An Overview Physics Through the 1990's (1986) / Chapter Skim
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2. Progress in Physics
2. Progress in Physics
Pages 11-43
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From page 11... ...
A host of experimental observations made possible by the current generation of particle accelerators and the accompanying rapid convergence of theoretical ideas have led to a radically new and simple picture of nature. All matter in its infinite diversity has been found to be composed of a few basic constituents called quarks and leptons, which are structureless and indivisible at current limits of resolution.
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Finding the answers represents an exciting frontier that may lead to more basic understanding of the strong forces and of nuclear structure and dynamics. Heavy ions have been used to probe nuclear dynamics under extreme conditions and to create new elements.
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Optical-frequency counting methods using laser light have become so precise that the meter is no longer defined in terms of the wavelength of light but as the distance light travels in a given time interval. Particle-trap techniques have led to ultraprecise studies of quantum electrodynamics and mass spectra; they have made it possible to study plasma liquids and to create new kinds of atomic clocks.
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Another example is the development of the free-electron laser, which can generate coherent radiation from microwaves to the ultraviolet. Cosmology, Gravitation, and Cosmic Rays The study of the universe is being transformed by new eyes, such as x-ray and infrared telescopes in space and very-large-array radio telescopes on the ground.
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This dramatic advance could take place in the next decade and open an important new window on the universe. Space-based studies of the enigmatic cosmic rays suggest that they originate in interstellar space, while ground-based instruments have discovered localized sources of gamma rays with 10'5 eV of energy.
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FREE ELECTRON LASERS SEMICONDUCTOR DEVICES INTEGRATED CIRCUITS, COMPUTERS. JUNCTION LASERS, OPTICAL DETECTORS SUPERCONDUCTORS HIGH-FIELD MAGNETS JOSEPHSON TECInINOLOGY MATERIALS MAGNETIC MATERIALS, OPTICAL FlaERS, QUARTZ RESONATORS LASER-QPTICS LASER SURGERY, OPTICAL COMMUNICATIONS, OPTICAL DATA PROCESSING, INTEGRATED OPTICS, LASERASSISTED PROCESSING, LASER PRINTII`IG ENVIRONMENTAL MONITORING SUPERSENSITIVE DETECTION, ANALYSIS, ATMOSPHERIC CHEMISTRY M ETROLOGY MAGNETOMETERS, ATOMIC CLOCKS, RING GYROSCOPES MAGNETIC RESONANCE IMAGING NUCLEAR POWER NUCLEAR MEDICINE RADIATION THERAPY, ISOTOPE TRACERS SYNCHROTRON LIGlIT SOURCES, DATA PROCESSING, PARTICLE DETECTORS stand physics it must be appreciated.
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Abrupt transitions from regular to chaotic behavior have been discovered in electrical, acoustical, and optical systems, in fluid flow, in chemical reactions, and in the behavior of simple differential equations. Cardiac arrest due to fibrillation of the heart is believed to be due to such an effect.
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PROGRESS IN PARTICLE PHYSICS Quarks and Leptons as Elementary Particles The longing to discover the most elementary particles in nature is deeply rooted in physics. At the beginning of this century, physicists discovered that the atom is not a single particle but that it consists of electrons moving rapidly around a central nucleus; in the 1930s, it was discovered that the nucleus is not a single particle but that it consists of protons and neutrons tightly bound together.
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The family of quarks was discovered relatively recently. There is a second family of elementary particles, the leptons, some of whose members have been known for many decades.
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carries or mediates the electromagnetic interactions, whereas the weak forces are mediated by massive charged particles called the W+ and W- and by a neutral particle called the Z°. Interactions mediated by the neutral particle, called neutral currents, have been discovered in experiments with high-energy neutrino beams and in studies of how electrons and positrons annihilate each other.
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Efforts to unify the electroweak forces and the strong force are leading to exciting new challenges in theoretical and experimental physics. Theories have been proposed predicting that the proton is not stable but will decay and that magnetic monopoles exist.
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44 =.8 ~ ~ ~ ems ~ ~ O ~ O ~ O O =.
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Other types of vibration have been predicted theoretically, and, within the past 10 years, they have been discovered experimentally. Observation of the breathing mode represents a major advance in understanding the basic properties of nuclear matter, because the measurements of the breathing mode have made it possible to determine the compressibility of nuclear matter.
