QED: the Strange Theory of Light and Matter

193 Pages·2013·12.096 MB·English

by  Feynman, Richard P

QED
ALIX C. MAUTNER
MEMORIAL LECTURES
Q E D
THE STRANGE THEORY OF
LIGHT AND MATTER
RICHARD P. FEYNMAN
With a new introduction by A. Zee
PRINCETON UNIVERSITY PRESS
PRINCETON AND OXFORD
Copyright © 1985 by Richard P. Feynman
New introduction by A. Zee Copyright © 2006 by Princeton University Press
Requests for permission to reproduce material from this work should be
sent to Permissions, Princeton University Press
Published by Princeton University Press,
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In the United Kingdom: Princeton University Press,
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All Rights Reserved
First printing, 1985
First Princeton Science Library Edition, 1988
Expanded Princeton Science Library Edition, with a new
introduction by A. Zee, 2006
Library of Congress Control Number 2005934342
ISBN-13: 978-0-691-12575-6 (paperback)
ISBN-10: 0-691-12575-9 (paperback)
ISBN-13: 978-0-691-12717-0 (cloth)
ISBN-10: 0-691-12717-4 (cloth)
This book has been composed in Linotron Baskerville
Printed on acid-free paper. ∞
pup.princeton.edu
Printed in the United States of America
1 3 7 9 10 8 6
Contents
Introduction to the 2006 Edition fry vii
A. Zee
Foreword xxi
by Leonard Mautner
Preface fry xxiii
Ralph Leighton
Acknowledgment xxv
1. Introduction 3
2. Photons: Particles of Light 36
3. Electrons and Their Interactions 77
4. Loose Ends 124
Index 153
A unique example of one of Feynman’s famous diagrams, in-
scribed and signed by Feynman himself; image appears courtesy
of Jay M. Pasachoff, Field Memorial Professor of Astronomy at
Williams College, for whom the diagram was drawn in the front
pages of his first-edition copy of QED.
Introduction to the
2006 Edition
The story of how we came to know light makes for one
gripping drama, complete with twists and turns and rever-
sals of fortune.
The photon is the most visible of all elementary parti-
cles: place yourself in a dusty room with one small window
open on a sunny day and watch a multitude of the little
buggers hurrying across the room. Newton quite naturally
thought that light consisted of a stream of particles (“cor-
puscles”), but already he had some doubts; even in the
seventeenth century, the diffraction of light could be
readily observed. Eventually, diffraction and other phe-
nomena appeared to show without doubt that light is an
electromagnetic wave. That monument of nineteenth-
century physics, Maxwell’s equations of electromagne-
tism, formulated light entirely as a wave. Then Einstein
came along and explained the photoelectric effect by pos-
tulating light as the sum of little packets (“quanta”) of
energy. Thus were the word “photon” and the quantum
theory of light born. (Here I will not digress and recall
Einstein’s famous discomfort with quantum mechanics,
even though he helped at its birth.) Meanwhile, from the
1920s through the 1940s physicists worked out the quan-
tum behavior of matter (“atoms”) thoroughly. Thus, it was
all the more puzzling that the quantum behavior of light
and its interaction with electrons resisted the efforts of
the best and the brightest, notably Paul Dirac and Enrico
Fermi. Physics had to wait for three young men—Feyn-
man, Schwinger, and Tomonoga—filled with optimism