The Quantum Challenge

  • George Greenstein &
  • Arthur G. Zajonc
Jones and Bartlett: 1997. Pp. 204 $50.

The conceptual foundations of quantum mechanics have been elaborated largely as a result of Gedanken experiments — thought experiments that are physically possible but are not designed to be carried out. Is there anything to learn by implementing a Gedanken experiment? Theoreticists may think not, but George Greenstein and Arthur G. Zajonc say that there is. To support this claim they have taken real experiments as a basis for presenting a detailed analysis of the mysteries of quantum mechanics.

The initial chapters of the book discuss experiments that are now more than ten years old, and the subjects are mature enough to be analysed with great clarity. They include wave-particle duality, illustrated through single-photon and delayed-choice interference experiments, and the uncertainty principle, associated with squeezed light. Special attention is devoted to entangled states and the Einstein-Podolsky-Rosen argument, accompanied by a convincing presentation of the experimental tests of Bell's inequalities.

The final chapters, dealing with measurement and decoherence and dissecting Schrödinger's cat, seem less polished, perhaps because direct experimental evidence was scarce when the book was written. But they nevertheless provide an interesting account of the slow evolution of experimental realization, and help one to appreciate the objectives and subtleties of the achievements that followed.

The book could be read with great profit by students who, after a term of a course on quantum mechanics, have grasped the basic calculatory techniques. A lot can be learnt about what practical quantum mechanics really is from the explanation and contemplation of elegant and subtle experiments.

The conceptual difficulties, carefully listed by the authors, have often been considered as “the dark side of quantum mechanics” and have been hidden away in standard textbooks. In that respect, the great intellectual honesty of the authors, who never hide the difficulties but also never overstate them, will be of great help to young readers. More knowledgeable readers will also learn a lot, but those looking for foggy philosophical arguments may be disappointed. The picture of quantum mechanics that emerges is far from obvious, but it is drawn from the weight of experimental reality.