Physics: QBism puts the scientist back into science
N. David Mermin
26 March 2014A participatory view of science resolves quantum paradoxes and finds room in classical physics for 'the Now', says N. David Mermin.
Physical science describes the objective external world: particles, waves and fields; how they change in time; and how they give rise to the forms of matter, terrestrial and extraterrestrial, microscopic and macroscopic. This world makes itself known to each of us through our own private internal perceptions. Yet physical science has ignored the 'subject' — the scientist — even though their subjective experience constitutes their only link with the external world.
In Nature and the Greeks, Austrian physicist Erwin Schrödinger traced the removal of the subject from science back more than two millennia. Alongside the spectacular success of physical science, this exclusion of personal experience has given rise to some vexing and persistent puzzles and paradoxes.
Two such unrelated long-standing problems are both resolved by recognizing that the perceiving subject has as important a role to play in understanding the nature of physical science as does the perceived object.
The first problem is the notorious disagreement, confusion and murkiness that for almost a century has plagued the foundations of quantum mechanics, in spite of the theory's extraordinary usefulness and power. The second, less famous, problem has been with us at least as long: there seems to be nothing in physics that singles out 'the present moment'. Albert Einstein called this the problem of 'the Now'. Both problems are symptoms of the exclusion from physical science of the perceiving subject, and are solved by restoring what the ancient Greeks removed.Quantum mechanics
Schrödinger wrote in a little-known 1931 letter to German physicist Arnold Sommerfeld that quantum mechanics “deals only with the object–subject relation”. Another founder of quantum mechanics, Danish physicist Niels Bohr, insisted in a 1929 essay that the purpose of science was not to reveal “the real essence of the phenomena” but only to find “relations between the manifold aspects of our experience”.
In spite of these early hints, it was only in the twenty-first century that US physicist Christopher Fuchs and British–German physicist Rüdiger Schack put forth an understanding of quantum mechanics that restored the balance between subject and object. They call their new point of view 'QBism': Q is for quantum and B is for Bayesian — a view of probability that includes an agent who makes bets and updates odds. QBism attributes the muddle at the foundations of quantum mechanics to our unacknowledged removal of the scientist from the science.
Much of this muddle is associated with the 'wavefunction' that quantum mechanics assigns to a physical system. This irritatingly uninformative term reveals the lack of clarity present in the field from its very beginning in 1925. People argue to this day about whether wavefunctions are real entities, like stones or ripples on a pond, or mathematical abstractions that help us to organize our thinking, like the calculus of probabilities.
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