Favorite Prefaces – II

Conceptual Foundations of Quantum Mechanics
by Bernard d’Espagnat

A few words are here in order concerning the guiding idea that inspired this book. It is that quantum mechanics can be formulated axiomatically, that, for clarity sake, it is of course quite appropriate to do so, but that the axioms in question then have to take the form of (precise and general) “rules of the game,” serving to predict what will be observed. This is a difference with classical mechanics, the axioms of which (Newton’s laws and the rest) are most simply expressed as statements bearing on the structure of some mind-independent reality. It is a fact that attempts at doing the same in quantum physics quickly lead to conceptual muddles (“Are wave functions real?,” “Is collapse real?,” etc.), while, in contrast, viewed as a set of observational predictive rules, quantum mechanics is crystal clear. The rules in question must therefore be considered as being—by far—what is most solid in quantum physics. And it is for this matter-of-fact reason—and not because of any a prior allegiance to positivism, empiricism or what not!—that it was here found advisable to begin by just stating these predictive rules and investigating their consequences. Since no allegiance to phenomenalism is made, the question of the possible interpretation of the said rules in terms of some underlying reality of course remains significant. In fact such a study constitutes, in a sense, the very purpose of the present book. But the corresponding analyses must—-and do, here—come in only in a second stage, after the rules have been duly stated and examined.

Note that the just explained standpoint is precisely the one that gives us maximal freedom concerning interpretation problems, since it bars out any a priori prejudice relative to what constitutes reality. Within it, we are not, right at the start, forced to conceive of reality in terms, either of waves, or of particles, or of “wavicles,” or etc. Any way of thinking of it is a priori admissible, provided only that, in the end, it turns out to be compatible with the observational predictions yielded by the basic quantum rules. But, as will be seen, this condition proves to be a demanding one. It does not leave many vistas open. Indeed the book shows that such an approach gently leads to quite definite ideas concerning the conceptual foundations of the incredibly powerful science that is called quantum mechanics.