Oct 17, 2004 #5
    Here is an Amazon link:



    Quantum Theory and Measurement
    by John A. & Zurek, Wojciech Wheeler
    Princeton Series in Physics

    This is a compilation of the most important papers on the subject up to 1983.

    I am little aware of the recent develoments (because I am doing more 'concrete' things) but you might also consider following new tracks related to 'quantum probabilities'. The following book can be found on Amazon:


    Science and Ultimate Reality : Quantum Theory, Cosmology, and Complexity

    contains some contributions related to your topic, specially the paper by L Hardy called "Why is nature described by quantum theory". In this paper, "quantum measurement" is at the start of the reasoning. The references in this paper, specially those by Hardy, Fuchs and Wooters might be of interrest for you.

    The literature exploring "quantum computing" and "quantum information theory" could be useful also. These topics, I believe, are at the heart of the interpretation of quantum mechanics.

    My personal opinion on the subject is that one should be very careful with this subject.

    The formulation of the postulates of quantum mechanics have awakened the imagination of so many people, most of them without any background in physics, and some with too much background and little critical thinking.

    I think that a critical synthesis on the subject should separate facts from interpretations, and testable interpretations from untestable interpretations. I think that one should avoid statements that do not refer to clearly defined experiments. You should maybe electronically eliminate all references where the word "mind" appears. An beware of internet! On this topic internet contains more noise than signal.

    In addition, I believe that during the last 20 years, the status of this subject has evolved. This, specially because of striking experiments, like those by Alain Aspect, or like all the recent experiments regarding entanglement. Basically, these experiments are technical and scientifical masterpieces. But, I think, they do not directly change any concept of quantum mechanics. On the contrary, they make physicist more comfortable with these concepts. Maybe also, these experiments make the "postulates" a little bit obsolete since these are now replaced by "laboratory facts".
  7. Oct 18, 2004 #6
    thank you all for the replies!

    lalbatros, im interested in this paper by L hardy, but i cant seem to find the paper. I am right it saying its this man?


    I've looked on a journal search and cant find that paper, nor is it on that website above (as it has a list of his publications).

    Also, youre comments about the internet are very true indeed, we have already been warned about the internet (there being a lot of crackpots etc hehe) the trouble is a lot of the things you read look like they are written by well versed people but they still maybe just wild theories!

    Also thank you very much for the suggestion about how to organise the facts from interpretations etc, i was planning on this, but wasnt going to explicitly explain the seperation, but i think i will now, as its important to know what is fact etc.
  8. Oct 18, 2004 #7
  9. Oct 18, 2004 #8
    thanks, didnt think to look there, i thought they only had papers that were not peer reviewed/published yet. I look at all his papers but stillcant find the one lalbatros mentioned. There is a "why quantum theory" but it doesnt seem to mention measurement at the start :(
  10. Oct 19, 2004 #9
    Hello zeta

    Here is the original paper from Hardy:


    and an easier-to-read version:


    My comments:

    This paper does not explicitely discuss the measurement 'problem'. Instead, it discusses 5 'reasonnable' axioms that could root QM. Since the usual 3 axioms make explicit reference to the process of measurement, this paper is relevant for your topic, I think. In addition, you will see that Hardy's paper actually discusses QM through a generic 3-step process: preparation-transformation-measurement.

    Probably you can find discussions of Hardy's work on the web, use keywords like "hardy five axioms".

    The pointer http://www.qubit.org/people/lucien_hardy/ is right.
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