Table Of ContentR L R H H. G U T H
THE
IHf lRTIOHRRY
UNIVERSE
T H E QU E S T F O R
A NEW THEORY OF
COSMIC ORIGINS
WITH A FOREWORD BY
ALAN LIGHTMAN
~+ - c .
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claimed as trademarks. Where those designations appear in this book and Addison-Wesley was
aware of a trademark claim, the designations have been printed in initial capital letters.
Library of Congress Cataloging-in-Publication Data
Guth, Alan H.
The inflationary universe : the quest for a new theory of cosmic
origins / Alan H. Guth.
p. cm.
Includes bibliographical references and index.
ISBN 0-201-14942-7 (hardcover)
ISBN 0-201-32840-2 (paperback)
1. Inflationary universe. l. Title.
QB991.I54G88 1997 96-46117
523 .1 '8-dc2 l CIP
Copyright © 1997 by Alan H. Guth
Foreword copyright © 1997 by Alan Lightman
Al! 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 written permission of the publisher. Printed in the United States
of America.
Addison-Wesley is an imprint of Addison-Wesley Longman, Inc.
Cover design by Suzanne Heiser
Text design by Jean Hammond
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First paperback printing, February 1998
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To my family
CONTENTS
Foreword ix
Preface xiii
The Ultimate Free Lunch 1
2 The Cosmic Vista from Ithaca, New York 17
3 The Birth of Modern Cosmology 33
4 Echoes of a Scorching Past 57
5 Condensation of the Primordial Soup 85
6 Matters of Matter and Antimatter 105
7 The Particle Physics Revolution of the 1970s 115
8 Grand U nified Theories 131
g Combatting the Magnetic Monopole Menace 14 7
1 O The Inflationary Universe 167
11 The Aftermath of Discovery 189
1 2 The New Inflationary Universe 201
1 3 Wrinkles on a Smooth Background 213
v111 e o N T E N T s
1 4 Observational Clues from Deep Below
and Far Beyond 237
1 5 The Eternally Existing, Self-Reproducing
Inflationary Universe 245
1 6 Wormholes and the Creation of Universes
in the Laboratory 25 3
1 7 A Universe Ex Nihilo 2 71
Epilogue 2 77
A P P ¡ HO 1 H A Gravitational Energy 289
A P P ¡ HO 1 H B Newton and the Infinite
Static Universe 295
A P P ¡ HO 1 H [ Blackbody Radiation 299
A P P ¡ HO 1 H O Units and Measures 305
Notes 311
Glossary 325
Credits 345
Index 347
FOREWORD
very culture has had its cosmology, its story of how the universe carne
Ei nto being, what it is made of, and where it is going. Astoundingly, cos-
mology in this century has become a science, a well-defined area of research
within astronomy and physics.
In the 1970s, the study of cosmology went through a majar conceptual
change. Prior to this time, modern cosmologists asked such questions as:
What is the composition of galaxies and where are they located in space?
How rapidly is the universe expanding? What is the average density of mat-
ter in the cosmos? After this time, in the "new cosmology," cosmologists
began seriously asking questions like: Why does matter exist at all, and
where did it come from? Why is the universe as homogeneous as it is over
such vast distances? Why is the cosmic density of matter such that the
energy of expansion of the universe is almost exactly balanced by its energy
of gravitational attraction? In other words, the nature of the questions
changed. The questions became more fundamental. "Why?" was added to
"What?" and "How?" and "Where?". Alan Guth was one of the young pio-
neers of the new cosmology, asking the Whys, and his Inflationary Universe
theory provided many answers.
Sorne of the why questions had been asked earlier but not pursued with
great stamina, mainly because there seemed no hope of answers, no explan-
atory theories had been proposed. The standard Big Bang theory, in hand
since the work of Einstein and Friedmann and Lemaitre in the 1920s,
offered no explanations. As a result, working cosmologists simply assumed
as givens sorne of the most interesting observed features of the universe,
such as its homogeneity and its very precise balance of energies. Indeed,
x FOREWORD
before the 1970s and early 1980s, many cosmologists took the attitude that
sorne of these features of the universe had to be accepted as "initial condi-
tions," present at the beginning, perhaps mere accidents, perhaps incalcula-
ble even in principie. In any case, these features, observed but unexplained,
were not taken as serious shortcomings of the standard big bang theory.
