Showing papers in "Physics Today in 1999"
TL;DR: The theory of interference and interferometers has been studied extensively in the field of geometrical optics, see as discussed by the authors for a survey of the basic properties of the electromagnetic field.
Abstract: Historical introduction 1. Basic properties of the electromagnetic field 2. Electromagnetic potentials and polarization 3. Foundations of geometrical optics 4. Geometrical theory of optical imaging 5. Geometrical theory of aberrations 6. Image-forming instruments 7. Elements of the theory of interference and interferometers 8. Elements of the theory of diffraction 9. The diffraction theory of aberrations 10. Interference and diffraction with partially coherent light 11. Rigorous diffraction theory 12. Diffraction of light by ultrasonic waves 13. Scattering from inhomogeneous media 14. Optics of metals 15. Optics of crystals 16. Appendices Author index Subject index.
4,439 citations
TL;DR: The Knitting Pattern as mentioned in this paper is a block copolymer that was discovered by Reimund Stadler and his coworkers and reflects a delicate free-energy minimization that is common to all blockcopolymer materials.
Abstract: Block copolymers are all around us, found in such products as upholstery foam, adhesive tape and asphalt additives. This class of macromolecules is produced by joining two or more chemically distinct polymer blocks, each a linear series of identical monomers, that may be thermodynamically incompatible (like oil and vinegar). Segregation of these blocks on the molecular scale (5–100 nm) can produce astonishingly complex nanostructures, such as the “knitting pattern” shown on the cover of this issue of PHYSICS TODAY. This striking pattern, discovered by Reimund Stadler and his coworkers, reflects a delicate free‐energy minimization that is common to all block copolymer materials.
2,824 citations
Abstract: Carbon nanotubes are cylindrical molecules with a diameter of as little as 1 nanometer and a length up to many micrometers They consist of only carbon atoms, and can essentially be thought of as a single layer of graphite that has been wrapped into a cylinder, (See figure 1 and the article by Thomas Ebbesen in PHYSICS TODAY, June 1996, page 26)
1,340 citations
TL;DR: In this article, the authors provide a comprehensive view of the formation of stars and planetary systems, from their beginnings in cold clouds of molecular gas to their emergence as new suns with planet-forming disks.
Abstract: Our understanding of the formation of stars and planetary systems has changed greatly since the first edition of this book was published. This new edition has been thoroughly updated, and now includes material on molecular clouds, binaries, star clusters and the stellar initial mass function (IMF), disk evolution and planet formation. This book provides a comprehensive picture of the formation of stars and planetary systems, from their beginnings in cold clouds of molecular gas to their emergence as new suns with planet-forming disks. At each stage gravity induces an inward accretion of mass, and this is a central theme for the book. The author brings together current observations, rigorous treatments of the relevant astrophysics, and 150 illustrations, to clarify the sequence of events in star and planet formation. It is a comprehensive account of the underlying physical processes of accretion for graduate students and researchers.
653 citations
TL;DR: In this article, the elastic behavior of a rock is probed, for instance, it shows extreme nonlinearity hysteresis and discrete memory (the Flintstones could have had a computer that used a sandstone for random access memory).
Abstract: A squash ball almost doesn't bounce; a Superball bounces first left then right, seeming to have a mind of its own. Remarkable and complex elastic behavior isn't confined to sports equipment and toys. Indeed, it can be found in some surprising places. When the elastic behavior of a rock is probed, for instance, it shows extreme nonlinearity hysteresis and discrete memory (the Flint‐stones could have had a computer that used a sandstone for random‐access memory). Rocks are an example of a class of unusual elastic materials that includes sand. soil, cement, concrete, ceramics and, it turns out, damaged materials, Many members of this class are the blue‐collar materials of daily life: They are in the bridges we cross on the way to work, the roofs over our heads and the ground beneath our cities—such as the Los Angeles basin (home to many earthquakes). The elastic behavior of these materials is of more than academic interest.
586 citations
TL;DR: In this paper, the authors discuss the effects of quantum mechanical effects on chip design parameters, such as charge distribution, and how these effects will affect performance as device sizes shrink and how to handle them.
