The Fabric Of The Cosmos By Brian Greene
Contents
Parti REALITY'S ARENA1. Roads to Reality 3
Space, Time, and Why Things Are as They Are
2. The Universe and the Bucket 23
Is Space a Human Abstraction or a Physical Entity?
3. Relativity and the Absolute 39
Is Spacetime an Einstemian Abstraction or a
Physical Entity?
4. Entangling Space 77
What Does It Mean to Be Separate in a
Quantum Universe?
Part II TIME AND EXPERIENCE
5. The Frozen River 127
Does Time Flow?
6. Chance and the Arrow 143
Does Time Have a Direction?
7. Time and the Quantum 177
Insights into Time's Nature from the Quantum Realm
Part III SPACETIMEAND COSMOLOGY
8. Of Snowflakes and Spacetime 219
Symmetry and the Evolution of the Cosmos
9, Vaporizing the Vacuum 251
Heat, Nothingness, and Unification
10. Deconstructing the Bang 272
What Banged?
11. Quanta in the Sky with Diamonds 304
Inflation, Quantum fitters, and the Arrow of Time
Part IV ORIGINS AND UNIFICATION
12. The World on a String 327
The Fabric According to String Theory
13. The Universe on a Brane 376
Speculations on Space and Time in M-Theory
PartV REALITY AND IMAGINATION
14. Up in the Heavens and Down in the Earth 415
Experimenting with Space and Time
15. Teleporters and Time Machines 437
Traveling Through Space and Time
16. The Future of an Allusion 470
Prospects for Space and Time
Notes 495
Glossary 537
Suggestions for Further Reading 543
Index 545
Preface
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 cosmos.
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 inexorably from past to future, as common experience
would indicate? Can we manipulate space and time? In this
book, we follow three hundred years of passionate scientific 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 question,
have access to the internal experiences of perception and thought, so how
as encompassing as it is elusive: What is reality'? We humans only
can we be sure they truly reflect an external world? Philosophers have
long recognized this problem. Filmmakers have popularized it through
story lines involving artificial worlds, generated by finely tuned neurological
stimulation that exist solely within the minds of their protagonists.
And physicists such as myself are acutely 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 observations
are all we have, we take them seriously. We choose hard data and
the framework of mathematics as our guides, not unrestrained imagination
or unrelenting skepticism, and seek the simplest yet most wide-reaching
theories capable of explaining and predicting the outcome of today's
and future experiments. This severely restricts the theories we pursue. (In
connected to thousands of brain-stimulating wires, making me merely
this book, for example, we won't find a hint that I'm floating in a tank,
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 by scientists in the centuries that followed.
For example, on the perplexing question of whether completely
empty space is, like a blank canvas, a real entity or merely an abstract
idea, we follow the pendulum of scientific opinion as it swings between
Mach's conclusion in the nineteenth century that it isn't, and Einstein's
Isaac Newton's seventeenth-century declaration that space is real, Ernst
twentieth-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 uniform
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 general
relativity, illustrating well the fascinating and tangled web of scientific
development.
In our own era we encounter inflationary cosmology's gratifying
insights into time's arrow, string theory's rich assortment of extra spatial
dimensions, M-theory's radical suggestion that the space we inhabit may
be but a sliver floating in a grander cosmos, and the current wild speculation
that the universe we see may be nothing more than a cosmic hologram.
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 cuttingedge
The Fabric of the Cosmos is intended primarily for the general reader
findings of modem physics.
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 complex and challenging concepts. As in my first book,
The Elegant Universe, I've stayed close to the core scientific ideas
throughout, while 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 professionals
should also find much of interest in the book. Although the initial
chapters cover the necessary but standard background material in relativity
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 experiments,
quantum measurement, accelerated expansion, the possibility of
producing black holes in the next generation of particle accelerators, fanciful
wormhole 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 consensus,
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 quick reference for some of the more specialized scientific
terms.
Even a book of this length can't exhaust the vast subject of space and
forming a full picture of the reality painted by modern science. No doubt,
time. I've focused on those features I find both exciting and essential to
who feel their own work or favorite area of study is not given adequate
many of these choices reflect personal taste, and so I apologize to those
attention.
While writing The Fabric of the 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 Goldstein,
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 extremely 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, Hiranya Peiris, Saul Perimutter, Koenraad Schalm, Paul Steinhardt,
Leonard Susskind, Neil Turok, Henry Tye, William Warmus, and
Erick 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,
During the course of my career, my scientific research has been
and sharp insight that substantially improved the quality of the presentation.
funded by the Department of Energy, the National Science Foundation,
and the Alfred P. Sloan Foundation. I gratefully acknowledge their support.
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