The Feynman LECTURES ON PHYSICS NEW MILLENNIUM EDITION FEYNMAN LEIGHTON SANDS • • VOLUME I Copyright © 1963, 2006, 2010 by California Institute of Technology, Michael A. Gottlieb, and Rudolf Pfeiffer Published by Basic Books, A Member of the Perseus Books Group 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, 250 West 57th Street, 15th Floor, New York, NY 10107. Books published by Basic Books are available at special discounts for bulk purchases in the United States by corporations, institutions, and other organizations. For more information, please contact the Special Markets Department at the Perseus Books Group, 2300 Chestnut Street, Suite 200, Philadelphia, PA 19103, or call (800) 810-4145, ext. 5000, or e-mail [email protected]. A CIP catalog record for the hardcover edition of this book is available from the Library of Congress. LCCN: 2010938208 Hardcover ISBN: 978-0-465-02414-8 E-book ISBN: 978-0-465-07293-4 About Richard Feynman Born in 1918 in New York City, Richard P. Feynman received his Ph.D. from Princeton in 1942. Despite his youth, he played an important part in the Manhattan Project at Los Alamos during World WarII. Subsequently, he taught at Cornell and at the California Institute of Technology. In 1965 he received the Nobel Prize in Physics, along with Sin-Itiro Tomonaga and Julian Schwinger, for his work in quantum electrodynamics. Dr.FeynmanwonhisNobelPrizeforsuccessfullyresolvingproblemswiththe theory of quantum electrodynamics. He also created a mathematical theory that accounts for the phenomenon of superfluidity in liquid helium. Thereafter, with MurrayGell-Mann,hedidfundamentalworkintheareaofweakinteractionssuch as beta decay. In later years Feynman played a key role in the development of quark theory by putting forward his parton model of high energy proton collision processes. Beyond these achievements, Dr. Feynman introduced basic new computa- tional techniques and notations into physics—above all, the ubiquitous Feynman diagramsthat, perhapsmorethananyotherformalisminrecentscientifichistory, have changed the way in which basic physical processes are conceptualized and calculated. Feynman was a remarkably effective educator. Of all his numerous awards, he was especially proud of the Oersted Medal for Teaching, which he won in 1972. The Feynman Lectures on Physics, originally published in 1963, were described by a reviewer in Scientific American as “tough, but nourishing and full of flavor. After 25 years it is the guide for teachers and for the best of beginning students.” In orderto increase the understanding ofphysics among the lay public, Dr. Feynman wrote The Character of Physical Law and QED: The Strange Theory of Light and Matter. He also authored a numberof advanced publications that have become classic references and textbooks for researchers and students. Richard Feynman was a constructive public man. His work on the Challenger commissioniswellknown,especiallyhisfamousdemonstrationofthesusceptibility of the O-rings to cold, an elegant experiment which required nothing more than a glass of ice water and a C-clamp. Less well known were Dr. Feynman’s efforts on the California State Curriculum Committee in the 1960s, where he protested the mediocrity of textbooks. A recital of Richard Feynman’s myriad scientific and educational accomplish- ments cannot adequately capture the essence of the man. As any reader of even his most technical publications knows, Feynman’s lively and multi-sided personality shines through all his work. Besides being a physicist, he was at various times a repairer of radios, a picker of locks, an artist, a dancer, a bongo player, and even a decipherer of Mayan Hieroglyphics. Perpetually curious about his world, he was an exemplary empiricist. Richard Feynman died on February 15, 1988, in Los Angeles. iii Preface to the New Millennium Edition NearlyfiftyyearshavepassedsinceRichardFeynmantaughttheintroductory physics course at Caltech that gave rise to these three volumes, The Feynman Lectures on Physics. In those fifty years our understanding of the physical world has changed greatly, but The Feynman Lectures on Physics has endured. Feynman’s lectures are as powerful today as when first published, thanks to Feynman’s unique physics insights and pedagogy. They have been studied worldwide by novices and mature physicists alike; they have been translated into at least a dozen languages with more than 1.5 millions copies printed in the English language alone. Perhaps no other set of physics books has had such wide impact, for so long. This New Millennium Edition ushers in a new era for The Feynman Lectures on Physics (FLP): the twenty-first century era of electronic publishing. FLP has been converted to eFLP, with the text and equations expressed in the LATEX electronic typesetting language, and all figures redone using modern drawing software. The consequences for the print version of this edition