A Brief History of Time - Stephen Hawking

Chapter 1 - Our Picture of the Universe
Chapter 2 - Space and Time
Chapter 3 - The Expanding Universe
Chapter 4 - The Uncertainty Principle
Chapter 5 - Elementary Particles and the Forces of Nature
Chapter 6 - Black Holes
Chapter 7 - Black Holes Ain't So Black
Chapter 8 - The Origin and Fate of the Universe
Chapter 9 - The Arrow of Time
Chapter 10 - Wormholes and Time Travel
Chapter 11 - The Unification of Physics
Chapter 12 - Conclusion
Glossary
Acknowledgments & About The Author
 
 
FOREWARD
I didn’t write a foreword to the original edition of A Brief History of Time. That was done by Carl Sagan. Instead,
I wrote a short piece titled “Acknowledgments” in which I was advi\
sed to thank everyone. Some of the
foundations that had given me support weren’t too pleased to have bee\
n mentioned, however, because it led to
a great increase in applications.
I don’t think anyone, my publishers, my agent, or myself, expected th\
e book to do anything like as well as it did.
It was in the London Sunday Times best-seller list for 237 weeks, longer than any other book (apparently,\
the
Bible and Shakespeare aren’t counted). It has been translated into s\
omething like forty languages and has sold
about one copy for every 750 men, women, and children in the world. As N\
athan Myhrvold of Microsoft (a
former post-doc of mine) remarked: I have sold more books on physics th\
an Madonna has on sex.
The success of A Brief History indicates that there is widespread interest in the big questions like: W\
here did
we come from? And why is the universe the way it is?
I have taken the opportunity to update the book and include new theoreti\
cal and observational results obtained
since the book was first published (on April Fools’ Day, 1988). I h\
ave included a new chapter on wormholes
and time travel. Einstein’s General Theory of Relativity seems to off\
er the possibility that we could create and
maintain wormholes, little tubes that connect different regions of space\
-time. If so, we might be able to use
them for rapid travel around the galaxy or travel back in time. Of cours\
e, we have not seen anyone from the
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future (or have we?) but I discuss a possible explanation for this.
I also describe the progress that has been made recently in finding “\
dualities” or correspondences between
apparently different theories of physics. These correspondences are a st\
rong indication that there is a complete
unified theory of physics, but they also suggest that it may not be poss\
ible to express this theory in a single
fundamental formulation. Instead, we may have to use different reflectio\
ns of the underlying theory in different
situations. It might be like our being unable to represent the surface o\
f the earth on a single map and having to
use different maps in different regions. This would be a revolution in o\
ur view of the unification of the laws of
science but it would not change the most important point: that the unive\
rse is governed by a set of rational laws
that we can discover and understand.
On the observational side, by far the most important development has bee\
n the measurement of fluctuations in
the cosmic microwave background radiation by COBE (the Cosmic Backgroun\
d Explorer satellite) and other
collaborations. These fluctuations are the finger-prints of creation, ti\
ny initial irregularities in the otherwise
smooth and uniform early universe that later grew into galaxies, stars, \
and all the structures we see around us.
Their form agrees with the predictions of the proposal that the universe\
has no boundaries or edges in the
imaginary time direction; but further observations will be necessary to \
distinguish this proposal from other
possible explanations for the fluctuations in the background. However, w\
ithin a few years we should know
whether we can believe that we live in a universe that is completely sel\
f-contained and without beginning or
end.
Stephen Hawking
 
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CHAPTER 1
OUR PICTURE OF THE UNIVERSE
 
A well-known scientist (some say it was Bertrand Russell) once gave a \
public lecture on astronomy. He
described how the earth orbits around the sun and how the sun, in turn, \
orbits around the center of a vast
collection of stars called our galaxy. At the end of the lecture, a litt\
le old lady at the back of the room got up and
said: “What you have told us is rubbish. The world is really a flat p\
late supported on the back of a giant
tortoise.” The scientist gave a superior