ebook img

Three Roads to Quantum Gravity PDF

255 Pages·2002·0.898 MB·English
Save to my drive
Quick download
Download
Most books are stored in the elastic cloud where traffic is expensive. For this reason, we have a limit on daily download.

Preview Three Roads to Quantum Gravity

““IItt wwoouulldd bbee hhaarrdd ttoo iimmaaggiinnee aa bbeetttteerr gguuiiddee ttoo tthhiiss ddiiffffiiccuulltt ssuubbjjeecctt..”” PHYSICS ——SSCCIIEENNTTIIFFIICCAAMMEERRIICCAANN The Holy Grail of modern physics is the theory of “quantum gravity.” It is a search for a view of the Universe that unites two seemingly opposed pillars of modern science: Einstein’s theory of general relativity, which deals with large scale phenomena like planets, solar systems and galaxies, and quantum theory, which deals with the world of the very small—molecules, atoms and electrons. In the last few years physicists have made steps toward their goal of a completely new theory of space, time and the universe, a “theory of everything.” In Three Roads to Quantum Gravity, Lee Smolin, who has spent his career at the forefront of these new discoveries, presents for the first time the main ideas behind the new developments that have brought a quantum theory of gravity in sight. Written with exceptional style and clarity, Three Roads to Quantum Gravity confronts the deepest questions of the nature of the universe and provides a preview of some of the remarkable scientific developments we can look forward to in the twenty-first century. PPrraaiissee ffoorr TTHHRREEEE RROOAADDSS TTOO QQUUAANNTTUUMM GGRRAAVVIITTYY N ““[[SSmmoolliinn]] aarrgguueess lluucciiddllyy aanndd eeffffeeccttiivveellyy……..TThhiiss iiss aa ddeeeeppllyy pphhiilloossoopphhiiccaall wwoorrkk E H O tthhaatt aasskkss uuss ttoo rreetthhiinnkk tthhee eeppiisstteemmoollooggiiccaall rroooottss ooff tthhee mmeennttaall ppiiccttuurreess wwee C mmaakkee aabboouutt nnaattuurree.. ——NNEEWWYYOORRKKTTIIMMEESSBBOOOOKKRREEVVIIEEWW RC A M ““AAbbssoolluutteellyy ccoommppeelllliinngg……LLeeee SSmmoolliinn iiss oonnee ooff aa ssmmaallll hhaannddffuull ooff pphhyyssiicciissttss aarroouunndd Y B tthhee wwoorrlldd wwhhoo hhaavvee bbeeeenn aabbllee ttoo mmaakkee ggeennuuiinnee pprrooggrreessss oonn aann eexxttrraaoorrddiinnaarriillyy ddiiff-- N G ffiiccuulltt pprroobblleemm tthhaatt hhaass ssttuummppeedd ssoommee ooff tthhee wwoorrlldd’’ss ffiinneesstt mmiinnddss ffoorr 8800 yyeeaarrss.. SI E D [[RR]]eeqquuiirreedd rreeaaddiinngg ffoorr aannyyoonnee iinntteerreesstteedd iinn tthhee pprroobblleemm ooff qquuaannttuumm ggrraavviittyy aanndd R E tthhee ffuuttuurree ooff tthheeoorreettiiccaall pphhyyssiiccss..””——TTHHEEAAMMEERRIICCAANNSSCCIIEENNTTIISSTT V O C LLEEEE SSMMOOLLIINNis a leading contributor to the search for a quantum theory of gravity. He is currently a researcher at Perimeter Institute for Theoretical Physics and WITH A NEW POSTSCRIPT BY THE AUTHOR Professor of Physics at Waterloo University. He is also the author of Life of the Cosmos. US $14.00 / $20.95 CAN A Member of the Perseus Books Group www.basicbooks.com T H R E E R O A D S TO Q U A N T U M G R AV I T Y LEE SMOLIN AMember of the Perseus Books Group SmolinNRM.qxd 5/16/02 2:37 PM Page iv To my parents Pauline and Michael Copyright © 2001 by Lee Smolin Published by Basic Books, A Member of the Perseus Books Group First Published in Great Britian in 2000 by Weidenfeld and Nicolson All rights reserved. Printed in the United States of America. No part of this book may be reproduced in any manner whatsoever without written permission except in the case of brief quotations embodied in critical articles and reviews. For information, address Basic Books, 387 Park Avenue South, New York, NY 10016-8810. Typeset at the Spartan Press Ltd Lymington, Hants A CIP record for this book is available from the Library of Congress. ISBN 0-465-07836-2 02 03 04 / 10 9 8 7 6 5 4 3 2 1 CONTENTS ............................................................................................ Acknowledgments vii Prologue:Thequestforquantumgravity 1 Part I Points of departure 15 1 Thereisnothingoutsidetheuniverse 17 2 Inthefutureweshallknowmore 26 3 Manyobservers,notmanyworlds 33 4 Theuniverseismadeofprocesses,notthings 49 Part II What we have learned 67 5 Blackholes and hidden regions 69 6 Acceleration and heat 77 7 Blackholes arehot 88 8 Areaand information 95 9 Howtocount space 106 10 Knots,linksandkinks 125 11 Thesound of space isastring 146 vi THREE ROADS TO QUANTUM GRAVITY PartIII Thepresentfrontiers 167 12Theholographicprinciple169 13Howtoweaveastring179 14Whatchoosesthelawsofnature?194 Epilogue:Apossiblefuture 207 Postscript 212 Glossary 226 Suggestions for further reading 235 Index 241 ACKNOWLEDGMENTS I must thank first of all the friends and collaborators who formed the community within which I learned most of what I know about quantum gravity. If I had not had the luck to know Julian Barbour, Louis Crane, John Dell, Ted Jacobson and Carlo Rovelli, I doubt that I would have got very far with this subject at all. They will