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PHYSICS THROUGH THE 1990s
Gravitation,
Cosmology, and
Cosmic-Ray Physics
Pane} on Gravitation, Cosmology,
and Cosmic-Ray Physics
Physics Survey Committee
Board on Physics and Astronomy
Commission on Physical Sciences,
Mathematics, and Resources
National Research Council
NATIONAL ACADEMY PRESS
Washington, D.C. 1986
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NATIONAL ACADEMY PRESS 2101 Constitution Avenue, NW Washington, DC 20418
NOTICE: The project that is the subject of this report was approved by the Governing
Board of the National Research Council, whose members are drawn from the councils of
the National Academy of Sciences, the National Academy of Engineering, and the
Institute of Medicine. The members of the committee responsible for the report were
chosen for their special competences and with regard for appropriate balance.
This report has been reviewed by a group other than the authors according to
procedures approved by a Report Review Committee consisting of members of the
National Academy of Sciences, the National Academy of Engineering, and the Institute
of Medicine.
The National Research Council was established by the National Academy of Sciences
in 1916 to associate the broad community of science and technology with the Academy's
purposes of furthering knowledge and of advising the federal government. The Council
operates in accordance with general policies determined by the Academy under the
authority of its congressional charter of 1863, which establishes the Academy as a
private, nonprofit, self- governing membership corporation. The Council has become the
principal operating agency of both the National Academy of Sciences and the National
Academy of Engineering in the conduct of their services to the government, the public,
and the scientific and engineering communities. It is administered jointly by both
Academies and the Institute of Medicine. The National Academy of Engineering and the
Institute of Medicine were established in 1964 and 1970, respectively, under the charter
of the National Academy of Sciences.
The Board on Physics and Astronomy is pleased to acknowledge generous support for
the Physics Survey from the Department of Energy, the National Science Foundation,
the Department of Defense, the National Aeronautics and Space Administration, the
Department of Commerce, the American Physical Society, Coherent (Laser Products
Division), General Electric Company, General Motors Foundation, and International
Business Machines Corporation.
Library of Congress Cataloging-in-Publication Data
Main entry under title:
Gravitation, cosmology, and cosmic-ray physics.
(Physics through the 1990s)
Includes index.
1. Gravitation. 2. Cosmology. 3. Cosmic rays.
I. National Research Council (U.S.). Panel on
Gravitation, Cosmology, and Cosmic-Ray Physics.
II. Series.
QC178.G64 1986 531'.14 85-32019
ISBN 0-309-03579-1
Printed in the United States of America
First Printing, March 19 86
Second Printing, August 1986
Third Printing, August 1987
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PANEL ON GRAVITATION, COSMOLOGY, AND
COSMIC-RAY PHYSICS
DAVID T. WILKINSON, Princeton University, Chairman
PETER L. BENDER, University of Colorado
DOUGLAS M. EARDLEY, University of California, Santa Barbara
THOMAS K. GAISSER, University of Delaware
JAMES B. HARTLE, University of California, Santa Barbara
MARTIN H. ISRAEL, Washington University
LAWRENCE W. JONES, University of Michigan
R. BRUCE PARTRIDGE, Haverford College
DAVID N. SCHRAMM, The University of Chicago
IRWIN I. SHAPIRO, Harvard-Smithsonian Center for Astrophysics
ROBERT F. C. VESSOT, Harvard-Smithsonian Center for
Astrophysics
ROBERT V. WAGONER, Stanford University
