"Time is a relationship that we have with the rest of the
universe; or more accurately, we are one of the clocks, measuring one kind
of time. Animals and aliens may measure it differently. We may even be
able to change our way of marking time one day, and open up new realms
of experience, in which a day today will be a million years."
- George Zebrowski, OMNI, 1994
"'It's against reason,' said Filby. 'What reason?' said
the Time Traveller."
- H. G. Wells, The Time Machine
"The job of science is to enable the inquiring mind to feel
at home in a mysterious universe." - Lewis Carroll Epstein, Relativity
"The brain is a three-pound mass you can hold in your hand
that can conceive of a universe a hundred-billion light-years across".
- Marian Diamond
"Does anybody really know what time it is?" - Chicago
The Quest for Eternity
What is time? Is time travel possible? For centuries, these
questions have intrigued mystics, philosophers, and scientists. Much of
ancient Greek philosophy was concerned with understanding the concept of
eternity, and the subject of time is central to all the worlds' religions
and cultures. Can the flow of time be stopped? Certainly some mystics thought
so. Angelus Silesius, a sixth-century philosopher and poet, thought the
flow of time could be suspended by mental powers:
Time is of your own making;
its clock ticks in your head.
The moment you stop thought
time too stops dead.
This book is mostly about the science of time travel
and only touches briefly on mysticism. However, the line between science
and mysticism sometimes grows thin. Today, physicists would agree that
time is one of the strangest properties of our universe. In fact, there
is a story circulating among scientists of an immigrant to America who
has lost his watch. He walks up to a man on a New York street and asks,
"Please, Sir, what is time?" The scientist replies, "I'm sorry, you'll
have to ask a philosopher. I'm just a physicist."
Most cultures have a grammar with past and future tenses,
and also demarcations like seconds and minutes, and yesterday and tomorrow.
Yet we cannot say exactly what time is. Although the study of time became
scientific during the time of Galileo and Newton, a comprehensive explanation
was given only in this century by Einstein who declared, in effect, time
is simply what a clock reads. The clock can be the rotation of a planet,
sand falling in an hour glass, a heartbeat, or vibrations of a cesium atom.
A typical grandfather clock follows the simple Newtonian law that states
that the velocity of a body not subject to external forces remains constant.
This means that clock hands travel equal distances in equal times. While
this kind of clock is useful for everyday life, modern science finds that
time can be warped in various ways, like clay in the hands of a cosmic
Science-fiction authors have had various uses for time
machines including: dinosaur hunting, tourism, visits to one's ancestors,
and animal collecting. Ever since the time of H. G. Wells's famous novel
Time Machine (1895), people have grown increasingly intrigued by the
idea of traveling through time. (I was lucky enough to have chats with
H. G. Wells's grandson who told me that his grandfather's book The Time
Machine has never been out of print, something rare for a book a century
old.) In the book, the protagonist uses a "black and polished brass" time
machine to gain mechanical control over time as well as return to the present
to bring back his story and assess the consequences of the present on the
future. Wells was a graduate of the Imperial College of Science and Technology,
and scientific language permeates his discussions. Many believe Wells's
book to be the first story about a time machine, but seven years before
22-year-old Wells wrote the first version of The Time Machine, Edward
Page Mitchell, an editor of the New York Sun, published "The Clock
That Went Backward." One of the earliest methods for fictional time travel
didn't even involve a machine; the main character in Washington Irving's
"Rip Van Winkle" (1819) simply fell asleep for decades. King Arthur's daughter
Gweneth slept for 500 years under Merlin's spell.
Ancient legends of time distortion are, in fact, quite
common. One of the most poetic descriptions of time travel occurs in a
popular medieval legend describing a monk entranced for a minute by the
song of a magical bird. When the bird stops singing, the monk discovers
that several hundred years have passed. Another example is the Moslem legend
of Mohamad carried by a mare into heaven. After a long visit, the prophet
returns to Earth just in time to catch a jar of water the horse had kicked
over before starting its ascent.
Today, we know that time travel need not be confined to
myths, science fiction, Hollywood movies, or even speculation by theoretical
physicists. Time travel is possible. For example, an object traveling at
high speeds ages more slowly than a stationary object.:sup.1:esup. This
means that if you were to travel into outer space and return, moving close
to light-speed, you could travel thousands of years into the Earth's future.
