iAPPLICATIONS OFCLASSICAL PHYSICSRoger D. Blandford and Kip S. ThorneCalifornia Institute of Technology2008—2009version 0800.1.K.pdf, September 28, 2008iiPrefacePlease send comments, suggestions, and erratavia email to [email protected], or on paper toKip Thorne,130 -33 Caltech, Pasadena CA 91125This book is an introduction to the fundamentals and 21st-century applications ofall t he major branches of classical physics except classical mechanics, electromagnetictheory, and elementary thermodynamics (which we assume the reader has already learnedelsewhere).Classical physics and this book deal with physical phenomena on macroscopic scales:scales where the particulate natures of matter and radiation are secondary to the behaviorof particles in bulk; scales where part icles’ statistical as oppo sed to individual propertiesare impo rtant, and where matter’s inherent graininess can be smoothed over. In thisbook, we shall take a journey through spacetime and phase space, through statisticaland continuum mechanics (including solids, fluids, a nd plasmas), and through optics andrelativity, both special and general. In our journey, we shall seek to comprehend thefundamental laws of classical physics in their ow n terms, and in relation to quantumphysics. Using carefully chosen examples, we shall show how the classical laws are appliedto important, contemporary, 21 st-century problems and to everyday phenomena, and weshall uncover some deep connections among the vari ous fundamental laws, and connectionsamong the practi cal techniq ues that are used in different subfields of physics.Many of the most important recent developments in physics—and more g enerally inscience and engineering—involve classical subjects such as optics, fluids, plasmas, randomprocesses, and curved spacetime. Unfortunately, many young phy si cists today have littleunderstanding these subjects and their applications. Our goal, in writing this book, is torectify that. More specifically :• We believe that every masters-level or PhD physicist should be familiar with thebasic concepts of all the major branches of classical physics, and should have hadsome experience in applying them to real-world phenomena; this b ook is designed tofacilitate that.• A large fraction of physics, astronomy and engineering graduate students in t he UnitediiiStates and aro und the world use classical physics ext ensively in their research, andeven more of them go o n to careers in which classical phy si cs is an essential component;this book is designed to facilitate that research and those careers.In pursuit of these goals, we seek, in this book, to give the reader a clear understandingof the basic concepts and princ iples of classical physics. We present these principles in thelanguage of modern physics (not nineteenth century applied mathematics), and presentthem for physicists as distinct from mathematicians or engineers — though we hope thatmathematicians a nd engineers will also find our presentat ion useful. As far as possible, weemphasize theory that involves general principles which extend well beyond the parti cularsubjects we study.In this book, we also seek to teach the reader how to apply classical physi cs ideas. Wedo so by presenting contemporary applications from a variety of fields, such as• fundamental 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 informati onscience & technology.Why i s the range of applications so wide? Because we believe that physicists should haveat their disposal enough understanding of general principles to attack problems that arisein unfamiliar environments. In the modern era, a large fraction of physics students willgo on to careers away from the core of fundamental phy sics. For such students, a broadexposure to non-core applications will be of g reat value; for those who wind up in the core,such an exposure is of value culturally, and also because ideas from other fields often turnout to have impact back in the core of physics. Our examples will illustrate how basicconcepts and problem solving techniques are freely interchanged between disciplines.Classical physics is defined as the physics where Planck’s constant can be approxi-mated as zero. To a large extent, it is the body of physics for which the fundamental equa-tions were established prior to the development of quantum mechanics in t he 1920’ s. Doesthis imply that it should be studied in isolation from quantum mechanics? Our answer is,most emphatically, “N o!”. The reasons are simple. First, quantum mechanics has primacyover classical physics: classical physics is an approxima tion, often excellent, sometimespoor, to quantum mechanics. Second, in recent decades many concepts and mathematicaltechniques developed for quantum mechanics have been imported into classical physicsand used to enlarge our classical understanding and enhance our computational capability.An example that we shall discuss occurs in plasma physics, where nonli nearly interact-ing waves are treated as quanta (“plasmons”), despite the fact that they are solutions ofclassical field equatio ns. Third, ideas developed initially for “ cl a ssical” problems are fre-quently adapted for application to avowedly q uantum mechanical subjects; examples (notdiscussed in this boo k) are found in supersymmetric string theory and in the liquid dropmodel of the atomi c nucleus. Because of these intimate connections between quantum andclassical physics, q uantum physics will appear frequently in this book, in a variety of ways.ivThe amount and variety of material covered in this boo k may seem overwhelming.If so, please keep in mind the key goals of the book: to teach the fundamental concepts,which are not so extensive that they should overwhelm, and to illustrate those concepts.Our goal i s not to provide a mastery the many i llustrative applications contained in thebook, but rather to convey the spirit of how to apply the basic concepts of cl a ssical physics.This book will also seem much more manageable and less overwhelming when onerealizes that the same concepts and problem solving techniques appear over and over again,in a variety of different subjects and applicati ons. These unifying concepts and techniquesare listed i n Appendix B, in outline form,
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