are not startling; it looksalmostthesameastheoriginalredbooksthatphysicsstudentshaveknown andlovedfordecades. Themaindifferencesareanexpandedandimprovedindex, the correction of 885 errata found by readers over the five years since the first printing of the previous edition, and the ease of correcting errata that future readers may find. To this I shall return below. The eBook Version of this edition, and the Enhanced Electronic Version are electronicinnovations. BycontrastwithmosteBookversionsof20thcenturytech- nical books, whose equations, figures and sometimes even text become pixellated when one tries to enlarge them, the LATEX manuscript of the New Millennium Edition makes it possible to create eBooks of the highest quality, in which all features on the page (except photographs) can be enlarged without bound and retain their precise shapes and sharpness. And the Enhanced Electronic Version, with its audio and blackboard photos from Feynman’s original lectures, and its links to other resources, is an innovation that would have given Feynman great pleasure. Memories of Feynman’s Lectures Thesethreevolumesareaself-containedpedagogicaltreatise. Theyarealsoa historical record of Feynman’s 1961–64 undergraduate physics lectures, a course required of all Caltech freshmen and sophomores regardless of their majors. Readersmaywonder,asIhave,howFeynman’slecturesimpactedthestudents whoattendedthem. Feynman,inhisPrefacetothesevolumes,offeredasomewhat negativeview. “Idon’tthinkIdidverywellbythestudents,”hewrote. Matthew Sands, in his memoirin Feynman’s Tips on Physics expresseda farmore positive view. Out of curiosity, in spring 2005 I emailed or talked to a quasi-random set of 17 students (out of about 150) from Feynman’s 1961–63 class—some who had great difficulty with the class, and some who mastered it with ease; majors in biology, chemistry, engineering, geology, mathematics and astronomy, as well as in physics. The intervening years might have glazed their memories with a euphoric tint, butabout80percentrecallFeynman’slecturesashighlightsoftheircollegeyears. “It was like going to church.” The lectures were “a transformational experience,” “the experience of a lifetime, probably the most important thing I got from Caltech.” “I was a biology major but Feynman’s lectures stand out as a high point in my undergraduate experience ... though I must admit I couldn’t do the homework at the time and I hardly turned any of it in.” “I was among the least promising of students in this course, and I never missed a lecture.... I remember and can still feel Feynman’s joy of discovery.... His lectures had an ... emotional impact that was probably lost in the printed Lectures.” Bycontrast,severalofthestudentshavenegativememoriesduelargelytotwo issues: (i) “You couldn’t learn to work the homework problems by attending the lectures. Feynman was too slick—he knew tricks and what approximations could be made, and had intuition based on experience and genius that a beginning student does not possess.” Feynman and colleagues, aware of this flaw in the course, addressed it in part with materials that have been incorporated into Feynman’s Tips on Physics: three problem-solving lectures by Feynman, and a set of exercises and answers assembled by Robert B. Leighton and Rochus Vogt. (ii) “The insecurity of not knowing what was likely to be discussed in the next lecture, the lack of a text book or reference with any connection to the lecture material, and consequent inability for us to read ahead, were very frustrating.... I found the lectures exciting and understandable in the hall, but theywereSanskritoutside[whenItriedtoreconstructthedetails].”Thisproblem, ofcourse, wassolvedbythesethreevolumes, theprintedversion ofThe Feynman Lectures on Physics. They became the textbook from which Caltech students studied for many years thereafter, and they live on today as one of Feynman’s greatest legacies. A History of Errata The Feynman Lectures on Physics was produced very quickly by Feynman and his co-authors, Robert B. Leighton and Matthew Sands, working from and expanding on tape recordings and blackboard photos of Feynman’s course lectures* (both of which are incorporated into the Enhanced Electronic Version of this New Millennium Edition). Given the high speed at which Feynman, LeightonandSandsworked,itwasinevitablethatmanyerrorscreptintothefirst edition. Feynman accumulated long lists of claimed errata over the subsequent years—errata found by students and faculty at Caltech and by readers around the world. In the 1960’s and early 70’s, Feynman made time in his intense life to check most but not all of the claimed errata for Volumes I and II, and insert corrections into subsequent printings. But Feynman’s sense of duty never rose high enough above the excitement of discovering new things to make him deal with the errata in Volume III.