t The central philosophical puzzle posed by the quantum theory is what attitude should one adopt to the apparently mysterious dual nature exhibited in the microphysics of matter and radiation, for example that radiation behaves in some respects—interference, diffraction, etc.—like a wave process governed by the classical Maxwell equations of an electromagnetic field, and in other respects —photoelectric effect, Compton scattering, etc.—like a beam of particles, the so-called quanta or photons. The bewilderment of physicists in this paradoxical situation was captured by Sir William Bragg in his famous remark, 'We use the classical theory on Mondays, Wednesdays, and Fridays and the quantum theory on Tuesdays, Thursdays and Saturdays'. A reciprocal duality for material subatomic particles emerged in the discovery of electron diffraction and other wave-like phenomena. There have been three main approaches to trying to come to terms with the duality problem. The first approach is simply to deny that quantum mechanics, QM, is basically mysterious. The slogan here is that, despite appearances, a particle is a particle is a particle, and mutatis mutandis neither need we equivocate about waves. On this view QM is really a sort of glorified statistical or perhaps more correctly stochastic mechanics. Exponents of this general approach would include Popper, Lande and Fine, and it is now vigorously defended by Professor Audi in his book The Interpretation of Quantum Mechanics. This approach can be extended to an attempt to reinstate determinism at the level of some hidden infrastructure, but the question of whether a hidden variable theory is intrinsically probabilistic or deterministic is quite a separate issue from whether in reality microsystems can be described as associated with the familiar classical variables, for example an electron can be regarded as possessing simultaneous position and momentum and tracing a classically describable trajectory in passing through a two-slit system designed to reveal electron interference phenomena. In particular Audi wants to defend an indeterministic particle interpretation of the electron. We shall consider his detailed arguments and the general difficulties associated with this approach in a moment.
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