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The Big Bang theory says that the entire universe was created
in a tremendous explosion about 20 billion years ago. The enormity
of this event is hard to grasp and it seems natural to ask ourselves
'What was it like then?' and 'What happened before the Big Bang?'.
To try to answer these queries, lets take a brief journey backwards
in time.
We first see the formation of our own sun about 15 billion years
after the Big Bang and then by 5 billion years, the formation
of the first galaxies. By 700,000 years, the universe is awash
with the fireball radiation that keeps all matter at a temperature
of 4,000 degrees. Because of this, darkness is completely absent
since every point in the sky glows with the brilliance of the
sun. No stars, planets or even dust grains exist, just a hot
dense plasma of electrons, protons and helium nuclei. By 3 minutes,
we see helium form from the fusion of hydrogen atoms while the
universe seeths at a temperature of nearly 1 billion degrees.
The average density of matter is that of lead. By 1 second,
the Lepton Era ends and the ratio of neutrons to protons has
become fixed at 1 neutron for every 5 protons. The temperature
is now 5 billion degrees everywhere. At about .0001 second,
we watch as the Quark Era ends and the temperature of the fireball
radiation rises to an incredable 1 trillion degrees. Quarks,
for the first time, can combine in groups of two and three to
become neutrons, protons and other types of heavy particles.
The universe is now packed with matter as densly as the nucleus
of an atom. A mountain like Mt. Everest could be squeezed into
a volume no greater than the size of a golf ball!
By 1 billionth
of a second, the temperature is 1 thousand trillion degrees
and we see the electromagnetic and weak forces merge into
one force. The density of the universe has increased to the
point where the entire earth could be contained in a thimble.
Quarks and anti-quarks are no longer confined inside of particles
like neutrons and protons but are now part of a superheated
plasma of unbound particles. As the remaining history of the
universe unfolds, a long period seems to pass when nothing
really new happens. Then, at a time 10(-35) second after the
Big Bang, a spectac ular change in the size of the universe
occurs. This is the GUT Era when the strong nuclear force
becomes distinguishable from the weak and electromagnetic
forces. The temperature is an incredable 10 thousand trillion
trillion degrees and the density of matter has sored to nearly
10(75) gm/cm3. This number is so enormous that even our analogies
are almost beyond comprehension. At these densities, the entire
Milky Way galaxy could easily be stuffed into a volume no
larger than a single hydrogen atom! Electrons and quarks together
with their anti-particles, were the major constituents of
matter and very massive particles called Leptoquark Bosons
caused the quarks to decay into electrons and vice versa.
If we now move forward in time we would witness the vacuum
of space undergoing a 'phase transition' from a higher energy
state to a lower energy state. This is analogous to a ball
rolling down the side of a mountain and coming to rest in
the lowest valley. As the universe 'rolls down hill' it begins
a brief but stupendous period of expansion. The universe swells
to billions of times its former size in almost no time at
all.
In addition
to this, a slight excess of matter over anti-matter appears
becaus of the decay of massive particles called X Higgs Bosons.
As we continue to watch the universe age, the remaining pairs
of particles and anti-particles find themselves and vanish
in a tremendous burst of annihilation. From this paroxysm,
the bulk of the fireball radiation that we now observe is
born.
The GUT Era
is the last stop in our fanciful journey through time. If
we had asked what it was like before the GUT Era, we would
immediately have entered a vast no mans land where few indisputable
facts would serve to gui de us. What does seem clear is that
gravity is destined to grow in importance, eventually becoming
the dominant force acting between parti cles, even at the
microscopic level.
G
R A V I T Y
According to
theories developed since the 1930's, what we call a 'force'
is actually a collective phenomenon caused by the exchange
of innumerable, force-carrying particles called gauge bosons.
The electromagnetic force, which causes like charges to attract
and dissimilar ones to repel, is transmitted by gauge bosons
called photons, the strong force that binds nucleii together
is transmitted by gluons and the weak force which causes particles
to decay is transmitted by the, recently discovered, W and
Z Intermediate Vector Bosons. In an analogous way, physicists
believe that gravity is transmitted by particles called Gravitons.
