Dear Joseph, Jerry, Pedro, and all: "1. QBism seems not to consider the option of using non-standard, non-Kolmogorivian probabilities to describe quantum and non-quantum nature, that is, with values >0 but <1."
It is difficult enough to get physicists to consider the standard interpretation of probability offered by Bayesianism, without straying off into the unknown territory in which probabilities 0 and 1 are excluded! However, it is true that those two cases do present special difficulties, and it might be interesting to see what happens when they are forbidden. The paper by Fuchs et al. strains to establish the case of probability 1, which is called a "fact", as nothing more than a very,very strong belief. (I enjoy astonishing my students by proving that even though most of them believe that 0.999...<1 it actually equals 1.) If a non-standard formalism is used, I would guess that a special category of probabilities very close to 0 and 1 would still have to be singled out, because we have been so thoroughly brainwashed that we parse the world around us in terms of absolute certainties, i.e. of probabilities 0 and1. "2. It excludes the case, impossible by classical logic, but basic to physics and LIR, of a dynamic interaction between the subject and the object which allows both views ("belief" and "facts") to be partly true or better operative at the same time or at different times." I don't know enough about LIR to understand what is meant by the word "fact" in that context. The interaction between subject and object is a central concept in QBism. It takes the place of the "measurement" of the older literature, which has the connotation of revealing something objective, real, and pre-existing. An interaction, on the other hand, changes both the external world, and the agent's belief. It creates brand-new "facts" that did not pre-exist the interaction. Thus we humans participate in tiny ways in the ongoing creation of the world. "3. Since the QBism interpretation does not deal with points 1. and 2. above (also in the Fuchs, Mermin, Shack paper), it leaves the door open to an anti-realist interpretation not only of quantum mechanical reality, but of reality /tout court/ which must be based on and reflect the quantum 'situation'. " Right! QBism seeks to establish a new worldview in which the entire material universe is quantum mechanical and described in terms of Bayesian probability -- even those things we think of as real, objective, and factual. Pedro wrote: "What I most like of this new quantum approach is the radicalism regarding meaning, experience, knowledge, science... This is good news for the people who sees information science as an occasion to contemplate anew the relationship of the individual with the increasing stock of knowledge accumulated by our civilization, where the ratio of our individual experience to the total is acceleratedly approaching zero!, and where the blind spots of collective intelligence are shining in too many areas of global life... It is healthy that the explicit limitation of the individual is also a message contained in QBism, at least in my understanding." I agree wholeheartedly. The way I see the interaction between the QBists and FIS evolving is this: The physicists are busy trying to rewrite all of quantum mechanics (not just its interpretation) along QBism-inspired lines. This means principally re-casting the entire formalism in terms of probabilities rather than wavefunctions. If they succeed (and the jury is still out on that) they will have created an entirely new theory that is mathematically equivalent to the Schroedinger-Heisenberg theory, but looks completely different. Meanwhile others, including members of FIS, can study the implications of QBism for a new worldview. By the success of quantum theory, nature seems to be urging us into a more personalist, anti-realist view of the world, a view that focuses on individual experience. As Pedro implies, communication with other persons -- information exchange -- is a key component of this experience. I see that tree out there myself, and I can even feel its bark, but the overwhelming majority of what I think and do is triggered by my experience of reading and listening and learning about the experiences of others. In this way information and communication continue to be crucial concepts. Another concept Pedro touches on is human limitation. I find it very liberating to feel that there is no such thing as a grand "Theory of Everything" -- only little patches of understanding of relationships encoded in rules of thumb with names like Relativity, The Standard Model, Quantum Field Theory, Evolution... With the help of the experiences of generations of scientists I can incorporate these rules in my own personal ordering and surveying of the world around me. So I don't worry, as the Greeks did, about what the world really, really is. It's good to talk to you all, as wee say in Virginia. Hans
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