Every once in a while, as regular readers know, I write about quantum mechanics. I don't write as an authority -- I was a solid "C" student in an adult-education course in calculus about 20 years ago and will never make a pretense to understand particle physics. The sphere diagrammed in this image has something to do with quantum theory, and something to do with calculus. And that is all I can tell you about it! But quantum mechanics is relevant to many of the philosophical questions in which I have a vested interest in my capacity as a thinking human. So I do need to keep struggling with it. I recently came across an interpretation I had not heard before: the transactional interpretation. By way of preface: The mainline interpretation is known simply as "Copenhagen" after a period in the mid 1920s when Heisenberg worked as assistant to Bohr at the University of Copenhagen. The Copenhagen view accepts the complementarity of wave and particle readings, acce...
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One can read much of the book free, through the Google Books platform. I was curious what if anything Ball would have to say about Quantum Bayesianism (QB), which I have mentioned in this blog a time or two. The answer is that he treats it as one interpretation of quantum mechanics among many, alongside Copenhagen, many worlds, collapse models and pilot waves. QBism is, he sees, the culmination of the Copenhagen view. "Quantum mechanics generally assumes that quantum states exist in some meaningful sense, and that the math tells us what we can know about these states. But in QBism there are no objective states. Rather, according to Chris Fuchs, 'quantum states represent observers' personal information, expectation and degrees of belief'. " Bohr had said (outlining what is now called the Copenhagen view) that (in Ball's paraphrase), "the purpose of quantum mechanics is not to tell us about reality but to predict outcomes of measurements." ...