If gravity really does have such a quantum property, its effects
should appear once quarks and electrons can be forced to within
10(-33) centimeter of one another, a distance called the Planck
length. To acheive these conditions, quarks and electrons
will have to be collided at energies of 10(19) GeV. An accelerator
patterned after the 2-mile, Stanford Linear Accelerator would
have to be 1 light-year in length to push particles to these
incredable energies! Fortunatly, what humans find impossible
to do, Nature with its infinite resources finds less difficult.
Before the universe was 10(-43) second old, matter routinely
experienced collisions at these energies. This period is what
we call the Planck Era.
THROUGH
A LOOKING GLASS, DARKLEY
Since our technology
will not allow us to physically reproduce the conditions during
these ancient times, we must use our mathematical theories
of how matter behaves to mentally explore what the universe
was like then. We know that the appearence of the universe
before 10(-43) second can only be adequatly described by modifying
the Big Bang theory because this theory is, in turn, based
on the General Theory of Relativity. General Relativity tells
us how gravity operates on the macroscopic scale of planets,
stars and galaxies. At the Planck scale, we need to extend
General Relativity so that it includes not only the macroscopic
properties of gravity but also is microscopic characteristics
as well. The theory of 'Quantum Gravity' is still far from
completion but physicists tend to agree that, at the very
least, Quantum Gravity must combine the conceptual elements
of the two great theories of modern physics: General Relativity
and Quantum Mechanics.
In the language
of General Relativity, gravity is a consequence of the deformati
on of space caused by the presence of matter and energy. Gravity
is just another name for the amount of curvature in the geometry
of 3-dimensional space. In Quantum Gravity theory, gravity
is produced by massless gravitons so that gravitons now represent
individual packages of curved space that travel through space
at the speed of light.
The appearence
and dissappearence of innumerable gravitons gives the geometry
of space a very lumpy and dynamic appearance. John Wheeler
at Princeton University thinks of this as a foamy, sub-structure
to space where the geometry of space twists and contorts so
that far flung regions of space may suddenly find themselves
connected by 'wormholes' which constantly appear and dissappear
within 10(-43) seconds. Even as you are reading this article,
this frenetic activity is occurring in the hyper-microscopic
domain, 100 billion billion times smaller than the nucleus
of an atom. For a comparison, the size of the sun and the
size of a single atom stand in about this same proportion.
Although Quantum Gravity effects are completely undetectable
today at the atomic and nuclear scale, during the Planck Era,
macroscopic and microscopic worlds merged and the Quantum
Gravity of the microcosm suddenly became the Quantum Cosmology
of the macrocosm!
QUANTUM
COSMOLOGY
As we approach
the end of the Planck Era, the random appearance and dissappearance
of innumerable gravitons will eventually force us to give
up the concept of a specific geometry to 3-dimensional space.
Instead, the geometry at a given moment will have to be thought
of as an average over all 3-dimensional space geometries that
are possible. Once again, the reason for this is that particles
are squeezed so closely together that we can now see individual
gravitons moving around in the space between them causing
space to become curved. We can no longer get away with saying
that the space between two quarks, for example, is flat. This
is what we mean when we say that the gravitational force between
them is insignificant when compared to the other three forces
of Nature.
To make matters
much worse, not only will Quantum Gravity not allow us to
calculate the exact 3-dimensional geometry to space but, at
the Planck scale, it will not allow us to simultaneously determine
its exact geometry and precise rate of change in time. What
this means is that we may never be able to calculate with
any certainty exactly what the history of the universe was
like before 10-43 second. Today, the large-scale geometry
of space is one of three possible types: flat and infinite,
negatively curved and infinite or positively curved and finite.
During the Planck Era, the 'large-scale' geometry was contorted
by wormholes and and infinite number of possibilities were
possible. To probe the history of the universe then would
be like trying to trace your ancestral roots if every human
being on earth had a possibility of being one of your parents.
Now try to trace your family tree back a few generations!