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PHYSICS SURVEY COMMITTEE
WILLIAM F. BRINKMAN, Sandia National Laboratories, Chairman
JOSEPH CERNY, University of California, Berkeley, and Lawrence
Berkeley Laboratory
RONALD c. DAVIDSON, Massachusetts Institute of Technology
JOHN M. DAWSON, University of California, Los Angeles
MILDRED s. DRESSEEHAUS, Massachusetts Institute of Technology
VAL L. FITCH, Princeton University
PAUL A. FLEURY, AT&T Bell Laboratories
WILLIAM A. FOWLER, w. K. Kellogg Radiation Laboratory
THEODOR w. HANSCH, Stanford University
VINCENT JACCARINO, University of California, Santa Barbara
DANIEL KEEPPNER, Massachusetts Institute of Technology
AEEXE! A. MARADUDIN, University of California, Irvine
PETER D. MACD. PARKER, Yale University
MARTIN L. PERK, Stanford University
WATT w. WEBB, Cornell University
DAVID T. WILKINSON, Princeton University
DONALD c. SHAPERO, Stay Director
ROBERT L. RIEMER, Staff Officer
CHARLES K. REED, Consultant
1V
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BOARD ON PHYSICS AND ASTRONOMY
HANS FRAUENFEEDER, University of Illinois, Chairman
FELIX H. BOEHM, California Institute of Technology
RICHARD G. BREWER, IBM San Jose Research Laboratory
DEAN E. EASTMAN, IBM T.J. Watson Research Center
JAMES E. GUNN, Princeton University
LEO P. KADANOFF, The University of Chicago
w. CARE LINEBERGER, University of Colorado
NORMAN F. RAMSEY, Harvard University
MORTON s. ROBERTS, National Radio Astronomy Observatory
MARSHALL N. ROSENBEUTH, University Of Texas at Austin
WILLIAM p. SEICHTER, AT&T Bell Laboratories
SAM B. TREIMAN, Princeton University
DONALD c. SHAPERO, Sta~Director
ROBERT L. RIEMER, Sta~O~icer
HELENE PATTERSON, Staf fAssistant
SUSAN WYATT, StaffAssistant
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COMMISSION ON PHYSICAL SCIENCES, MATHEMATICS,
AND RESOURCES
HERBERT FRIEDMAN, National Research Council, Chairman
THOMAS D. BARROW, Standard Oil Company (Retired)
ELKAN R. BLOUT, Harvard Medical School
WILLIAM BROWDER, Princeton University
BERNARD F. BURKE, Massachusetts Institute of Technology
GEORGE F. CARRIER, Harvard University
CHARLES L. DRAKE, Dartmouth College
MILDRED s. DRESSEEHAUS, Massachusetts Institute of Technology
JOSEPH L. FISHER, Office of the Governor, Commonwealth of
Virginia
JAMES c. FLETCHER, University of Pittsburgh
WILLIAM A. FOWLER, California Institute of Technology
GERHART FRIEDEANDER, Brookhaven National Laboratory
EDWARD D. GOLDBERG, Scripps Institution of Oceanography
MARY L. GOOD, Signal Research Center
J. Ross MACDONALD, University of North Carolina
THOMAS F. MALONE, Saint Joseph College
CHARLES J. MANKIN, Oklahoma Geological Survey
PERRY L. MCCARTY, Stanford University
WILLIAM D. PHILLIPS, Mallinckrodt, Inc.
ROBERT E. SIEVERS, University of Colorado
JOHN D. SPENGEER, Harvard School of Public Health
GEORGE w. WETHERIEE, Carnegie Institution of Washington
RAPHAEL G. KASPER, Executive Director
LAWRENCE E. MCCRAY, Associate Executive Director
V1
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Preface
Gravitation, cosmology, and cosmic-ray physics are often regarded
as subfields of astrophysics, as well as physics, because they are
practiced by using physical techniques in an astronomical setting.
However, this report makes no pretense of surveying all of astrophys-
ics; that enormous task was excellently done by the Astronomy Survey
Committee (George B. Field, chairman). Their report, Astronomy and
Astrophysics for the 1980's (National Academy Press, Washington,
D.C., 1982), has been widely circulated, and its recommendations are
currently being considered and implemented. We have restricted our
review to the above-named three areas of physics and astrophysics
currently of particular interest to physicists.
