by Jeremy Bernstein
Princeton University Press, 178 pp., $17.95
Of all the remarkable advances in scientific understanding that have been achieved over many centuries, it is the theory of quantum mechanics that is the most enigmatic. Introduced in the first quarter of the twentieth century, it grew to a beautiful mathematical structure that became the most revolutionary, broad-ranging, and successful of modern theories: yet despite the multitude of insights that quantum mechanics has given us, it remains the most baffling of all successful theories. Quantum mechanics has such mathematical precision and range of predictive power that it provides explanations for the stability of atoms and solid materials; for phase changes such as melting, freezing, and boiling; for the colors of heated materials, including a detailed description of the puzzling phenomenon of spectral lines; for low temperature superconductivity and superfluidity; and for the behavior of lasers, transistors, and television screens, not to mention the whole of chemistry and much of biology and genetics. How can it be that such a successful theory can still remain an enigma, even to the greatest of physical scientists?
It may be recalled that, for a time, that other great revolutionary physical theory, Einstein’s general relativity, introduced in about 1915, was supposed to have been understood by but a handful of people; yet today that theory is not considered to be exceptionally hard to grasp in its entirety, and it provides us with a mathematically consistent and philosophically satisfying picture of a universe. We may ask the question why has the same not happened with quantum mechanics—for indeed it has not: even one of the greatest quantum physicists of modern times, Richard Feynman, was led to write a few years ago in his book QED^* “I don’t understand it, nobody does.” Yet the answers that different physicists might give to this question would vary greatly, depending upon the views they might hold regarding the quantum theory.
It is not that the theory is particularly difficult to comprehend as a mathematical structure. Rather, the theory exhibits a baffling mixture of extreme physical precision with utter absurdity, with regard to the way it relates to the macroscopic world that we actually perceive. The irony of the situation was once captured very succinctly by Robert Wald, a colleague from the University of Chicago, in a dinnertable discussion about attitudes to the validity of the theory: “If you really believe in quantum mechanics then you can’t take it seriously.” This viewpoint expresses essentially that of those who support the “conventional wisdom” referred to as the “Copenhagen interpretation.” They indeed claim that the very precise formalism of the theory is not to be taken seriously as a picture of actual “reality.” They often assert, accordingly, that the whole question of quantum reality is a nonquestion. One should not think of the theory as providing us with a picture of actuality, they argue, but merely as giving us a calculational procedure that accurately provides the correct mathematical probabilities for the different possible outcomes of experiments. This, they …