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The Once and Future Cosmos WWW.SCIAM.COM Display until December 31, 2002 thethe onceonce andand futurefuture •Echoes from the Big Bang •Does Space Have Borders? •Parallel Universes •Energy in Empty Space? •The Fate of All Life •Dark Energy and Dark Matter $5.95 U.S. $6.50 CAN. COPYRIGHT 2002 SCIENTIFIC AMERICAN, INC. contents 2002 the once and future cosmoscosmosSCIENTIFIC AMERICAN Volume 12 Number 2 INTRODUCTION EXPANSION 2 Making Sense 22 Surveying Spacetime of Modern Cosmology with Supernovae by P. James E. Peebles by Craig J. Hogan, Robert P. Kirshner Confused about all the theories? Good. and Nicholas B. Suntzeff Exploding stars seen across immense distances show that the cosmic expansion may be accelerating—a sign that an EVOLUTION exotic form of energy could be driving the universe apart. 30 Cosmological Antigravity 4 The First Stars by Lawrence M. Krauss in the Universe The long-derided cosmological constant— by Richard B. Larson and Volker Bromm a contrivance of Albert Einstein’s—may explain changes Exceptionally massive and bright, the earliest in the expansion rate of the universe. stars changed the course of cosmic history. 40 The Quintessential Universe by Jeremiah P. Ostriker and Paul J. Steinhardt 12 The Life Cycle of Galaxies The universe has recently been commandeered by by Guinevere Kauffmann and Frank van den Bosch an invisible energy field, which is causing its expansion Astronomers are on the verge of explaining to accelerate outward. the bewildering variety of galaxies. 50 The Fate of Life in the Universe by Lawrence M. Krauss and Glenn D. Starkman Billions of years ago the universe was too hot for life to exist. Countless aeons from now, it will become so cold and empty that life, no matter how ingenious, will perish. Cone Nebula, captured in April 2002 by the Hubble Space Telescope C2 SCIENTIFIC AMERICAN THE ONCE AND FUTURE COSMOS COPYRIGHT 2002 SCIENTIFIC AMERICAN, INC. Spheres of gravitational influence, page 66 STRUCTURE DESTINY 58 Is Space Finite? by Jean-Pierre Luminet, Glenn D. Starkman and Jeffrey R. Weeks 74 A Cosmic Cartographer Conventional wisdom says the universe is infinite. by Charles L. Bennett, Gary F. Hinshaw and Lyman Page But it could be finite, merely giving the illusion The Microwave Anisotropy Probe will provide of infinity. Upcoming measurements may a much sharper picture of the early universe. finally resolve the issue. 76 Echoes from the Big Bang 66 The Universe’s by Robert R. Caldwell and Marc Kamionkowski Unseen Dimensions Scientists may soon glimpse the universe’s beginnings by Nima Arkani-Hamed, Savas Dimopoulos by studying subtle fluctuations in the cosmic and Georgi Dvali microwave background. The visible universe could lie on a membrane floating in a higher-dimensional space. 82 Exploring Our Universe The extra dimensions would help unify the and Others forces of nature and could hold parallel universes. by Martin Rees In this century cosmologists will unravel the mystery of our universe’s birth—and perhaps prove the existence of other universes as well. 88 Ripples in Spacetime by W. Wayt Gibbs LIGO, a controversial observatory for detecting gravitational waves, is coming online after eight years and $365 million. 98 Plan B for the Cosmos by João Magueijo If the new cosmology fails, what’s the backup plan? Cover illustration by Edwin Faughn; NASA/Associated Press (opposite page); Bryan Christie Design (left and above) Scientific American Special (ISSN 1048-0943), Volume 12, Number 2, 2002, published by Scientific American, Inc., 415 Madison Avenue, New York, NY 10017-1111. Copyright © 2002 by Scientific American, Inc. All rights reserved. No part of this issue may be reproduced by any mechanical, photographic or electronic process, or in the form of a phonographic recording, nor “Infinity box” may it be stored in a retrieval system, transmitted or otherwise copied for public or private use without written permission of the publisher. Canadian BN No. 127387652RT; QST No. Q1015332537. To purchase additional quantities: 1 to 9 copies: U.S. $5.95 each plus $2.00 per copy for postage creates the effect and handling (outside U.S. $5.00 P&H). Send payment to Scientific American, Dept. COSM, 415 Madison Avenue, New York, NY 10017-1111. Inquiries: Fax 212-355-0408 or telephone with mirrors, page 58 212-451-8890. Printed in U.S.A. www.sciam.com THE ONCE AND FUTURE COSMOS 1 COPYRIGHT 2002 SCIENTIFIC AMERICAN, INC. TION ® Established 1845 Confused by all those theories? Good The Once and Future Cosmos NTRODUC is published by the staff of I Scientific American, with project management by: EDITOR IN CHIEF: John Rennie making sense EXECUTIVE EDITOR: Mariette DiChristina ISSUE EDITOR: Mark Fischetti ISSUE CONSULTANT: George Musser ART DIRECTOR: Edward Bell of modern ISSUE DESIGNER: Jessie