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Sometime between 15 and 20 billion years ago the universe
came into existence. Since the dawn of human awareness, we
have grappled with the hows and whys of this event and out
of this effort have sprung many ideas. An ancient Egyptian
legend describes how the universe was created by Osiris Khepera
out of a dark, boundless ocean called Nu and that Osiris Khepera
created himself out of this ocean by uttering his own name.
Human inventiveness has not stood still in the 5000 years
since these ideas were popular. The modern theory of the Big
Bang states that our universe evolved from an earlier phase
billions of times hotter than the core of our sun and trillions
of times denser than the nucleus of an atom. To describe in
detail such extreme physical conditions, we must first have
a firm understanding of the nature of matter and of the fundamental
forces. At the high temperatures likely to have attended the
Big Bang, all familiar forms of matter were reduced to their
fundamental constituents. The forces of gravity and electromagnetism
together with the strong and weak nuclear forces, were the
essential means through which the fundamental particles of
matter interacted.
The feedback between cosmology and particle physics is nowhere
more clearly seen than in the study of the early history of
the universe. In October, 1985 the giant accelerator at Fermilab
acheived for the first time, the collision of protons and
anti-protons at energies of 1.6 trillion electron volts, about
1600 times the rest mass of the proton. This was a unique
event because for one split second, on a tiny planet in an
undistinguished galaxy, a small window onto the Creation Event
was opened for the first time in at least 15 billion years.
THE
LIMITS OF CERTAINTY
The persuit
by physicists of a single, all encompassing theory capable
of describing the four natural forces has, as a by-product,
resulted in some surprising glimpses of the Creation Event.
Although such a theory remains perhaps several decades from
completion, it is generally recognized that such a theory
will describe physical conditions so extreme it is quite possible
that we may never be able to explore them first- hand, even
with the particle accelerators that are being designed today.
For example, the Superconducting Supercollider to be built
by the early 1990's will cost 6 billion dollars and it will
allow physicists to collide particles at energies of 40 trillion
electron volts ( 40,000 GeV) matching the conditions prevailing
10 seconds after the Big Bang. The expected windfall from
such an accelerator is enormous and will help to answer many
nagging questions now plaguing the theoretical community,
but can we afford to invest perhaps vastly larger sums of
money to build machines capable of probing the quantum gravity
world at 10 GeV? At these energies, the full unification of
the natural forces is expected to become directly observable.
How curious it is that definite answers to questions such
as, 'What was Creation like?' and 'Do electrons and quarks
have internal structure?' are so inextricably intertwined.
Our ability to find answers to these two questions, among
others, does not seem to be hampered by some metaphysical
prohibition, but by the resources our civilization can afford
to devote to finding the answers. Fortunatly, the situation
is not quite so bleak, for you see, the 'machine' has already
been 'built' and every possible experiment we can ever imagine
has already been performed!
WHAT
WE THINK WE KNOW
We are living
inside the biggest particle accelerator ever created - the
universe. Ten billion years before the sun was born, Nature's
experiment in high-energy physics was conducted and the experimental
data can now be examined by studying the properties and contents
of the universe itself. The collection of fundamental facts
that characterize our universe is peculiar in that it derives
from a variety of sources. A partial list of these 'meta-facts'
looks like this:
1) We are here,
therefore, some regions of the universe are hospitible to
the creation of complex molecules and living, rational organisms.
2) Our Universe
has 4 big dimensions and all are increasing in size as the
universe expands in time and space.
3) There are
4 dissimilar forces acting in Nature.
4) Only matter
dominates; no anti-matter galaxies exist and this matter is
built out of 6 quarks and 6 types of leptons.
