The 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.
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