Gravitation was explicitly not considered in the Field report and thus
becomes a focus of this report. Cosmology has been an active area of
astronomy for 60 years, and the many successes and opportunities of
astronomical techniques are eloquently described in the Field report.
The cosmology part of this report attempts to supplement the report of
the Astronomy Survey Committee by emphasizing new results and
ideas, particularly those triggered by recent contributions from other
areas of physics. There is also some overlap between this report and
the Field report in the area of cosmic rays; however, the vast scope of
the earlier report allowed only cursory treatment. The study of cosmic
rays, developed and practiced mainly by physicists, is an appropriate
topic for the present report. Choosing which areas of astrophysics not
. .
V11
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Vlll PREFACE
to emphasize in this study was more difficult. Related areas that could
logically have been included are x-ray and gamma-ray astrophysics,
most topics in theoretical astrophysics, nuclear astrophysics, solar
physics, atomic and molecular astrophysics, and astrophysical plas-
mas. The interconnectedness of astrophysics leads to some discussion
in our report of all of these active areas. Also, reviews and recommen-
dations concerning some of these areas can be found in the Astronomy
Survey Committee report and in the reports of other panels of the
Physics Survey Committee.
In this report we have tried to characterize the fields by reporting
some recent successes (Highlights) and by discussing some open
questions that are guiding current research (Opportunities). The level
and style of the presentation were chosen assuming that the reader is
a student or a colleague not currently active in these fields. Experts will
no doubt find regrettable omissions and technical errors; we did put
clarity and perspective above completeness and detailed accuracy
when it seemed that a choice was necessary. Our hardest task, how-
ever, was to attempt to look into the future and chart a reasonable
course (Recommendations). At best one can extrapolate ahead the
most promising current research and ideas, hoping that work on this
predictable program will best facilitate discoveries and new directions.
Indeed, we wish to emphasize that all three of these research areas are
developing rapidly and that flexibility will be needed to respond
effectively to new ideas and discoveries. We expect that some of our
recommendations will appear quite foolish 10 years from now because
of unanticipated new developments.
Our activities began with the formation of the panel in September
1983. In October about 90 "Dear Colleague" letters solicited advice
from physicists and astronomers active in gravitation and cosmology.
The letters requested views on facilities or major instrumentation
needs, promising new areas, and a draft outline of this report. Based on
that advice a meeting was called in December to consider proposed
initiatives in gravitation. A list of participants and the agenda were
widely circulated before the meeting. No panel meetings were held in
cosmology or cosmic rays as responses to our solicitations did not
indicate that meetings were needed. In these areas we relied on letters
from colleagues and the comments, criticism, and advice of readers.
We are particularly indebted to an active group of expert, critical
readers. Their extensive comments on our first draft and guidance on
the recommendations have substantially affected the content and
conclusions of this report. We thank the readers: Marc Davis, Univer-
sity of California, Berkeley; Stanley Deser, Brandeis University;
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PREFACE 1X
Francis Everitt, Stanford University; George Field, Center for Astro-
physics; Alan Guth, Massachusetts Institute of Technology; Peter
Michelson, Stanford University; Ezra T. Newman, University of
Pittsburgh; James Peebles, Princeton Universiy; Jean-Paul Richard,
University of Maryland; Joseph Silk, University of California,
Berkeley; Joseph Taylor, Princeton University; Kip Thorne, California
Institute of Technology; V. K. Balasubrahmanyan, Goddard Space-
flight Center; Rainer Weiss, Massachusetts Institute of Technology;
Clifford Will, Washington University; and Gaurang B. Yodh, Univer-
sity of Maryland.
The gravitation part of this report benefits greatly from the earlier
report of the Space Science Board's Committee on Gravitational
Physics (Irwin I. Shapiro, chairman): Strategy for Space Research in
Gravitational Physics in the 1980's. Also, the authors of the cosmic-ray
portion of this report (Thomas Gaisser, Martin Israel, and Lawrence
Jones) acknowledge the assistance of the reports of NASA's Cosmic-
Ray Program Working Group (1982, 19854.