Abstract: Semiconductors are ubiquitous in device electronics because their charge distributions are easily shaped and controlled to make logic gates. Since gate switching and intercommunication rates limit device speed, efforts to improve computational power have led the semiconductor industry to push devices to ever‐shrinking sizes. Yet, as advances in this area have improved the function of today's chip architectures, miniaturization may soon bring additional complications in the form of quantum mechanical effects. Because quantum systems tend to behave statistically, these effects will introduce unpredictable fluctuations in essential; design parameters, such as charge distribution, that will affect performance as device sizes shrink.
383 citations
TL;DR: The idea of gravitational waves was already implicit in the 1905 special theory of relativity, with its finite limiting speed for information transfer as mentioned in this paper, and the explicit formulation for gravitational waves in general relativity was put forward by Einstein in 1916 and 1918.
Abstract: The idea of gravitational waves was already implicit in the 1905 special theory of relativity, with its finite limiting speed for information transfer. The explicit formulation for gravitational waves in general relativity was put forward by Einstein in 1916 and 1918. He showed that the acceleration of masses generates time‐dependent gravitational fields that propagate away from their sources at the speed of light as warpages of spacetime. Such a propagating warpage is called a gravitational wave. Large detectors on opposite sides of the country are about to start monitoring the cosmos for the gravitational waves that general relativity tells us should be emanating from catastrophic astrophysical events.
367 citations
TL;DR: In this article, the authors present a simple picture using the Bloch Equation of femtosecond Pulses and demonstrate how to manipulate and change the characteristics of laser pulses.
Abstract: Laser Basics.- Pulsed Optics.- Methods for the Generation of Ultrashort Laser Pulses: Mode-Locking.- Further Methods for the Generation of Ultrashort Optical Pulses.- Pulsed Semiconductor Lasers.- How to Manipulate and Change the Characteristics of Laser Pulses.- How to Measure the Characteristics of Laser Pulses.- Spectroscopic Methods for Analysis of Sample Dynamics.- Coherent Effects in Femtosecond Spectroscopy: A Simple Picture Using the Bloch Equation.- Terahertz Femtosecond Pulses.- Coherent Control in Atoms, Molecules and Solids.- Attosecond Pulses.
312 citations
TL;DR: This paper found that physics faculty members often come away from teaching college-level introductory courses deeply dismayed about how little their students have learned and the growing importance of having a workforce that is literate in science and technology makes this situation more than an academic problem.
Abstract: Physics faculty members often come away from teaching college‐level introductory courses deeply dismayed about how little their students have learned. The growing importance of having a workforce that is literate in science and technology makes this situation more than an academic problem.
288 citations
TL;DR: In this article, the Boltzmann equation and the ergodic hypothesis of the Baker's transformation have been studied in the context of non-equilibrium statistical mechanics, and a number of interesting results have been obtained.
Abstract: Preface 1. Non-equilibrium statistical mechanics 2. The Boltzmann equation 3. Liouville's equation 4. Poincare recurrence theorem 5. Boltzmann's ergodic hypothesis 6. Gibbs' picture-mixing systems 7. The Green-Kubo formulae 8. The Baker's transformation 9. Lyapunov exponents for a map 10. The Baker's transformation is ergodic 11. Kolmogorov-Sinai entropy 12. The Frobenius-Perron equation 13. Open systems and escape-rates 14. Transport coefficients and chaos 15. SRB and Gibbs measures 16. Fractal forms in Green-Kubo relations 17. Unstable periodic orbits 18. Lorentz lattice gases 19. Dynamical foundations of the Boltzmann equation 20. The Boltzmann equation returns 21. What's next Appendices Bibliography.
286 citations
TL;DR: A catalyst is a substance that accelerates the rate of a chemical reaction without being part of its final products as mentioned in this paper, and it acts by forming intermediate compounds with the molecules involved in the reaction, offering them an alternate, more rapid path to the final products.
Abstract: In 1835 the Swedish chemist Jons Jakob Berzelius coined the term “catalysis” to describe chemical reactions in which progress is affected by a substance that is not consumed in the reaction and hence is apparently not involved in the reaction. Both the term and the phenomenon were heavily debated throughout the rest of the 19th century until the German chemist Wilhelm Ostwald proposed a now generally accepted definition: “A catalyst is a substance that accelerates the rate of a chemical reaction without being part of its final products.” the catalyst acts by forming intermediate compounds with the molecules involved in the reaction, offering them an alternate, more rapid path to the final products.
TL;DR: The authors' ability to localize warns us of danger and helps us sort out individual sounds from the usual cacophony of their acoustical world.
