Halpern P., Wesson P. Brave New Universe.. Illuminating the Darkest
Total Page：16
File Type：pdf, Size：1020Kb
BRAVE NEW UNIVERSE ILLUMINATING THE DARKEST SECRETS OF THE COSMOS PAUL HALPERN AND PAUL WESSON Joseph Henry Press Washington, D.C. Joseph Henry Press • 500 Fifth Street, NW • Washington, DC 20001 The Joseph Henry Press, an imprint of the National Academies Press, was created with the goal of making books on science, technology, and health more widely available to professionals and the public. Joseph Henry was one of the founders of the National Academy of Sciences and a leader in early American science. Any opinions, findings, conclusions, or recommendations expressed in this volume are those of the author and do not necessarily reflect the views of the National Academy of Sciences or its affiliated institutions. Library of Congress Cataloging-in-Publication Data Halpern, Paul, 1961- Brave new universe : illuminating the darkest secrets of the cosmos / by Paul Halpern and Paul Wesson.— 1st ed. p. cm. Includes bibliographical references and index. ISBN 0-309-10137-9 (hardcover : alk. paper) — ISBN 0-309-65823-3 (PDFs : alk. paper) 1. Cosmology. I. Wesson, Paul S. II. Title. QB981.H248 2006 523.1—dc22 2006004464 Cover Image © Mark Garlick/Photo Researchers, Inc. Copyright 2006 by Paul Halpern and Paul Wesson. All rights reserved. Printed in the United States of America. O, wonder! How many goodly atoms are there here! How myste- rious the dark substances and energies are! O brave new uni- verse that hath such diverse materials in it! The Cosmic Tempest (with apologies to William Shakespeare) Contents Preface vii Introduction: The Quest for Cosmic Understanding 1 1To See the World in a Grain of Sand: What We Can Observe from Earth 7 2Infinity in the Palm of Your Hand: Einstein’s Far-Reaching Vision 27 3Eternity in an Hour: The Accelerating Universe 75 4Darkness Apparent: The Hidden Stuff of the Cosmos 121 5Ever-Changing Moods: Did Nature’s Constants Evolve? 147 6 Escape Clause: Circumventing the Big Bang Singularity 173 7 What Is Real? 195 Conclusion: The Spirit of Eddington 215 Acknowledgments 235 Notes 237 Further Reading 245 Index 249 v Preface In this book the two Pauls wish to share with readers the fascination that is modern cosmology—the study of the universe. Recent years have seen monumental progress in this field, transforming it from a compendium of rough observations and general trends into a finely honed science, analyzed through statistical and computational techniques. This revolution is akin to the leap taken in weather fore- casting when meteorologists turned to detailed mathematical models and to the strides in genetics when biologists began mapping out the precise structures of chromosomes. As with other human pursuits, we can learn a lot about cosmology by looking at its puzzles and seeing how they can be solved. Archaeologists do this when they study the structure of the ancient pyramids. Musicians do it when they pore over the scores of bygone composers. Painters do it when they scrutinize the techniques of the Old Masters. Even physicians do it, when in setting out to cure an illness they develop a better understanding of what it means to be healthy. Our aim is to examine the conundrums posed by cosmology so that, through their resolution, we can obtain a deeper compre- hension of the universe. A typical example is Olbers’ paradox—the mystery of why the night sky is dark. Under what appear to be fairly simple assump- tions, the universe should be ablaze with the light from trillions of stars and galaxies, instead of the speckled black we observe. Anyone vii viii BRAVE NEW UNIVERSE with a clear mind, anyone who has been awed by the darkness of a clear night, can solve this paradox—and thus reveal deep truths about the nature of space. Delving into other basic issues offers valuable insight about additional aspects of reality: Where are the aliens? What would happen if we fell into a black hole? Was there really a Big Bang? Can matter have negative mass? Are there extra dimensions and perhaps parallel universes? Are we as humans affected by the most remote objects we see through large telescopes, such as quasars? In this book we demonstrate how even in this age of fantastic new technologies—with reams of telescopic data flooding astronomers’ computers—some of the most poignant dilemmas can be tackled through sheer reasoning. Often, one does not need fancy machines or complicated mathematics to get to the crux of a subject. An old English saying warns of the danger of not being able to see the wood for the trees. As we will show, our insights help us reveal the “solid wood” of modern cosmology. With all our grand explorations, nothing is more extraordinary than the power of the human mind. Introduction: The Quest for Cosmic Understanding I am greatly relieved that the universe is finally explainable. I was beginning to think it was me. As it turns