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to this boson model. PROGRESS IN CONDENSED-MATTER PHYSICS During the 1950s and 1960s, physicists explored the electronic properties of crystalline solids and constructed a comprehensive picture of electron energy levels, transport mechanisms, and optical properties of most simple metals, insulators, and semiconductors.
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In this effect, the Hall conductivity that is associated with the current flowing perpendicular to both the magnetic field and the electric field is quantized in units of the square of the electron charge divided by Planck's constant. This relation appears to hold accurately irrespective of the material used.
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The most striking feature of systems near a phase change is the strong fluctuation in their properties as the new phase builds up. These fluctuations, and the singular behavior at a phase transition, are now understood in detail, and a wide variety of phase changes has been analyzed.
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PROGRESS IN ATOMIC, MOLECULAR, AND OPTICAL PHYSICS The physics of atoms, molecules, and light underlies our understanding of the world about us. Research in this area has advanced rapidly during the past decade, propelled by a host of new techniques based on lasers and nonlinear optics, by other experimental methods such as supersonic molecular beams, particle traps, clusters, and highly charged ions, and by new theoretical concepts and calculational techniques.
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From page 29... ...
These traps are also being employed in the study of collective motion in a charged plasma, in new types of atomic clocks and optical frequency standards, and in sensitive tests of the isotropy of space. The Lamb shift of hydrogen the shift in energy levels due to intrinsic fluctuations in the electromagnetic field has been measured to such high precision that the comparison between experiment and theory is now limited only by our understanding of the internal structure of the proton.
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30 PHYSICS THROUGH THE 1990s: AN OVERVIEW 1 it_ l truck z.o ions can be trapped in high vacuum, using static and oscillating electric fields, and viewed by laser light. The experiments can be so sensitive that single ions can be observed under close to ideal conditions of isolation.
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The National Magnetic Fusion Energy Computer Center, linked to the major fusion centers, has been established to pursue this research. Mastery of plasma physics at the level needed to understand fusion and space plasmas requires a complete synthesis of classical electrodynamics and nonequilibrium statistical mechanics.
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A notable advance in plasma physics is the solution to the problem of magnetic-field reconnection. This is the mechanism by which magnetic field lines reconnect on either side of a current sheet as the field dissipates.
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The tandem mirror concept, in which the electric fields are generated Flora magnetic field lines, has been introduced to suppress plasma leakage through the ends. Results point toward the possibility of mirror confinement systems adequate for fusion-reactor applications.
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The Earth has a relatively quiet magnetosphere, which we are understanding in increasing detail. For example, we are beginning to understand how the reconnection of the Earth's magnetic field lines is related to auroral activity.
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Thus, any advance in our understanding of flows, particularly turbulent and unsteady fluid flows, can be expected to have enormous technological impact. For example, recent advances in the theory of acoustic damping and turbulent flow, applied to jet noise, led to a thousandfold reduction in the acoustic energy emitted by aircraft, providing a major reduction in perceived noise levels.
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One of the most dramatic quests in gravitational physics today is the search for gravitational radiation. The radiation from known sources is predicted to be so weak that detecting it requires highly innovative experimental techniques.
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The positive energy theorem has proved that, in general relativity, any isolated system must have positive total energy. This is by no means obvious, because gravitational binding energy is negative.
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(1) At 10-35 S the strong force separates from the electroweak forces.
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CHEMISTRY The interface between physics and chemistry is among the best developed interdisciplinary areas in science. Advances in spectroscopy, including laser spectroscopy, nonlinear optics, extended x-ray absorption fine structure (EXAFS)
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Today, solid-earth geophysics is dominated by the concepts of plate tectonics. Modern seismology and innovative techniques of metrology, particularly those using lasers and atomic clocks, have made it possible to monitor terrestrial motions with
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To this effort, physics contributes fundamental theory, such as the rapidly developing theory of disordered materials. It also contributes new experimental tools, such as synchrotron light sources and the free-electron laser.
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To this task physics brings essential data, analytical techniques, and theoretical tools for monitoring the earth, the oceans, and the atmosphere. MEDICINE Physics is addressing increasingly complex problems of biophysics and physiology.
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INDUSTRY Physics contributes broadly to industry through the creation of new materials, instruments, and technologies. Beyond these, discoveries in basic research can lead to the creation of industries such as microelectronics and laser optics.
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