Abstract: For as long as we humans have lived on Earth, we have been able to use our ears to localize the sources of sounds. Our ability to localize warns us of danger and helps us sort out individual sounds from the usual cacophony of our acoustical world. Characterizing this ability in humans and other animals makes an intriguing physical, physiological, and psychological study (see figure 1).
TL;DR: In this paper, the theory of gases is used to describe flow of gases through tubes and orifices of a high-Vacuum system with positive displacement and positive displacement.
Abstract: Kinetic Theory of Gases. Flow of Gases Through Tubes and Orifices. Positive Displacement Vacuum Pumps. Kinetic Vacuum Pumps. Capture Vacuum Pumps. Vacuum Gauges. Partial Pressure Analysis. Leak Detection and Leak Detectors. High-Vacuum System Design. Gas-Surface Interactions and Diffusion. Ultrahigh and Extreme High Vacuum. Calibration and Standards Appendix. Indexes.
TL;DR: Just like human twins who evoke amazement and a ense of mystery by reporting empathetic experiences across great distances, photons born in pairs also astonish us by their quantum-correlated behavior as mentioned in this paper.
Abstract: Just like human twins who evoke amazement and a ense of mystery by reporting empathetic experiences across great distances, photons born in pairs also astonish us by their quantum‐correlated behavior.
TL;DR: The subject of friction and lubrication still fascinates me as discussed by the authors, even though many of my friends thought I was crazy when I began, ten years ago, to work on friction.
Abstract: My friends thought I was crazy when I began, ten years ago, to work on friction and lubrication—words that seemed to evoke the triviality of replacing the dirty oil in one's automobile. What could be fundamental or beautiful about friction? In this article, I try to explain why the subject still fascinates me.
TL;DR: The H•theorem as discussed by the authors is a result of Boltzmann's kinetic equation for a gas of molecules that required monotonic growth of entropy, which is the basis for modern thermodynamics.
Abstract: The problem of the foundation of statistical physics emerged with the derivation by Ludwig Boltzmann of a kinetic equation for a gas of molecules that required monotonic growth of entropy. Boltzmann's theory leads to modern thermodynamics, and, for example, to the impossibility of gas spontaneously gathering in one part of a container in the absence of external forces. This result, known as the H‐theorem, met with strong contemporary opposition, especially from mathematician Ernst Zermelo.
TL;DR: Bennett et al. as discussed by the authors used quantum computers to perform tasks that would be inconceivable with conventional digital technology, such as search and discovery, search and discover, and discovery.
Abstract: Information carried by a quantum system has notoriously weird properties. Physicists and engineers are now learning how to put that weirdness to work. Quantum computers, which manipulate quantum states rather than classical bits, may someday be able to perform tasks that would be inconceivable with conventional digital technology. (See the article by Charles H. Bennett, PHYSICS Today, October 1995, page 24, and the “Search and Discovery” report in PHYSICS Today, March 1996, page 21.)b
TL;DR: Barish and Weiss as mentioned in this paper showed that the usefulness of astronomical observations in testing fundamental theory depends upon how well tested the theory is already, and since general relativity is the basis for virtually all discussion of gravitational wave detectors and sources, the extent of its "upfront" validity is of some concern to us.
Abstract: While the detection of gravitational radiation may usher in a new era of “gravitational wave” astronomy (see the accompanying article by Barry Barish and Rainer Weiss, on page 44), it should also yield new and interesting tests of Einstein's general theory of relativity, especially in the radiative and strong‐field regimes. Consequently, we are in an unusual situation. After all, we rarely think of electromagnetic astronomy as providing tests of Maxwell's theory. Neutrino astronomy may be a closer cousin: We can observe neutrinos to learn about the solar interior or about supernovae, while also checking such fundamental phenomena as neutrino oscillations. To some extent, the usefulness of astronomical observations in testing fundamental theory depends upon how well tested the theory is already. At the same time, since general relativity is the basis for virtually all discussion of gravitational‐wave detectors and sources, the extent of its “upfront” validity is of some concern to us.
TL;DR: The psychosomatic disorder observed in the 15 million people in Belarus, Ukraine, and Russia who were affected by the April 1986 Chernobyl accident are probably the accident's most important effect on public health.
