The Philosophers 13

LIGHT YEARS AND TIME TRAVEL LIGHT YEARS AND TIME TRAVEL AN EXPLORATION OF MANKIND’S ENDURING FASCINATION WITH LIGHT BRIAN CLEGG John Wiley & Sons, Inc. This book is printed on acid-free paper. ࠗ∞ Copyright © 2001 by Brian Clegg. All rights reserved Published by John Wiley & Sons, Inc., New York Published simultaneously in Canada First published in Great Britain in 2001 by Judy Piatkus (Publishers) Limited Illustrations by Rodney Paul 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, scanning, or otherwise, except as permitted under Section 107 or 108 of the 1976 United States Copyright Act, without either the prior written permission of the Publisher, or authorization through payment of the appropriate per-copy fee to the Copyright Clearance Center, 222 Rosewood Drive, Danvers, MA 01923, (978) 750-8400, fax (978) 750-4744. Requests to the Publisher for permission should be addressed to the Permissions Department, John Wiley & Sons, Inc., 605 Third Avenue, New York, NY 10158-0012, (212) 850-6011, fax (212) 850-6008, email: [email protected]. This publication is designed to provide accurate and authoritative information in regard to the subject matter covered. It is sold with the understanding that the publisher is not engaged in rendering professional services. If professional advice or other expert assistance is required, the services of a competent professional person should be sought. Library of Congress Cataloging-in-Publication Data: Clegg, Brian. Light years and time travel / Brian Clegg. p. cm. Includes bibliographical references and index. ISBN 0-471-21182-6 (cloth : alk. paper) 1. Light—Popular works. 2. Time travel—Popular works. I. Title. QC358.5 .C54 2001 535—dc21 2001046736 Printed in the United States of America 10987654321 To Gillian, Chelsea and Rebecca C ONTENTS Introduction ix 1. At the Speed of Light 1 2. The Philosophers 13 3. Out of the Darkness 32 4. Engines of Light 63 5. Seeing Further 90 6. Light’s Anatomy 134 7. Death of the Ether 171 8. Fearful Symmetry 216 9. QED 246 10. Tyger! Tyger! 281 Further Reading 302 Picture Credits 306 Index 307 I NTRODUCTION And God said ‘Let there be light’: And there was light. GENESIS, CHAPTER 1 IGHT IS SOMETHING THAT WE TAKE FOR GRANTED. LIt is a fact of everyday life, available at the press of a switch. It is the absence of darkness, the gift of the sun. It is a small part of the physics we are taught at school, a thing of ray diagrams and geometry, without substance. But light is not so easily compartmentalized. Its beguiling combination of fragility and endurance, of delicacy and power, captures the imagination just as it has fascinated scientists through the ages. For thousands of years, uncovering the nature of light has proved an irresistible challenge. It forms a scientific quest that has endured from the conjectures of the ancient Greeks to the work of twentieth-century geniuses like Albert Einstein and Richard Feynman. By combining light’s history with the latest research we can assemble a ix L IGHT Y EARS AND T IME T RAVEL complete picture of this remarkable phenomenon and its place at the centre of creation. What first was seen as merely the mechanism of sight has proved to be so much more. The source of all life on Earth, providing warmth, powering the weather, driving the photosynthetic process that generates oxygen. The self- sustaining interplay of magnetism and electricity that lies behind Einstein’s Special Relativity. The fundamental glue that keeps all matter together. And perhaps even the key to time itself. Looking back at the life and work of the extraordinary people who have uncovered light’s secrets provides both an understanding of light and a front row seat in the develop- ment of the remarkable new light-based technologies that are appearing as we enter the twenty-first century. Technologies that have the potential to transform reality itself. When I was at university studying physics, I was over- whelmed by the power and beauty of light, yet so much that I read at the time on this remarkable subject made it seem dull. Coming back to light now has been wonderful, rekindling the amazement and delight I felt 25 years ago. That sense of wonder is what Light Years and Time Travel is all about. x CHAPTER. ONE A T THE S PEED OF L IGHT For now we see through a glass, darkly. ST. PAUL MAGINE THIS. THE DAWN LIGHT IS CREEPING I into your room. You get up from your bed and open the curtains. Outside