Analogy in Quantum Theory: From Insight to Nonsense

Abstract

Analogy, like the Indian monkeys, is found in every household and everyone admires its fertility but nobody examines it carefully and no one trusts it. The ubiquity and fruitfulness of analogy in hypothesis formation are so obvious that they hardly need be extolled.1 We all remember that in many respects the molecule behaves like a hard sphere, that the atom used to be pictured as a mini-solar system, that the 'magic' atomic nucleus may be likened to a closed atomic shell system, and that the photon can put on a particle-like face. But we also know that, on closer inspection, these and most other analogies in physics proved to be just that-analogies not literal descriptions. We have learned to tolerate and even encourage daring analogising in the search for new ideas-which is a way of getting extra mileage with the old ones. But we have also learned to mistrust analogy both as a constituent of theories and as an index for their evaluation: we