The Panel is indebted to Donald C. Shapero for providing advice and
services throughout this project and to Robert L. Riemer for oversee-
ing publication of the report. Finally, we acknowledge the assistance
and patience of Marion Fugill (Princeton), who held us together and
made order out of the chaos of many drafts of this report.
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Contents
I SUMMARY OF PRINCIPAL RECOMMENDATIONS
Recommendations on Gravitational Physics, 3
Space Program in Gravitation, 3
Ground-Based Studies in Gravitation, 4
Gravitation Theory, 4
Recommendations on Cosmology, 5
Space Program in Cosmology, 5
Ground-Based Studies in Cosmology, 5
Growth in Cosmology Research, 6
Recommendations on Cosmic-Ray Physics, 6
Space Program in Cosmic Rays, 6
Ground-Based Cosmic-Ray Studies, 7
II GRAVITATION
1 EXPERIMENTAL TESTS OF GENERAL
RELATIVITY: INTRODUCTION....
2 EXPERIMENTAL TESTS OF GENERAL
RELATIVITY: HIGHLIGHTS ......
Equivalence Principle, Eotvos to Lunar Laser
Ranging, 15
X1
11
15
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X11
CONTENTS
Gravitational Redshift, Mossbauer to Rocketborne
Maser, 17
Light Deflection, Eclipses to Radio
Interferometry, 19
Signal Retardation, Newest and Most
Accurate Test, 19
Perihelion Advance, Einstein's only Handle, 21
Changing Gravitational Constant, Solar-System
Time Versus Atomic Time, 21
Laboratory Testing of Gravitation, Searching
for the Unexpected, 22
3 EXPERIMENTAL TESTS OF GENERAL
RELATIVITY: OPPORTUNITIES . . .
Tests for "Magnetic" Gravitational Effects 24
Relativity Gyroscope Experiment, 24
Black-Hole Jets, 26
Ranging to the Moon and Inner Planets, 27
Radar Ranging, 28
Ranging to Planetary Landers and Orbiters, 28
Lunar Laser Ranging, 30
Measurement of Second-Order Solar-System
Effects, 31
Gravitational Quadrupole Moment of the Sun, 33
Systems of Compact Stars, 34
4 SEARCH FOR GRAVITATIONAL WAVES:
INTRODUCTION
Theory, 37
Sources, 38
Detectors, 40
SEARCH FOR GRAVITATIONAL WAVES:
HIGHLIGHTS.
Binary Pulsar, 42
Bar Detectors, 43
Interferometric Detectors, 44
Pulsar Timing and Millisecond Pulsars, 46
24
· ·
·
36
42
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CONTENTS Xiii
Sources of Gravitational Waves Recent
Developments, 47
6 SEARCH FOR GRAVITATIONAL WAVES:
OPPORTUNITIES .