In addition to high-speed travel, researchers have proposed numerous ways
in which time machines can be built that do not seem to violate any known
laws of physics. These methods allow you to travel to any point in the
world's past or future and are discussed towards the end of this book.
Newton's most important contribution to science was his
mathematical definition of how motion changes with time (Figure 1). He
showed the force causing apples to fall is same as the force that drives
planetary motions and produces tides. However, Newton was puzzled by the
fact that gravity seemed to operate instantaneously at a distance. He admitted
he could only describe it without understanding how it worked. Not until
Einstein's general theory of relativity was gravity changed from a "force"
to the movement of matter along the shortest path in a curved spacetime.
The Sun bends spacetime, and spacetime tells the planets how to move. For
Newton, both space and time were absolute. Space was a fixed, infinite,
unmoving metric against which absolute motions could be measured. Newton
also believed the universe was pervaded by a single absolute time that
could be symbolized by an imaginary clock off somewhere in space. Einstein
changed all this with his relativity theories, and once wrote "Newton,
Einstein's first major contribution to the study of time
occurred when he revolutionized physics with his "special theory of relativity"
by showing how time changes with motion. Today, scientists do not see problems
of time or motion as "absolute" with a single correct answer. Because time
is relative to the speed one is traveling at, there can never be a clock
at the center of the Universe to which everyone can set their watches.
Your entire life is the blink of an eye to an alien traveling close to
the speed of light. Today, Newton's mechanics have become a special case
within Einstein's theory of relativity. Einstein's relativity will eventually
become a subset of a new science more comprehensive in its description
of the fabric of our universe. (The word "relativity" derives from the
fact that the appearance of the world depends on our state of motion; it
We are a moment in astronomic time, a transient guest of
the Earth. Our wet, wrinkled brains do not allow us to comprehend many
mysteries of time and space. Our brains evolved to make us run from sabre-toothed
tigers on the African savanna, to hunt deer, and to efficiently scavenge
from the kills of large carnivores. Despite our mental limitations, we
have come remarkably far. We have managed to pull back the cosmic curtains
a crack to let in the light. Questions raised by physicists, from Newton
to Goedel to Einstein to Hawking, are among the most profound we can
Is time real? Does it flow in one direction only? Does
it have a beginning or end? What is eternity? None of these questions can
be answered to scientists' satisfaction. Yet the mere asking of these questions
stretches our minds, and the continual search for answers provides useful
insights along the way.
Who this Book is For
This book will allow you to travel through time and space,
and you needn't be an expert in physics. Some information is repeated so
that each chapter contains sufficient background information, but I suggest
you read the chapters in order as you gradually build your knowledge. To
facilitate your journey, I start most chapters with a dialog between quirky
explorers who experiment with time from within the (usually) safe confines
of a Museum of Music in New York City. This simple science fiction is not
only good fun but it also serves a serious purpose, that of expanding your
imagination. We might not yet be able to easily travel in time like the
characters in the story, but at least time travel is not forbidden by the
current laws of physics. As you read the story, think about how humans
might respond to future developments in science that could lead to time
When writing this book, I did not set out to write a systematic
and comprehensive study of time. Instead, I have chosen a selection of
topics relating to time travel which I think will enlighten a wide range
of readers. Although Einstein's theory of relativity is nearly a century
old, its strange consequences are still not widely known. People still
often learn of them with a sense of awe, mystery and bewilderment. Even
armed with Einstein's theories, humans have only a vague understanding
of time, and various problems and paradoxes still need to be solved.
By the time you've finished this book, you will be able
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have a good understanding of spacetime diagrams, light cones, and time
impress your friends with such terms as: "cosmic moment lines", "transcendent
infinite speeds", "Lorentz transformations", "causal linkages", "superluminal
and ultraluminal motions", "Minkowskian space- times", "Goedel universes",
"closed timelike curves", and "Tipler cylinders".
write better science-fiction stories for shows such as Star Trek
or the X-Files.
write computer simulations for various aspects of time travel.
understand humanity's rather limited view of time.
understand that time travel is possible.You might even want to go
out and buy a Chopin recording.
here for reviews of Time: A Traveler's Guide.
Cliff Pickover's home page which includes computer art, educational
puzzles, higher dimensions, fractals, virtual caverns, JAVA/VRML, alien
creatures, black hole artwork, and animations.