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A Where does Von Neumann say that consciousness causes collapse

  1. Sep 4, 2016 #1
    It's often claimed that in Mathematical Foundations of Quantum Mechanics Von Neumann concluded that it's the observer's consciousness that collapses the wavefunction (Process 1).

    But I am reading Chapter 6 of the book (both original and translation) word by word, and I don't find this conclusion. The closest is where he mentions the observer "abstract 'ego'" as one of the possible endpoints of the measurement chain (p. 421 in the 1955 translation).

    This doesn't seem a "conclusion" to me. Is he more explicit elsewhere (in the same book or other writings)?
     
  2. jcsd
  3. Sep 4, 2016 #2
    There is no conclusion that observer's consciousness causes a collapse of wavefunctions.
    The foundations of QM claims that measurement cause it. And not just any measurement but measurement that has enough precision.
    If for example, in the famous double slit experiment, you are measuring the position of the electron by photon of wavelength which is larger than the space between the slits you will not cause a collapse because you will not be able to know by the measurement from which slit it went by.
     
  4. Sep 6, 2016 #3

    Demystifier

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    Some quotes from the 1955 translation (boldings are mine):

    Page 418:
    "-- undergoes in a measurement a non-causal change in which each of the states ... can result, and in fact does result, with the respective probabilities ..."

    Pages 419-420:
    " But in any case, no matter how far we calculate -- to the mercury vessel, to the scale of the thermometer, to the retina, or into the brain, at some time we must say: and this is perceived by the observer.That is, we must always divide the world into two parts, the one being the observed system, the other the observer. In the former, we can follow up all physical processes (in principle at least) arbitrarily precisely. In the latter, this is meaningless. ... That this boundary can be pushed arbitrarily deeply into the interior of the body of the actual observer is the content of the principle of the psycho-physical parallelism — but this does not change the fact that in each method of description the boundary must be put somewhere, if the method is not to proceed vacuously, i.e., if a comparison with experiment is to be possible. Indeed experience only makes statements of this type: an observer has made a certain (subjective) observation; and never any like this: a physical quantity has a certain value."

    Page 420:
    "Now quantum mechanics describes the events which occur in the observed portions of the worlds so long as they do not interact with the observing portion, with the aid of the process 2. (V.i.), but as soon as such an interaction occurs, i.e., a measurement, it requires the application of process 1."
     
  5. Sep 6, 2016 #4
    Thanks Demystifier. This confirms my impression: Von Neumann formulated a veiled suggestion that consciousness causes collapse, but that's as far as he went (in this book at least). He didn't really claim that consciousness causes collapse.

    Von Neumann argued that the collapse of the wavefunction (Process 1) can be placed anywhere in a measurement chain, from the first measuring device to the observer's conscious perception of the measurement result.

    He implicitly suggested that the observer's consciousness ("his abstract 'ego'") could be where Process 1 happens, but didn't explicitly conclude that it is so.

    Stronger claims were then made by London and Bauer (The Theory of Observation in Quantum Mechanics) and Wigner (Remarks on the Mind-Body Question). Both essays are included in the "Quantum Theory and Measurement," edited by Wheeler and Zurek.
     
  6. Sep 6, 2016 #5

    vanhees71

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    Better read the scientific work of scientists! ;-)).
     
  7. Sep 6, 2016 #6

    dextercioby

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    That IS the scientific work of those people, the referenced essays have at least a historical value, even if now, in 2016, the current belief in the part philosophy part physics realm of QM interpretation has fundamentally changed.
     
  8. Sep 6, 2016 #7
    It has really changed that much? We are still discussing the same interpretative issues in QM that were discussed in the 1030s. Only now there are more interpretations on the table (decoherence-solves-everything, MWI, transactional, consistent histories...)
     
  9. Sep 6, 2016 #8

    dextercioby

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    I had just googled the Fritz London essay and found it to be dated 1939. I know a lot has changed since then, even in the Copenhagen (collapse) formulation.
     
  10. Sep 6, 2016 #9

    Strilanc

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    You can't conclude, based on seeing someone make weaker claims, that they never made stronger claims. You have to do a proper search for stronger quotes and fail to find them, or find quotes of them explicitly saying they won't accept the stronger views, etc. You should go to woo forums who believe that kind of thing and ask people to point you at quotes, since they're more likely to know the location of that kind of quote than this forum.

    That being said...

    The wikipedia article on the Von Neumann–Wigner interpretation doesn't contain any quotes or citations from Von Neumann beyond the "could be placed at any point in the causal chain" note. (And there doesn't seem to be controversy about that on the talk page either, but the talk page is tiny.) Also, wikiquotes doesn't have any Von Neumann quotes containing the word "consciousness". So probably you're right... which would make it really unfortunate that the interpretation was named after him.
     
  11. Sep 6, 2016 #10
    Right. In fact, reading Von Neumann's book, one has the impression that he did have stronger claims in his mind. He just didn't write them down.
     
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