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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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Representative terms from entire chapter:
principal recommendations