The benign neglect of certain observed facts, or anomalies, that cannot
be explained within the reigning theory is not uncommon in science. For
example, prior to the work of Alfred Wegner in 1912 and his theory of
"continental drift, " the conceptual framework in which geologists worked
held that landmasses could move only vertically. In this picture there was no
explanation of the observed remarkable similarity of shapes of the opposite
coasts on the two sides of the Atlantic. South America and Africa, in partic-
ular, are shaped as if they were two fitting pieces of a jigsaw puzzle. Geolo-
gists commented on this peculiar feature of geography but mainly accepted
it as a curiosity, scarcely a puzzle waiting for a solution. After Wegner pro-
posed his new theory, which offered a natural mechanism for how the conti-
nents could have drifted horizontally apart after once being joined in a
single landmass, the fit of the continents was recognized as a major problem
in the old theory.
Another example comes from biology, namely the lack of adaptation of
certain organisms to their environments. There are ducks with feet designed
for swimming that do not swim; there are animals, like the dark-cave rat
Neotoma, that have eyes but never use them; there are birds, like the pen-
guin, that have wings but never fly. Before Darwin's theory of natural selec-
tion, these anomalous facts were observed but swept under the rug in the
prevailing creationist framework , which held that each species is exquisitely
designed for its habitat and never changes. However, nonadaptation as well
as adaptation is explained in Darwin's theory because natural selection
requires evolution and change. An organism that has adapted to a particular
environment may change environments but still pass clown the previously
adapted trait, such as a long line of rats that move from the daylight to a
dark cave. After Darwin's work, the nonadaptation of some animals was
seen as a major flaw in the creation theory. Such is the conservative nature
and the psychological forces of the scientific enterprise.
Similarly, the observed homogeneity of the universe and the precise bal-
ance of its energies were considered by most of the scientific community to
represent serious deficiencies in the standard Big Bang model only after the
Inflationary Universe theory was proposed. The conception of that new the-
ory was made possible by a new stock of ideas from theoretical physicists
who, in the past, had concerned themselves with the fundamental particles
and forces of nature. In the early 1970s, new theories of particle physics
called Grand Unified Theories proposed that three of the four fundamental
FO RE wo RO XI
forces of nature-the strong and weak nuclear forces and the electromag-
netic force-were actually manifestations of a single, underlying force. (Uni-
fication and simplicity have been the eternal Holy Grail of physicists and
artists. Aristotle wanted to reduce ali substance to five elements; Picasso said
that a painter should work with as few elements as possible.) According to
the new theories, the temperature at which the single force would become
29
evident was an incredible 10 degrees centigrade, far higher than any tem-
perature that existed on earth or even at the centers of stars. Such a fantasti-
cally high temperature could have existed at only one place, or more
precisely at one time: in the very young universe, shortly after its big bang
beginning. Thus the particle physicists became interested in cosmology. One
of the most well known and accomplished particle physicists to combine
Grand Unified Theories with cosmology at this time was Steven Weinberg.
One of the younger scientists was Alan Guth.
Guth's great achievement was the proposal that, as a natural conse-
quence of the properties of the Grand Unified Theories, the very young uni-
verse would have gone through a brief period of extremely rapid expansion,
after which it would return to the more leisurely rate of growth dictated by
the standard Big Bang theory. Guth's proposed modification of the older the-
ory has been called the Inflationary Universe theory. That theory, and its
various improved versions, provide explanations for sorne of the previously
unexplained "anomalies" observed by cosmologists. In my view, the Infla-
tionary Universe theory is the most significant new development in cosmo-
logical thinking since the foundational work in the 1920s.
Because the key phenomenon of the Inflationary Universe theory, the
extremely rapid cosmic expansion, purportedly happened so long ago, we
will probably never know with certainty whether that event in fact occurred.
(The theory also makes sorne precise predictions about the universe toda y but
cannot be proven true on the basis of these predictions.) However, like the
notion that the continents were once joined in a single landmass, the "infla-
tion" idea has such explanatory power that it has become an underlying
assumption of many working cosmologists today. Thus, an intellectual revo-
lution has occurred in cosmological thinking. In the language of the late MIT
historian of science Thomas Kuhn, we have a new paradigm in cosmology.
This book that Alan Guth has written is extraordinary for severa] rea-
sons. lt explains complex scientific ideas without the use of equations. lt is
written with the same clarity and elegance as Guth's original, pathbreaking
scientific paper in the Physical Review of 1981. lt is thorough and thought-
ful. lt gives an honest portrait of a personal career in science, as well as the
human and scientific history of a major discovery. But what is most extraor-
dinary is that this book, like James Watson's Double Helix, is unique in its
field. It has been written by a key scientist involved with the discovery.
Xll FO RE wo RO
Although other physicists played various roles in the discovery and develop-
ment of the Inflationary Universe theory, Alan Guth is internationally recog-
nized as the leading actor. Other popular books may be written (and have
been written) about the subject, but only one book can be written by Alan
Guth. This is the book.
Alan Lightman
Cambridge, Massachusetts May 1997
