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Connecting Quarks with the Cosmos Eleven Science Questions for the New Century Committee on the Physics of the Universe Board on Physics and Astronomy Division on Engineering and Physical Sciences NATIONAL RESEARCH COUNCIL OF THE NATIONAL ACADEMIES THE NATIONAL ACADEMIES PRESS Washington, D.C. www.nap.edu
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THE NATIONAL ACADEMIES PRESS 500 Fifth Street, N.W. Washington, DC 20001 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 project was supported by Grant No. DE-FG02-00ER41141 between the National Academy of Sciences and the Department of Energy, Grant No. NAG5-9268 between the National Academy of Sciences and the National Aeronautics and Space Administration, and Grant No. PHY-0079915 between the National Academy of Sciences and the National Science Foundation. Any opinions, findings, and conclusions or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the organizations or agencies that provided support for the project. International Standard Book Number 0-309-07406-1 Library of Congress Control Number 2003100888 Additional copies of this report are available from the National Academies Press, 500 Fifth Street, N.W., Lockbox 285, Washington, DC 20055; (800) 624-6242 or (202) 334-3313 (in the Washington metropolitan area); Internet, http://www.nap.edu and Board on Physics and Astronomy, National Research Council, NA 922, 500 Fifth Street, N.W., Washington, DC 20001; Internet, http://www.national-academies.org/bpa. Cover: Artwork ©2002 by Don Dixon/cosmographica.com Copyright 2003 by the National Academy of Sciences. All rights reserved. Printed in the United States of America
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THE NATIONAL ACADEMIES Advisers to the Nation on Science, Engineering, and Medicine The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished scholars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare. Upon the authority of the charter granted to it by the Congress in 1863, the Academy has a mandate that requires it to advise the federal government on scientific and technical matters. Dr. Bruce M. Alberts is president of the National Academy of Sciences. The National Academy of Engineering was established in 1964, under the charter of the National Academy of Sciences, as a parallel organization of outstanding engineers. It is autonomous in its administration and in the selection of its members, sharing with the National Academy of Sciences the responsibility for advising the federal government. The National Academy of Engineering also sponsors engineering programs aimed at meeting national needs, encourages education and research, and recognizes the superior achievements of engineers. Dr. Wm. A. Wulf is president of the National Academy of Engineering. The Institute of Medicine was established in 1970 by the National Academy of Sciences to secure the services of eminent members of appropriate professions in the examination of policy matters pertaining to the health of the public. The Institute acts under the responsibility given to the National Academy of Sciences by its congressional charter to be an adviser to the federal government and, upon its own initiative, to identify issues of medical care, research, and education. Dr. Harvey V. Fineberg is president of the Institute of Medicine. The National Research Council was organized 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 advising the federal government. Functioning in accordance with general policies determined by the Academy, the Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in providing services to the government, the public, and the scientific and engineering communities. The Council is administered jointly by both Academies and the Institute of Medicine. Dr. Bruce M. Alberts and Dr. Wm. A. Wulf are chair and vice chair, respectively, of the National Research Council. www.national-academies.org
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COMMITTEE ON THE PHYSICS OF THE UNIVERSE MICHAEL S. TURNER, University of Chicago, Chair ERIC G. ADELBERGER, University of Washington2 ARTHUR I. BIENENSTOCK, Stanford University2 ROGER D. BLANDFORD, California Institute of Technology SANDRA M. FABER, University of California at Santa Cruz1 THOMAS K. GAISSER, University of Delaware FIONA HARRISON, California Institute of Technology JOHN P. HUCHRA, Harvard-Smithsonian Center for Astrophysics JOHN C. MATHER, NASA Goddard Space Flight Center2 JOHN PEOPLES, JR., Fermi National Accelerator Laboratory2 HELEN R. QUINN, Stanford Linear Accelerator Center R.G. HAMISH ROBERTSON, University of Washington BERNARD SADOULET, University of California at Berkeley FRANK J. SCIULLI, Columbia University DAVID N. SPERGEL, Princeton University1 HARVEY TANANBAUM, Smithsonian Astrophysical Observatory2 J. ANTHONY TYSON, Lucent Technologies FRANK A. WILCZEK, Massachusetts Institute of Technology CLIFFORD WILL, Washington University, St. Louis BRUCE D. WINSTEIN, University of Chicago EDWARD L. (NED) WRIGHT, University of California at Los Angeles2 Staff DONALD C. SHAPERO, Director JOEL R. PARRIOTT, Senior Program Officer MICHAEL H. MOLONEY, Program Officer TIMOTHY I. MEYER, Program Associate CYRA A. CHOUDHURY, Project Associate NELSON QUIÑONES, Project Assistant VAN AN, Financial Associate 1,2 Served for only phase 1 or 2 of the study (see Preface).
