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The Strange Story of the Quantum THE STRANGE STORY OF QUANTUM An account for the GENERAL READER of the growth of the IDEAS underlying our present ATOMIC KNOWLEDGE B A N E S H HOFFMANN DEPARTMENT OF MATHEMATICS, QUEENS COLLEGE, NEW YORK Second Edition DOVER PUBLICATIONS, INC. NEW YORK Copyright 1947, by Banesh Hoffmann. Copyright 1959, by Banesh Hoffmann. All rights reserved under Pan American and International Copyright Conventions. Published simultaneously in Canada by McClelland & Stewart, Ltd. This new Dover edition first published in 1959 is an unabridged and corrected republication of the First Edition to which the author has added a 1959 Postscript. Manufactured in the United States of America. Dover Publications, Inc. 180 Varick Street New York 14, N. Y. My grateful thanks are due to my friends Carl G. Hempel, Melber Phillips, and Mark W. Zemansky, f r many valuable sug- gestions, and to the Institute for Advanced Study where this booJc was begun. B. HOFFMCANIST The Institute for Advanced Study Princeton, N, J v February, 1947 ' / fit, (,. ,,,.| CONTENTS Preface ix I PROLOGUE i ACT I II The Quantum is Conceived 16 III It Comes to Light 24 IV Tweedledum and Tweedledee 34 V The Atom of Niels Bohr 43 VI The Atom of Bohr Kneels 60 INTERMEZZO VII Author's Warning to the Reader 70 ACT II VIII The Exploits of the Revolutionary Prince 72 IX Laundry Lists Are Discarded 84 X The Asceticism of Paul 105 XI Electrons Arc Smeared 109 XII Unification 124 XIII The Strange Denouement 140 XIV The New Landscape of Science 174 XV EPILOGUE 200 Postscript: 1999 235 PREFACE THIS book is designed to serve as a guide to those who would explore the theories by which the scientist seeks to comprehend the mysterious world of the atom. Nuclear fission and atomic bombs are not the whole of atomic science. Behind them lie extraordinary ideas and stirring events without which our understanding would be meager indeed. The story of the quantum is the story of a confused and groping search for knowledge conducted by scientists of many lands on a front wider than the world of physics had ever seen before, illumined by flashes of insight, aided by accidents and guesses, and enlivened by coincidences such as one would expect to find only in fiction. It is a story of turbulent revolution; of the undermining of a complacent physics that had long ruled a limited domain, of a subsequent interregnum predestined for destruction by its own inherent contradictions, and of the tempestuous emer gence of a much chastened regime Quantum Mechanics. Though quantum mechanics rules newly discovered lands with a firm hand, its victory is not complete. What look like mere scratches on the brilliant surface of its domain reveal ix X PREFACE themselves as fascinating crevasses betraying the darkness within and luring the intrepid on to new adventure. Nor does quantum mechanics hold undisputed sway but must share dominion with that other rebel, relativity; and though, to gether, these two theories have led to the most penetrating advances in our search for knowledge, they must yet remain enemies. Their fundamental disagreement will not be re solved until both are subdued by a still more powerful theory which will sweep away our present painfully won fancies con cerning such things as space and time, and matter and radi ation, and causality. The nature of this theory may only be surmised, but that it will ultimately come is as certain as that our civilization will endure no more nor less. What are those potent wraiths we call space and time, without which our universe would be inconceivable? What is that mystic essence, matter, which exists within us and around in so many wondrous forms; which is at once the servant and master of mind, and holds proud rank in the hierarchy of the universe as a primary instrument of divine creation? And what is that swiftest of celestial messengers, radiation, which leaps the empty vastnesses of space with lightning speed? Though true answers there can be none, science is fated to fret about such problems. It must forever spin tentative theories around them, seeking to entrap therewith some germ of truth upon which to poise its intricate superstructure. The balance is delicate and every change sends tremors cours ing through the edifice to its uttermost tip. The story of relativity tells what happened to science when one provisional theory of space and time yielded to another. The story of the quantum tells of adventures which recently befell our theories PREFACE Xl of matter and radiation, and of their unexpected consequences. well as So abstract a matter as the quantum theory serves with the the basis for learned treatises whose pages overflow mathematics. Here in this book unfriendly symbols of higher without omis is its story without mathematics yet