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

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

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

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

Preface 11

(including my own) listed under 'Suggestions for Further

Reading' (p. 189).

I should also make clear what subject I intended this book

to cover. It is definitely not a book about all aspects of

cosmology. There is a 'classic' part of the subject, which has

to do mostly with the large-scale structure of the present

universe: the debate over the extragalactic nature of the

spiral nebulae; the discovery of the red shifts of distant

galaxies and their dependence on distance; the general relativ-

istic cosmological models of Einstein, de Sitter, Lemaitre, and

Friedmann; and so on. This part of cosmology has been

described very well in a number of distinguished books, and

I did not intend to give another full account of it here. The

present book is concerned with the early universe, and in

particular with the new understanding of the early universe

that has grown out of the discovery of the cosmic microwave

radiation background in 1965.

Of course, the theory of the expansion of the universe is

an essential ingredient in our present view of the early uni-

verse, so I have been compelled in Chapter 2 to provide a

brief introduction to the more 'classic' aspects of cosmology.

I believe that this chapter should provide an adequate back-

ground, even for the reader completely unfamiliar with

cosmology, to understand the recent developments in the

theory of the early universe with which the rest of the book

is concerned. However, the reader who wants a thorough

introduction to the older parts of cosmology is urged to

consult the books listed under 'Suggestions for Further

Reading'.

On the other hand, I have not been able to find any

coherent historical account of the recent developments in

cosmology. I have therefore been obliged to do a little digging

myself, particularly with regard to the fascinating question

of why there was no search for the cosmic microwave radia-

tion background long before 1965. (This is discussed in

Chapter 6.) This is not to say that I regard this book as a

definitive history of these developments - I have far too much

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