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BOARD ON PHYSICS AND ASTRONOMY JOHN P. HUCHRA, Harvard-Smithsonian Center for Astrophysics, Chair ROBERT C. RICHARDSON, Cornell University, Vice Chair JONATHON A. BAGGER, Johns Hopkins University GORDON A. BAYM, University of Illinois at Urbana-Champaign CLAUDE R. CANIZARES, Massachusetts Institute of Technology WILLIAM EATON, National Institutes of Health WENDY L. FREEDMAN, Carnegie Observatories FRANCES HELLMAN, University of California at San Diego KATHY LEVIN, University of Chicago CHUAN SHENG LIU, University of Maryland LINDA J. (LEE) MAGID, University of Tennessee THOMAS M. O’NEIL, University of California at San Diego JULIA M. PHILLIPS, Sandia National Laboratories BURTON RICHTER, Stanford University ANNEILA I. SARGENT, California Institute of Technology JOSEPH H. TAYLOR, JR., Princeton University KATHLEEN C. TAYLOR, General Motors Corporation THOMAS N. THEIS, IBM T.J. Watson Research Center CARL E. WIEMAN, University of Colorado/JILA Staff DONALD C. SHAPERO, Director JOEL R. PARRIOTT, Senior Program Officer ROBERT L. RIEMER, Senior Program Officer MICHAEL H. MOLONEY, Program Officer TIMOTHY I. MEYER, Program Associate CYRA A. CHOUDHURY, Project Associate PAMELA A. LEWIS, Project Associate NELSON QUIÑONES, Project Assistant VAN AN, Financial Associate
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Preface The fall 1999 meeting of the National Research Council’s (NRC’s) Board on Physics and Astronomy (BPA) featured a stimulating science session on the frontiers of research at the intersection of physics and astronomy. National Aeronautics and Space Administration (NASA) administrator Daniel Goldin attended the session and at its conclusion asked the BPA to assess the science opportunities in this interdisciplinary area and devise a plan for realizing those opportunities. Robert Eisenstein, assistant director of the National Science Foundation’s (NSF’s) Mathematical and Physical Sciences Directorate, and S. Peter Rosen, associate director for high-energy and nuclear physics at the Department of Energy (DOE), expressed their desire to work with NASA and supported the initiation of this study. The Committee on the Physics of the Universe was formed and held the first of its eight meetings in March 2000 (see Appendix A). Mr. Goldin strongly urged the BPA to finish the report in time for the recommendations to play a role in the science planning of the new administration that would be taking office in 2001. To meet that ambitious goal, the BPA decided to divide the study into two phases: a first phase to assess the science opportunities and a second phase to address the implementation of those opportunities. In carrying out the study, the BPA enlisted the help of the Space Studies Board (SSB). The charge to the committee was as follows: The committee will prepare a science assessment and strategy for this area of research at the intersection of astronomy and physics. The study will encompass astrophysical phenomena that give insight into fundamental physics as well as fundamental physics that is relevant to understanding astrophysical phenomena and the structure and evolution of the universe. The science assessment will be carried out as the first phase of the study over a period of 1 year. The assessment will summarize progress in ad-
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dressing the key research issues facing the research community and evaluate opportunities for further progress. Among the science topics to be included in the science assessment are cosmology, the creation of matter and energy at the initiation of the universe, the dark matter known to pervade the cosmos, the dark energy that appears to be causing the expansion of the universe to accelerate, additional dimensions beyond the usual three of space and one of time, strong-field gravitational physics, very-high-energy cosmic rays, neutrino astrophysics, and extreme physics at black holes and magnetized neutron stars. The second phase of the study, which will require an additional year of work, will result in a strategy for this interdisciplinary area of research. The strategy will include scientific objectives identified in the first phase along with priorities and a plan of action to implement the priorities, including ways to facilitate continued coordinated planning involving NASA, NSF, DOE, and the research community. During the first phase, the committee held one open meeting to gather input and to hear from the