We each exist for but a short time, and in that time explore but a small
part of the whole universe. But humans are a curious species. We wonder,
we seek answers. Living in this vast world that is by turns kind and
cruel, and gazing at the immense heavens above, people have always asked
a multitude of questions: How can we understand the world in which we
find ourselves? How does the universe behave? What is the nature of
reality? Where did all this come from? Did the universe need a creator?
Most of us do not spend most of our time worrying about these questions,
but almost all of us worry about them some of the time.
Traditionally these are questions for philosophy, but philosophy is
dead. Philosophy has not kept up with modern developments in science,
particularly physics. Scientists have become the bearers of the torch of
discovery in our quest for knowledge. The purpose of this book is to
give the answers that are suggested by recent discoveries and
theoretical advances. They lead us to a new picture of the universe and
our place in it that is very different from the traditional one, and
different even from the picture we might have painted just a decade or
two ago. Still, the first sketches of the new concept can be traced back
almost a century.
According to the traditional conception of the universe, objects move on
well-defined paths and have definite histories. We can specify their
precise position at each moment in time. Although that account is
successful enough for everyday purposes, it was found in the 1920s that
this "classical" picture could not account for the seemingly bizarre
behavior observed on the atomic and subatomic scales of existence.
Instead it was necessary to adopt a different framework, called quantum
physics. Quantum theories have turned out to be remarkably accurate at
predicting events on those scales, while also reproducing the
predictions of the old classical theories when applied to the
macroscopic world of daily life. But quantum and classical physics are
based on very different conceptions of physical reality.
Quantum theories can be formulated in many different ways, but what is
probably the most intuitive description was given by Richard (Dick)
Feynman, a colorful character who worked at the California Institute of
Technology and played the bongo drums at a strip joint down the road.
According to Feynman, a system has not just one history but every
possible history. As we seek our answers, we will explain Feynman's
approach in detail, and employ it to explore the idea that the universe
itself has no single history, nor even an independent existence. That
seems like a radical idea, even to many physicists. Indeed, like many
notions in today's science, it appears to violate common sense. But
common sense is based upon everyday experience, not upon the universe as
it is revealed through the marvels of technologies such as those that
allow us to gaze deep into the atom or back to the early universe.
Until the advent of modern physics it was generally thought that all
knowledge of the world could be obtained through direct observation,
that things are what they seem, as perceived through our senses. But the
spectacular success of modern physics, which is based upon concepts such
as Feynman's that clash with everyday experience, has shown that that is
not the case. The naive view of reality therefore is not compatible with
modern physics. To deal with such paradoxes we shall adopt an approach
that we call model-dependent realism. It is based on the idea that our
brains interpret the input from our sensory organs by making a model of
the world. When such a model is successful at explaining events, we tend
to attribute to it, and to the elements and concepts that constitute it,
the quality of reality or absolute truth. But there may be different
ways in which one could model the same physical situation, with each
employing different fundamental elements and concepts. If two such
physical theories or models accurately predict the same events, one
cannot be said to be more real than the other; rather, we are free to
use whichever model is most convenient.
In the history of science we have discovered a sequence of better and
better theories or models, from Plato to the classical theory of Newton
to modern quantum theories. It is natural to ask: Will this sequence
eventually reach an end point, an ultimate theory of the universe, that
will include all forces and predict every observation we can make, or
will we continue forever finding better theories, but never one that
cannot be improved upon? We do not yet have a definitive answer to this
question, but we now have a candidate for the ultimate theory of
everything, if indeed one exists, called M- theory. M-theory is the only
model that has all the properties we think the final theory ought to
have, and it is the theory upon which much of our later discussion is
M-theory is not a theory in the usual sense. It is a whole family of
different theories, each of which is a good description of observations
only in some range of physical situations. It is a bit like a map. As is
well known, one cannot show the whole of the earth's surface on a single
map. The usual Mercator projection used for maps of the world makes
areas appear larger and larger in the far north and south and doesn't
cover the North and South Poles. To faithfully map the entire earth, one
has to use a collection of
maps, each of which covers a limited region. The maps overlap each
other, and where they do, they show the same landscape.
M-theory is similar. The different theories in the M-theory family may
look very different, but they can all be regarded as aspects of the same
underlying theory. They are versions of the theory that are applicable
only in limited ranges-for example, when certain quantities such as
energy are small. Like the overlapping maps in a Mercator projection,
where the ranges of different versions overlap, they predict the same
phenomena. But just as there is no flat map that is a good
representation of the earth's entire surface, there is no single theory
that is a good representation of observations in all situations.
We will describe how M-theory may offer answers to the question of
creation. According to M-theory, ours is not the only universe. Instead,
M-theory predicts that a great many universes were created out of
nothing. Their creation does not require the intervention of some
supernatural being or god. Rather, these multiple universes arise
naturally from physical law. They are a prediction of science. Each
universe has many possible histories and many possible states at later
times, that is, at times like the present, long after their creation.
Most of these states will be quite unlike the universe we observe and
quite unsuitable for the existence of any form of life. Only a very few
would allow creatures like us to exist. Thus our presence selects out
from this vast array only those universes that are compatible with our
existence. Although we are puny and insignificant on the scale of the
cosmos, this makes us in a sense the lords of creation.
To understand the universe at the deepest level, we need to know not
only how the universe behaves, but why.
Why is there something rather than nothing?
Why do we exist?
Why this particular set of laws and not some other?
This is the Ultimate Question of Life, the Universe, and Everything. We
shall attempt to answer it in this book. Unlike the answer given in The
Hitchhiker's Guide to the Galaxy, ours won't be simply "42."