The farther back in time you go, the greater are the number
of possible ancestors you could have had. An entirely new
conception of what we mea n by 'a history for the universe'
will have to be developed. Even the concepts of space and
time will have to be completely re-evaluated in the face of
the qua ntum fluctuations of spacetime at the Planck Era!
THE
BIRTH OF THE UNIVERSE
The picture
that seems to emerge from using our sketchy outline of what
Quantum Gravity theory might look like is that as we approach
the Planck Era, gravitons are exchanged between quarks and
electrons with increasingly higher energy and in greater number.
By the time we reach the end of the Planck Era at 10(-43)
second, gravitons will begin to carry as much energy as the
other force carriers (Gluons, IVBs and Photons). At still
earlier times, a period of complet e symmetry and unification
between all the natural forces will ensue. Only one super-unified
force exists here (gravity) and only one kind of particle
dominates the activity of this age(Gravitons).
During the early
70's, the Russian physicists Ya. Zel'dovitch and A. Starobinski
of the USSR Academy of Science proposed that the rapidly changing
geometry of space during the Planck Era may actually have
created all the matter, anti-matter and radiation that existed
soon after Creation. In their picture of Creation, the rapidly
changing geometry of space created particles and anti-particles
with masses of 10(19) GeV. This production of matter and anti-matter
removed energy from the enormous fluctuations occuring in
the geometry of space and eventually succeeded in damping
them out altogether by the end of the Planck Era. They also
found that the rate of particle creation increased as more
and more particles were created.
Several recent
studies by Physicists Edward Tryon of Hunter College, R. Brout,
F. Englert and E. Gunzig of the University of Brussels and
david Atkatz and Heinz Pagels of the Rockefeller University
have shed additional light on what Creation may have been
like. Imagine if you can, nothing at all! This is the primordial
vacuum of space. There is complete darkness here, no light
yet exists. The number of dimensions to space was probably
not the normal 3 that we are so accustomed to but may have
been as high as 11 according to Supergravity theory! In this
infinite emptiness, random fluctuations occurred that ever
so slightly changed the energy of the vacuum at various points
in space. Eventually, one of these fluctuations attained a
critical energy and began to grow. As it grew, very massive
particles called leptoquarks and anti-leptoquarks were created,
causing the expansion to accelerate. This is much like a ball
rolling down a hill that moves slowly at first and then gains
momentum. The expansion of the proto-universe, in turn, caused
still more leptoquarks to be created. This furious cycle continued
until, at long last, the leptoquarks decayed into quarks,
leptons (electrons, muons etc) and their anti-particles and
the universe emerged from the Planck Era. Particle creation
stopped once the fluctuations in the geometry of space subsided.
So, we are left
with the remarkable possibility that, in the beginning, there
ex isted quite literally, nothing at all and from it emerged
nearly all of the matter and radiation that we now see. This
process has been described by the physicist Frank Wilczyk
at the University of California, Santa Barbara by saying,
" The reason that there is something instead of nothing
is that nothing is unstable". A ball sitting on the summit
of a steep hill needs but the slightest tap to set it in motion.
A random fluctuation in space was apparently all that was
required to unleash the incredable latent energy of the vacuum,
thus creating matter and energy and an expanding universe
from 'nothing at all'.
The universe
did not spring into being instantaneously but was created
a little bit at a time in a 'bootstrap' process. Once a few
particles were created by quantum fluctuations of the empty
vacuum, it became easier for a few more to appear and so,
in a rapidly escalating process, the universe gushed forth
from nothingness.
How long did
this take? The primordial vacuum could have existed for an
eternity before the particular fluctuation that gave rise
to our universe happened. Physicist Edward Tryon expresses
this best by saying that " Our universe is simply one
of those things that happens from time to time".
The principles
of Quantum Gravity may ultimatly force us to reconsider questions
like 'What happened before the Big Bang?' because they imply
the existence of something (time) that may not have any meaning
at all. These questions may be as empty of meaning as an explorer
on the north pole asking, 'Which way is North?'. Only the
complete theory of Quantum Gravity may tell us how to ask
the right questions!
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