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Questions on the Copenhagen Interpretation

  1. Feb 3, 2008 #1
    Just had four quick questions on the Copenhagen Interpretation (CI).

    1. Where is the boundary between realm (classical) space and quantum space. I understand that there is no solid definition for this boundary, but where would we begin to see quantum events occur and see classical events stop? According to Everett, why are there two contradictory conceptual schemes to describe reality - the quantum one of wave functions and the classical one with us and the measuring device.

    2. What is an observer? Can it be just another particle, or must it be conscious?

    3. Why do wave functions collapse when observed?

    4. Why is there an abrupt, random change in the wave function, which violates the Schrodinger equation?

    I was wondering what the answers were to these questions after reading a Scientific American article on Hugh Everett. Sorry if these questions seem dumb, but I'm a newbie to quantum mechanics, so I hope to learn. Thanks :)
    Last edited: Feb 3, 2008
  2. jcsd
  3. Feb 3, 2008 #2
    1) In CI, the boundary is defined by the experiment. Theoretically, quantum effects can be seen in objects of any size if the experiment is designed with enough precision. However, for anything larger than a few atoms, the DeBroglie length becomes smaller than the Planck Length, meaning the double slit through which a large object might display quantum interference would be too small for us to actually observe any interference.

    2) CI does not provide a coherent definition of observer or observation. The wave-function collapses as soon as new "information" is learned. That implies some necessity for comprehension of that nformation, I think. But since the wave function doesn't have any physical meaning other than in its predictive value, it doesn't bother a CI supporter that consciousness is required for all this to work.

    3) Because new information is introduced, and so the eigenstates which previously had been possible but have since been proven not to be the case thanks to the new information become zero and the new state vector is derived.

    4) A CI supporter would tell you that the change is merely mathematical and that the wave function doesn't actually correspond to any element of physical reality. Therefore, the collapse is akin to taking the equation y=sin(x) and then saying x=pi. y was previiously a sine wave but then "suddenly" y was given a well defined value (0). The real question is did it always have that value or not? That's where CI and other interpretations begin to differ.
  4. Feb 10, 2008 #3
    In the sure knowledge that I will be challenged, I give you what I believe is correct.

    1. The boundary is defined by the experiment. Experiments are classical - the results is a set of measurements (outcomes).

    2. An observer does not have to be conscious. It just something that "consumes" a measurement. It could be a robot, for example, that uses it's knowledge of QM to make decisions.

    3. Waveforms do not "collapse" because in CI they are not "elements of reality". They are just subjective (observer dependent) probability calculation devices. Waveforms change because measurements alter the information available to the observer.

    4. See answer to 3.
  5. Feb 12, 2008 #4
    Theorethically is: your system goes in an eigenstate of the set of commuting observables you are experementing on; and you are meausiring their eigenvalues distributions.

    For my granny is: "If you are looking at the sea, you'll probably find some water".

    the last is just a little joke.

    marco ;
  6. Feb 14, 2008 #5
    Waveforms do not collapse to pure eignestates so I can't seen how the formalism A.[tex]\Psi[/tex] = [tex]\lambda\Psi[/tex] has much to do with "collapse". The waveform is just a probability distribution. The measurement alters the observers knowledge of the system under investigations, so measurement changes the waveform. I.e. [tex]\Psi\rightarrow\Phi[/tex] where [tex]\Psi[/tex] and [tex]\Phi[/tex] are just probability distributions.
  7. Feb 14, 2008 #6
    Just Googling around on this without understanding it all myself, it seems the “http://en.wikipedia.org/wiki/Quantum_Zeno_effect" [Broken]” might be demonstrating some of the principles involved?
    Last edited by a moderator: May 3, 2017
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