Bell's Theorem

Discussion in 'Science and Technology' started by egger, Sep 11, 2017.

  1. Kerri

    Kerri Member

    I certainly can’t say myself what the motivations are
     
  2. wooleeheron

    wooleeheron Brain Damaged Lifetime Supporter HipForums Supporter

    Physicists routinely make up and throw around terminology and invent funny names for particles and stuff like that. The mathematics are what they care about, while linguistic analysis is actually their weakness. They're all using classical mathematics to describe nonclassical mechanics and confusing themselves in the process by just making up terminology as they go along. My favorite example of physics terminology is John Wheeler who famously declared:

    "A black hole has no hair! Gravity without mass! Time is what prevents everything from happening at once! There is no law except the law there is no law!"
     
    Kerri likes this.
  3. egger

    egger Member

    Einstein didn't measure hidden variables or describe their nature precisely. Using thought experiments, he tried to argue that quantum mechanics is an incomplete theory. He was interested in finding a possible more-complete theory.

    Bell theory and associated experiments show that localism, realism, and free choice can't all be retained together when trying to explain quantum mechanics. Assuming Bell theory and experiments based on it are valid, one or more of those elements (as they are known in the classical sense) needs to be foregone.

    The following paper provides evidence that, in addition to realistic, local, hidden variable explanations, some realistic, non-local, hidden variable explanations must also be foregone in order the explain the results of Bell-like incompatibility theory and experimental test results of quantum mechanics.


    An experimental test of non-local realism
    Simon Groblacher, Tomasz Paterek, Rainer Kaltenbaek, Caslav Brukner, Marek Zukowski, Markus Aspelmeyer, and Anton Zeilinger
    (Submitted on 19 Apr 2007 (v1), last revised 6 Aug 2007 (this version, v2))

    [0704.2529] An experimental test of non-local realism

    excerpt:

    "Quantum theory gives only probabilistic predictions for individual events. Can one go beyond this? Einstein's view was that quantum theory does not provide a complete description of physical reality: "While we have thus shown that the wavefunction does not provide a complete description of the physical reality, we left open the question of whether or not such a description exists. We believe, however, that such a theory is possible.". It remained an open question whether the theory could be completed in Einstein's sense. If so, more complete theories based on objective properties of physical systems should be possible. Such models are referred to as hidden-variable theories.

    Bell's theorem proves that all hidden-variable theories based on the joint assumption of locality and realism are at variance with the predictions of quantum physics. Locality prohibits any inuences between events in space-like separated regions, while realism claims that all measurement outcomes depend on pre-existing properties of objects that are independent of the measurement.

    The more refined versions of Bell's theorem by Clauser, Horne, Shimony and Holt and by Clauser and Horne start from the assumptions of local realism and result in inequalities for a set of statistical correlations (expectation values), which must be satisfied by all local realistic hidden-variable theories. The inequalities are violated by quantum mechanical predictions. Greenberger, Horne and Zeilinger showed that already perfect correlations of systems with at least three particles are inconsistent with these assumptions. So far, all experiments motivated by these theorems are in full agreement with quantum predictions. For some time, loopholes existed that allowed the observed correlations to be explained within local realistic theories. In particular, an ideal Bell experiment has to be performed with detectors of sufficiently high efficiency (to close the 'detection loophole') and with experimental settings that are randomly chosen in space-like separated regions (to close the 'locality loophole'). Since the first successful Bell experiment by Freedman and Clauser, later implementations have continuously converged to closing both the locality loophole on the one hand and the detection loophole on the other hand. Therefore it is reasonable to consider the violation of local realism a well established fact.

    The logical conclusion one can draw from the violation of local realism is that at least one of its assumptions fails. Specifically, either locality or realism or both cannot provide a foundational basis for quantum theory. Each of the resulting possible positions has strong supporters and opponents in the scientific community. However, Bell's theorem is unbiased with respect to these views: on the basis of this theorem, one cannot, even in principle, favour one over the other. It is therefore important to ask whether incompatibility theorems similar to Bell's can be found in which at least one of these concepts is relaxed."
     
    Last edited: May 9, 2018
  4. wooleeheron

    wooleeheron Brain Damaged Lifetime Supporter HipForums Supporter

    They miss the whole symmetry of the issue. Bell's Inequality can be compared to a Feynman diagram and then you can ask yourself, what questions do they both not answer. Its the symmetry of what you are observing that matters, and to ignore it and insist there must be some sort of mechanism behind the symmetry is to chase your own tail. For me, a Feynman diagram simply expressed synergistic-normalization, or the Two Faces of Janus which are observable throughout nature. Synergy normalizes the impact of its own individual parts, that's the big mystery behind what we call synergy.
     
    Last edited: May 10, 2018
  5. egger

    egger Member

    A Scientific American article from 1979 that covers quantum theory and the classical view of nature.

    Journal Article
    The Quantum Theory and Reality
    Bernard d'Espagnat
    Scientific American
    Vol. 241, No. 5 (November 1979), pp. 158-181
    Published by: Scientific American, a division of Nature America, Inc.
    Stable URL: The Quantum Theory and Reality on JSTOR
    Page Count: 24

    free pdf:

    https://static.scientificamerican.com/sciam/assets/media/pdf/197911_0158.pdf

    excerpt:

    "It now turns out that even this renunciation is not entirely satisfactory. Even if quantum mechanics is considered to be no more than a set of rules, it is still in conflict with a view of the world many people would consider obvious or natural. This world view is based on three assumptions, or premises that must be accepted without proof. One is realism, the doctrine that regularities in observed phenomena are caused by some physical reality whose existence is independent of human observers. The second premise holds that inductive inference is a valid mode of reasoning and can be applied freely, so that legitimate conclusions can be drawn from consistent observations. The third premise is called Einstein separability or Einstein locality, and it states that no influence of any kind can propagate faster than the speed of light. The three premises, which are often assumed to have the status of well-established truths, or even self-evident truths, form the basis of what I shall call local realistic theories of nature. An argument derived from these premises leads to an explicit prediction for the results of a certain class of experiments in the physics of elementary particles. The rules of quantum mechanics can also be employed to calculate the results of these experiments. Significantly, the two predictions differ, and so either the local realistic theories or quantum mechanics must be wrong."

    [​IMG]

    LOCAL REALISTIC THEORIES and quantum mechanics make conflicting predictions for certain experiments in which distant events are correlated. In particular, local realistic theories predict that a relation called the Bell inequality will be obeyed, whereas quantum mechanics predicts a violation of the inequality. There is strong experimental evidence that the inequality is violated in the way predicted by quantum mechanics. Local realistic theories therefore seem to be untenable, and at least one of the premises underlying those theories must be in error.
     

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