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To escape the
latest run-in with hostile aliens, Captain Kirk of the starship
Enterprise orders Engineer Scotty to take the ship to 'warp
factor 6'. The mighty engines open a doorway into the magical
world of 'hyperspace' and in an instant, the Enterprise is
taking a short cut through space. A trip to the nearest star
now takes only a minute or so, not centuries, and Captain
Kirk survives to continue his 'five year' mission.
Science fantasy
has always delt with fantastic ideas at the very limits of
believability, but sometimes the distinction between science
fact and science fiction can become murky indeed. "Space...the
final frontier" is a truism that takes-on a very different
meaning in light of what is now known or suspected about space.
Today, physicists and astronomers are exploring exciting new
ideas that may be the basis for a future at least as exciting
as Captain Kirk's 23rd century.
Of course 'outer
space' is filled with planets, stars and galaxies. Without
these ingredients space would be a sterile 'nothingness'.
But a simple glance at the infinite blackness of the night
sky shows that this intangeable ingredient is one of the most
common in the physical world; It is also the least understood.
Unlike most things that can be directly experienced, it is
difficult to speak critically about something you can neither
touch nor see. Fortunatly, when it comes to pure, empty space,
the situation is not quite so bleak.
As we all learned
in high school, one of the most basic properties of space
is its extension, also called its dimensionality. The world
in which we work, pay taxes and take vacations is a three-dimensional
one. In it, we are free to move forward and backward, side-to-side,
and to a limited extent, up and down. The intricate gyrations
of a ballerina or a gymnast tell us that no matter how we
might move, we never 'turn a fourth corner' and find ourselves
moving along a new direction through space. This tells you
right away that Captain Kirk's world of hyperspace is not
going to be an easy one to break into, especially by something
as big as a human or a starship!
And then there's
Time.
A strictly three-dimensional
world is pretty boring. Nothing happens in it. Suppose you
tell your friend that you will meet her at the entrance to
the Washington Monument. Your well intentioned instructions
will help her narrow your location in the universe to a six
foot cube of space at a particular point on the surface of
the earth. But unless you also say when to be there, the instructions
are useless. Time is a vital fourth coordinate or dimension
to our world. Without it, we would all be trapped in a perpetual
Now, much like the frozen images captured on a photograph.
Space and Time taken together define the complete arena in
which we live. They form such an integral, cohesive framework
for our existence that physicists since Albert Einstein refer
to their combination as simply 'spacetime'.
Spacetime is
vast. It extends well beyond the earth and solar system, encompassing
the entire universe out to the farthest galaxy. Its indivisable
time-like aspect also extends from the instant that the universe
flashed into existence, through the present moment, and on
into the future.
Where did spacetime
come from? Astronomers who study the universe have developed
a detailed model of its evolution called the Big Bang Theory.
About 15 to 20 billion years ago, everything in the universe
came into existence in an awesome explosion. The feeble light
from the fireball of creation can still be detected by sensitive
instruments as they peer into the depths of space. The magnitude
of this event is truely mind boggeling. Earthbound explosions
begin with a bomb whose detonation sends debris flying out
into space. But in the Big Bang, not only did matter come
into existence, but space and time as well!
According to
some recent theories, before the Big Bang, our particular
spacetime simply did not exist. Anywhere. Anywhen. In the
distant future if gravity wins the upper hand, this universe
may finally recollapse under its own weight, once again vanishing
into the absolute nothingness of no-time and no- place. It
is difficult and somewhat troubling to imagine that time and
space had a beginning and may someday come to an end. Even
among religeous cosmologies, both ancient and modern, this
has been a common theme. Science may, in the next few decades,
prove true what humans have long suspected, and perhaps even
feared, about the fate of the universe.
More amazing
and profound than its scope and possible transcience are new
discoveries that may portend even more remarkable revelations
about the nature of spacetime. These discoveries have come
not from the study of the grand design of the universe, but
from a meticulous investigation of the composition of matter
spanning over 300 years of experimental and theoretical work.
From this intense human activity has emerged a detailed understanding
of just how matter and force come together in spacetime to
build-up the complex structures in our world.