The task confronting
the physicist and the astronomer is to create, hopefully,
a single theory consistent with these metafacts that can then
be used to derive the secondary characteristics of our universe
such as the 2.7 K background radiation, the primordial element
abundances, and galaxy formation. The interplay between the
study of the macrocosm and the microcosm has now become so
intense that astronomers have helped physicists set limits
to the number of lepton families --- No more than 4 are allowed
otherwise the predicted cosmological abundance of helium would
seriously disagree with what is observed. Physicists, on the
other hand, use the astronomical upper limits to the current
value of the cosmological constant to constrain their unification
theories.
An extention
to the standard Big Bang model called the Inflationary Universe
(see The Decay of the False Vacuum) was created by MIT physicist
Alan Guth in 1981. This theory combined Grand Unification
Theory with cosmology and, if correct, allows astronomers
to trace the history of the universe all the way back to 10
seconds after the Big Bang when the strong, weak and electromagnetic
forces were unified into a single 'electro-nuclear' force.
During the 4 years since the Inflationary Universe model was
proposed, other theoretical developments have emerged that
may help us probe events occurring at an even earlier stage,
perhaps even beyond the Creation Event itself. Ten years ago,
theoreticians discovered a new class of theories called Supersymmetric
Grand Unified Theories ( SUSY GUTs). These theories, of which
there are several competing types, have shown great promise
in providing physicists with a unified framework for describing
not just the electro-nuclear force but also gravity, in addition
to the particles they act on (see The Planck Era: March 1984).
Unfortunately, as SUSY GUTs were studied more carefully, it
was soon discovered that even the most promising candidates
for THE Unified Field Theory suffered from certain fundamantal
deficiencies. For instance:
1) There were
not enough basic fields predicted to accomodate the known
particles.
2) Left and
right-hand symmetry was mandated so that the weak force, which
breaks this symmetry, had to be put in 'by hand'.
3) Anomalies
exist which include the violation of energy conservation and
charge.
4) The Cosmological
Constant is 10 times larger than present upper limits suggest.
In recent years,
considerable effort has gone into extending and modifying
the postulates of SUSY GUTs in order to avoid these problems.
One avenue has been to question the legitimacy of a very basic
premise of the field theories developed heretofore. The most
active line of theoretical research in the last 25 years has
involved the study of what are called 'point symmetry groups'.
For example, a hexagon rotated by 60 degrees about a point
at its center is indistinguishable from one rotated by 120,
180, 240, 300 and 360 degrees. These 6 rotation operations
form a mathematical group so that adding or subtracting any
two operations always result in a rotation operation that
is already a member of the group ( 180 = 120 + 60 etc). The
Grand Unification Theories of the electro-nuclear interaction
are based on point symmetry groups named SU(3), SU(2) and
U(1) which represent analogous 'rotations' in a more complex
mathematical space. In the context of ponderable matter, point
symmetry groups are also the mathematical statement of what
we believe to be the structure of the fundamental particles
of matter, namely, that particles are point-like having no
physical size at all. But what if this isn't so? The best
that experimental physics has to offer is that the electron
which is one of a family of 6 known Leptons, behaves like
a point particle at scales down to 10 cm, but that's still
an enormous distance compared to the gravitational Planck
scale of 10 cm where complete unification with gravity is
expected to occur.
By assuming
that fundamental particles have internal structure, Michael
Green at Queen Mary College and John Schwartz at Caltech made
a remarkable series of discoveries which were anounced in
the journal NATURE in April 1985. They proposed that, if a
point particle were replaced by a vibrating 'string' moving
through a 10-dimensional spacetime, many of the problems plaguing
SUSY GUTs seemed to vanish miraculously. What's more, of all
the possible kinds of 'Superstring' theories, there were only
two ( called SO(32) and E8 x E8') that were: 1) Consistent
with both the principles of relativity and quantum mechanics,2)
Allowed for the asymmetry between left and right-handed processes
and, 3) Were free of anomalies. Both versions were also found
to have enough room in them for 496 different types of fields;
enough to accomodate all of the known fundamental particles
and then some! Superstring theories also have very few adjustable
parameters and from them, certain quantum gravity calculations
can be performed that give finite answers instead of infinite
ones. In spite of their theoretical successes, Superstring
theories suffer from the difficulty that the lightest Superstring
particles will be completely massless while the next more
massive generation will have masses of 10 GeV. It is not even
clear how these supermassive string particles are related
to the known particles which are virtually massless by comparison
(a proton has a mass of 1 GeV!). It is also not known if the
496 different particles will cover the entire mass range between
0 and 10 GeV. It is possible that they may group themselves
into two families with masses clustered around these two extreems.