† After his untimely death in 1988, lists of errata for all three volumes were deposited in the Caltech Archives, and there they lay forgotten. In 2002 Ralph Leighton (son of the late Robert Leighton and compatriot of Feynman) informed me of the old errata and a new long list compiled by Ralph’s friend Michael Gottlieb. Leighton proposed that Caltech produce a new edition ofThe Feynman Lectures withallerratacorrected,andpublishitalongsideanew volume of auxiliary material, Feynman’s Tips on Physics, which he and Gottlieb were preparing. Feynman was my hero and a close personal friend. When I saw the lists of errata and the content of the proposed new volume, I quickly agreed to oversee this project on behalf of Caltech (Feynman’s long-time academic home, to which *FordescriptionsofthegenesisofFeynman’slecturesandofthesevolumes,seeFeynman’s Preface and the Forewords to each of the three volumes, and also Matt Sands’ Memoir in Feynman’s Tips on Physics,andtheSpecial Preface to the Commemorative Edition ofFLP, writtenin1989byDavidGoodsteinandGerryNeugebauer,whichalsoappearsinthe2005 Definitive Edition. †In1975,hestartedcheckingerrataforVolumeIIIbutgotdistractedbyotherthingsand neverfinishedthetask,sonocorrectionsweremade. v he, Leighton and Sands had entrusted all rights and responsibilities for The Feynman Lectures). After a year and a half of meticulous work by Gottlieb, and carefulscrutinybyDr.MichaelHartl(anoutstandingCaltechpostdocwhovetted all errata plus the new volume), the 2005 Definitive Edition of The Feynman Lectures on Physics was born, with about 200 errata corrected and accompanied by Feynman’s Tips on Physics by Feynman, Gottlieb and Leighton. I thought that edition was going to be “Definitive”. What I did not antic- ipate was the enthusiastic response of readers around the world to an appeal from Gottlieb to identify further errata, and submit them via a website that Gottlieb created and continues to maintain, The Feynman Lectures Website, www.feynmanlectures.info. In the five years since then, 965 new errata have beensubmittedandsurvivedthemeticulousscrutinyofGottlieb,Hartl,andNate Bode (an outstanding Caltech physics graduate student, who succeeded Hartl as Caltech’s vetter of errata). Of these, 965 vetted errata, 80 were corrected in the fourth printing of the Definitive Edition (August 2006) and the remaining 885 are corrected in the first printing of this New Millennium Edition (332 in volume I, 263 in volume II, and 200 in volume III). For details of the errata, see www.feynmanlectures.info. Clearly, making The Feynman Lectures on Physics error-free has become a world-wide community enterprise. On behalf of Caltech I thank the 50 readers whohavecontributedsince2005andthemanymorewhomaycontributeoverthe comingyears. Thenamesofallcontributorsarepostedatwww.feynmanlectures. info/flp_errata.html. Almost all the errata have been of three types: (i) typographical errors in prose; (ii) typographical and mathematical errors in equations, tables and figures—sign errors, incorrect numbers (e.g., a 5 that should be a 4), and missing subscripts, summation signs, parentheses and terms in equations; (iii) incorrect cross references to chapters, tables and figures. These kinds of errors, though not terribly serious to a mature physicist, can be frustrating and confusing to Feynman’s primary audience: students. It is remarkable that among the 1165 errata corrected under my auspices, only several do I regard as true errors in physics. An example is Volume II, page 5-9, which now says “... no static distribution of charges inside a closed grounded conductor can produce any [electric] fields outside” (the word grounded was omitted in previous editions). This error was pointed out to Feynman by a number of readers, including Beulah Elizabeth Cox, a student at The College of William and Mary, who had relied on Feynman’s erroneous passage in an exam. To Ms. Cox, Feynman wrote in 1975,* “Your instructor was right not to give you any points, for your answer was wrong, as he demonstrated using Gauss’s law. You should, in science, believe logic and arguments, carefully drawn, and not authorities. You also read the book correctly and understood it. I made a mistake, so the bookis wrong. I probably was thinking ofa groundedconducting sphere, or else of the fact that moving the charges around in different places inside does not affect things on the outside. I am not sure how I did it, but I goofed. And you goofed, too, for believing me.” How this New Millennium Edition Came to Be Between November 2005 and July 2006, 340 errata were submitted to The Feynman Lectures Website www.feynmanlectures.info. Remarkably, the bulk of these came from one person: Dr. Rudolf Pfeiffer, then a physics postdoctoral fellow at the University of Vienna, Austria. The publisher, Addison Wesley, fixed 80errata,butbalkedatfixingmorebecauseofcost: thebookswerebeingprinted by a photo-offset process, working from photographic images of the