‘Many Minds’ Interpretations of Quantum Mechanics

Abstract

Seventy years after the discovery of modern quantum mechanics, there is still no consensus as to how the theory should be understood. The philosophies of Niels Bohr and of the logical positivists, which once served to deter physicists and philosophers from asking embarrassing questions about the observer-independent reality underlying the observational predictions of quantum mechanics, have long ceased to satisfy. Yet the foundational work of John Bell and others has now revealed that any realist construal of quantum mechanics, if it is to reproduce the predictions of the conventional theory, must inevitably conflict with deeply rooted and intuitively appealing principles of classical physics or of common sense. There are no conservative options. In quantum mechanics, possible states of a physical system are represented by vectors in an abstract space called Hilbert space. These vectors can be multiplied by numbers, known as coefficients, and added together (by way of a generalization of the familiar parallelogram law) so as to yield new vectors which then stand for states which are said to be superpositions of the original states. It is a feature of quantum mechanics that any such linear combination of any set of distinct state vectors of a physical system corresponds to a possible state of this system. This is known as the superposition principle. From a classical perspective it is a bizarre proposition. Consider, for example, a set of distinct states of the gears of my car. The superposition principle implies that, since being in first gear is a state, and so are being in second, third, and reverse gear, there is a possible state of my car in which it is, say, l in first gear plus l in second, 1 in third, and1 in 21113 jCI~U 21 3VlU 2 2 III~ LI