the window, the inferno of an active volcano distorts the air. A river of red-hot lava is streaming down the scarred mountainside. A rain of ash falls near the window, yet you hear nothing, feel nothing. Quickly, you move to the second window and pull back the curtain. Here, even though it’s morning, the sky is black, a crisper black than you have ever seen. The stars stand out, laser sharp. Before you is a rugged, near-white plain, surrounded by impossibly high needle peaks. And then your eye is caught by something else. Standing out from the blackness is a bright circle of blues and greens with traceries of white. You are seeing the Earth from the surface of the moon. 1 L IGHT Y EARS AND T IME T RAVEL Nervously, half-expecting the air to rush out of the room, you open the window, to be struck by a burst of ver- tigo. Behind the glass is a leaden yellow-grey sky, hanging heavy over the already-bustling city streets 25 floors below. Nothing that you saw through the window exists. There is no volcano, no lunar landscape, there are no stars. A MAGICAL TUNNEL Close the window again and still the Earth is riding serenely in the sky. It’s as if the window were not looking out of the side of the building, but opening instead onto a magical tunnel leading straight to the surface of the moon. The device that makes this possible is called ‘slow glass’, first dreamed up by 1970s’ visionary writer Bob Shaw. It is glass that takes light months or even years to pass through. With such remarkable glass it would only take a good site to capture a view. If the light takes a year to pass through the glass, then 12 months after it has been put in position, the first glimpse of the landscape will reach the other side. After the light has made its slow journey through the window pane, everything that has happened in front of the glass will be seen a year later behind it. Shift the glass into a building and it will carry a year’s worth of light with it. You’ll have a window onto an exotic location for as long as it takes the remaining light to travel through the glass. This may sound like a dream, but in the last years of the twentieth century, technology caught up with science fiction and made slow glass a reality. 2 At the Speed of Light It has always been received wisdom that the speed of light is a fixed, immutable, universal constant. Yet from both theoretical and practical scientific work now being undertaken around the world, evidence is accumulating that light’s speed can be altered. And if the speed of light can be controlled, then so can reality itself. Extraordinary scientific work is now under way, work that will make tech- nical miracles such as slow glass possible … and that will, in a few short years, make light the most exciting area of study in all science. THE ULTIMATE SPEED A beam of light travels at around 300,000 kilometres each second in the vacuum of space. A hummingbird’s wings flap 4,200 times a minute, near invisible to the human eye. Yet in the duration of a single flap of those wings, a beam of light could have crossed the Atlantic Ocean. On 20 July 1969, Apollo 11 landed on the moon after a journey of four days. If it had, instead, set off for the nearest star, Alpha Centauri, which light takes four years to reach, the Apollo capsule would still be travelling after a million years. In glass, light moves a little slower, but it would still require a window 5,000,000,000,000 kilometres thick to hold a year’s worth of light. If slow glass is to be made, there has to be a way to apply the brakes, to slow light down by a factor of a billion billion or more. Unlikely though this sounds, in the final decade of the last century a substance was created that can do just that. 3 L IGHT Y EARS AND T IME T RAVEL EINSTEIN’S STRANGE MATTER The substance with the amazing effect is a strange form of matter called a ‘Bose-Einstein condensate’ (physicists have to be having a particularly good day to come up with a snappy name like ‘photon’ or ‘quark’). We are used to matter coming in three types – solid, liquid and gas. Since the 1920s it has been known that there is a fourth form of matter, generated in the raging nuclear furnace of the sun – plasma. This is the next stage beyond a gas, where the easily removed electrons have been broken off the atoms and the result is a soup of ions – atoms with some electrons missing – and the electrons themselves.

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