Monday, June 9, 2014

Mermin has pedantic quibble about QBism

Cornell physicist David Mermin was quoted in NewScientist magazine, and then wrote a hair-splitting letter attempting to somehow correct his view of quantum mechanics:
I am delighted that you take the quantum Bayesianist view of science seriously enough to feature it on your cover (10 May, p 32). But you overemphasize the subjectivity of the scientist almost as much as conventional physics underemphasizes it.

Your article attributes to QBism the view that "measurements do not cause things to happen in the real world, they cause things to happen in our heads". The actual QBist position is that a measurement is any action that a particular person (Alice) takes in her external world, and the outcome of that measurement is the experience this world prompts in Alice through its response to her action.

Other consequences of Alice's action are part of her external world and potentially accessible to others. Alice has her own private subjective experience, but she can attempt to describe this to others through the imperfect medium of language, which helps account for the common features of the different external worlds that each of us individually infers from our own private experience.

It is of course hard to convey all this in three pages, let alone a short letter. After all, it has escaped the awareness of almost all physicists for nearly 90 years. For a more nuanced view of QBism I recommend the paper cited in your article,
Ithaca, New York, US
No, QBism is not some view that has escaped physicists for 90 years. It is nearly the same as Bohr's view, as I have noted previously.

Recent Mermin explanations of his view of quantum mechanics are here and here, and how he has gripes about how the above letter was edited.
The first omission — of the New Scientist’s own words — diminishes the degree to which their article misrepresents QBism as antirealist. The second omission — from both my versions — eliminates the heart of my explanation of QBist realism. Their combined effect is to turn my correction of the New Scientist’s gross misrepresentation of realism in QBism into what sounds like a pedantic quibble.
His letter is a stupid pedantic quibble because he cannot explain how hi view is any different from what Bohr and others said in 1930.

He seems unhappy to be put in the antirealist camp. That is a confusing term. It is not that quantum mechanics is contrary to realism, but some physicists, like Einstein, Bell, and other quantum-haters, had a belief that realism requires that measurements be equated with hidden variables. Quantum mechanics rejects that view, and for that it is called antirealist.

Mermin complains about the shortness of his letter, but go ahead and read his longer articles to see how empty they are. He thinks that he has discovered something, because he used to pitch a different interpretation of quantum mechanics, and he seems to have finally come around to the view that Bohr and Heisenberg and Schroedinger had it right all along. But there is no need to read his papers; just read an old textbook and ignore the modern physics gurus who babble nonsense about quantum mechanics being wrong.

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