Big Bang Theory
It is always a mystery about how the universe began, whether if and when
it will
end. Astronomers construct hypotheses called cosmological models that
try to
find the answer. There are two types of models: Big Bang and Steady
State.
However, through many observational evidences, the Big Bang theory
can best
explain the creation of the universe. The Big Bang model postulates
that about
15 to 20 billion years ago, the universe violently exploded
into being, in an
event called the Big Bang. Before the Big Bang, all of the
matter and radiation
of our present universe were packed together in the
primeval fireball—an
extremely hot dense state from which the universe
rapidly expanded.1 The Big
Bang was the start of time and space. The
matter and radiation of that early
stage rapidly expanded and cooled. Several
million years later, it condensed
into galaxies. The universe has continued
to expand, and the galaxies have
continued moving away from each other ever
since. Today the universe is still
expanding, as astronomers have observed.
The Steady State model says that the
universe does not evolve or change in
time. There was no beginning in the past,
nor will there be change in the
future. This model assumes the perfect
cosmological principle. This principle
says that the universe is the same
everywhere on the large scale, at all
times.2 It maintains the same average
density of matter forever. There are
observational evidences found that can
prove the Big Bang model is more
reasonable than the Steady State model. First,
the redshifts of distant
galaxies. Redshift is a Doppler effect which states
that if a galaxy is
moving away, the spectral line of that galaxy observed will
have a shift to
the red end. The faster the galaxy moves, the more shift it has.
If the
galaxy is moving closer, the spectral line will show a blue shift. If
the
galaxy is not moving, there is no shift at all. However, as
astronomers
observed, the more distance a galaxy is located from Earth, the
more redshift it
shows on the spectrum. This means the further a galaxy is,
the faster it moves.
Therefore, the universe is expanding, and the Big
Bang model seems more
reasonable than the Steady State model. The second
observational evidence is the
radiation produced by the Big Bang. The Big
Bang model predicts that the
universe should still be filled with a small
remnant of radiation left over from
the original violent explosion of the
primeval fireball in the past. The
primeval fireball would have sent strong
shortwave radiation in all directions
into space. In time, that radiation
would spread out, cool, and fill the
expanding universe uniformly. By now it
would strike Earth as microwave
radiation. In 1965 physicists Arno Penzias
and Robert Wilson detected microwave
radiation coming equally from all
directions in the sky, day and night, all
year.3 And so it appears that
astronomers have detected the fireball radiation
that was produced by the Big
Bang. This casts serious doubt on the Steady State
model. The Steady State
could not explain the existence of this radiation, so
the model cannot best
explain the beginning of the universe. Since the Big Bang
model is the better
model, the existence and the future of the universe can also
be explained.
Around 15 to 20 billion years ago, time began. The points that
were to become
the universe exploded in the primeval fireball called the Big
Bang. The
exact nature of this explosion may never be known. However,
recent
theoretical breakthroughs, based on the principles of quantum theory,
have
suggested that space, and the matter within it, masks an infinitesimal
realm of
utter chaos, where events happen randomly, in a state called
quantum
weirdness.4Before the universe began, this chaos was all there was.
At some
time, a portion of this randomness happened to form a bubble, with a
temperature
in excess of 10 to the power of 34 degrees Kelvin. Being that
hot, naturally it
expanded. For an extremely brief and short period,
billionths of billionths of a
second, it inflated. At the end of the period
of inflation, the universe may
have a diameter of a few centimetres. The
temperature had cooled enough for
particles of matter and antimatter to form,
and they instantly destroy each
other, producing fire and a thin haze of
matter-apparently because slightly more
matter than antimatter was formed.5
The fireball, and the smoke of its burning,
was the universe at an age of
trillionth of a second. The temperature of the
expanding fireball dropped
rapidly, cooling to a few billion degrees in few
minutes. Matter continued to
condense out of energy, first protons and neutrons,
then electrons, and
finally neutrinos. After about an hour, the temperature had
dropped below a
billion degrees, and protons and neutrons combined and formed
hydrogen,
deuterium, helium. In a billion years, this cloud of energy, atoms,
and
neutrinos had cooled enough for galaxies to form. The expanding cloud
cooled
still further until today, its temperature is a couple of degrees
above absolute
zero. In the future, the universe may end up in two possible
situations. From
the initial Big Bang, the universe attained a speed of
expansion. If that speed
is greater than the universe’s own escape velocity,
then the universe will not
stop its expansion. Such a universe is said to be
open. If the velocity of
expansion is slower than the escape velocity, the
universe will eventually reach
the limit of its outward thrust, just like a
ball thrown in the air comes to the
top of its arc, slows, stops, and starts
to fall. The crash of the long fall may
be the Big Bang to the beginning of
another universe, as the fireball formed at
the end of the contraction leaps
outward in another great expansion.6 Such a
universe is said to be closed,
and pulsating. If the universe has achieved
escape velocity, it will continue
to expand forever. The stars will redden and
die, the universe will be like a
limitless empty haze, expanding infinitely into
the darkness. This space will
become even emptier, as the fundamental particles
of matter age, and decay
through time. As the years stretch on into infinity,
nothing will remain. A
few primitive atoms such as positrons and electrons will
be orbiting each
other at distances of hundreds of astronomical units.7 These
particles will
spiral slowly toward each other until touching, and they will
vanish in the
last flash of light. After all, the Big Bang model is only an
assumption. No
one knows for sure that exactly how the universe began and how it
will end.
However, the Big Bang model is the most logical and reasonable theory
to
explain the universe in modern science.
Bibliography
Boslough,
John. Stephen Hawking’s Universe. New York: Cambridge University
Press,
1980. Caes, J. Charles. Cosmology, The Search For The Order Of
The
Universe. USA: Tab Books Inc., 1986. Gribbin, John. In Search Of The
Big Bang.
New York: Bantam Books, 1986. Holt, Terry. The Universe Next
Door. New York:
Charles Scribner’s Sons, 1985. Kaufmann, J. William III.
Astronomy: The
Structure Of The Universe. New York: Macmillan Publishing
Co., Inc., 1977. Mache,
L. Dinah. Astronomy. New York: John Wiley &
Sons, Inc., 1987. Silk, Joseph.
The Big Bang. New York: W.H. Freeman and
Company, 1989.