Abstract: The psychosomatic disorder observed in the 15 million people in Belarus, Ukraine, and Russia who were affected by the April 1986 Chernobyl accident are probably the accident's most important effect on public health. These disorders could not be attributed to the ionizing radiation, but were assumed to be linked to the popular belief that any amount of man‐made radiation—even minuscule, close to zero doses—can cause harm, an assumption that gained wide currency when it was accepted in the 1950s, arbitrarily, as the basis for regulations on radiation and nuclear safety.
TL;DR: The Light That Shines Straight as discussed by the authors is a classic example of a light-that-shines-straight story about a light that shines straight in the sky, and it can be seen as a metaphor for the Rains of Orion.
Abstract: 1. The Light That Shines Straight 2. Physics, Furman, Molecules, and Me 3. Bell Labs and Radar, a (Fortunate) Detour from Physics 4. Columbia to Franklin Park and Beyond 5. Maser Excitement-And a Time for Reflection 6. From Maser to Laser 7. The Patent Game 8. On Moon Dust, and Other Science Advice 9. The Rains of Orion
TL;DR: In this paper, the authors introduce Quantum Fields and introduce the Dirac Field and describe the process of Quantum Electrodynamics in terms of the relationship between the two fields and their properties.
Abstract: 1. Introducing Quantum Fields 2. Scalar Fields 3. Relativistic Fields 4. Canonical Formalism 5. Electromagnetic Field 6. Dirac Equation 7. The Dirac Field 8. Dynamics of Interacting Fields 9. Feynman Graphs 10. Vacuum Correlation Functions 11. Quantum Electrodynamics 12. Processes in Quantum Electrodynamics 13. Perturbative Renormalization 14. Path Integrals 15. Broken Symmetry 16. Renormalization 17. The Gaussian Fixed Point 18. In Two Dimensions 19. Topological Excitations Appendix A. Background Material Appendix B. Superfluidity Appendix C. Polchinski's Renormalization Equation
TL;DR: In this paper, the authors present a theoretical analysis of the second-harmonic generation and four-wave mixing in anisotropic dielectric materials and show that it is possible to achieve the phase matching condition.
Abstract: 1. Introductory Remarks.- Problems.- 2. Linear Dielectric Response of Matter.- 2.1 Frequency Dependence of the Dielectric Tensor.- 2.2 Wave Vector Dependence of the Dielectric Tensor.- 2.3 Electromagnetic Waves in Anisotropic Dielectrics.- Problems.- 3. Nonlinear Dielectric Response of Matter.- 3.1 Frequency Variation of the Nonlinear Susceptibilities.- 3.2 Wave Vector Dependence of the Nonlinear Susceptibilities.- 3.3 Remarks on the Order of Magnitude of the Nonlinear Susceptibilities.- Problems.- 4. Basic Principles of Nonlinear Wave Interactions: Second Harmonic Generation and Four Wave Mixing.- 4.1 Perturbation Theoretic Analysis of Second-Harmonic Generation.- 4.2 Methods of Achieving the Phase Matching Condition.- 4.3 Evolution of the Second-Harmonic Wave under Phase Matched Conditions.- 4.4 Other Examples of Nonlinear Wave Interactions.- 4.4.1 Four Wave Mixing Spectroscopy.- 4.4.2 Optical Phase Conjugation.- Problems.- 5. Inelastic Scattering of Light from Matter: Stimulated Raman and Brillouin Scattering.- 5.1 Quantum Theory of Raman Scattering.- 5.2 Stimulated Raman Effect.- 5.3 Contribution to Four Wave Mixing from the Raman Nonlinearity.- 5.4 Brillouin Scattering of Light.- Problems.- 6. Interaction of Atoms with Nearly Resonant Fields: Self-Induced Transparency.- 6.1 Description of the Wave Function under Near Resonant Conditions.- 6.2 Bloch Equations: Power Broadening and Saturation Effects in Absorption Spectra.- 6.3 Self-Induced Transparency.