Faith and Science Peter Hodgson
THE QUANTUM world of atoms and nuclei is often described as fuzzy and uncertain, in sharp contrast to the clear-cut deterministic world of classical physics. This is illustrated by Heisenberg's uncertainty principle, which says, according to most textbooks. that it is not possible to measure at the same time the position and the momentum (or velocity) of an electron, or indeed any fundamental particle. The more accurately we measure the position, the less we know about the momentum, and vice versa. More precisely, the product of the uncertainties in the
position and in the momentum is always greater than Planck's constant.
The reason for this is not just that the act of measuring one variable disturbs the measurement of the other. Heisenberg meant something much more radical than this. He said: "It is possible to ask whether there is still concealed behind the statistical universe of perception a "true" universe in which the law of causality would be valid. But such speculations seem to us to without value and meaningless, for physics must confine itself to the description of the relationship between perceptions." He went on to say that "since all experiments are subjected to the laws of quantum mechanics and thereby to the uncertainty principle, the invalidity of the law of causality is definitely proved by quantum mechanics.
If this were true, it would be an example of a profound philosophical conclusion following from a physical theory. and the conclusion would throw doubt on many arguments that invoke the law of causality. It is, however, incorrect on several counts. Firstly, our inability to measure position and momentum exactly does not imply that the electron does not have an exact position and momentum. This would only follow if one believed the positivistic dictum that what cannot be measured does not exist. Secondly, the uncertainty principle only applies to measurements on a large number of electrons, not of an individual electron; it is easy to show that the position and the momentum of a single electron can indeed be measured much more accurately
than is specified by the uncertainty principle.
This is unfamiliar even to most physicists and is contrary to what is found in many textbooks on quantum mechanics. The arguments are given in detail in a book by Karl Popper called Quantum Theory and the Schism in Physics. He emphasises that "there can be no question whether, according to the quantum theory. an electron can "have" a precise position and momentum. it can ". The detailed physics is also described in an article by Leslie Ballentine on the statistical interpretation of quantum mechanics, published in the Review of Modern_ Physics (42.358.1970).
Heisenberg's remarks about causality follow from what is called the Copenhagen interpretation of quantum mechanics, which gives rise to a whole range of pseudo
problems. It gives a conceptually clear account of the behaviour of electrons and other fundamental particles and leaves open the way to a deeper understanding of the physical world. The essential point is that quantum mechanics is a statistical theory that applies only to large numbers of systems, and the fundamental error, that gives rise to all the confusion, is to suppose that it can be applied to just one system.
This story shows how theories of modem physics — no less than religious doctrines — can be misinterpreted in the context of a false and supposedly "scientific" philosophy, in this case positivism, and used to support very general but false conclusions. These quantum myths are very widespread and appeal to those who like to see the world as full of mysteries.