STEPHEN W. HAWKING SPECIAL ANNIVERSARY EDITION

THE THEORY OF EVERYTHING THE ORIGIN AND FATE OF THE UNIVERSE

PHOENIX 5F9A4512-DBD2-4640-B53D-F3CF22FFE0A2

BOOKS  Copyright �2005 Phoenix Books First published under the title The Cambridge Lectures: Life Wo r k s Copyright � 1996 by Dove Audio, Inc.

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10 9 8 7 6 5 4  CONTENTS Introduction

FIRST LECTURE ideas about the universe . . . . . . . . . . . . . . . . . . . . . . .1

SECOND LECTURE the expanding universe . . . . . . . . . . . . . . . . . . . . . . . .13

THIRD LECTURE black holes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35

FOURTH LECTURE black holes ain't so black . . . . . . . . . . . . . . . . . . . . .57

FIFTH LECTURE the origin and fate of the universe . . . . . . . . . . . . .77

SIXTH LECTURE the direction of time . . . . . . . . . . . . . . . . . . . . . . . . .103

SEVENTH LECTURE the theory of everything . . . . . . . . . . . . . . . . . . . . .119 5F9A4512-DBD2-4640-B53D-F3CF22FFE0A2

INDEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .137 5F9A4512-DBD2-4640-B53D-F3CF22FFE0A2

INTRODUCTION  INTRODUCTION

I n this series of lectures I shall try to give an outline of what we think is the history of the universe from the big bang to black holes. In the first lecture I shall briefly review past ideas about the universe and how we got to our present picture. One might call this the history of the history of the universe.

In the second lecture I shall describe how both Newton's and Einstein's the- ories of gravity led to the conclusion that the universe could not be static; it had to be either expanding or contracting. This, in turn, implied that there must have been a time between ten and twenty billion years ago when the density of the universe was infinite. This is called the big bang. It would have been the beginning of the universe.

In the third lecture I shall talk about black holes. These are formed when a massive star or an even larger body collapses in on itself under its own gravitational pull. According to Einstein's general theory of relativity, anyone foolish enough to fall into a black hole will be lost forever. They will not be able to come out of the black hole again. Instead, history, as far as they are concerned, will come to a sticky end at a singularity. However, general relativity is a classical theory--that is, it doesn't take into account the uncertainty principle of quantum mechanics. 5F9A4512-DBD2-4640-B53D-F3CF22FFE0A2

IV  INTRODUCTION

In the fourth lecture I shall describe how quantum mechanics allows energy to leak out of black holes. Black holes aren't as black as they are painted.

In the fifth lecture I shall apply quantum mechanical ideas to the big bang and the origin of the universe. This leads to the idea that space�time may be finite in extent but without boundary or edge. It would be like the surface of the Earth but with two more dimensions.

In the sixth lecture I shall show how this new boundary proposal could explain why the past is so different from the future, even though the laws of physics are time symmetric.

Finally, in the seventh lecture I shall describe how we are trying to find a unified theory that will include quantum mechanics, gravity, and all the other interactions of physics. If we achieve this, we shall really understand the universe and our position in it. 5F9A4512-DBD2-4640-B53D-F3CF22FFE0A2

V  FIRST LECTURE IDEAS ABOUT THE UNIVERSE 5F9A4512-DBD2-4640-B53D-F3CF22FFE0A2  IDEAS ABOUT THE UNIVERSE

A s long ago as 340 B.C. Aristotle, in his book On the Heavens, was able to put forward two good arguments for believing that the Earth was a round ball rather than a flat plate. First, he realized that eclipses of the moon were caused by the Earth coming between the sun and the moon. The Earth's shad- ow on the moon was always round, which would be true only if the Earth was spherical. If the Earth had been a flat disk, the shadow would have been elon- gated and elliptical, unless the eclipse always occurred at a time when the sun was directly above the center of the disk.