- 6.4 Area Theorem.- 6.5 Sine-Gordon Equation.- Problems.- 7. Self-Interaction Effects in One-Dimensional Wave Propagation: Solitons in Optical Fibers and in Periodic Structures.- 7.1 Normal Modes of Optical Fibers.- 7.2 Nonlinear Schroedinger Equation.- 7.3 Linear Theory of Pulse Propagation in a Dispersive Medium: Application to Optical Fibers.- 7.4 Solitons and the Nonlinear Schroedinger Equation.- 7.5 Gap Solitons in Nonlinear Periodic Structures.- Problems.- 8. Nonlinear Optical Interactions at Surfaces and Interfaces.- 8.1 Second-Harmonic Generation from Surfaces General Discussion.- 8.2 Nonlinear Optical Interactions at Surfaces and Interfaces Examples.- 8.2.1 Second-Harmonic Generation from Clean Crystal Surfaces.- 8.2.2 Second-Harmonic Generation from Adsorbate Layers on Surfaces.- 8.2.3 The Generation of Sum Frequencies from Adsorbates on Surfaces.- 8.3 Resonant Enhancement of Electromagnetic Fields Near Surfaces and Interfaces and Their Role in Surface Nonlinear Optics.- 8.3.1 Resonant Enhancement of Electric Fields Near Small Conducting Spheres.- 8.3.2 Resonant Response of a Slightly Roughened Surface to Electromagnetic Fields The Role of Surface Polaritons.- 8.3.3 Resonant Enhancement of Electromagnetic Fields Near Rough Surfaces of Conducting Media.- 8.4 Experimental Studies of Surface Enhanced Nonlinear Optical Interactions.- Problems.- 9. Optical Interactions in Magnetic Materials.- 9.1 Introductory Remarks.- 9.2 Electromagnetic Wave Propagation in Ferromagnetic Materials Faraday Rotation and the Cotton-Mouton Effect.- 9.2.1 Propagation Parallel to the Magnetization Faraday Rotation and the Kerr Effect.- 9.2.2 Propagation Perpendicular to Magnetization the Cotton-Mouton Effect.- 9.2.3 Final Remarks.- 9.3 Second-Harmonic Generation from Magnetic Materials Surface Effects.- 9.4 Dynamic Response of the Magnetization and the Origin of Nonlinear Magnetooptic Interactions.- 9.4.1 General Remarks.- 9.4.2 Collective Excitations (Spin Waves) in Magnetic Materials Ferromagnets as an Example.- 9.4.3 Surface Spin Waves on Ferromagnetic Surface the Damon-Eshbach Mode and Non Reciprocal Propagation on Magnetic Surfaces.- 9.5 Nonlinear Interaction of Light with Spin Waves in Ferromagnets.- 9.5.1 Brillouin Scattering of Light by Thermally Excited Spin Waves.- 9.5.2 Nonlinear Mixing of Light with Macroscopic Spin Waves the Magneto-optic Bragg Cell as an Example.- Problems.- 10. Chaos.- 10.1 Duffing Oscillator: Transition to Chaos.- 10.2 Routes to Chaos.- 10.3 Experimental Observations of Chaos in Optical Systems.- Problems.- Appendix A: Structure of the Wave Vector and Frequency Dependent Dielectric Tensor.- Appendix B: Aspects of the Sine-Gordon Equation.- Appendix C: Structure of the Electromagnetic Green's Functions.- References.
TL;DR: Several experimental studies of Bose-Einstein condensation in a dilute gas of sodium atoms are described, including studies of static and dynamic behavior of the condensate, and of its coherence properties.
Abstract: The possibility of creating optical fields with many photons in a single mode of a resonator was realized with the creation of the laser in 1960. The possibility of creating a matter‐wave field with many atoms in a single mode of an atom trap—the atomic equivalent of an optical resonator—was realized with the achievement of Bose–Einstein condensation (BEC) in 1995.
TL;DR: The Liquid Drop Model Approach: A Semi-Empirical Method The Simplest Independent Particle Model: The Fermi-Gas Model The Nuclear Shell Model NUCLEAR STRUCTURE: RECENT DEVELOPMENTS The Nuclear Mean Field: Single Particle Excitations and Global Nuclear Properties as discussed by the authors.