out, physics, like a grating relative, has all the answers. Woody Allen (The New Yorker, July 28, 2003) A short time ago cosmology seemed settled in the comfy chair of complacency, confident in the apparent resolution of many of its major issues. All known data converged on a uniform chronology of cosmic history—an account so widely accepted that it had come to be known as the standard model. Every student of astronomy could recite the then-known facts: The universe began in a fiery explosion called the Big Bang and then expanded for billions of years. Over time its rate of expansion has gradually slowed and its constituent particles have come together to form galaxies, planets . and us. Eventually, depending on its material density, it will either fizzle out in a “Big Whimper” or shrink back down to an infinitesimal point in a “Big Crunch.” These options were delineated by what are technically known as the Friedmann models: simple solutions discovered by Russian cosmolo- gist Alexander Friedmann of the gravitational equations developed by Albert Einstein. The task of cosmology appeared relatively straightforward—to establish the precise age of the universe, firm up 1 2 BRAVE NEW UNIVERSE the sequence of events and reduce the possible endgames down to one. Sure there were open questions, but mainstream cosmologists saw these as refinements. Most researchers believed in a clear-cut model of the universe that had little room for change after the first few moments of its history. Much debate was centered on pinning down what happened during the initial ticks of the cosmic clock. A few of us pondered alternatives to the canon—theories of the universe that strayed from the simplest version of the Big Bang. Like the standard model, these were legitimate mathematical solutions— albeit of variations, reinterpretations, or extensions—of Einstein’s equations. Mainstream cosmologists knew about such alternatives but tended to treat them as mere curiosities. In the absence of evi- dence to the contrary, these researchers advised, why reach beyond conventional approaches? The situation was akin, in some ways, to the state of affairs be- fore the age of Johannes Kepler and Galileo Galilei. From the 2nd century until the 16th century AD, astronomy relied on the coarse measurements of planetary motion recorded by the Alexandrian thinker Claudius Ptolemy (born circa 85 AD). In his pivotal text, the Almagest, Ptolemy developed a clockwork model of the solar system that corresponded well to his data. Consisting of wheels within wheels ultimately turning around Earth, Ptolemy’s model showed how planets could follow distinct patterns as they moved across the sky. Because his scheme explained all known facts and fit in well with religious views, scholars found little reason to dispute it. True, it could be simplified, as the Polish astronomer Nicholas Copernicus pointed out, by placing the Sun at the center instead of Earth. But even Copernicus had no new data to back up his proposition. What changed matters at the turn of the 17th century—as well as at the turn of the 21st century—were substantial improvements in astronomical measuring techniques that led to an enhanced under- standing of the movements of celestial bodies. Superior naked-eye INTRODUCTION 3 measurements of the Martian orbit taken by the Danish astronomer Tycho Brahe led Kepler to conclude in 1609 that the planets follow elliptical paths around the Sun. At approximately that time, images from the first astronomical telescope inspired Galileo to propose that the planets are worlds in their own right and that the stars are distant suns. These findings, in turn, led to the Newtonian portrait of a vast, possibly infinite, universe—home to myriad celestial objects inter- acting with one another according to the law of gravity. Telescopes became larger and larger, revealing deeper layers of cosmic order. As they demonstrated, in the race across the celestial plains, stars are hardly lone rangers. Rather, they ride like horses on grand merry-go-rounds called galaxies. Galaxies belong to clusters— assembled, in turn, into even greater superclusters. In 1929, Edwin Hubble, using a colossal device on Mount Wilson in California, dis- covered that all distant galaxies are receding from each other. This finding led to the standard Big Bang model of an expanding universe—the crown jewel of 20th-century cosmology. Just as it was enhanced observations that led science to abandon the Ptolemaic model and usher in the modern age, it is the dramati- cally improved equipment and techniques that have resulted in a rethinking of the standard cosmological approach. In the 1990s and early 2000s astronomy leapt above the clouds with extraordinary new orbiting instruments. Circling high above Earth at distances ranging from hundreds to hundreds of thousands of miles, these telescopic satellites have spanned the spectrum with their light- gathering power.