Einstein’s Miraculous Year Image Not Available Einstein’s Miraculous Year (cid:1) Five Papers That Changed the Face of Physics EDITED AND INTRODUCED BY John Stachel WITH THE ASSISTANCE OF Trevor Lipscombe, Alice Calaprice, and Sam Elworthy AND WITH A FOREWORD BY Roger Penrose PRINCETON UNIVERSITY PRESS Copyright©1998byPrincetonUniversityPress PublishedbyPrincetonUniversityPress,41WilliamStreet, Princeton,NewJersey08540 IntheUnitedKingdom:PrincetonUniversityPress, Chichester,WestSussex AllRightsReserved LibraryofCongressCataloging-in-PublicationData Einstein’smiraculousyear:fivepapersthatchangedthe faceofphysics/editedandintroducedbyJohnStachel; withtheassistanceofTrevorLipscombe, AliceCalaprice,SamElworthy; withaforewordbyRogerPenrose. p. cm. ISBN0-691-05938-1(cloth:alk.paper) 1.Physics—History—20thcentury. 2.Einstein,Albert, 1879–1955. I.Stachel,JohnJ.,1928– . QC7.E52 1998 530.1—dc21 97-48441 ThisbookhasbeencomposedinCaledonia PrincetonUniversityPressbooksare printedonacid-freepaperandmeettheguidelines forpermanenceanddurabilityoftheCommittee onProductionGuidelinesforBookLongevity oftheCouncilonLibraryResources http://pup.princeton.edu PrintedintheUnitedStatesofAmerica 2 4 6 8 10 9 7 5 3 1 Disclaimer: Some images in the original version of this book are not available for inclusion in the eBook. CONTENTS foreword, byRogerPenrose vii publisher’spreface xv introduction, byJohnStachel 3 PART ONE Einstein’s Dissertation on the Determination of Molecular Dimensions 29 Paper 1. A New Determination of Molecular Dimensions 45 PART TWO Einstein on Brownian Motion 71 Paper 2. On the Motion of Small Particles Suspended in Liquids at Rest Required by the Molecular-Kinetic Theory of Heat 85 PART THREE Einstein on the Theory of Relativity 99 Paper 3. On the Electrodynamics of Moving Bodies 123 Paper 4. Does the Inertia of a Body Depend on Its Energy Content? 161 PART FOUR Einstein’s Early Work on the Quantum Hypothesis 165 Paper 5. On a Heuristic Point of View Concerning the Production and Transformation of Light 177 This page intentionally left blank FOREWORD In the twentieth century, we have been greatly privileged to witness two major revolutions in our physical picture of the world. The first of these upturned our conceptions of space and time, combining the two into what we now call space-time, a space-time which is found to be subtly curved in a way that gives rise to that long-familiar, omnipresent but mysterious, phenomenon of gravity. The second of these revolutions completely changed the way in which we under- stand the nature of matter and radiation, giving us a picture ofrealityinwhichparticlesbehavelikewavesandwaveslike particles, where our normal physical descriptions become subject to essential uncertainties, and where individual ob- jects can manifest themselves in several places at the same time. We have come to use the term “relativity” to encom- pass the first of these revolutions and “quantum theory” to encompass the second. Both have now been observationally confirmed to a precision unprecedented in scientific history. I think that it is fair to say that there are only three pre- vious revolutions in our understanding of the physical world that can bear genuine comparison with either. For the first of these three, we must turn back to ancient Greek times, wherethenotionofEuclideangeometrywasintroducedand someconceptionwasobtainedofrigidbodiesandstaticcon- figurations. Moreover, there was a beginning of an appreci- ation of the crucial role of mathematical reasoning in our insights into Nature. For the second of the three, we must leap to the seventeenth century, when Galileo and Newton vii FOREWORD told us how the motions of ponderable bodies can be under- stood in terms of forces between their constituent particles and the accelerations that these forces engender. The nine- teenth century gave us the third revolution, when Faraday and Maxwell showed us that particles were not enough, and we must consider, also, that there are continuous fields per- vading space, with a reality as great as that of the particles themselves. These fields were combined into a single all- pervasive entity, referred to as the electromagnetic field, and the behavior of light could be beautifully explained in terms of its self-propagating oscillations. Turning now to our present century, it is particularly re- markable that a single physicist—Albert Einstein—had such extraordinarily deep perceptions of the workings of Nature thathelaidfoundationstonesofbothofthesetwentieth-cen- tury revolutions in the single year of 1905. Not only that, but in this same year Einstein also provided fundamental new insights into two other areas, with his doctoral disserta- tion on the determination of molecular dimensions and with his analysis of the nature of Brownian motion. This latter analysis alone would have earned Einstein a place in his- tory. Indeed, his work on Brownian motion (together with the independent and parallel work of Smoluchowski) laid the foundations of an important piece of statistical under- standing which has had enormous implications in numerous other fields. This volume brings together the five papers that Einstein published in that extraordinary year. To begin with, there is the one just referred to on molecular dimensions (paper 1), followed by the one on Brownian motion (paper 2). Then come two on the special theory of relativity: the first initi- ates the “relativity” revolution, now so familiar to physicists viii FOREWORD (and also perceived by the public at large), in which the no- tion of absolute time is abolished (paper 3); the second is a short note deriving Einstein’s famous “E = mc2” (paper 4). Finally, the (only) paper that Einstein himself actually re- ferred to as “revolutionary” is presented, which argues that we must, in some sense, return to the (Newtonian) idea that light consists of particles after all—just when we had be- come used to the idea that light consists solely of electro- magnetic waves (paper 5). From this apparent paradox, an important ingredient of quantum mechanics was born. To- gether with these five classic Einstein papers, John Stachel has provided fascinating and highly illuminating introduc- tions that set Einstein’s achievements in their appropriate historical settings. I have referred above to the twentieth century’s two ex- traordinary revolutions in physical understanding. But it should be made clear that, fundamental as they were, Ein- stein’s papers of 1905 did not quite provide the initial shots of those revolutions; nor did these particular papers set out the final nature of their new regimes. The revolution in our picture of space and time that Ein- stein’s two 1905 relativity papers provided concerned only what we now call the special theory. The full formulation of the general theory of relativity, in which gravitation is in- terpreted in terms of curved space-time geometry, was not achieved until ten years later. And even for special relativity, the wonderful insights presented by Einstein in 1905 pro- vided a theory that was not totally original with him, this theory having been grounded in earlier ideas (notably those of Lorentz and Poincare´). Moreover, Einstein’s viewpoint in 1905 still lacked one important further insight—that of space-time—introduced by Hermann Minkowski three years ix