important of the scientific theorist sion of concept. Here too is a glimpse as he at work, pen and paper his implements, experiments is a talent for with ideas. Not the least of his gifts reaching valuable conclusions from what later prove to be faulty Be it a hint here or premises. For his insight is penetrating. or a wild he fashions a clue there, a crude analogy guess, material is at hand, and, working hypotheses from whatever intuition for with the divine gift of guide, courageously him a follows the faintest will-o'-the-wisp till it show way toward truth. to a dominant The magnificent rise of the quantum position of drama and in modern science and philosophy is a story incredible. It is a chaotic tale, high adventure often well-nigh discerns a but amid the apparent chaos one gradually splendid irrelevant or architecture, each discovery, however seemingly into its till nonsensical, falling cunningly appointed place as one of the the whole intricate jigsaw is revealed major discoveries of the human mind. THE STRANGE STORY OF THE QUANTUM CHAPTER I PROLOGUE IN THE corner of a carefully darkened laboratory stands an electrical machine on which two small, shining spheres of metal frown menacingly at each other's proximity. It is a standard machine for making electric sparks to which one small addition has been made. Two metallic plates have been joined to the spheres by slender conducting rods, as if to add enormous ears to the two-eyed monster. On another table stands a simple, almost closed hoop of stiff wire mounted on an insulating stand. For the experimenter the small gap in this hoop is the crucial part of the whole apparatus. If his surmise is correct, it is here that the secret will be revealed. All is in readiness and the experimenter closes a switch to set the sparks crackling and spitting between the spheres. Turning his back on the flashing sparks he waits for his eyes to grow accustomed to the darkness. Is it imagination or does faint is he really see a glow filling the gap in the ring? It not easy to tell. It may be only a reflection. Gently he turns the screw that forces the ends together, and as the gap becomes narrower the glow seems to brighten. Closer yet, and closer, 2 THE STORY OF THE QUANTUM till the ends are almost touching. Now there can be no doubt The experimenter breathes a sigh of relief. Tiny electric sparks are passing across the gap. In so strangely simple a fashion did man first wittingly detect a radio signal. This was in 1887, the experimenter a brilliant young German physicist, Heinrich Hertz. The commercial value of this discovery was beyond estima tion. Why, then, did so able a man as Hertz leave it for Marconi to capture the rich rewards of its exploitation? It was not at all with the idea of inventing anything so practical as radio telegraphy that Hertz embarked on his epochal experiments, nor, perhaps, was radio telegraphy their most significant result. Hertz had set himself a task which had long baffled scientists: to test the truth of a highly mathematical theory concerning light, electricity, and magne tism proposed twenty-three years before by the Scottish physicist, James Clerk Maxwell. The thought of the commer cial value of the work seems not to have troubled his mind at all, and this passion for pure research for its own sake was in a sense responsible for a most ironical situation. For without it Hertz might never have bothered about a seemingly trivial effect he had noticed in the course of his experiments. These experiments were everywhere hailed as brilliantly establishing the truth of Maxwell's theory on a rocklike basis of experi mental fact Yet the seemingly trivial phenomenon which he noticed was destined, in the hands of Einstein, to play a momentous part in the evolution of the quantum theory and thereby to aim at the theory of Maxwell a shattering blow from which it can never fully recover. To appreciate the work of Maxwell and Hertz, and the PROLOGUE 3 at some whole story of the quantum, we must first look briefly of the theories men have proposed about light. Though there have been many notable Jewish scientists in modern times, the ancient Hebrew sages had no great instinct for scientific inquiry. Having disposed of the whole Let problem of light with the pronouncement And God said, to there be light: and there was light, they quickly passed on more important matters. Light, for them, was little more than the opposite of darkness, the circumstance of being able to see. The Greeks, however, with surer scientific instinct, intro duced a new idea of great importance. Realising there must be something bridging the distances between our eyes, the things we see, and the lamps illuminating them, they gave it objective reality and set about studying it and inventing theories about it.
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