LOUIS DE BROGLIE AND THE SINGLE QUANTUM PARTICLE By A. O. Barut We have abundant evidence and testimony that Louis de Broglie deeply cared about the foundations, the meaning, and our understanding of quantum theory in general and of wave mechanics in particular. So, too, did Erwin Schrodinger, along with Einstein, Bohr, Dirac, and Heisenberg. For de Broglie and Schrodinger this preoccupation meant not simply the acceptance of a novel set of rules, but a constant struggle and a search for complete clarity about the way in which the new theory fits into the great classical traditions of an objective physical world view. We may call this a striving for "physical rigor," rigor in reasoning, or intellectual rigor. There is not only mathematical rigor inside an axiomatic system with which everybody agrees, but there is, and there should be, rigor also in our concepts and methods. To this kind of rigor belongs the unity, the economy and simplicity, and the consistency of physical theories; naturally along with as complete and as clear an understanding of phenomena as possible. No loose ends, no proliferation of poorly tested and phenomenological entities, no bending of logic and compromise, and no handwaiving arguments can be tolerated. Unfortunately this kind of rigor seems to be missing in today's forefront of fundamental physical theories, viz. , particle or high-energy physics.