Big Bang Theory
...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. 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. 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....
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