INTRODUCTION

In 1965 Hilary Putnam published the standard work on the interpretation of quantum mechanics, a piece that all philosophers of quantum mechanics of the time had to come to terms with. He laid out one-by-one in a clear non-technical way each of the available approaches to the problem and explained, again non-technically but very exactly, what is wrong with them. In his own final words Putnam took ‘the modest but essential step of becoming clear on the nature and magnitude of the difficulties’ (1965, 158).

In the almost forty years since there have been a variety of advances, technical developments and new points of view. But none of these is uncontroversial. In fact each suffers from some one or another of the very difficulties that Putnam summarised. Many of the newer approaches explain why the problem is not a problem after all; a few bury the problems in technical detail; and some make heroic assumptions, often metaphysical, that cause the problems to disappear. My conclusion surveying the contemporary literature is the same as Putnam's in 1965: ‘no satisfactory interpretation of quantum mechanics exists today’ (1965, 157).

The time scale is amazing. Putnam's important piece was written forty years after the first formulations and successes of quantum mechanics. I am writing forty years later, and about a theory that has transformed our technology and our way of thinking about the world. Why does this theory still have ‘no satisfactory interpretation’?