John Bell Workshop 2014

Measurement and Macroscopicity (Online 12/22 @ 11 a.m. UTC-4)

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  • #1533
    AvatarGregg Jaeger
    Participant

    John S. Bell, of course, is most well known for the result now referred to simply as “Bell’s theorem”, which removed from consideration the class of so-called local hidden-variable theories which at the time of its publishing appeared to be the most natural class of theories among those which would render quantum mechanics a form of statistical mechanics. If, as this and further other results suggest, quantum theory is to serve as a truly fundamental theory, conceptual precision in its interpretation is not only desirable but paramount. John Bell was accordingly concerned about what he viewed as conceptual imprecision, from the physical point of view, within the standard approaches to the theory. He saw this as most acute in the case of their treatment of measurement at the level of principle. His concerns were strongly expressed in the article “Against Measurement.” This item was published in 1990 in a volume of proceedings of the 1989 Erice meeting “Sixty-Two Years of Uncertainty,” during which it was my pleasure to meet and eat with Bell, and to listen to him present this paper. He pointed out that this conceptual imprecision is reflected in the terminology of the foundations of quantum theory, a great deal of which he explicitly deemed worthy of banishment from discussions of principle, because it corresponds to a set of what he saw as vague and, in some instances, outright destructive concepts. His concern was thus not one regarding mathematics so much as regarding basic concepts used in contemporary quantum physics, which he viewed as failing the needs of natural philosophy and so of fundamental physics, despite their practical adequacy. Here, I consider John Bell’s critique of standard quantum measurement theory and some alternative treatments wherein he saw greater conceptual precision, and make further suggestions as to how to improve conceptual precision, as he advocated. Full text

    #1685

    Hi Gregg,

    I fully agree with Bell and you that if quantum theory is to serve as a truly fundamental theory, conceptual precision in its interpretation is not only desirable but paramount. In my view, even in current realistic quantum theories, there is still conceptual imprecision. For example, in collapse theories favored by me, the source that collapses the wave function still needs to be specified in physics. On the other hand, I also think experimental tests are very important and can help improve the conceptual precision.

    Best,
    Shan

    #1692
    AvatarGregg Jaeger
    Participant

    Absolutely Shan.

    Indeed, I intentionally ended my paper with a discussion of an experiment. The example I mention involves, in particular, measuring a system that is capable of quantum superpositions states of large systems, that is, systems with many degrees of freedom. Undoubtedly, the exploration of situations similar to the schema set out by the Schrödinger cat experiment, particularly those involving novel experimental technologies, will provide added insight into measurement and help us to distinguish the set of factors, which a realist should expect to find, common to all or subsets of measurement-like situations. If and when such factors are found, they may be meaningfully associated with a natural kind, the measurer, giving measurement an explanatory though non-fundamental role, in accordance with John Bell’s call in “Against measurement.”

    Best,

    Gregg

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