iAPPLICATIONS OFCLASSICAL PHYSICSRoger D. Blandford and Kip S. ThorneCalifornia Institute of Technology2011—201 2version 1100.2.K.pdf, September 16, 2011PrefacePlease send comments, suggestions, and errata via email to [email protected], or on paper toKip Thorne, 350-17 Caltech, Pasadena CA 91 125This bo ok is an introduction to the fundamentals and 21st-century applications of all themajor branches of classical physics except classical mechanics, electromagnetic theory, andelementary thermodynamics (which we assume the reader has already learned elsewhere).Classical physics and this bo ok deal with physical phenomena on macroscopic scales:scales where the particulate natures of matter a nd radiation are secondary to the behaviorof particles in bulk; scales where particles’ statistical as opposed to individual properties a reimportant, and where matter’s inherent graininess can be smoothed over. In this book, weshall take a journey through spacetime and phase space, through statistical and continuummechanics (including solids, fluids, a nd plasmas), and through optics and relativity, bothspecial and general. In our j ourney, we shall seek to comprehend the fundamental laws ofclassical physics in their own terms, and in relation to quantum physics. Using carefully cho-sen examples, we shall show how t he classical laws are applied to important, contemporary,21st-century problems and to everyday phenomena, and we shall uncover some deep connec-tions among the various fundamental laws, a nd connections among the practical techniquesthat are used in different subfields of physics.Many of the most important recent developments in physics—and more generally inscience and engineering—involve classical subjects such as optics, fluids, plasmas, randomprocesses, and curved spacetime. Unfortunately, many young physicists today have littleunderstanding t hese subjects and their applications. Our goa l, in writing this book, is torectify that. More specifically:• We believe that every masters-level or PhD physicist should be familiar with the basicconcepts of a ll the major branches of classical physics, and should have had someexperience in applying them to real-world phenomena; this book is designed to facilitatethat.• A large fraction of physics, astronomy and engineering graduate students in the UnitedStates and around the world use classical physics extensively in their research, and evenmore of them go on to careers in which classical physics is an essential component; thisbo ok is designed to f acilitate that research a nd those careers.In pursuit of these goals, we seek, in this book, to give the reader a c l ear understandingof the basic concep ts and principle s of classical p hysics. We present these principles iniiiiithe languag e of modern physics (not nineteent h century applied mathematics), and presentthem fo r physicists as distinct from mathematicians or engineers — thoug h we hope thatmathematicians and engineers will also find our presentation useful. As far as possible, weemphasize theory that invo lves general principles which extend well beyond the particularsubjects we study.In this book, we also seek to teach the reader how to apply classical physic s ideas. We doso by presenting contemporary applications from a variety of fields, such as• fundament al physics, experimental physics and applied physics,• astrophysics and cosmology,• geophysics, oceanography and meteorology,• biophysics and chemical physics,• engineering, optical science & technology, radio science & technology, and informationscience & technology.Why is the range of applications so wide? Because we believe that physicists should haveat their disp osal enough understanding of general principles to attack problems that arise inunfamiliar environments. In the modern era, a large fraction of physics students will go onto careers away f r om the core of fundamental physics. For such students, a broad exposureto non-core applications will be of great value. For those who wind up in the core, such anexposure is of value culturally, and also because ideas from ot her fields often turn out tohave impact back in the core of physics. Our examples will illustrate how basic concepts andproblem solving techniques are fr eely interchanged between disciplines.Classical physics is defined as the physics where Planck’s constant can be approximatedas zero. To a large extent, it is the body of physics for which the fundamental equationswere established prior to the development of quantum mechanics in the 192 0’s. Does thisimply tha t it should be studied in isolation from quantum mechanics? Our answer is, mostemphatically, “No!”. The reasons are simple. First, quantum mechanics has primacy overclassical physics: classical physics is an approximation, often excellent, sometimes poor, toquantum mechanics. Second, in recent decades many concepts and mathematical techniquesdeveloped for quantum mechanics have been imported into classical physics and used toenlarge our classical understanding and enhance our computational capability. An examplethat we shall discuss occurs in plasma physics, where nonlinearly interacting waves aretreated as quanta (“plasmons”), despite the fact that they are solutions of classical fieldequations. Third, ideas developed initially for “classical” problems are fr equently adaptedfor application to avowedly quantum mechanical subjects; examples (not discussed in thisbo ok) are found in supersymmetric string theory and in the liquid dro p model of the atomicnucleus. Because of these intimate connections between quantum and classical physics,quantum physics will appear frequently in this book, in many ways.The amount and variety of material covered in this book may seem overwhelming. If so,please keep in mind the key goals of the book: to teach t he fundamental concepts, whichare not so extensive that they should overwhelm, and to illustrate those concepts. Our goalivis not to provide a mastery of the many illustrative applications contained in the book, butrather to convey the spirit of how to apply the basic concepts of classical physics. To helpstudents and readers who feel overwhelmed, we have labeled as “track two” sections that caneasily be skipped on a first reading, or skipped entirely — but are sufficiently interestingthat many readers may choose to browse or study them. Track-two sections are labeled bythe symbol T2 .This book will also seem
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