About the Author
Jim Al-Khalili was born in 1962 and works as a theoretical
physicist at the University of Surrey in Guildford. He is a
pioneering popularizer of science and is dedicated to
conveying the wonder of science and to demystifying its
frontiers for the general public. He is an active member
of the Public Awareness of Nuclear Science European
committee. His current research is into the properties of
new types of atomic nuclei containing neutron halos. He
obtained his PhD in theoretical nuclear physics from
Surrey in 1989 and, after two years at University College
London, returned to Surrey as a Research Fellow before
being appointed lecturer in 1992. He has since taught
quantum physics, relativity theory, mathematics and
nuclear physics to Surrey undergraduates. He is married
with two young children and lives in Portsmouth in
Hampshire.
CONTENTS
P R E FACE ix
ACKNOWLEDGMENTS xiii
INTRODUCTION xv
SPACE
1 THE 4 T H DIMENSION 3
To do with shapes • What is space? • 2Dworld and 2D’ers •
Curved space • Is there really a fourth dimension?
2 MAT T E R S OF SOME GRAV I T Y 22
Apples and moons • Einstein’s gravity • Free fall • Rubber
space • Twinkle, twinkle • Cooking the elements • Champagne
supernovae in the sky
3 THE U N I V E R S E 41
The night sky • How big is the Universe? • The expanding
Universe • Hubble, bubble . . . • Space is stretching • Did the Big
Bang really happen? • The edge of space •Aclosed universe •
Anopen universe •Whatshape is the Universe then? • Invisible
matter • 1998: a big year in cosmology • Is the Universe infinite?
• Why is it dark at night? • Before the Big Bang? • Summary
4 BLACK HOLES 78
More to light than meets the eye! • Invisible stars • Beyond the
horizon •Ahole that can never be filled • Spinning black holes
• Falling into a black hole • To see a black hole • Not so black
after all • White holes
TIME
5 T I M E S ARE CHANGING 111
What is time? • Who invented time? • The first moment •
Does time flow? • Something called entropy • Arrows of time
• Stephen Hawking gets it wrong • A possible solution
6 E I N S T E I N ’ S T I M E 139
What is so special about special relativity? • The two faces of
light • Thought experiments and brain teasers • Slowing down
time • Shrinking distances • Light—the world speed record •
When time runs backwards • Little green men • Fast forward to
the future • Spacetime—the future is out there • Gravitational
times
7 T I M E TRAV E L PARADOXES 174
The Terminator paradox • Trying to save the dinosaurs • Mona
Lisa’s sister • No way out? • Parallel universes • Where are
all the time travellers?
TIME MACHINES
8 WORMHOLES 195
A bridge to another world • Alice through the looking glass •
When science fact met science fiction • Wormholes—keeping
the star gate open • Visiting a parallel universe
9 HOW TO B U I L D A T I M E MACHINE 216
Time loops • The Tipler time machine • Cosmic string
time machines • A recipe for a wormhole time machine •
Insurmountable problems?
10 WHAT DO WE KNOW? 240
The mother of all theories • The end of theoretical physics •
Astronomy versus astrology • The fascination of science
B I B L I O G R A P H Y 254
I N D E X 259
PREFACE
Over the past few years there has been an explosion in thenumber of books and television programmes popularizing current
scientific ideas and theories and making them accessible to a wider
audience. So is there any need for this, yet another book on a
subject that has received more attention than most: the nature of
space and time and the origin of our Universe? The other day, I
was looking through the web site of a large Internet book club.
Under the category of science and nature, I searched for all books
with the word ‘time’ in their title. I found 29! Of course, Stephen
Hawking’s Brief History of Time is the best known of these, but there
were many others with titles like About Time, The Birth of Time, The
Edge of Time, The River of Time and so on. It seems that questioning
the nature of time at a fundamental level is the ‘in’ topic at the
moment. What was most surprising for me was to see that many
of those 29 titles had been published since I began writing this
book.
Established science writers such as Paul Davies, John
Gribbin and Richard Dawkins were an inspiration to me as an
undergraduate in the mid-1980s. But they were preaching to the
converted. At best, they were aimed at the ‘intelligent layperson’,
whoever that is supposed to be. My ambition has therefore been
to write a book at a more basic level, which would explain some of
the ideas and theories of modern physics for anyone to understand,
provided of course that they are interested enough to pick up such
a book in the first place. I have also tried to make it a little more
fun, aiming (probably without much success) for a sort of Stephen
Hawking-meets-Terry Pratchett. Many scientists would argue that difficult subjects like
Einstein’s theories of relativity can only be ‘dumbed down’ so
much before reaching a level where the explanations are no longer
correct. I hate that term: dumbed down. It sounds so patronizing.
And while it is flattering to be considered by society to be more
intelligent than everyone else, scientists are just people who have
spent many years being trained to understand the relevant jargon,
abstract concepts and mathematical formulae. The hard part is to
translate these into words and ideas that someone without their
training can appreciate.
Because of the way this book developed it has been written
with a teenage audience in mind. However, it is aimed at anyone
who finds its title fascinating or intriguing. It does not matter if
you have not picked up a science book since you were fifteen.
So how did this book come about? Well, about three years
ago the then head of my physics department at the University of
Surrey, Bill Gelletly, suggested that I should give, as one of a series
of lectures to first year undergraduates covering a range of general
interest topics in modern physics, a lecture on ‘wormholes’. Such
a topic is certainly not part of a traditional undergraduate degree
course in physics. In fact, fans of the TV series Star Trek: Deep
Space Nine are probably better informed about wormholes than
your average physicist. Anyway, I thought it would be fun, and
proceeded to do some background reading in preparation for the
lecture. On the day, I was surprised to find in the audience many
students not on the course, as well as postdoctoral researchers and
members of staff. There seemed to be something magical about
the title.
Each year, my department sends out a list of speakers, from
among its academic staff, and lecture titles to local schools and
colleges. This is mainly as publicity for the department in the
hope that these lectures might play a part in our recruitment drive
to attract new students. I offered my ‘wormholes’ talk as one of
these. Such was its success, I was asked by the Institute of Physics
whether I would be the 1998 Schools Lecturer. This involved the
substantially greater commitment of having to travel around the
country giving the lecture to 14–16 year-olds, with audiences of several hundred at a time. And, having put a significant amount of
preparation into this performance, I found that I had accumulated
far too much fascinating material to cram into a one hour lecture
and decided to put it all down in a book.
I have tried as much as possible to be up to date. In fact,
when the manuscript came back to me fromthe publishers for final
corrections and changes, I had to completely revise the chapter on
cosmology. Due to recent astronomical discoveries, many of the
ideas about the size and shape of the Universe had changed during
the few short months since I had written that chapter.
Jim Al-Khalili
Portsmouth, England, July 1999
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