MATTER AND LIGHT The New Physics By LOUIS DE BROGLIE. Originally published in 1937. TRANSLATORS NOTE: THE Author has in certain places modified the original French text for the English translation, for the sake of greater cohesion, and has also revised some passages, in order to bring them into accord with the results of later research. Occasional Translators Notes are shown in square brackets. The chapter on The Undulatory Aspects of the Electron has the special historical interest of having been delivered as a Lecture on the occasion of the Authors receipt of the Nobel Award, while that on Wave Mechanics and its Interpretations was given as an Address at the Glasgow meeting of the British Association in 1928. I am indebted to Dr. J. E. Turner, of the University of Liver pool, for assistance with the translation and the proofs, and to Dr. C. Strachan, of the same University, I am indebted for valuable assistance in dealing with the equations and the more technical passages, as well as for reading the proofs. W. H. J. PREFACE: THE amiable insistence of my friend Andr George has induced me to collect in the present Volume a number of Studies on con temporary Physics written from both the general and the more metaphysical point of view. Each of these Studies forms an inde pendent whole, and can be read by itself. A slight degree of repeti tion which the reader is asked to overlook has been the inevi table result for on more than one occasion I have been compelled to duplicate a summary of the great fundamental stages of con temporary Physics, such as the classification of simple substances, the investigation of the photo-electric effect and the origin of the Theory of Light Quanta and of Wave Mechanics the subjects are somewhat technical, and I cannot well assume that they are common knowledge. But though the same subject is outlined in several of these Studies, I have tried to take up a different point of view in each, and have endeavoured to throw light on different aspects of the essential problems of Quantum Physics in order to facilitate a grasp of their importance. On comparing the different chapters the reader will observe that, while overlapping, they also complement one another and he will feel the fascination and greatness inherent in the vast structure of modern Physics. And while admiring the vast number and the extreme delicacy of experimental facts which laboratory physicists have succeeded in revealing, and the strange and brilliant concepts devised by theorists to explain them, he will appreciate to what a degree the methods and ideas of physicists have grown in subtlety during recent years, and how great has been the progress from the somewhat ingenuous Realism and the over-simplified Mechanics of earlier thinkers. The more deeply we descend into the minutest structures of Matter, the more clearly we see that the concepts evolved by the mind in the course of everyday experience especially those of Time and Space must fail us in an endeavour to describe the new worlds which we are entering. One feels tempted to say that the outlines of our concepts must undergo a progressive blurring, in order that they may retain some semblance of relevance to the realities of the subatomic scales. Time and Space, in other words, are too loose a dress for the elementary entities individuality becomes attenuated in the mysterious pro cesses of interaction, and even Determinism, the darling of an older generation of physicists, is forced to yield...