At some time
in our schooling we are told that matter consists of atoms;
one for each element like oxygen or iron. The atoms themselves
are built from even more elementary particles called electrons,
protons and neutrons of which the latter reside in the dense
atomic nucleus. Since the 1960's, gigantic machines commonly
called 'atom smashers' have uncovered an even finer structure
to matter. Neutrons and protons are, themselves, made from
minute particles called quarks. All common forms of matter
can now be represented by the combination of just three particles:
one electron and two kinds of quarks.
But there is
more to Nature than matter. Without forces such as gravity,
the world would be formless and devoid of living matter. Once
again, although the dynamics of the world seem bewilderingly
complex, there are only four distinct types of forces in Nature,
each playing its own crucil role in orchestrating the universe.
The force of
gravity acting over billions of years assembles matter into
galaxies and stars, choreographs the dance of the planets
around the sun, and keeps our feet planted firmly on the ground.
The electro- magnetic force holds electrons captive inside
atoms and allows matter to give off light for us to see. The
strong nuclear force binds atomic nuclei together, and its
release in nuclear fusion keeps the sun and stars shining.
Last but not least is the weak nuclear force which causes
matter to decay, and stars to detonate as supernovae in devastating
explosions.
Detailed mathematical
descriptions are available for each of these phenomena which
allow anyone interested in such matters to comprehend and
perceive the physical world with unprecedented clarity. Basic
phenomena in the world, from the color of a sunset to the
birth a star, are no longer regarded as capricious and mysterious,
but can actually be predicted with fair accuracy. Physicists,
however, want to do more than merely describe how each separate
force acts upon matter. Physics is more than merely the passive
'high-tech' bookkeeping of Nature's comings and goings. It
is a search, guided by experiment, for the basic, universal
principles that underlie how the physical world operates at
every imaginable scale, from the most distant galaxy to the
innermost workings of the atom. In creating such a comprehensive
'Theory of Everything', somewhere along the way one of the
greatest remaining challenges to our understanding of the
physical world must be faced. A glimpse of this challenge
can be seen by thinking about a simple electron.
If you were
to draw an imaginary line through space, piercing the center
of an electron, why is it that you single out one of these
points as an electron but call all of its neighbors 'empty'
space? It is easy to semantically define them as being different,
"This one is the electron, that one over there is space",
but how do you go about handeling this difference quantitatively?
Many schemes
for describing the essential difference between matter and
empty space have been tried over the decades; many have failed.
The electron was at first thought to be a tiny sphere of matter
whirling around the nucleus of an atom like a mineature planet.
As intuitively seductive as it was, this idea fell into disrepute
once Albert Einstein developed the Theory of Relativity. Then
the revolution of Quantum Mechanics showed that all matter
had wave-like properties; electrons at a particular instant
were not located at fixed positions in space, but seemed to
be in many places at once. For the last 50 years, electrons
and other elementary particles like quarks are routinely thought
of as small dots of pure energy whose boundaries vanish into
the undefined fabric of space itself. It isn't that physicists
have directly measured this to be the case, only that this
is the only remaining working model for the electron that
has survived, and is consistent with all that we know about
electrons, both theoretically and experimentally.
Theoreticians
since Einstein have speculated about the geometric features
of spacetime, and the structure of electrons and matter for
decades. The growing opinion now seems to be that, ultimately,
only the properties of space such as its geometry or dimensionality
can play a fundamental role in the defining what matter really
is. In a word, matter may be just another form of space. If
the essence of matter is to be found in the geometric properties
of 'empty' space, our current understanding of space will
not be sufficient to describe all of matter's possible aspects.
Remember, you
needed to specify four coordinates in order to meet your friend
at the Washington Monument at the right time and place. For
most things in the world, including the motions of the planets,
stars and galaxies, four dimensions is enough. But to describe
the world of elementary particles, physicists have to add
some additional coordinates to spacetime to keep track of
the properties of subatomic particles. There does not seem
to be enough room in a strictly four-dimensional universe
to explain why matter looks and acts the way it does. Some
of the most promissing theories require that the universe
exists in as many as 7, 10 or even 26 dimensions at once!
These added
dimensions do much more than just tell where a particle is
located in the universe. They actually determine how that
particle will look! According to Superstring Theory which
was developed by physicists John Schwartz and Michael Green
in 1982, every point in spacetime is represented by its usual
four coordinates, along with up to 22 more 'stunted' coordinates.
Every particle, on the other hand, is given an address in
this 26-dimensional universe; an address telling whether the
particle is located in a star or in the paper you are reading.
