Philip Ball, Quantum Mechanics, etc.

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." QBism extends this prediction-is-everything notion to the molecular world as well, to objects such as unobserved cats in boxes, in dealing with the usual paradoxes.

I'll quote ALbert Einstein on a related point, in my Sunday posting.

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