The Fabric of the Cosmos - Space, Time, and the Texture of Reality (Brian Greene)

The Fabric of the Cosmos - Space, Time, and the Texture of Reality (Brian Greene)

(Parte 1 de 10)


Copyright O 2004 by Brlan R. Greene

All rights resented under International and PanAmerican Copyright Conventions. Published In the Unlted States by Alfred A. Knopf, a divmon of Random House, Inc., New York, and In Canada by Random Souse of Canada Limited, Toronto. Distributed by

Random House, Inc., New York.

Knopf, Borzo~ Books, and the colophon are registered trademarks of Random House, Inc.

Library of Congress Catalog~ng-in-Publication Data

Greene, B. (Brlan).

The fabr~c of the cosmos . space, tlme, and the texture of reality 1

Brran Greene. p. cm.

Includes bibliographical references (p. 543-4). ISBY 0-375-41288-3 1. Cosmology-Popular works. I. Title. QB982.G742004 523.1-dci2 2003058918

To Tracy

Manufactured In the United States of Amer~ca Fmt Edlt~on




1. Roads to Reality Space, Time, and Why Thmgs Are as They Are

2. The Universe and the Bucket Is Space a Human .%bstractton or a Physlcal Enttfy?

3 Relativity and the Absolute

Is Spacetzme an Einsteznian Abstraction or a Physical Entzt)..?

4. Entangling Space '\\'hat Does It Mean to Be Separate zn a Quantum Unwerse!


5. The Frozen River Does Time Flow!

6. Chance and the Arrow Does Time Have a Direction?

7. Time and the Quantum Insights into Time's Nature fion2 the Quantum Realm viii Contents


8. Of Snowflakes and Spacetime Symmetry and the Evolution of the Cosmos

9. Vaporizing the Vacuum Heat, Nothzngness, and Unificatzon

10. Deconstructing the Bang What Banged?

1. Quanta in the Sky with Diamonds Inflation, Quantum Jitters, and the L4rrow ofTime


12. The World on a String The Fabnc Accordmg to String Theory

13. The Universe on a Brane Speculatzons on Space and Time zn M-Theov


14. Up in the Heavens and Down in the Earth Experimenting wth Space and Time

15. Teleporters and Time Machines Traveling Through Space and Time

16. The Future of an Allusion Prospects for Space and Time

Notes Glossary Sz~ggestions for Further Reading Index


Space and time capture the imagination like no other scientific subject. For good reason. They form the arena of reality, the very fabric of the cos- mos. Our entire existence-everything we do, think, and experience- takes place in some region of space during some interval of time. Yet science is still struggling to understand what space and time actually are. Are they real physical entities or simply useful ideas? If they're real, are they fundamental, or do they emerge from more basic constituents? What does it mean for space to be empty? Does time have a beginning? Does it have an arrow, flowing inexorabiy from past to future, as common ex- perience would indicate? Can we manipulate space and time? In this book, we follow three hundred years of passionate sc~entific investigation seeking answers, or at least glimpses of answers, to such basic but deep questions about the nature of the universe.

Our journey also brings us repeatedly to another, tightly related ques- tion, as encompassing as it is elusive: What is reali~? We humans only have access to the internal experiences of perception and thought, so how can we be sure they truly reflect an externai world? Philosophers have long recognized this problem. Filmmakers have popularized it through story lines involving artificial worlds, generated by finely tuned neurolog- ical stimulation that exist solely within the minds of their protagonists. And physicists such as myself are acuteiy aware that the reality we observe-matter evolving on the stage of space and time-may have little to do with the reality, if any, that's out there. Nevertheless, because obser- vations are all we have, we take them seriously. We choose hard data and the framework of mathematics as our guides, not unrestrained imagina- tion or unrelenting skepticism, and seek the simplest yet most wide-reach- ing theories capable of explaining and predicting the outcome of today's and future experiments. This severely restricts the theories we pursue. (In this book, for example, we won't find a hint that I'm floating in a tank, x Preface connected to thousands of brain-stimulating wires, making me merely think that I'm now writing this text.) But during the last hundred years, discoveries in physics have suggested revisions to our everyday sense of reality that are as dramatic, as mind-bending, and as paradigm-shaking as the most imaginative science fiction. These revolutionary upheavals will frame our passage through the pages that follow.

Many of the questions we explore are the same ones that, in various guises, furrowed the brows of Aristotle, Galileo, Newton, Einstein, and countless others through the ages. And because this book seeks to convey science in the making, we follow these questions as they've been declared answered by one generation, overturned by their successors, and refined and reinterpreted b!; scientists in the centuries that followed.

For example, on the perpiexing question of whether completely empty space is, like a blank canvas, a real entity or merely an abstract idea, we follow the penduium of scientific opinion as it swings between Isaac Newton's seventeenth-century declaration that space is real, Ernst Mach's conclusion in the nineteenth century that it isn't, and Einstein's hventieth-century dramatic reformulation of the question itself, in which he merged space and time, and largely refuted Mach. We then encounter subsequent discoveries that transformed the question once again by redefining the meaning of "empty," envisioning that space is unavoidably suffused with what are called quantum fields and possibly a diffuse uni- form energy called a cosmological constant-modern echoes of the old and discredited notion of a space-filling aether. What's more, we then describe how upcoming space-based experiments may confirm particular features of Mach's conclusions that happen to agree with Einstein's gen- eral relativity, illustrating well the fascinating and tangled web of scien- tific development.