The additional coordinates tell us what kind of a particle
it is. Depending on how a particle 'moves' in these other
directions it might, for example, be seen as an electron,
a quark, or even 'empty' space.
How can a particle's
motion along a particular dimension change its character so
drastically? Fortunatly, you don't have to be an expert in
physics to get some idea of how this might happen. For instance,
your entire life's history, stretching along the fourth dimension
of time, contains versions of you that are an infant, a young
adult, or a senior citizen. Now suppose that we could move
freely through time, we would be able to witness your drastic
physical transformation from one kind of human 'particle'
to another! By knowing your position along the fourth dimension
the rest of us can keep track of how to interact with you.
At some point it will, of course, be better to interact with
you using 'baby language' than at other times!
We know from
the gyrations of ballerinas and gymnasts that, if they exist
at all, these dimensons can't be very big. There is no danger
of taking a walk to the store and suddenly finding yourself
in the 17th dimension! Only subatomic particles like electrons
are small enough to gain any benefit from such a journey.
Superstring Theory and some of its predecessors say that these
added dimensions are rolled up into miniscule balls one trillion
trillion times smaller than an atom. An atom would have to
be enlarged to the size of the Milky Way galaxy 100,000 light
years across, before any signs of them would be apparent!
Just as the
lumps and bumps in the geometric shape of a piece of paper
will control the motion of marbles moving across them, there
is also an intimate relationship between the geometry of a
26-dimensional spacetime and the behavior of matter. Since
the properties of the elementary particles and forces in the
universe are already known, this can be used to discover what
kind of geometry a 26-dimensional universe would have to have
in order to resemble the universe we are familiar with.
The answer to
this question is still being searched for today. But if and
when it is found, it is believed that the geometric basis
for the Theory of Everything will at last have been uncovered.
To say that this will be a major accomplishment is an understatement.
In fact, some physicists like Stephen Hawking in 'A Brief
History of Time' even predict that the discovery of the correct
geometry will herald the end of physics as we know it.
It has been
said that to understand the motions of the clouds in the sky,
you must first study the winds and currents of the invisible
atmosphere itself. Like clouds, it may well be that matter
is merely a tracer of activity at a more basic level in the
physical world. The deep roots that elementary particles have
may reach down into the bedrock of spacetime whose geometry
ultimately controls their properties and how they are destined
to interact with one another. Like an oak or a maple tree,
we measure and perceive only their broad canopies. Their roots
remain forever hidden.
It would seem
that if our modern theories are correct, Captain Kirk will
have to do something else other than duck into hyperspace
to escape his enemies! Because the universe may manifest these
other 'hyper' dimensions at the subatomic scale, only electrons
can take advantage of them. Few of us would especially enjoy
being squeezed to the size of an electron to escape even the
most hostile alien! Although such rapid travel through hyperspace
may never be possible given the rules upon which our universe
may be based, there are other even more exciting possibilities.
If matter is
'simply' twisted space, would it be possible to create matter
and perhaps even entire, artificial mini-universes out of
warped space? Though technically difficult, some physicists
such as MIT's Alan Guth have seriously thought about these
possibilities and consider them within the realm of possibility
in the distant future. Although it may not be possible for
humans to travel through any of the other dimensions to space
as a short cut to some distant star, what about the massless
particles of light called photons? Could we at least send
radio messages through hyperspace almost instantaneously,
and not have to wait hundreds of years to get a reply from
our colonists orbiting Antares? Then again, just because the
physical world may not naturally include something like hyperspace
on the interstellar scale, is it possible that no injunction
exists forbidding its artificial creation? Perhaps given enough
raw energy focussed on a small enough region of spacetime,
many natural barriers could be overcome.
The scientific
exploration of the world has taught us much about the way
the universe is put together. We are now familiar with nearly
all of its most important rules and regulations for living
in harmony with its basic phenomena. It is always difficult
to predict where the next great revolution in thinking will
come from. Perhaps some of the current ideas about matter
and space will not even survive the end of the 20th century
as new experiments are developed. Then again, the scientific
advancement of the last three centuries would have been impossible
had not some ideas, as far fetched as they seemed at the time,
been correct in one form or another!
So, the next
time you gaze at the night sky, take a moment to reflect on
the nature of the vast emptiness between the stars. Even perfectly
empty space, the quintessential nothingness, may be a far
more sublime and complex ingredient to our universe that we
have ever before imagined!
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