In the later instance, experimental physicists may literally
run out of new particles to discover until accelerators powerful
enough to create supermassive particles can be built.
An attractive
feature of the SO(32) model, which represents particles as
open-ended strings, is that gravity has to be included from
the start in order to make the theory internally consistent
and capable of yielding finite predictions. It is also a theory
that reduces to ordinary point field theories at energies
below 10 GeV. The complimentary theory, E8 x E8', is the only
other superstring theory that seems to work as well as SO(32)
and treats particles as though they were closed strings without
bare endpoints. This model is believed to show the greatest
promise for describing real physical particles. It also includes
gravity, but unlike SO(32), E8 x E8' does seem to reduce at
low energy, to the symmetry groups associated with the strong,
weak and electromagnetic interactions, namely, SU(3), SU(2)
and U(1).
If E8 x E8'
is destined to be the 'ultimate, unified field theory', there
are some additional surprises in store for us. Each group,
E8 and E8', can be reduced mathematically to the products
of the groups that represent the strong, weak and electromagnetic
forces; SU(3) x SU(2) x U(1). If the E8 group corresponds
to the known particles what does E8' represent? In terms of
its mathematical properties, symmetry considerations alone
seem to require that the E8' group should be a mirror image
of E8. If E8 contains the groups SU(3), SU(2) and U(1) then
E8' contains SU(3)', SU(2)' and U(1)'. The primed fields in
E8' would have the same properties as those we ascribe to
the strong, weak and electromagnetic forces. The E8' particle
fields may correspond to a completly different kind of matter,
whose properties are as different from matter and anti-matter
as ordinary matter is from anti-matter! 'Shadow Matter' as
it has been called by Edward Kolb, David Seckel and Michael
Turner at Fermilab, may actually co-exist with our own - possibly
accounting for the missing mass necessary to close the universe.
Shadow matter is only detectable by its gravitational influence
and is totally invisible because the shadow world electromagnetic
force (shadow light) does not interact with any of the particles
in the normal world.
BEYOND
SPACE AND TIME
The quest for
a mathematical description of the physical world uniting the
apparent differences between the known particles and forces,
has led physicists to the remarkable conclusion that the universe
inhabits not just the 4 dimensions of space and time, but
a much larger arena whose dimensionality may be enormous (see
Does Space Have More Than 3 Dimensions?). Both the Superstring
theories and SUSY GUTs agree that our physical world has to
have more than the 4 dimensions we are accustomed to thinking
about. A remarkable feature of Superstring theory is that
of all the possible dimensionalities for spacetime, only in
10-dimensions ( 9 space dimensions and 1 time dimension) will
the theory lead to a computationally finite and internally
consistent model for the physical world that includes the
weak interaction from the outset, and where all of the troublesome
anomalies cancil exactly. In such a 10-dimensional world,
it is envisioned that 6 dimensions are now wrapped-up or 'compactified'
into miniscule spheres that accompany the 4 coordinates of
every point in spacetime. What would a description of the
early universe look like from this new viewpoint? The 6 internal
dimensions are believed to have a size of order 10 cm.
As we follow
the history of the universe back in time, the 3 large dimensions
of space rapidly shrink until eventually they become only
10 cm in extent. This happened during the Planck Era at a
time, 10 seconds after the Creation Event. The appearance
of the universe under these conditions is almost unimaginable.
Today as we look out at the most distant quasar, we see them
at distances of billions of lightyears. During the Planck
Era, the matter comprising these distant systems was only
10 cm away from the material that makes-up your own body!
