The Strange World of Quantum Mechanics

  • Daniel F. Styer
Cambridge University Press: 2000. 154 pp. £14.95,$24.95 (pbk)
Quantum Cloud: Antony Gormley's sculpture was created using, among other tools, chaos theory. Credit: NMEC

The proposition that the world is so weird that it defies common sense has always been a major theme in popularizations of quantum mechanics. Generally, the claim is self-fulfilling — the subject is presented in such a way as to make this conclusion inescapable. Leaving aside the commercial opportunities afforded by the New Age market, these popularizations reflect the dominant view of professional physicists since the genesis of quantum theory in the 1920s.

The current generation of writers is heavily influenced by Richard Feynman's pragmatic approach to interpretation. Since his death, collections of Feynman's writings have appeared more frequently than Beach Boys compilations, providing a rich source of ready-made catchphrases (“Nobody understands quantum mechanics”). Two Feynman works, in particular, set the agenda for Daniel Styer's book: The Character of Physical Law (BBC Publications, 1965), which sets up the conceptual conundrum and asserts a primary role for probability, and QED (Princeton University Press, 1985), in which the task of computing probabilities is translated into pictorial terms. Like Feynman, Styer addresses a non-technical audience.

In this approach, physical processes are ‘black boxes’ — they have inputs and outputs, and the weirdness arises because, supposedly, these are not causally connected. Quantum mechanics is then not a physical theory but an abacus for computing the relative probability of outputs.

Styer believes one must master this ‘standard view’ before considering alternative views. This is problematic from several standpoints. Traditionally, the standard view has been associated with Niels Bohr and Werner Heisenberg, but Styer dissociates himself from that lineage. So the standard view itself has no unique formulation. Moreover, given that alternatives exist, the author does not explain what singles out the ‘standard’ one as that preferred. After all, no one adheres to black-box models in practice; as the author admits, physicists instinctively make informal models of the world.

Within its terms of reference, the book gives a clear account of Feynman's approach. At times this is quite compelling, as in the treatment of the quantum bouncing ball. One valuable idea that I haven't seen before in this kind of book is the inclusion of challenging problems at the end of each chapter.

Styer is forthright in pointing out defects in other popular works, but his own analysis is at times questionable. For instance, he tells us that we mustn't dictate to nature, yet in several places declares that an electron does not have a trajectory. How does he know this? Certainly, nothing in quantum mechanics or in Styer's presentation dictates this conclusion. There is, after all, a perfectly consistent view of quantum mechanics — that drawn up by Louis de Broglie and David Bohm — which does attribute a trajectory to an electron. Styer actually alludes to this theory several times (although he does not give a reference for it, which is strange, as his other referencing is excellent), but dismisses it as weird. What a weird criticism, when one's aim is precisely to establish weirdness!

I wonder what Styer's student readership would have thought had he reproduced the iconic figure of Bohm's trajectories for the two-slit experiment. My experience is that they would have asked why this model isn't fully explained in books such as this one, and, indeed, why it isn't the ‘standard view’. To be sure, Bohm's theory has unresolved problems (fertile theories do). But the point is that it allows one to analyse how the black box functions through a causally connected sequence of events from input to output. As probability is no longer the basic concept, this view is more complete than the standard one, with no need to invoke images of “shimmering colours” when referring to electrons. Surely, students should be told of this.

If you are looking for an original account of Feynman's approach, I recommend this book. But surely the weirdness card has been played enough by now — isn't it time to do it differently?