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.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