The Rule of Law
Skoll the wolf who shall scare the Moon
Till he flies to the Wood-of-Woe:
Hati the wolf, Hridvitnir's kin,
Who shall pursue the sun.
-"Grimnismal," The Elder Edda
n Viking mythology, Skoll and Hati chase the sun and the moon. When the
wolves catch either one, there is an eclipse. When this happens, the
people on earth rush to rescue the sun or moon by making as much noise
as they can in hopes of scaring off the wolves. There are similar myths
in other cultures. But after a time people must have noticed that the
sun and moon soon emerged from the eclipse regardless of whether they
ran around screaming and banging on things. After a time they must also
have noticed that the eclipses didn't just happen at random: They
occurred in regular patterns that repeated themselves. These patterns
were most obvious for eclipses of the moon and enabled the ancient
Babylonians to predict lunar eclipses fairly accurately even though they
didn't realize that they were caused by the earth blocking the light of
the sun. Eclipses of the sun were more difficult to predict because they
are visible only in a corridor on the earth about 30 miles wide. Still,
once grasped, the patterns made it clear the eclipses were not dependent
on the arbitrary whims of supernatural beings, but rather governed by
Despite some early success predicting the motion of celestial bodies,
most events in nature appeared to our ancestors to be impossible to
predict. Volcanoes, earthquakes, storms, pestilences, and ingrown
toenails all seemed to occur without obvious cause or pattern. In
ancient times it was natural to ascribe the violent acts of nature to a
pantheon of mischievous or malevolent deities. Calamities were often
taken as a sign that we had somehow offended the gods. For example, in
about 4800 bc the Mount Mazama volcano in Oregon erupted, raining rock
and burning ash for years, and leading to the many years of rainfall
that eventually filled the volcanic crater today called Crater Lake. The
Klamath Indians of Oregon have a legend that faithfully matches every
geologic detail of the event but adds a bit of drama by portraying a
human as the cause of the catastrophe. The human capacity for guilt is
such that people can always find ways to blame themselves. As the legend
goes, Llao, the chief of the Below World, falls in love with the
beautiful human daughter of a Klamath chief. She spurns him, and in
revenge Llao tries to destroy the Klamath with fire. Luckily, according
to the legend, Skell, the chief of the Above World, pities the humans
and does battle with his underworld counterpart. Eventually Llao,
injured, falls back inside Mount Mazama, leaving a huge hole, the crater
that eventually filled with water.
Ignorance of nature's ways led people in ancient times to invent gods to
lord it over every aspect of human life. There were gods of love and
war; of the sun, earth, and sky; of the oceans and rivers; of rain and
thunderstorms; even of earthquakes and volcanoes. When the gods were
pleased, mankind was treated to good weather, peace, and freedom from
natural disaster and disease. When they were displeased, there came
drought, war, pestilence, and epidemics. Since the connection of cause
and effect in nature was invisible to their eyes, these gods appeared
inscrutable, and people at their mercy. But with Thales of Miletus (ca.
ca. 546 bc) about 2,600 years ago, that began to change. The idea arose
that nature follows consistent principles that could be deciphered. And
so began the long process of replacing the notion of the reign of gods
with the concept of a universe that is governed by laws of nature, and
created according to a blueprint we could someday learn to read.
Viewed on the timeline of human history, scientific inquiry is a very
new endeavor. Our species, Homo sapiens, originated in sub-Saharan
Africa around 200,000 bc. Written language dates back only to about 7000
bc, the product of societies centered around the cultivation of grain.
(Some of the oldest written inscriptions concern the daily ration of
beer allowed to each citizen.) The earliest written records from the
great civilization of ancient Greece date back to the ninth century bc,
but the height of that civilization, the "classical period," came
several hundred years later, beginning a little before 500 bc. According
to Aristotle (384 bc-322 bc), it was around that time that Thales first
developed the idea that the world can be understood, that the complex
happenings around us could be reduced to simpler principles and
explained without resorting to mythical or theological explanations.
Thales is credited with the first prediction of a solar eclipse in 585
bc, though the great precision of his prediction was probably a lucky
guess. He was a shadowy figure who left behind no writings of his own.
His home was one of the intellectual centers in a region called Ionia,
which was colonized by the Greeks and exerted an influence that
eventually reached from Turkey as far west as Italy. Ionian science was
an endeavor marked by a strong interest in uncovering fundamental laws
to explain natural phenomena, a tremendous milestone in the history of
human ideas. Their approach was rational and in many cases led to
conclusions surprisingly similar to what our more sophisticated methods
have led us to believe today. It represented a grand beginning. But over
the centuries much of Ionian science would be forgotten-only to be
rediscovered or reinvented, sometimes more than once.
According to legend, the first mathematical formulation of what we might
today call a law of nature dates back to an Ionian named Pythagoras (ca.
580 bc-ca. 490 bc), famous for the theorem named after him: that the
square of the hypotenuse (longest side) of a right triangle equals the
sum of the squares of the other two sides. Pythagoras is said to have
discovered the numerical relationship between the length of the strings
used in musical instruments and the harmonic combinations of the sounds.
In today's language we would describe that relationship by saying that
the frequency-the number of vibrations per second-of a string vibrating
under fixed tension is inversely proportional to the length of the
string. From the practical point of view, this explains why shorter
guitar strings produce a higher pitch than longer ones. Pythagoras
probably did not really discover this-he also did not discover the
theorem that bears his name- but there is evidence that some relation
between string length and pitch was known in his day. If so, one could
call that simple mathematical formula the first instance of what we now
know as theoretical physics.
Excerpted from "The Grand Design" by Stephen Hawking. Copyright © 0 by Stephen Hawking. Excerpted by permission. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher. Excerpts are provided solely for the personal use of visitors to this web site.