What was so
special about this era that only 4 of the 10 dimensions were
singled-out to grow to their enormous present size?. Why not
3 ( 2 space + 1 time) or 5 ( 4 space + 1 time)? Physicists
have not as yet been able to develope an explanation for this
fundamental mystery of our plenum, on the other hand, it may
just be that had the dimensional breakdown of spacetime been
other than '4 + 6', the physical laws we are the products
of, would have been totally inhospitable to life as we know
it.
As we relentlessly
follow the history of the universe to even earlier times,
the universe seems to enter a progressively more and more
symmetric state. The universe at 10 seconds after the Big
Bang may have been populated by supermassive particles with
masses of 10 GeV or about 10 gm each. These particles ultimatly
decayed into the familiar quarks and leptons once the universe
had grown colder as it expanded. In addition, there may only
have been a single kind of 'superforce' acting on these particles;
a force whose character contained all of the individual attributes
we now associate with gravity, electromagnetism and the strong
and weak nuclear forces. Since the particles carrying the
'superforce' had masses similar to those of the supermassive
particles co-existing then, the distinction between the force-carriers
and the particles they act on probably broke-down completely
and the world became fully supersymmetric.
To go beyond
the Planck Era may require a radical alteration in our conventional
way of thinking about time and space. Only glimpses of the
appropriate way to think about this multidimensional landscape
can be found in the equations and theories of modern-day physics.
Beyond the Planck Era, all 10 dimensions (and perhaps others)
become co-equal at least in terms of their physical size.
The supermassive Superstring particles begin to take-on more
of the characteristics of fluctuations in the geometry of
spacetime than as distinguishable, ingredients in the primordial,
cosmological 'soup'. There was no single, unique geometry
for spacetime but, instead, an ever-changing quantum interplay
between spacetimes with an unlimited range in geometry. Like
sound waves that combine with one another to produce interference
and reinforcement, the spacetime that emerged from the Planck
Era is thought to be the result of the superposition of an
infin ite number of alternate spacetime geometries which,
when added together, produced the spacetime that we are now
a part of.
Was there light?
Since the majority of the photons were probably not created
in large numbers until at least the beginning of the Inflationary
Epoc, 10 seconds after the Big Bang, it is not unthinkable
that during its earliest moments, the universe was born out
of darkness rather than in a blinding flash of light. All
that existed in this darkness before the advent of light,
was an empty space out of which our 10-dimensional spacetime
would later emerge. Of course, under these conditions it is
unclear just how we should continue to think about time itself.
In terms of
the theories available today, it may well be that the particular
dimension we call Time had a definite zero point so that we
can not even speak logically about what happened before time
existed. The concept of 'before' is based on the presumption
of time ordering. A traveler standing on the north pole can
never move to a position on the earth that is 1 mile north
of north! Nevertheless, out of ingrained habit, we speak of
the time before the genesis of the universe when time didn't
exist and ask, "What happened before the Big Bang?".
The list of physicists investigating this 'state' has grown
enormously over the last 15 years. The number of physicists,
worldwide, that publish research on this topic is only slightly
more than 200 out of a world population of 5 billion!
QUANTUM
COSMOLOGY
In the early
1970's Y. Zel'dovitch and A. Starobinski of the USSR along
with Edward Tryon at Hunter College proposed that the universe
emerged from a fluctuation in the vacuum. This vacuum fluctuation
'ran away' with itself, creating all the known particles out
of empty space at the 'instant' of no-time. To understand
what this means requires the application of a fundamental
fact of relativistic quantum physics discovered during the
latter half of the 1920's. Vacuum fluctuations are a direct
consequence of Heisenberg's Uncertainty Principle which limits
how well we can simultaneously know a particle's momentum
and location (or its total energy and lifetime). What we call
empty space or the physical vacuum is a Newtonian fiction
like absolute space and time. Rather than a barren stage on
which matter plays-out its role, empty space is known to be
filled with 'virtual particles' that spontaneously appear
and disappear beyond the ability of any physical measurement
to detect directly. From these ghost particles, a variety
of very subtle phenomena can be predicted with amazing accuracy.
