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G E N E S I S O F T H E B I G B A N G This is a story of the theory of the Big Bang model of the birth of the Universe. All of it is here, pre-Big Bang cosmology, development of the Big Bang theory, obser vational confirmations, alternatives to the model and the future of the Universe accord ing to laws of the Big Bang theory. But more than just a concise, readable exploration of theory, “Genesis of the Big Bang” is a first hand account of the work and struggle that went into proposing and developing these models by two of the scientists who were first to suggest possible proof of a Big Bang: residual background radiation. Alpher lets us into the world of the working physicist and shows us the frustrations, the exhilara tion, and the realities of taking part in one of the most significant, fundamental cosmo logical transitions. “Genesis of the Big Bang” is a fascinating account of what it is like to be at the forefront of theoretical physics and the emotion that can ride along with it, as well as a clear and refreshing look at our current knowledge of the way the universe works. Genesis of the Big Bang GENESIS OF THE BIG BANG Ralph A. Alpher Robert Herman OXFORD UNIVERSITY PRESS 2001 OXFORD UNIVERSITY PRESS Oxford New York Athens Auckland Bangkok Bogota Buenos Aires Calcutta Cape Town Chennai Dar es Salaam Delhi Florence * Hong Kong Istanbul Karachi Kuala Lumpur Madrid Melbourne Mexico City Mumbai Nairobi Paris Sao Paulo Shanghai Singapore Taipei Tokyo Toronto Warsaw and associated companies in Berlin Ibadan Copyright © 2001 by Oxford University Press, Inc. Published by Oxford University Press, Inc. 198 Madison Avenue, New York, New York 10016 Oxford is a registered trademark of Oxford University Press. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior permission of Oxford University Press. Library of Congress Cataloging-in-Publication Data Alpher, Ralph. Genesis of the big bang / by Ralph A. Alpher and Robert Herman, p. cm. Includes bibliographical references and index. ISBN 0-19-511182-6 1. Big bang theory. I. Herman, Robert, 1914- II. Title. QB991.B54 A47 2000 523.1'8-dc21 00-023888 135798642 Printed in the United States of America on acid-free paper Preface ^)ne of the reasons for writing a preface is to explain why the authors have felt moved to write a book in the first place. A second reason in this case is not only to arouse curiosity and interest in cosmology and its scholarship but also to stimulate potential readers to read this book, since there are others dealing with many of the same topics we cover. Our book has had a long gestation period. We have had in mind writing about the development of the Big Bang model of the universe ever since a landmark event took place in 1965. It was in that year that Arno A. Penzias and Robert W. Wilson, then at the Bell Telephone Laboratories, published their discovery of a residual cosmic microwave background, the now- famous three-degree radiation, which pervades the universe. Almost over night the scientific community as well as the lay public found reason to believe that a dynamic, evolving universe beginning with a singular event, the so-called Big Bang, was a credible model. This discovery was only the most recent significant step, because it had become clear many years ear lier that the idea of an expanding universe was not only consistent with but virtually required by Einstein's general theory of relativity. Moreover, the observation of that expansion by the astronomers Vesto M. Slipher, Edwin Hubble, and Milton Humason had come to be widely accepted. Finally, it had also become evident that it was necessary to invoke an extremely hot, dense early stage in the expanding universe in order to understand the cosmic abundances of the lightest elements—namely, deuterium, helium, and lithium—relative to hydrogen. In our view, the discussion of these concepts by Steven Weinberg in his book The First Three Minutes, first published in 1977 (the revised edition of 1988 is still in print), made a significant contribution to the widespread acceptance of the Big Bang model by many scientists, despite its targeting a general audience. Since 1977, other books have dealt with the model in more or less detail and with more recent observational and theoretical developments. Some of these books purport to convey the human side of the conception and development of the model as well. So, again, why another book? We have been intimately connected with the conception and develop ment of the Big Bang model since 1947. Following the late George Gamow's ideas in 1942 and more particularly in 1946 that the early universe was an appropriate site for the synthesis of the elements, we became deeply involved in the question of cosmic nucleosynthesis and particularly the synthesis of the light elements. In the course of this work, we developed a general relativistic model of the expanding universe with physics folded in, which led in a progressive, logical sequence to our prediction of the existence of a present cosmic background radiation some seventeen years before the observation of such radiation was reported by Penzias and Wilson. In addition, we carried out with James W. Follin, Jr. a detailed study of the physics of what was then considered to be the very early universe, starting a few seconds after the Big Bang, which still provides a methodology for studies of light-element nucleosynthesis. Because of our involvement, we can bring a personal perspective to the subject. Our goal is to present a picture of what is now believed to be the state of knowledge about the evolution of the expanding universe and to delineate from our own unique vantage point the story of the devel opment of the Big Bang model as we have seen and lived it. Our princi pal contributions have been our work on the synthesis of the chemical elements in the early stages of the Big Bang and our prediction of the existence and magnitude of a thermal cosmic background radiation with intensity peaking in the microwave region of the electromagnetic spectrum. Because we were closely associated with the late George Gamow from the end of World War II until his death in 1968, we intersperse some reflections and anecdotal material about this remarkable physicist, his legacy in science, and the influence of his personality and image on the way our joint and individual contributions in cosmology have been per ceived by the scientific community. Gamow was a prolific writer of books vi Preface