The First Three Minutes, A Modern View of the Origin of the Universe - Steven Weinberg.pdf

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Steven Weinberg
The First
Three
Minutes
A
modem view
of the origin of
the universe
FLAMINGO
Published by Fontana Paperbacks
Contents
Preface 9
1 Introduction: the Giant and the Cow 13
2 The Expansion of the Universe 20
3 The Cosmic Microwave Radiation Background 52
4 Recipe for a Hot Universe 81
5 The First Three Minutes 102
6 A Historical Diversion 120
7 The First One-hundredth Second 130
8 Epilogue: the Prospect Ahead 145
Afterword 151
TABLES : 1. Properties of Some Elementary Particles 163
2. Properties of Some Kinds of Radiation 164
Glossary 165
Preface
This book grew out of a talk I gave at the dedication of the
Undergraduate Science Center at Harvard in November
1973. Erwin Glikes, president and publisher of Basic Books,
heard of this talk from a mutual friend, Daniel Bell, and
urged me to turn it into a book.
At first I was not enthusiastic about the idea. Although I
have done small bits of research in cosmology from time to
time, my work has been much more concerned with the
physics of the very small, the theory of elementary particles.
Also, elementary particle physics has been extraordinarily
lively in the last few years, and I had been spending too
much time away from it, writing non-technical articles for
various magazines. I wanted very much to return full time
to my natural habitat, the
Physical Review.
However, I found that I could not stop thinking about the
idea of a book on the early universe. What could be more
interesting than the problem of Genesis? Also, it is in the
early universe, especially the first hundredth of a second, that
the problems of the theory of elementary particles come
together with the problems of cosmology. Above all, this is
a good time to write about the early universe. In just the last
decade a detailed theory of the course of events in the early
universe has become widely accepted as a 'standard model'.
It is a remarkable thing to be able to say just what the
universe was like at the end of the first second or the first
minute or the first year. To a physicist, the exhilarating
thing is to be able to work things out numerically, to be able
to say that at such and such a time the temperature and
density and chemical composition of the universe had such
10
The First Three Minutes
and such values. True, we are not absolutely certain about
all this, but it is exciting that we are now able to speak of
such things with any confidence at all. It was this excitement
that I wanted to convey to the reader.
I had better say for what reader this book is intended.
I have written for one who is willing to puzzle through some
detailed arguments, but who is not at home in either mathe-
matics or physics. Although I must introduce some fairly
complicated scientific ideas, no mathematics is used in the
body of the book beyond arithmetic, and little or no knowl-
edge of physics or astronomy is assumed in advance. I have
tried to be careful to define scientific terms when they are
first used, and in addition I have supplied a glossary of
physical and astronomical terms (p. 165). Wherever possible,
I have also written numbers like 'a hundred thousand million'
in English, rather than use the more convenient scientific
notation: 10
11
.
However, this does not mean that I have tried to write an
easy book. When a lawyer writes for the general public, he
assumes that they do not know Law French or the Rule
Against Perpetuities, but he does not think the worse of them
for it, and he does not condescend to them. I want to return
the compliment: I picture the reader as a smart old attorney
who does not speak
my
language, but who expects nonethe-
less to hear some convincing arguments before he makes up
his mind.
For the reader who does want to see some of the calcula-
tions that underlie the arguments of this book, I have pre-
pared 'A Mathematical Supplement', which follows the body
of
the
book (p. 175). The level of mathematics used here
would make these notes accessible to anyone with an under-
graduate concentration in any physical science or mathe-
matics. Fortunately, the most important calculations in
cosmology
are
rather simple; it is only here and there that
the finer points of general relativity or nuclear physics come
into play. Readers who want to pursue this subject on a
more technical level will find several advanced treatises

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