Nathans cosmology PHOTOGRAPHY EDITOR: Bridget Gerety PRODUCTION EDITOR: Richard Hunt COPY DIRECTOR: Maria-Christina Keller BY P. JAMES E. PEEBLES COPY CHIEF: Molly K. Frances COPY AND RESEARCH: Daniel C. Schlenoff, Rina Bander, Shea Dean, David Labrador his is an exciting time for cosmologists: findings are pouring in, ideas EDITORIAL ADMINISTRATOR: Jacob Lasky SENIOR SECRETARY: Maya Harty are bubbling up, and research to test those ideas is simmering away. But ASSOCIATE PUBLISHER, PRODUCTION: it is also a confusing time. All the ideas under discussion cannot possi- William Sherman bly be right; they are not even consistent with one another. How is one MANUFACTURING MANAGER: Janet Cermak to judge the progress? Here is how I go about it. µµµµµµµµµµµµµ ADVERTISING PRODUCTION MANAGER: Carl Cherebin PREPRESS AND QUALITY MANAGER: Silvia Di Placido For all the talk of overturned theories, cosmologists have firmly es- PRINT PRODUCTION MANAGER: Georgina Franco tablished the foundations of our field. Over the past 70 years we have gathered abun- PRODUCTION MANAGER: Christina Hippeli T dant evidence that our universe is expanding and cooling. First, the light from dis- CUSTOM PUBLISHING MANAGER: Madelyn Keyes-Milch tant galaxies is shifted toward the red, as it should be if space is expanding and gal- ASSOCIATE PUBLISHER/VICE PRESIDENT, axies are pulled away from one another. Second, a sea of thermal radiation fills CIRCULATION: Lorraine Leib Terlecki space, as it should if space used to be denser and hotter. Third, the universe contains CIRCULATION MANAGER: Katherine Robold large amounts of deuterium and helium, as it should if temperatures were once much CIRCULATION PROMOTION MANAGER: Joanne Guralnick higher. Fourth, distant galaxies, seen as they were in the past because of light’s trav- FULFILLMENT AND DISTRIBUTION MANAGER: el time, look distinctly younger, as they should if they are closer to the time when no Rosa Davis galaxies existed. Finally, the curvature of spacetime seems to be related to the ma- PUBLISHER: Bruce Brandfon terial content of the universe, as it should be if the universe is expanding according ASSOCIATE PUBLISHER: Gail Delott to the predictions of Einstein’s gravity theory, the general theory of relativity. SALES DEVELOPMENT MANAGER: David Tirpack SALES REPRESENTATIVES: Stephen Dudley, That the universe is expanding and cooling is the essence of the big bang theo- Hunter Millington, Stan Schmidt, Debra Silver ry. You will notice I have said nothing about an “explosion”—the big bang theory ASSOCIATE PUBLISHER, STRATEGIC PLANNING: describes how our universe is evolving, not how it began. Laura Salant I compare the process of establishing such compelling results, in cosmology or PROMOTION MANAGER: Diane Schube RESEARCH MANAGER: Aida Dadurian any other science, to the assembly of a framework. We seek to reinforce each piece PROMOTION DESIGN MANAGER: Nancy Mongelli of evidence by adding cross bracing from diverse measurements. Our framework GENERAL MANAGER: Michael Florek for the expansion of the universe is braced tightly enough to be solid. The big bang BUSINESS MANAGER: Marie Maher theory is no longer seriously questioned; it fits together too well. Even the most rad- MANAGER, ADVERTISING ACCOUNTING AND COORDINATION: Constance Holmes ical alternative—the latest incarnation of the steady state theory—does not dispute that the universe is expanding and cooling. You still hear differences of opinion in DIRECTOR, SPECIAL PROJECTS: Barth David Schwartz cosmology, to be sure, but they concern additions to the solid part. MANAGING DIRECTOR, SCIENTIFICAMERICAN.COM: Mina C. Lux For example, we do not know what the universe was doing before it was ex- DIRECTOR, ANCILLARY PRODUCTS: Diane McGarvey panding. A leading theory, inflation, is an attractive addition to the framework, but PERMISSIONS MANAGER: Linda Hertz it lacks cross bracing. That is precisely what cosmologists are now seeking. If mea- MANAGER OF CUSTOM PUBLISHING: Jeremy A. Abbate P. JAMES E. PEEBLES is one of the world’s most distinguished cosmologists, a key player CHAIRMAN EMERITUS: John J. Hanley in the early analysis of the cosmic microwave background radiation and the bulk compo- CHAIRMAN: Rolf Grisebach PRESIDENT AND CHIEF EXECUTIVE OFFICER: sition of the universe. He has received some of the highest awards in astronomy, includ- Gretchen G. Teichgraeber ing the 1982 Heineman Prize, the 1993 Henry Norris Russell Lectureship of the Ameri- VICE PRESIDENT AND MANAGING DIRECTOR, can Astronomical Society and the 1995 Bruce Medal of the Astronomical Society of the Pa- INTERNATIONAL: Charles McCullagh VICE PRESIDENT: Frances Newburg THE AUTHOR cific. He is emeritus professor at Princeton University. 2 SCIENTIFIC AMERICAN Updated from the January 2001 issue COPYRIGHT 2002
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