pages from the 1960s. Correcting an error involved re-typesetting the entire page, and to ensure no new errors crept in, the page was re-typeset twice by two different *Pages288–289ofPerfectly Reasonable Deviations from the Beaten Track, The Letters of Richard P. Feynman,ed.MichelleFeynman(BasicBooks,NewYork,2005). vi people, then compared and proofread by several other people—a very costly process indeed, when hundreds of errata are involved. Gottlieb, Pfeiffer and Ralph Leighton were very unhappy about this, so they formulated a plan aimed at facilitating the repair of all errata, and also aimed at producing eBook and enhanced electronic versions of The Feynman Lectures on Physics. They proposed their plan to me, as Caltech’s representative, in 2007. I was enthusiastic but cautious. After seeing further details, including a one-chapter demonstration of the Enhanced Electronic Version, I recommended that Caltech cooperate with Gottlieb, Pfeiffer and Leighton in the execution of theirplan. TheplanwasapprovedbythreesuccessivechairsofCaltech’sDivision of Physics, Mathematics and Astronomy—Tom Tombrello, Andrew Lange, and Tom Soifer—and the complex legal and contractual details were worked out by Caltech’s Intellectual Property Counsel, Adam Cochran. With the publication of this New Millennium Edition, the plan has been executed successfully, despite its complexity. Specifically: Pfeiffer and Gottlieb have converted into LATEX all three volumes of FLP (and also more than 1000 exercises from the Feynman course for incorporation into Feynman’s Tips on Physics). The FLP figures were redrawn in modern electronic form in India, under guidance of the FLP German translator, Henning Heinze, for use in the German edition. Gottlieb and Pfeiffer traded non-exclusive use of their LATEX equations in the German edition (published by Oldenbourg) for non-exclusive use of Heinze’s figures in this New Millennium English edition. Pfeiffer and Gottlieb have meticulously checked all the LATEX text and equations and all the redrawn figures, and made corrections as needed. Nate Bode and I, on behalf of Caltech, have done spot checks of text, equations, and figures; and remarkably, we have found no errors. Pfeiffer and Gottlieb are unbelievably meticulous and accurate. Gottlieb and Pfeiffer arranged for John Sullivan at the Huntington Library to digitize the photos of Feynman’s 1962–64 blackboards, and for George Blood Audio to digitize the lecture tapes—with financial support and encouragement from Caltech Professor Carver Mead, logistical support from Caltech Archivist Shelley Erwin, and legal support from Cochran. Thelegalissueswereserious: Inthe1960s,CaltechlicensedtoAddisonWesley rightstopublishtheprintedition,andinthe1990s, rightstodistributetheaudio ofFeynman’slecturesandavariantofanelectronicedition. Inthe2000s,through a sequence of acquisitions of those licenses, the print rights were transferred to thePearsonpublishinggroup, whilerightstotheaudioandtheelectronicversion were transferred to the Perseus publishing group. Cochran, with the aid of Ike Williams, an attorney who specializes in publishing, succeeded in uniting all of these rights with Perseus (Basic Books), making possible this New Millennium Edition. Acknowledgments On behalf of Caltech, I thank the many people who have made this New Millennium Edition possible. Specifically, I thank the key people mentioned above: Ralph Leighton, Michael Gottlieb, Tom Tombrello, Michael Hartl, Rudolf Pfeiffer,HenningHeinze,AdamCochran,CarverMead,NateBode,ShelleyErwin, AndrewLange,TomSoifer,IkeWilliams,andthe50peoplewhosubmittederrata (listed at www.feynmanlectures.info). And I also thank Michelle Feynman (daughter of Richard Feynman) for her continuing support and advice, Alan Rice for behind-the-scenes assistance and advice at Caltech, Stephan Puchegger and Calvin Jackson for assistance and advice to Pfeiffer about conversion of FLP to LATEX, Michael Figl, Manfred Smolik, and Andreas Stangl for discussions about corrections of errata; and the Staff of Perseus/Basic Books, and (for previous editions) the staff of Addison Wesley. Kip S. Thorne The Feynman Professor of Theoretical Physics, Emeritus California Institute of Technology October 2010 vii L E C T U R E S O N P H Y S I C S MAINLY MECHANICS, RADIATION, AND HEAT RICHARD P. FEYNMAN Richard Chace Tolman Professor of Theoretical Physics California Institute of Technology ROBERT B. LEIGHTON Professor of Physics California Institute of Technology MATTHEW SANDS Professor of Physics California Institute of Technology Copyright © 1963 CALIFORNIA INSTITUTE OF TECHNOLOGY ————————— Printed in the United States of America ALL RIGHTS RESERVED. THIS BOOK, OR PARTS THEREOF MAY NOT BE REPRODUCED IN ANY FORM WITHOUT WRITTEN PERMISSION OF THE COPYRIGHT HOLDER. Library of Congress Catalog Card No. 63-20717 Sixth printing, February 1977 ISBN 0-201-02010-6-H 0-201-02116-1-P CCDDEEFFGG-MU-89