In our own era we encounter inflationary cosmology's gratifying insights into time's arrorv, string theory's rich assortment of extra spatial dimensions, hI-theory's radical suggestion that the space we inhabit may be but a sliver floating in a grander cosn~os, and the current wild specula- tion that the universe we see may be nothing more than a cosmic holo- gram. We don't yet know if the more recent of these theoretical proposals are right. But outrageous as they sound, we take them seriously because they are where our dogged search for the deepest laws of the universe leads. Not only can a strange and unfamiliar reality arise from the fertile imagination of science fiction, but one may also emerge from the cutting- edge findings of modern physics.

Preface x 1

The Fabric ojthe Cosmos is intended primarily for the general reader who has little or no formal training in the sciences but whose desire to understand the workings of the universe provides incentive to grapple with a number of con~plex and challenging concepts. As in my first book, The Elegant Universe, I've stayed close to the core scientific ideas throughout, bvhile stripping away the mathematical details in favor of metaphors, analogies, stories, and illustrations. When we reach the book's most difficult sections, I forewarn the reader and provide brief summaries for those who decide to skip or skim these more involved discussions. In this way, the reader should be able to walk the path of discovery and gain not just knowledge of physics' current worldview, but an understanding of how and why that worldview has gained prominence.

Students, avid readers of general-level science, teachers, and profes- sionals should also find much of interest in the book. Although the initial chapters cover the necessary but standard background material in relativ- ity and quantum mechanics, the focus on the corporeality of space and time is somewhat unconventional in its approach. Subsequent chapters cover a wide range of topics-Bell's theorem, delayed choice experi- ments, quantum measurement, accelerated expansion, the possibilib of producing black holes in the next generation of particle accelerators, fan- ciful worn~hole time machines, to name a few-and so will bring such readers up to date on a number of the most tantalizing and debated advances.

Some of the material I cover is controversial. For those issues that remain up in the air, I've discussed the leading viewpoints in the main text. For the points of contention that I feel have achieved more of a con- sensus, I've relegated differing viewpoints to the notes. Some scientists, especially those holding minority views, may take exception to some of my judgments, but through the main text and the notes, I've striven for a balanced treatment. In the notes, the particularly diligent reader will also find more complete explanations, clarifications, and caveats relevant to points I've simplified, as well as (for those so inclined) brief mathematical counterparts to the equation-free approach taken in the main text. A short glossary provides a reference for some of the more specialized sci- entific terms. Even a book of this length can't exhaust the vast subject of space and time. I've focused on those features I find both exciting and essential to forming a full picture of the reality painted by modern science. No doubt, many of these choices reflect personal taste, and so I apologize to those

~ x!i Preface who feel their own work or favorite area of study is not given adequate attention.

While writing The Fabric ofthe Cosmos, I've been fortunate to receive valuable feedback from a number of dedicated readers. Raphael Kasper, Lubos Motl, David Steinhardt, and Ken Vineberg read various versions of the entire manuscript, sometimes repeatedly, and offered numerous, detailed, and insightful suggestions that substantially enhanced both the clarity and the accuracy of the presentation. I offer them heartfelt thanks. David Albert, Ted Baltz, Nicholas Boles, Tracy Day, Peter Demchuk, Richard Easther, Anna Hall, Keith Goldsmith, Shelley Goidstein, Michael Gordin, Joshua Greene, Arthur Greenspoon, Gavin Guerra, Sandra Kauffman, Edward Kastenmeier, Robert Krulwich, Andrei Linde, Shani Offen, Maulik Parikh, Michael Popowits, Mariin Scully, John Stachel, and Lars Straeter read all or part of the manuscript, and their comments were extremeiy useful. I benefited from conversations with Andreas Albrecht, Michael Bassett, Sean Carrol, Andrea Cross, Rita Greene, Alan Guth, Mark Jackson, Daniel Kabat, Will Kinney, Justin Khoury, Iiiranya Peiris, Saul Perimutter, Koenraad Schalm, Paul Stein- hardt, Leonard Susskind, Neil Turok, Henry Tye, William V7armus, and Eiick Weinberg. I owe special thanks to Raphael Gunner, whose keen sense of the genuine argument and whose willingness to critique various of my attempts proved invaluable. Eric Martinez provided critical and tireless assistance in the production phase of the book, and Jason Severs did a stellar job of creating the illustrations. I thank my agents, Katinka Matson and John Brockman. And I owe a great debt of gratitude to my editor, Marty Asher, for providing a wellspring of encouragement, advice, and sharp insight that substantially improved the qualit). of the presen- tation.

During the course of my career, my scientific research has been funded by the Department of Energy, the Nationai Science Foundation, and the Alfred P. Sloan Foundation. I gratefully acknowledge their sup- port.

(Parte 1 de 10)