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How does the classical world emerge from the quantum world?

  1. Jan 22, 2016 #1
    Why do billiard balls does not pass through both the slits at once or tunnel through walls while electrons and photons do? Quantum phenomena are observed at room temperatures so how does decoherence theory account for such phenomena? I think only Caslav Brukner and Johannes Kofler have seriously addressed this question.

    Classical world arising out of quantum physics under the restriction of coarse-grained measurements.

    A coarse-grained Schrödinger cat

    Do classical laws arise from quantum laws?

    Does this really solve the problem?
  2. jcsd
  3. Jan 22, 2016 #2


    Staff: Mentor

    Last edited by a moderator: May 7, 2017
  4. Jan 22, 2016 #3


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    The idea of photon passing through both slits at once is only an interpretation of interference and I would even say that it is false as photons from independent lasers can show interference too.

    So the first question is what sets "quantum world" and "classical world" apart. It seems that Kofler and Brukner are using Leggett and Garg version:
    1. Macrorealism per se: A macroscopic object which has available to it two or more macroscopically distinct states is at any given time in a definite one of those states.
    2. Noninvasive measurability: It is possible in principle to determine which of these states the system is in without any effect on the state itself or on the subsequent system dynamics.

    While first is OK the second one is too antropocentric. And we could factor into the model invasive measurements. So I don't see that it limits applicability of classical models.

    I don't think so. Before there was anyone who could do coarse-grained measurements there was no classical world?
  5. Jan 23, 2016 #4

    A. Neumaier

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    I looked at this paper. It is a step in the right direction. But they write on p.2, right column, end of first paragraph in the arXiv version: ''It seems thus unavoidable that certain features of classicality have to be assumed beforehand.'' Thus it is not a full solution.

    But it gives an explicit example verifying that the coarse-graining inherent in all macroscopic views of quantum physics makes the world classical. This is best visible in derivations of hydromechanics (a classical theory of fluids) from quantum field theory, and is consistent with my thermal interpretation of quantum mechanics.

    Note that the coarse-graining in Nature is not done by measurement (the setting chosen in the paper) but simply by the fact that nothing can be resolved by its environment to arbitrarily high precision.
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