Abstract: KNOWING THE NUCLEUS: THE NUCLEAR CONSTITUENTS AND CHARACTERISTICS Global Nuclear Properties General Nuclear Radioactive Decay Properties and Transmutations NUCLEAR INTERACTIONS: STRONG, WEAK AND ELECTROMAGNETIC FORCES General Methods Alpha Decay: The Strong Interaction at Work Beta Decay: The Weak Interaction at Work Gamma decay: The Electromagnetic Interaction at Work NUCLEAR STRUCTURE: AN INTRODUCTION The Liquid Drop Model Approach: A Semi-Empirical Method The Simplest Independent Particle Model: The Fermi-Gas Model The Nuclear Shell Model NUCLEAR STRUCTURE: RECENT DEVELOPMENTS The Nuclear Mean Field: Single Particle Excitations and Global Nuclear Properties The Nuclear Shell Model: Including Residual Interactions Nuclear Physics of Very Light Nuclei Collective Modes of Motion Deformation in Nuclei Nuclear Physics at the Extremes of Stability: Weakly Bound Quantum Systems and Exotic Nuclei Deep Inside the Nucleus: Subnuclear Degrees of Freedom and Beyond Outlook: The Atomic Nucleus as Part of a Larger Structure Appendices Units and Conversion Between Various unit Systems Spherical Tensor Properties Second Quantization - An Introduction References
TL;DR: In this paper, the authors provide a clear and concise introduction to the theory of general relativity, suitable for final-year undergraduate mathematics or physics students, where the emphasis is on the geometric structure of spacetime rather than the traditional coordinate-dependent approach.
Abstract: Starting with the idea of an event and finishing with a description of the standard big-bang model of the Universe, this textbook provides a clear and concise introduction to the theory of general relativity, suitable for final-year undergraduate mathematics or physics students. Throughout, the emphasis is on the geometric structure of spacetime, rather than the traditional coordinate-dependent approach. Topics covered include flat spacetime (special relativity), Maxwell fields, the energy-momentum tensor, spacetime curvature and gravity, Schwarzschild and Kerr spacetimes, black holes and singularities, and cosmology. All physical assumptions are clearly spelled out and the necessary mathematics is developed along with the physics. Exercises are provided at the end of each chapter and key ideas are illustrated with worked examples. Solutions and hints to selected problems are provided at the end of the book. This textbook will enable the student to develop a sound understanding of the theory of general relativity.
TL;DR: A short biography of Boltzmann is given in this paper, along with a short history of physics and its history in the twenty-first century, as well as a discussion of the influence of Boltmann's ideas on the science and technology of the twentieth century.
Abstract: Foreword Preface Introduction 1. A short biography of Ludwig Boltzmann 2. Physics before Boltzmann 3. Kinetic theory before Boltzmann 4. The Boltzmann equation 5. Time irreversibility and the H-theorem 6. Boltzmann's relation and the statistical interpretation of entropy 7. Boltzmann, Gibbs and equilibrium statistical mechanics 8. The problem of polyatomic molecules 9. Boltzmann's contributions to other branches of physics 10. Boltzmann as a philosopher 11. Boltzmann and his contemporaries 12. The influence of Boltzmann's ideas on the science and technology of the twentieth century Epilogue Chronologys \"A German professor's journey to Eldorado\" Appendices
TL;DR: In this paper, the first materials (Stone Age and Copper-Stone Age) and the first metals (Gold and Man-Made Plastics) have been discussed, and the physical properties of materials have been studied.
Abstract: Preface * Part I: Mechanical Properties of Materials: The First Materials (Stone Age and Copper-Stone Age). Fundamental Mechanical Properties of Materials. Mechanisms. The Bronze Age. Alloys and Compounds. Atoms in Motion. The Iron Age. Iron and Steel. Degradations of Materials (Corrosion) * Part II: Electronic Properties of Materials: The Age of Electronic Materials. Electronic Properties of Materials. Magnetic Properties of Materials. Optical Properties of Materials. Thermal Properties of Materials * Part III: Materials and the World: No Ceramics Age? From Natural Fibers to Man-Made Plastics. Gold. Economic and Environmental Considerations. What Does the Future Hold?- Appendices * Index.
TL;DR: The problem of finding two professional jobs, possibly two physics jobs, in the same geographic area is a two-body problem for women in the physics profession as discussed by the authors, and women are increasingly faced with a difficult twobody problem.
Abstract: Physicists are increasingly faced with a difficult two‐body problem—the challenge of finding two professional jobs, possibly two physics jobs, in the same geographic area. More women than ever are entering the physics profession, and they are preferentially marrying scientists. Naturally, they are seeking employment in the same region as their spouses. Yet, in most locales, it's difficult enough to find one physics position, much less a pair of them. If one of the two partners fails to find suitable employment, he or she may be forced to forgo a career in physics.