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I Summary of Principal Recommendations
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This brief section summarizes the findings and principal recommen- dations of this report for each of the fields studied. The basis of the recommendations is solely scientific merit. We asked: what are cur- rently the most important questions, and the most promising ways to get answers? Cost considerations played a major role only when comparing various approaches to a single scientific question. Recommendations such as these tend to focus on large new facilities and to understate the importance of ongoing research by individuals and small groups. It is important to keep in mind that the ideas and basic research of small groups constitute the core of physics research in this country a highly successful enterprise. Indeed, only out of these studies grow the initiatives and needs for large facilities. We wish to emphasize that U.S. research in each of the fields surveyed in this report is of high caliber. In implementing any of these recommenda- tions care should be taken that productive ongoing work remains healthy. Additional recommendations appear at the end of Parts II, III, and IV of this report. The scientific perspective and justification for these recommendations are presented in the sections titled Highlights and Opportunities. RECOMMENDATIONS ON GRAVITATIONAL PHYSICS Space Program in Gravitation In the last two decades gravitation has evolved from a predomi- nantly theoretical subject to a state where experimental work is making substantial contributions. Several erects predicted by general relativ- ity have been checked experimentally and found to agree with theory to better than 1 percent accuracy. Also, basic assumptions such as the metric nature of gravity and the equivalence principle have been tested experimentally with high accuracy. Much of this rapid experimental progress is due to the careful application of space techniques to
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4 S UMMAR Y OF PRINCIPA f RECOMMENDA TIONS precision solar-system measurements; we are fortunate that the Na- tional Aeronautics and Space Administration (NASA) has recognized its special capabilities for experimental gravitation research. Noting that much fundamental work still remains, we recommend that NASA pursue a vigorous gravitational-physics program in the years ahead in order to maintain U.S. leadership in this fundamental area of physics. · Test for "magnetic" gravitation Relativity gyroscope experiment (Gravity Probe B) · Improve solar-system tests Improve laser and radar ranging to the Moon and planets Improve accuracy of ranging to future planetary spacecraft · Study ideas at frontiers Millihertz gravity waves and second-order tests Ground-Based Studies in Gravitation Most ground-based research in gravitation is focused on the detec- tion of gravitational waves. These difficult experiments are driven by the need to test a basic prediction of general relativity and by the hope to one day have an entirely new technique for exploring fundamental processes such as gravitational collapse. The National Science Foun- dation (NSF) has played an important role in fostering this work and is currently considering a major initiative a Long-Baseline Gravitation- al-Wave Facility. We have studied this idea and enthusiastically en- dorse it, assuming that other ongoing work of high quality will not be adversely affected. We recommend that the NSF enhance its leader- ship in gravitation research by funding the Long-Baseline Facility, while continuing to support a vigorous program to search for gravita- tional waves with resonant bar detectors. Extend the search for gravity waves Build 5-km-baseline interferometers (10 Hz to 10 kHz) Improve resonant bars Gravitation Theory Theory plays a uniquely important role in gravitation. By exploring a wide range of theoretical possibilities it guides the field, pointing experimenters to the key questions. Currently, fundamental questions are being asked with important connections with other areas of physics and with mathematics. We urge that a healthy level of activity be fostered in this essential part of gravitation research.
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SUMAdAR Y OF PRINCIPAL RECOMMENDATIONS 5 · Maintain and strengthen a healthy, productive program · Foster natural links to other areas of physics and to pure mathe- matics RECOMMENDATIONS ON COSMOLOGY Space Program in Cosmology We are in a period of great excitement for cosmology. Our under- standing of the physics of diverse cosmological epochs and processes is undergoing fundamental changes, and our meager data base is growing rapidly. Much of this growth is traceable to the highly suc- cessful U.S. space program. Besides providing unique observations from satellites, space-inspired technology has greatly enhanced the capabilities of ground-based telescopes. Looking ahead cosmologists can anticipate a decade of fascinating new data from a wide spectral range. We endorse NASA's forward-looking program and hope that the following missions of great importance to cosmology can be started soon. · Space initiatives important to cosmology Advanced X-Ray Astrophysics Facility, Space Infrared Telescope Facility, Large Deployable Reflector Ground-Based Studies in Cosmology Astronomical telescopes have told us most of what we know about the universe, and cosmology has much to gain from the major ground-based instruments recommended by the Astronomy Survey Committee.* They will provide extreme resolution (the Very Long Baseline Array) and a much deeper view into the visible universe (the National New Technology Telescope). Recent applications of particle- physics theory to cosmology make the Superconducting Super Collider (recommended in the report of the Panel on Elementary-Particle Physics) of great interest as a probe of physics in the early universe. We wish to take note of the importance of these facilities to cosmology. * Astronomy Survey Committee, National Research Council (G. B. Field, chairman) Astronomy and Astrophysics for the 1980's (National Academy Press, Washington, D.C., 1982).
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6 SUMMARY OF PRINCIPAL RECOMMENDATIONS · Major ground-based facilities important to cosmology Very Long Baseline Array National New Technology Telescope Superconducting Super Collider · Maintain high quality of U.S. astronomy and astrophysics Growth in Cosmology Research As a rapidly growing field, drawing on many areas of physics and astronomy, cosmology has outstripped its scattered funding base. The multidisciplinary character of the field needs to be recognized and fostered. We urge the NSF to find ways to address these problems. · Restructure support New funding for growing opportunities in cosmology Foster groups with diverse expertise RECOMMENDATIONS ON COSMIC-RAY PHYSICS Space Program in Cosmic Rays Galactic cosmic rays provide a direct sample of material from out- side the solar system, while solar energetic particles provide a sample of material from the Sun and the low-energy anomalous component of cosmic rays probably provides a sample of the local interstellar medium. All these energetic particles are evidence of processes in nature that accelerate particles to relativistic energies. We recommend that NASA continue a vigorous program of extended cosmic-ray observations in space in order to measure the elemental and isotopic composition of cosmic rays over a wide range of energies; measure electrons, positrons, and antiprotons; and search for heavier antimat- ter. These observations will address questions of nucleosynthesis and galactic chemical evolution, astrophysical particle acceleration, and the particle/antiparticle asymmetry of the universe. · Particle Astrophysics Magnet Facility Superconducting magnetic spectrometer on the Space Station · Cosmic Ray Explorer Spacecraft outside the magnetosphere measuring low-energy galactic cosmic rays, solar energetic particles, and anomalous cosmic rays
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S UMMAR Y OF PRINCIPA ~ RECOMMENDA TI ONS 7 Ground-Based Cosmic-Ray Studies The search for the origin of high-energy cosmic rays has long been a major goal of cosmic-ray physics. Observations with ground-based cosmic-ray shower detectors of multi-Ted gamma rays from sources such as Cygnus X-3 have provided a first glimpse of specific sources of cosmic rays. Evidence is fragmentary at present but very exciting. Order-of-magnitude improvements in detection of these signals would allow direct study of particle accelerators at work in nature. On another front, ongoing construction and operation of large under- ground detectors (originally motivated by the search for proton decay) constitutes a new level of sophistication and collecting power in the study of cosmic-ray muons and neutrinos. At the same time these detectors make possible more-sensitive searches for possible new particles and for neutrinos of extraterrestrial origin. Meanwhile the Fly's Eye detector in Utah is collecting unique data on the highest- energy cosmic rays (above 10'9 eV). · New and improved detectors for gamma-ray astronomy in the multi-Ted range 0 Continued support of the Fly's Eye and of large underground detectors
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