three sponsoring agencies about their current plans and hopes for this study. It also met twice in closed session to prepare an interim report for phase I (see Appendix A for meeting agendas). Community input was gathered during briefings at meetings of the American Astronomical Society, the American Physical Society (APS), the APS Division of Particles and Fields (DPF), the APS Division of Astrophysics and Nuclear Physics, and the APS Topical Group on Gravitation. The committee chose these divisions because the intersection between astronomy and physics largely touches on nuclear, particle, and gravitational physics. An e-mail announcement inviting public comment was widely distributed through the professional societies and their subunits. The interim phase I report contained the science assessment, which was presented in the form of 11 questions that are ripe for progress. The phase I report was released to the public on January 9, 2001, at the meeting of the American Astronomical Society. The committee began its second phase, the formulation of a strategy for addressing the 11 science questions, by soliciting ideas from the community. A call for proposals was widely circulated in the community (see Appendix B). Some 80 proposals for projects that address the scientific questions identified in the phase I report were received (see Appendix C). A series of three open meetings was held to hear about projects and ideas. The first was held in association with the April 2001 meeting of the APS; the second was held in conjunction with the June meeting of the American Astronomical Society; and the final meeting was held in Snowmass, Colorado, during the DPF’s Future of High-Energy Physics Study. Two closed
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meetings were held, one in Chicago, Illinois, and one in Irvine, California, to formulate recommendations. During the 2-year study the committee kept the BPA, SSB, and Committee on Astronomy and Astrophysics (CAA, a standing committee of the NRC) informed by means of periodic progress reports from its chair. This final report consists of the phase I report, a series of committee recommendations for realizing the science opportunities, and a new chapter (Chapter 7) devoted to how the science objectives can be addressed. It complements the NRC surveys Physics in a New Era: An Overview and Astronomy and Astrophysics in the New Millennium (both from the National Academy Press, Washington, D.C., 2001). It builds on the science priorities identified in those studies and focuses on areas at the intersection of astronomy and physics that although peripheral to each discipline separately, become important when considered in the context of both. This report, together with the physics and astronomy surveys, provides a clear and comprehensive picture of the exciting and timely science opportunities that exist in physics and astronomy as we enter a new century. The committee acknowledges BPA program staff members Don Shapero, Timothy Meyer, Michael Moloney, and Joel Parriott, whose extraordinary effort during the rigorous NRC review process enabled the committee to meet a very aggressive prepublication schedule. The committee and I also thank the NRC review coordinator for the phase I report, Martha Haynes, for her willingness to oversee the review process during the busy winter holiday season and the NRC review coordinator for the final report, Kenneth Kellerman, who worked hard to help the committee meet its ambitious schedule. I end with a personal note. The committee brought together an extraordinary group of astronomers and physicists. The great diversity in scientific backgrounds was more than balanced by an even greater interest in and appreciation of science far from the members’ own research interests. The science opportunities before us made every meeting exciting. Working with this group was a pleasure that I will long remember, and I thank the committee for its hard work and commitment to the study. Michael S. Turner, Chair Committee on the Physics of the Universe