certainly see their ideas and views represented here. Fotini Markopoulou-Kalamara is re- sponsible for changing my views on several important as- pects of quantum gravity over the last several years, which got me out of space and back into spacetime. Large parts of Chapters 2, 3 and 4 are suffused by her thinking, as will be clear to anyone who has read her papers. I am also indebted to Chris Isham for the several ideas of his that have seeped into my work, in some cases without my fully realizing it, and for his friendship and for the example of his life and thought. Stuart Kauffman has taught me most of what I know about how to think about self-organized systems, and I thank him for both the gift of his friendship and his willingness to walk with me in the space between our two subjects. I am also very indebted for discussions, collaborations and encouragement to Giovanni Amelino-Camelia, Abhay Ashte- kar, Per Bak, Herbert Bernstein, Roumen Borissov, Alain Connes, Michael Douglas, Laurant Friedel, Rodolfo Gambini, Murray Gell-Mann, Sameer Gupta, Eli Hawkins, Gary Horowitz, Viqar Husain, Jaron Lanier, Richard Livine, Yi Ling, Renate Loll, Seth Major, Juan Maldecena, Maya Paczuski, Roger Penrose, Jorge Pullin, Martin Rees, Mike Reisenberger, viii THREE ROADS TO QUANTUM GRAVITY Jurgen Renn, Kelle Stelle, Andrew Strominger, Thomas Thiemann and Edward Witten. I add a special word of appreciation for the founders of the field of quantum gravity, including Peter Bergmann, Bryce DeWitt, David Finkelstein, Charles Misner, Roger Penrose and John Archibald Wheeler. Iftheyseemanyoftheirideashere,itisbecausethesearethe ideas that continue to shape how we see our problem. Our workhasbeensupportedgenerouslybytheNationalScience Foundation, for which I especially have to thank Richard Issacson. In the last several years generous and unexpected giftsfromtheJessePhillipsFoundationhavemadeitpossible to concentrate on doing science at a time when nothing was moreimportantthanthetimeandfreedomtothinkandwork. I am grateful also to Pennsylvania State University, and especially to my chair, Jayanth Banavar, for the supportive and stimulating home it has given me over the last six years, as well as for showing some understanding of the conflicting demands placed upon me when I found myself with three full-time jobs, as a scientist, teacher and author. The theory group at Imperial College provided a most stimulating and friendly home from homeduring the year’s sabbaticalduring whichthisbookwaswritten. This book would not exist were it not for the kind encouragement of John Brockman and Katinka Matson, and I am also very grateful to Peter Tallack of Weidenfeld & Nicolson,bothforhisencouragementandideasandforbeing such a good editor, in the old-fashioned sense. Much of the clarityofthetextisalsoduetotheartistryandintelligenceof JohnWoodruff’scopyediting.BrianEnoandMichaelSmolin readadraftandmadeinvaluablesuggestionsfortheorganiza- tionofthebook,whichhavegreatlyimprovedit.Thesupport of friends has continued to be essential to keeping my own spirit alive, especially Saint Clair Cemin, Jaron Lanier and Donna Moylan. Finally, as always, my greatest debt is to my parentsandfamily,notonlyforthegiftoflifebutforimparting inmethedesiretolookbeyondwhatistaughtinschool,totry toseetheworldasitmayactuallybe. LeeSmolin London,July2000 PROLOGUE ............................................................................................ THE QUEST FOR QUANTUM GRAVITY Thisbook is about the simplest ofall questionsto ask:‘What aretimeandspace?’Thisisalsooneofthehardestquestions to answer, yet the progress of science can be measured by revolutionsthatproducenewanswerstoit.Wearenowinthe midstofsucharevolution,andnotonebutseveralnewideas about space and time are being considered. This book is meanttobeareportfromthefront.Myaimistocommunicate these new ideas in a language that will enable any interested readertofollowtheseveryexcitingdevelopments. Spaceandtimearehardtothinkaboutbecausetheyarethe backdrop to all human experience. Everything that exists existssomewhere,andnothinghappensthatdoesnothappen atsometime.So,justasonecanlivewithoutquestioningthe assumptions in one’s native culture, it is possible to live without asking about the nature of space and time. But there is at least a moment in every child’s life when they wonder about time. Does it go on for ever? Was there a first moment? Willtherebealastmoment?Iftherewasafirstmoment,then how was the universe created? And what happened just a moment before that? If there was no first moment, does that meanthateverythinghashappenedbefore?Andthesamefor space:doesitgoonandonforever?Ifthereisanendtospace, what is just on the other side of it? If there isn’t an end, can onecountthethingsintheuniverse? I’msurepeoplehavebeenaskingthesequestionsforaslong astherehavebeenpeopletoaskthem.Iwouldbesurprisedif

See more

The list of books you might like

Most books are stored in the elastic cloud where traffic is expensive. For this reason, we have a limit on daily download.