Conversations on Electric and Magnetic Fields In the Cosmos (ebook)

Argumento de Conversations on Electric and Magnetic Fields In the Cosmos (ebook)

Today's standard textbooks treat the theoretical structure of electric and magnetic fields, but their emphasis is on electromagnetic radiation and static-electric and magnetic fields. In this book, Eugene Parker provides advanced graduate students and researchers with a much-needed complement to existing texts, one that discusses the dynamic electromagnetism of the cosmos--that is, the vast magnetic fields that are carried bodily in the swirling ionized gases of stars and galaxies and throughout intergalactic space.

Parker is arguably the world's leading authority on solar wind and the effects of magnetic fields in the heliosphere, and his originality of thought and distinctive approach to physics are very much in evidence here. Seeking to enrich discussions in standard texts and correct misconceptions about the dynamics of these large-scale fields, Parker engages readers in a series of "conversations" that are at times anecdotal and even entertaining without ever sacrificing theoretical rigor. The dynamics he describes represents the Maxwell stresses of the magnetic field working against the pressure and inertia of the bulk motion of ionized gases, characterized in terms of the magnetic field and gas velocity. Parker shows how this dynamic interaction cannot be fully expressed in terms of the electric current and electric field.

Conversations on Electric and Magnetic Fields in the Cosmos goes back to basics to explain why classical hydrodynamics and magnetohydrodynamics are inescapable, even in the deepest reaches of space.

"Nobody has contributed more, or more deeply, to our understanding of the physics of astrophysical magnetofluids than Eugene Parker. Conversations on Electric and Magnetic Fields in the Cosmos provides those of us who have had the privilege of learning directly from him a chance to revisit the elegant insight, structure, and breezy wit that Parker brings to the subject. For those who have not had that privilege, this book provides lasting opportunity to visit with a master."--Eugene H. Levy, Rice University

"This small book, which describes the basic physics that governs the electrodynamics of the cosmos, is graced by insights the author gleaned during a lifelong fascination with the subject matter. We owe to him the explanation of many natural phenomena including how the solar wind blows and why its magnetic field lines form Archimedian spirals. Another of his creations, the α-Ω dynamo model affords us our understanding of how the magnetic fields of planets are maintained against resistive decay and why the Sun's magnetic field reverses every eleven years."--Peter Goldreich, Institute for Advanced Study, Princeton

"This is a book by one of the leaders in the field of plasma astrophysics. Parker sets the record straight on many misunderstandings concerning electric and magnetic fields in the cosmos. The book also presents a revealing picture of the author's thinking and displays how he was able to arrive at such original solutions to so many important astrophysical problems."--Russell M. Kulsrud, author of Plasma Physics for Astrophysics

"This is a unique undertaking by a scientist who is one of the most accomplished and outstanding in our field. The book takes the reader from the elementary principles of Newtonian mechanics and Maxwell's equations to hydrodynamics and magnetohydrodynamics equations. The author has intended this book to be conversations, as the title indicates. The style is informal but the physical ideas and concepts are presented with precision."--B. C. Low, National Center for Atmospheric Research

"Parker is one of the leaders in the field and has his own novel approach to plasma astrophysics. I believe that both students and active researchers will benefit from this book."--David Spergel, Princeton University

"I shall strongly recommend my students to read this book in addition to their standard reading . . . not only to clarify their understanding of cosmic magnetism but also to learn how to present their ideas in a clear and understandable way."--Dimitri Sokoloff, Journal of Geophysical and Astrophysical Fluid Dynamics0List of Illustrations xi Acknowledgments xiii

Chapter 1: Introduction 1
1.1 General Remarks 1
1.2 Electromagnetic Field Equations 3
1.3 Electrical Neutrality 7
1.4 Electric Charge and Magnetic Field Dominance 12

Chapter 2: Electric Fields 15
2.1 Basic Considerations 15
2.2 Definition of Charge and Field 16
2.3 Concept of Electric Field 17
2.4 Physical Reality of Electric Field 20
2.5 Electric Field Pressure 22

Chapter 3: Magnetic Fields 25
3.1 Basic Considerations 25
3.2 Experimental Connection 26
3.3 Differential Form of Ampere's Law 27
3.4 Energy and Stress 29
3.5 Detecting a Magnetic Field 32

Chapter 4: Field Lines 37
4.1 Basic Considerations 37
4.2 The Optical Analogy 39

Chapter 5: Maxwell's Equations 43

Chapter 6: Maxwell and Poynting 48
6.1 Poynting's Momentum and Energy Theorems 48
6.2 Applications 52
6.3 Electric and Magnetic Fields in Matter 52
6.4 SI Units 55
6.5 Systems of Units 59
6.6 Chaucer Units 63

Chapter 7: Moving Reference Frames 65
7.1 Lorentz Transformations 65
7.2 Electric Fields in the Laboratory 66
7.3 Occam's Razor and the Tree in the Forest 67
7.4 Electric Field in a Moving Plasma 68
7.5 Net Charge in a Swirling Plasma 71

Chapter 8: Hydrodynamics 74
8.1 Basic Considerations 74
8.2 Derivation of the HD Equations 76
8.3 The Pressure Tensor 79
8.4 Pressure Variation in Uniform Dilatations 82
8.5 Shear Flow 85
8.6 Effects of Collisions 86
8.7 Off-diagonal Terms and Viscosity 89
8.8 Summary 91

Chapter 9: Magnetohydrodynamics 92
9.1 Basic Considerations 92
9.2 Diffusion and Dissipation 96
9.3 Application of Magnetic Diffusion 98
9.4 Discussion 101
9.5 Partially Ionized Gases 102
9.6 An Electric Current to Satisfy Ampere 108
9.7 Particle Motion Along B 114
9.8 Time-varying Magnetic Field 119
9.9 Comments 121

Chapter 10: Singular Properties of the Maxwell Stress Tensor 123
10.1 Magnetic Equilibrium 123
10.2 Calculation of the Equilibrium Field 128
10.3 Equilibrium in Stretched Field 129
10.4 Resolving the Contradiction 132
10.5 Formation of TDs 133
10.6 Rapid Reconnection at an Incipient TD 137
10.7 Quasi-steady Dissipation at a TD 142

Chapter 11: Comments 147
11.1 Summary 147
11.2 Electric Circuit Analogy 148
11.3 A Simple Example of an Electric Circuit 149
11.4 Popular Electric and Magnetic Fields 154
Appendix A Electrostatically Driven Expansion of the Universe 157
Appendix B Relaxation of Electric Charge Inhomogeneity 159
Appendix C Imposition of a Large-scale Electric Field 162
Appendix D Electric Charge Density in an Electric Field 165
Appendix E The Transverse Invariant 167
Appendix F Blocking the Flow of Electric Current 169

References 173
Index 179