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.4
Before 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
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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.