Gott - Time travel in Einsteins universe : the physical possibilities of travel through time

First Mariner Books edition 2002

Copyright 2001 by J. Richard Gott III

ALL RIGHTS RESERVED

For information about permission to reproduce selections from this book, write to Permissions, Houghton Mifflin Harcourt Publishing Company, 215 Park Avenue South, New York, New York 10003.

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The Library of Congress has cataloged the print edition as follows:

Gott, J. Richard, III.

Time travel in Einsteins universe : the physical possibilities of travel through time / J. Richard Gott III

p. cm.

Includes bibliographical references and index.

ISBN 978-061-825-7355

ISBN 0-395-95563 7

ISBN 0-618-25735-7 (pbk.)

1. Space and time. 2. Time travel. I. Title.

QC173.59.S65 G67 2001

530.11dc21 00-054243

e ISBN 978-0-547-52657-7
v1.0815

Dedicated to

My mother and father, wife and daughter

my past, present, and future

First and foremost, I thank my lovely wife, Lucy, my soul matefor believing. Since Lucy is one of the smartest people around (summa cum laude at Princeton), I always take her advice very seriously! For this book she has added her considerable professional skills as an editor and writer to help me produce a much improved manuscript. To my daughter, Elizabethone could not hope for a better daughter. In addition to lighting up our lives, she has taken time from her stellar high school career to help me as well, sometimes by creating a computer system, but more often by helping me find the right visual aids to explain physics concepts. She found the cute, chubby space shuttle I used to show how one might circle two cosmic strings (pictured in Time), and she discovered the tiny, flag-waving astronaut for me to drop into a funnel to illustrate the properties of black holes (for The McNeil-Lehrer Newshour). To my mother and father, Marjorie C. Gott and Dr. John Richard Gott, Jr., I offer my thanks for their support over the years, including the way my mother cheerfully took me to countless Astronomical League conventions and science fairs during my high school years.

I would like to thank especially Laura van Dam, my wonderful editor at Houghton Mifflin, who first came to me with the idea that I should write a book on time travel. Her enthusiasm, incisive judgment, and abundant editorial talent have made working with her a joy. I also thank Liz Duvall, Susanna Brougham, and Lisa Diercks for gracious help during the production process.

For turning my sketches into beautiful line drawings and graphics, I thank JoAnn Boscarino and Li-Xin Li, respectively. Some of the diagrams were created with the Mathematica program, Claris-Works, or Design It! 3-D.

Charles Allen (president of the Astronomical League) and Neil de Grasse Tyson (director of the Hayden Planetarium) read the entire manuscript. Their feedback has been essential; more so, their friendship over the years. Jonathan Simon and Li-Xin Li read selected chapters and offered useful comments. I also benefited from comments by Jeremy Goodman, Suketu Bhavsar, Deborah Freedman, Jim Gunn, Frank Summers, Douglas Heggie, Ed Jenkins, Michael Hart, Matthew Headrick, Jim Peebles, Bharat Ratra, and Martin Rees.

I am grateful to all my teachers (from my high school math teacher, Ruth Pardon, to my thesis adviser, Lyman Spitzer) and my many colleagues, who include my students. Special thanks to Li-Xin Li whose collaboration on our research described in has been pivotal. Figure 27 is from our 1998 Physical Review paper Can the Universe Create Itself? I would like to thank George Gamow and Charles Misner, Kip Thorne, and John Wheeler, whose books have been a source of inspiration to me; Hugh Downs, for many lively cosmology dinners; and Carl Sagan and again Kip Thorne, whose interest in my work I have greatly appreciated. I thank Dorothy Schriver and all the people Ive known at Science Service; my mother-in-law, Virginia Pollard; and Drs. William Barton and Alexander Vukasin. I also wish to acknowledge the science writers who have done excellent pieces on my work: Timothy Ferris, Michael Lemonick, Sharon Begley, James Gleick, Malcolm Browne, Marcus Chown, Ellie Boettinger, Kitta MacPherson, Gero von Boehm, Joel Achenbach, Marcia Bartusiak, Mitchell Waldrop, and Rachel Silverman. Because of science writers like these, the wide panoply of scientific endeavor is opened to all. I hope this book will add to this in some small measure.

Finally, I salute Albert Einstein, whose ideas challenge us still.

The neighborhood children think I have a time machine in my garage. Even my colleagues sometimes behave as if I have one. Astrophysicist Tod Lauer once sent me a formal letter inviting me to Kitt Peak National Observatory to give a talk on time travel. He sent this invitation six months after I had already given the talk. The invitation explained that since I was an expert in time travel, I should presumably have no trouble in returning to the past to make the appearance. On another occasion, at a cosmology conference in California, I happened to wear a turquoise sports jacketwhich I imagined might fit in nicely with the California ambiance. Bob Kirshner, then chair of Harvards astronomy department, came up to me and said, Richard, this is the Coat of the Future; you must have gotten this in the future and brought it back, because this color hasnt been invented yet! Since then, Ive always worn this coat when giving talks on time travel.

Time travel is certainly one of the most fun topics in physics, but it has a serious side as well. I have received calls from people who want to know about recent developments in time travel because they wish to return to the past to rescue a loved one who died under tragic circumstances. I treat such calls with great seriousness. I have written this book partly to answer such questions. One reason that time travel is so fascinating is that we have such a great desire to do it.

Physicists like me who are investigating time travel are not currently at the point of taking out patents on a time machine. But we are investigating whether building one is possible in principle, under the laws of physics. Its a high-stakes game played by some of the brightest people in the world: Einstein showed that time travel to the future is possible and started the discussion. Kurt Gdel, Kip Thorne, and Stephen Hawking have each been interested in the question of whether time travel to the past is possible. The answer to that question would both give new insights into how the universe works and possibly some clues as to how it began.

This book is a personal story, not a history of science. Imagine me as your guide, taking you to the summit of Mount Everest. The climb is sometimes challenging, sometimes easy, but I promise that we will ascend by the easiest possible route. Its a path of ideas I know well, having marked some of the trail myself. Along the way, we will intersect the work of many of my colleagues. I have mentioned many of them to give you a fair idea of the other trailblazers of this terrain. Some contributions are emphasized and others briefly noted, in or out of historical sequence, as they play into telling my story. To those whose work Ive not mentionedthough it may be equally important but following a different route up the mountainI apologize in advance.

We start our journey at base camp: the dream of time travel itself and the pathbreaking science fiction of H. G. Wells.

Man... can go up against gravitation in a balloon, and why should he not hope that ultimately he may be able to stop or accelerate his drift along the Time-Dimension, or even turn about and travel the other way.

H. G. W ELLS , T HE T IME M ACHINE ,