Depending on
the total rest mass energy of the virtual particles created
in the vacuum fluctuation, they may live for a specific lifetime
before Heisenberg's Uncertainty Principle demands that they
vanish back into the nothingness of the vacuum state. In such
a quantum world, less massive virtual particles can live longer
than more massive ones. Edward Tyron proposed that the universe
is just a particularly long-lived vacuum fluctuation differing
only in magnitude from those which occur imperceptably all
around us. The reason the universe is so long lived in spite
of its enormous mass is that the positive energy latent in
all the matter in the universe is offset by the negative potential
energy of the gravitational field of the universe. The total
energy of the universe is, therefore, exactly zero and its
maximum lifetime as a 'quantum fluctuation' could be enormous
and even infinite! According to Tryon, "The Universe
is simply one of those things which happens from time to time."
This proposal
by Tryon was regarded with some scepticism and even amusement
by astronomers, and was not persued much further. This was
a fate that had also befallen the work on 5-dimensional general
relativity by Theodore Kaluza and Oskar Klein during the 1920's
which was only resurrected in the late 1970's as a potent
remedy for the ills plaguing supersymmetry theory.
In 1978, R.
Brout, P. Englert, E. Gunzig and P. Spindel at the University
of Brussels, proposed that the fluctuation that led to the
creation of our universe started out in an empty, flat, 4-dimensional
spacetime. The fluctuation in space began weakly, creating
perhaps a single matter- antimatter pair of supermassive particles
with masses of 10^19 GeV. The existence of this 'first pair'
stimulated the creation from the vacuum of more particle-antiparticle
pairs which stimulated the production of still others and
so on. Space became highly curved and exploded, disgorging
all of the superparticles which later decayed into the familiar
leptons, quarks and photons.
Heinz Pagels
and David Atkatz at Rockefeller University in 1981 proposed
that the triggering agent behind the Creation Event was a
tunneling phenomenon of the vacuum from a higher-energy state
to a lower energy state. Unlike the Brout-Englert-Gunzig-Spindel
model which started from a flat spacetime, Pagels and Atkatz
took the complimentary approach that the original nothingness
from which the universe emerged was a spatially closed, compact
empty space, in other words, it had a geometry like the 2-D
surface of a sphere. but the dimensionality of its surface
was much higher than 2. Again this space contained no matter
what-so-ever. The characteristics (as yet unknown) of the
tunneling process determined, perhaps in a random way, how
the dimensionality of spacetime would 'crystallize' into the
6+4 combination that represents the plenum of our universe.
Alex Vilenkin
at Tufts University proposed in 1983 that our spacetime was
created out of a 'nothingness' so complete that even its dimensionality
was undefined. In 1984, Steven Hawkings at Cambridge and James
Hartle at UCSB came to a similar conclusion through a series
of quantum mechanical calculations. They described the geometric
state of the universe in terms of a wavefunction which specified
the probability for spacetime to have one of an infinite number
of possible geometries. A major problem with the ordinary
Big Bang theory was that the universe emerged from a state
where space and time vanished and the density of the universe
became infinite; a state called the Singularity. Hawkings
and Hartle were able to show that this Big Bang singularity
represented a specific kind of geometry which would become
smeared-out in spacetime due to quantum indeterminacy. The
universe seemed to emerge from a non-singular state of 'nothingness'
similar to the undefined state proposed by Vilenkin. The physicist
Frank Wilczyk expresses this remarkable situation the best
by saying that, " The reason that there is Something
rather than Nothing is that Nothing is unstable."
