The Emperor's New Mind: Concerning Computers, Minds, and the Laws of Physics (Oxford Landmark Science)

by Roger Penrose

Unfortunately, different theorists tend to have very different (though observationally equivalent) viewpoints about the actuality of this picture. Many physicists, taking their lead from the central figure of Niels Bohr, would say that there is no objective picture at all. Nothing is actually ‘out there’, at the quantum level. Somehow, reality emerges only in relation to the results of ‘measurements’. Quantum theory, according to this view, provides merely a calculational procedure, and does not attempt to describe the world as it actually ‘is’. This attitude to the theory seems to me to be too defeatist, and I shall follow the more positive line which attributes objective physical reality to the quantum description: the quantum state. There is a very precise equation, the Schrödinger equation, which provides a completely deterministic time-evolution for this state. But there is something very odd about the relation between the time-evolved quantum state and the actual behaviour of the physical world that is observed to take place. From time to time–whenever we consider that a ‘measurement’ has occurred–we must discard the quantum state that we have been laboriously evolving, and use it only to compute various probabilities that the state will ‘jump’ to one or another of a set of new possible states. In addition to the strangeness of this ‘quantum jumping’, there is the problem of deciding what it is about a physical arrangement that decrees that a ‘measurement’ has actual...