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Acknowledgment of Reviewers This report has been reviewed in draft form by individuals chosen for their diverse perspectives and technical expertise, in accordance with procedures approved by the National Research Council’s Report Review Committee. The purpose of this independent review is to provide candid and critical comments that will assist the institution in making its published report as sound as possible and to ensure that the report meets institutional standards for objectivity, evidence, and responsiveness to the study charge. The review comments and draft manuscript remain confidential to protect the integrity of the deliberative process. We wish to thank the following individuals for their review of this report: David Arnett, University of Arizona,1,2 Jonathan Bagger, Johns Hopkins University,2 Barry Barish, California Institute of Technology,2 Gordon Baym, University of Illinois at Urbana-Champaign,1,2 Beverly Berger, Oakland University,1 John Carlstrom, University of Chicago,2 Marc Davis, University of California at Berkeley,1 Sidney Drell, Stanford Linear Accelerator Center,1 Richard Fahey, Goddard Space Flight Center,1 Wendy Freedman, Carnegie Observatories,1,2 David Gross, University of California at Santa Barbara,1 Alice Harding, Goddard Space Flight Center,1 Steve Kahn, Columbia University,2 Marc Kamionkowski, California Institute of Technology,1,2 Richard Kron, Yerkes Observatory, University of Chicago,2 Louis Lanzerotti, Lucent Technologies,1 Rene Ong, University of California at Los Angeles,2 Anneila Sargent, California Institute of Technology,1
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Peter Stetson, Dominion Astrophysical Observatory,1 Joseph H. Taylor, Jr., Princeton University,1,2 and Edward L. Wright, University of California at Los Angeles.1 Although the reviewers listed above have provided many constructive comments and suggestions, they were not asked to endorse the conclusions or recommendations, nor did they see the final draft of the report before its release. The review of this report was overseen by Martha Haynes,1 Cornell University, and Kenneth Kellermann,2 National Radio Astronomy Observatory. Appointed by the National Research Council, they were responsible for making certain that an independent examination of this report was carried out in accordance with institutional procedures and that all review comments were carefully considered. Responsibility for the final content of this report rests entirely with the authoring committee and the institution. 1,2 Participated in the review for phase 1 or phase 2 of the study or both.
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Dedication The Committee on the Physics of the Universe dedicates this report to a dear friend and valued colleague, David N. Schramm. His vision, research, enthusiasm, and energy helped to open this blossoming area of research, and his strong voice helped bring it to the attention of astronomers and physicists alike. Reproduced below is a viewgraph in his own hand that concisely summarized his vision.
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Contents Executive Summary 1 1 Introduction: Where We Are and Where We Can Be 9 2 Foundations: Matter, Space, and Time 15 Background, 15 Physics of Matter: The Standard Model and Beyond, 16 Physics of Space and Time: Relativity and Beyond, 34 The Convergence of Matter and Space-Time Physics, 37 3 How Are Matter, Space, and Time Unified? 43 Looking for Signatures of Unification, 44 Unification and the Identity of Dark Matter, 53 Examining the Foundations of Unification, 55 New Opportunities, 58 4 How Did the Universe Get Going? 60 Big Bang Cosmology: The Basic Model, 60 Refining the Big Bang: The Inflationary Paradigm, 63 How Did the Universe Get Its Lumps?, 65 The Origin of Matter: Why Are We Here?, 72 Gravitational Waves: Whispers from the Early Universe, 73 Even Before Inflation: The Initial Conditions, 76 New Opportunities, 77 5 What Is the Nature of Dark Matter and Dark Energy? 78 An Emerging Cosmic Recipe, 78 Exotic Dark Matter, 87 Dark Energy, 95
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Two Major Challenges: Deciphering Dark Matter and Dark Energy, 98 New Opportunities, 102 6 What Are the Limits of Physical Law? 105 Extreme Cosmic Environments, 106 New Challenges in Extreme Astrophysics, 112 New Opportunities, 129 7 Realizing the Opportunities 132 The Eleven Questions, 133 Understanding the Birth of the Universe, 140 Understanding the Destiny of the Universe, 144 Exploring the Unification of the Forces from Underground, 148 Exploring the Basic Laws of Physics from Space, 153 Understanding Nature’s Highest-Energy Particles, 157 Exploring Extreme Physics in the Laboratory, 160 Striking the Right Balance, 162 Recommendations, 164 Appendixes A Meeting Agendas, 175 B Call for Community Input, 185 C Project Proposals Received, 187 D Glossary and Acronyms, 191