Laser Interferometer Detector with 5-Kilometer
Baseline, 49
Bar Detector Sensitivity and Bandwidth, 52
Observations with Bar Detectors, 54
Pulsar Searches, 55
Spacecraft Tracking, 55
Space Interferometers, 56
Event Rates and Source Calculations, 57
Computation, 58
7 GRAVITATION THEORY: INTRODUCTION
8 GRAVITATION THEORY: HIGHLIGHTS
Neutron Stars, 61
Gravitational Collapse and Black Holes, 62
Quantum Particle Creation by Black Holes, 64
Quantum Effects in the Early Universe, 64
Alternative Theories, 65
Exact Solutions of the Einstein Equations, 65
Asymptotic Properties of Space-Time, 66
Numerical Relativity, 67
Emission of Gravitational Radiation, 67
The Positive Energy Theorem, 68
Quantum Field Theory in Curved Space-Time, 69
Quantum Gravity, 69
Supergravity, 71
Kaluza-Klein Theories, 71
9 GRAVITATION THEORY: OPPORTUNITIES
Classical Gravitation, Singularities, Asymptotic
Structure, 72
Quantum Gravity, 73
Astrophysical Properties of Neutron Stars and
Black Holes, 75
· ·
·
·
49
59
61
72
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Xiv CONTENTS
Computation, 77
New Kinds of Experimental Tests, 77
Communication with Other Subfields: Gravitation
Experiment, Astronomy and Astrophysics, Field
Theory and Elementary-Particle Physics, Pure
Mathematics, 78
10 RECOMMENDATIONS . .
Space Techniques, 80
Ground-Based Techniques, 81
Gravitation Theory, 81
III COSMOLOGY
11 INTRODUCTION THE STANDARD MODEL
12 HIGHLIGHTS.............
Big-Bang Nucleosynthesis, 90
Large-Scale Properties of the Universe, 92
Structure in the Universe, 94
Invisible Mass, 96
Cosmology and Grand Unification, 98
The Inflationary Universe, 99
Gravitational Lenses, 100
13 OPPORTUNITIES ...........
Observations from Space, 101
Continued Ground-Based Observations, 104
Particle Physics and Cosmology, 106
Theory, 106
14 RECOMMENDATIONS.
Space Program, 108
Ground-Based Program, 109
Human and Computational Resources, 109
. · —
IV COSMIC RAYS
15 OVERVIEW
80
.
87
90
101
108
115
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CONTENTS XV
16 HIGHLIGHTS
Nucieosynthesis, 123
Isotope Ratios, 125
Abundances of Heavy Elements, 125
Solar Neutrinos, 126
Acceleration, 127
Shock Acceleration, 128
Acceleration Fractionation, 129
Termination of Acceleration Mechanism, 130
High-Energy Gamma Rays, 13
Anomalous Component, 132
Galactic Cosmic-Ray Transport and the Interstellar
Medium, 132
Energy Dependence of Escape from Galaxy, 133
Correlation Between Anisotropy and Energy, 135
Secondaries from Light Nuclei, 135
Propagation in Galactic Halo, 136
Connection with Gamma and Radio
Astronomy, 137
High-Energy Nuclear and Particle Physics, 137
Nucleon Decay Experiments as Cosmic-Ray
Detectors, 138
NucIeus-Nucleus Collisions, 139
Cross Sections, Spectra, Anisotropies, and
Composition of Primary Cosmic Rays Above
)0~7 Electron Volts, 140
Magnetic Monopoles, 141
17 OPPORTUNITIES
Spaceborne Experiments, 143
Isotopes, 144
Galactic Cosmic-Ray Isotopes, 144; Solar-Flare
Isotopes, 145
Ultraheavy Elements, 145
High-Energy Composition and Spectra, 146
Positrons, Antiprotons, Deuterium, and 3He, 147
Antimatter, 148
Nucleus-NucIeus Interactions, 148
Solar Modulation of Cosmic Rays, 149
121
143
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Xvi CONTENTS
Ground-Based Experiments, 149
Gamma-Ray Astronomy, 149
Air-Shower Detectors, 150
Neutrino Astronomy, 151
Magnetic Monopoles, 153
Nucleon Decay Detectors, 153
Solar Neutrinos, 154
Future Opportunities, 155
Theory, 155
18 RECOMMENDATIONS. .
Spaceborne Experiments, 157
Major New Programs, 158
Continuing Programs, 159
Studies for the Future, 160
Ground-Based Experiments, 161
Gamma-Ray Astronomy, 162
Highest-Energy Cosmic Rays and Extensive Air
Showers, 162
High-Energy Neutrino Astronomy, 163
Magnetic Monopoles, 163
Large Underground Detectors, 163
Solar Neutrinos, 164
Theory, 164
INDEX
157
165
