Space and time in the modern universe /

246 Pages·34.922 MB·English

by  P. C. W. Davies.

Space and time in the
modern
universe
P.C.W.DAVIES
LecturerinAppliedMathematics,King'sCollege,London
CAMBRIDGE UNIVERSITY PRESS
CAMBRIDGE
LONDON NEW YORK MELBOURNE
• •
Published by the Syndics ofthe Cambridge University Press
The Pitt Building, Trumpington Street, Cambridge CB2 IRP
Bentley House, 200 Euston Road, London NWl 2DB
32 East 57th Street, New York, NY 10022, USA
296 Beaconsfield Parade, Middle Park, Melbourne 3206, Australia
©
Cambridge University Press 1977
First published 1977
Reprinted 1977,1978
Filmset byCox & Wyman Ltd, London, Fakenham and Reading
Reprinted in the United States of America
by R.R.Donnelley andSonsCo. Crawfordsville, Ind.
Library ofCongress Cataloguing in Publication Data
Davies, P. C. W.
Space and time in the modem universe.
1. Space and time. L Title.
QC173.59.S65D39 530.n 76-27902
ISBN 521 21445 9
ISBN 521 29151 8 pbk.
CONTENTS
Preface VI
1 The many faces of space and time 1
2 The relativity revolution 29
3 The asymmetry of past and future 56
4 Gravitation and the bending of space-time 86
5 Modern cosmology 141
6 The beginning and the end 172
7 Mankind in the universe 200
Index 223
PREFACE
The structure of space and time lies at the very foundation of
bothphysicalscienceandourperceptualexperienceoftheworld.
They are concepts so fundamental that in everyday life we do
notquestiontheirproperties. Yetmodern sciencehas discovered
situations in which space and time can change their character
sodrasticallythatremarkableandunexpectedphenomenaoccur.
Many ofthesesituationsowetheirappearanceto recentdevelop-
ments in astronomy. The possibilities of the existence of black
holesorabigbangoriginoftheuniversehavestimulateddetailed
investigationsintothebehaviourofspace,timeandmatter,when
gravity becomes overwhelmingly strong. The results indicate
that space-time itselfmay collapse out ofexistence under some
circumstances. The consequences of these recent developments
for the nature and evolution of the universe are far-reaching
and profound.
This book sets out to examine the exciting and sometimes
enigmatic discoveries about space, time and the universe made
by scientists in recent years. Any proper understanding ofthese
modern advances depends on the reader having a grasp of the
physicists' new model ofspace-time structure.
Thechangingnature ofthis model overthelast 150 years, and
ourevolving perspective ofthe universe that accompanies it, are
carefully described in the forthcoming chapters. The reader will
discover how the space-time picture ofNewton, so close to that
ofour familiar experience, has been repeatedly remodelled and
modified to accommodate new physical theories. The laws of
electromagnetism, with the abortive invention of an ether, the
strange four-dimensional space-time of the theory of special
relativity, the intriguing notion of curved space in the general
theory of relativity, not to mention the sheer outlandishness of
the quantum theory, which predicts that black holes may
evaporate away to nothing and space-time may break apart
below microscopic dimensions - all have demanded a fresh
Preface Vll
conceptual structure for these most primitive of all physical
entities.
Woven into this changing picture of space-time structure is
a parallel story ofconfusion and paradox concerning the asym-
metry of the world between past and future. The nature and
origin ofthis time asymmetry reside inthebasiclaws ofthermo-
dynamics and the conditions placed on the universe at its very
A
beginning. study of time asymmetry allows us to choose
between two distinct models ofthe universe: one which slowly
runs down to cold, featureless sterility, or one which undergoes
rejuvenation, time-reversal, or simply crushes itself out of
existence.
Somuchofthesubjectmatterdiscussedoverlapswithdomains
of human intellectual activity normally associated more with
religion and metaphysics than hard science. Yet today, science
is on the brink of suggesting answers to many ofthe questions
so long puzzling to theologians and philosophers alike. No
account of these developments is complete therefore, without
an examination of the place ofmankind and human society in
thenewuniverse. Theimpacton society ofchangingideas about
space, time and the nature of the cosmos has always been
profound. The revolution now in progress could alter forever
mankind's perspectivenot only ofthe universe, but also ofour
own place in that universe.
Ihaveintendedthisbooktobebotheducativeandentertaining,
for that is the experience ofthe researchers and teachers ofthe
subjects expounded. Unravelling the scientific mysteries of our
world is one of the most satisfying of human endeavours, and
I have attempted to communicate the sense of excitement and
awefeltbythepractitionersofmodernscienceinthesechallenging
times.
I have not assumed a high level ofexpertise from the reader.
Scientifically inclined laymen with no mathematics and a
sprinkling of physics should have little difficulty in following
much ofthe discussion. However, because a lot ofthe material
isveryadvanced, studentsofphysics, astronomy,appliedmathe-
maticsandphilosophy will findawealthofinformationrelevant
to their lecture courses or research.
viii Preface
Finally,IshouldliketothankmycolleaguesatKing'sCollege,
London, whose opinions and observations have helped shape
my own view ofspace-time physics and cosmology.
Note on nomenclature. Physicists and astronomers often have
to deal with very large or very small numbers, and it is usually
inconvenienttowritethemout in full. Forthat reason the short-
hand'powersoften'notationwillfrequentlybeusedinthisbook.
In this system, the number one followed by n noughts is simply
written 10". Thus one thousand is 10^, one million is 10^and
USA
onebillion,heretakenasthe billion(onethousandmillion)
is 10^. Small numbers are similarly represented using negative
powers (10""). For example, one-thousandth is 10~^, one-
millionth is 10"^ and one-billionth is 10"^.
King's College, London P. C. W. Davies