A. Zee - On Gravity: A Brief Tour of a Weighty Subject

on gravity

on gravity

a brief tour of a weighty subject a. zee

Princeton University PressPrinceton and Oxford

Copyright 2018 by Princeton University Press

Published by Princeton University Press

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ISBN 978-0-691-17438-9

Library of Congress Control Number: 2018933625

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To all those who taught me about gravity

Contents

Preface

After writing a massive textbook on Einstein gravity, called appropriately enough Einstein Gravity in a Nutshell and referred to henceforth as GNut, I was a bit stung by a native of the Amazon who jokingly said that, while he liked the book, he had to ask a friend to carry it for him. (What a weakling! Dont physics students go to the gym any more? Bring back the compulsory gym of my undergrad years!) Of course, the books weight reflects the innate beauty and importance of the subject it covers.

In any case, my lamentations to Ingrid Gnerlich, my longtime editor at Princeton University Press, led to the thought of writing a short book for a change. I felt that, since I had written a long book on Einstein gravity, I had a license to write a short book on Einstein gravity.

I had also published in 1989 a popular book about Einstein gravity titled An Old Mans Toy and later republished as Einsteins Universe: Gravity at Work and Play, referred to henceforth as Toy. Thus, I think of this book as between a toy and a nutshell.

One motivation for this book is to help people bridge the gap between popular books and textbooks on Einstein gravity. You could read popular books until you are blue in the face, but if you want to have a true understanding of Einstein gravity, there is no getting around tackling a serious textbook. From the emails I receive, I know that many would like to cross that gap. So consider this book as a stepping stone toward GNut.

Actually, Einstein gravity is much less demanding mathematically than quantum mechanics. I have placed some of the mathematics involved, mainly that needed to describe curved spacetime, into an appendix. That appendix provides a good gauge. If you could follow the material in there easily, then you might be ready for GNut.

On the other hand, if you dont feel like slugging through the appendix, you could still enjoy this book as a popular book written at a somewhat higher level than the standard popular literature about Einstein gravity.

Sitting between a toy and a nutshell, I feel that I can afford to be somewhat sketchier in some of my explanations. The way these sketches could be fleshed out calls for more math, not more words. I could always refer the motivated reader to further details in GNut.

A week after I signed the contract for this book, gravity waves were detected, and thus naturally, the book weaves around gravity waves, starting and ending with them. One thing I do not do is to go through a detailed description of the detector and the observational protocol, not because I dont think thats important, but for that, firsthand accounts by those who lived through the design, setup, and actual detection would be best.

Instead, I focus on the conceptual framework of Einsteins theoryand yes, its beautyin keeping with my being, after all, a professor of theoretical physics. Reluctantly, I have to omit several topics. For instance, the reader will find no mention of the three classic tests of Einstein gravity, nor of such figures as Arthur Eddington, who through his observations of distant starlight curving in the gravitational field helped bring the new theory to the attention of the general public. But I do discuss Faraday, Maxwell, and Hertz, because I want to emphasize the concepts of field, wave, and action as fundamental to theoretical physics. With the example of the electromagnetic wave in front of us, we are led naturally to gravity waves, at least with the benefit of hindsight. For a short book such as this, I am obliged to pick and choose.

Acknowledgments

Once again, I am deeply grateful to Ingrid Gnerlich, who has worked on all my Princeton University Press books. In addition to all her good advice, she has entrusted the manuscript to the capable hands of my long-time copyeditor Cyd Westmoreland. I also thank Karen Carter, Chris Ferrante, and Arthur Werneck. As with all my other books, Craig Kunimotos patient help taming the computer was indispensable. I completed this book in Paris, and I am enormously indebted to Henri Orland for all his efforts in making my stay pleasant and productive. I thank the research center at Saclay and the cole Normale Suprieure for their hospitality, and Jean-Philippe Bouchaud for financing my chair through the Foundation of the cole Normale Suprieure. Needless to say, but as always, I appreciate the support of my wife, Janice. Incidentally, some time after turning in the manuscript, I left on a lecture tour of Israel. At the Hebrew University in Jerusalem, I had the opportunity to visit the Einstein archive. For a theoretical physicist, seeing Einstein gravity written out longhand in Einsteins handwriting is almost a religious experience.

Timeline