PERFECT
SYMMETRY
Theories like
those of SUSY GUTS and Superstrings seem to suggest that just
a few moments after Creation, the laws of physics and the
content of the world were in a highly symmetric state; one
superforce and perhaps one kind of superparticle. The only
thing breaking the perfect symmetry of this era was the definite
direction and character of the dimension called Time. Before
Creation, the primordial symmetry may have been so perfect
that, as Vilenkin proposed, the dimensionality of space was
itself undefined. To describe this state is a daunting challenge
in semantics and mathematics because the mathematical act
of specifying its dimensionality would have implied the selection
of one possibility from all others and thereby breaking the
perfect symmetry of this state. There were, presumably, no
particles of matter or even photons of light then, because
these particles were born from the vacuum fluctuations in
the fabric of spacetime that attended the creation of the
universe. In such a world, nothing happens because all 'happenings'
take place within the reference frame of time and space. The
presence of a single particle in this nothingness would have
instantaneously broken the perfect symmetry of this era because
there would then have been a favored point in space different
from all others; the point occupied by the particle. This
nothingness didn't evolve either, because evolution is a time-ordered
process. The introduction of time as a favored coordinate
would have broken the symmetry too. It would seem that the
'Trans-Creation' state is beyond conventional description
because any words we may choose to describe it are inherently
laced with the conceptual baggage of time and space. Heinz
Pagels reflects on this 'earliest' stage by saying, "The
nothingness 'before' the creation of the universe is the most
complete void we can imagine. No space, time or matter existed.
It is a world without place, without duration or eternity..."
A perusal of
the scientific literature during the last 20 years suggests
that we may be rapidly approaching a major crossroad in physics.
One road seems to be leading to a single unification theory
that is so unique among all others that it is the only one
consistent with all the major laws we know about. It is internally
consistent; satisfies the principles of relativity and quantum
mechanics and requires no outside information to describe
the particles and forces it contains . A prototype of this
may be superstring theory with its single adjustable parameter,
namely, the string tension. The other road is much more bleak.
It may also turn out that we will create several theoretical
systems that seem to explain everything but have within them
hard to detect flaws. These flaws may stand as barracades
to further logical inquiry; to be uncovered only through experiments
that may be beyond our technological reach. It is possible
that we are seeing the beginning of this latter process even
now, with the multiplicity of theories whose significant deviations
only occur at energies near 10^19 GeV.
I find it very
hard to resist the analogy between our current situation and
that of the Grecian geometers. For 2000 years the basic postulates
of Eulidean geometry and the consequences of this logical
system, remained fixed. It became a closed book with only
a few people in the world struggling to find exceptions to
it such as refutations of the parallel line postulate. Finally
during the 19th century, non-euclidean geometry was discovered
and a renaissance in geometry occurred. Are physicists on
the verge of a similar great age, finding themselves hamstrung
by not being able to devise new ways of thinking about old
problems? Egyptian cosmology was based on motifs that the
people of that age could see in the world around them; water,
sky, land, biological reproduction. Today we still use motifs
that we find in Nature in order to explain the origin of the
universe; the geometry of space, virtual particles and vacuum
fluctuations. We can probably expect that in the centuries
to follow, our descendents will find still other motifs and
from them, fashion cosmologies that will satisfy the demands
of that future age with, possibly, much greater accuracy and
efficiency than ours do today. Perhaps, too, in those future
ages, scientists will marvel at the ingenuity of modern physicists
and astronomers, and how in the space of only 300 years, we
had managed to create our own quaint theory as the Egyptians
had before us.
In the meantime,
physicists and astronomers do the best they can to fashion
a cosmology that will satisfy the intellectual needs of our
age. Today, as we contemplate the origin of the universe we
find ourselves looking out over a dark, empty void not unlike
the one that our Egyptian predecessors might have imagined.
This void is a state of exquisite perfection and symmetry
that seems to defy description in any linguistic terms we
can imagine. Through our theories we launch mathematical voyages
of exploration, and watch the void as it trembles with the
quantum possibilities of universes unimaginable.
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