What is the Big Bang? The Big Bang is a theory that explains how the Universe began twelve
to fifteen billion years ago.
Until this century, most people believed that the Universe had no beginning. It had always
just been there. Then in the 1920’s, Edwin Hubble, a famous astronomer, discovered
something that led to the Big Bang theory. He found that the Universe is expanding in
every direction. He also discovered that galaxies twice as far away from us are moving
away twice as fast. Something BIG had to cause this movement.
The Universe is expanding from the force of a huge explosion--the Big Bang. Before the
explosion there was nothing. Just emptiness. Then a huge fireball--the Primordial
Fireball--exploded. The fireball was unbelievably hot and bright. It sent out radiation.
It's hard to believe, but in an instant all matter was created. Then bits of matter began
to cool and form atoms. We think that hydrogen formed first. Helium was formed soon after
that.
As the Universe expanded and cooled, giant clouds of gases formed. Then these clouds broke
up and became galaxies of stars. Today, billions of years later, these galaxies continue
moving away from each other because of the force of the Big Bang. This is called the Red
Shift.
Scientists are still making discoveries that prove the Big Bang
theory. Astronomers have found primordial helium in the farthest parts of the Universe. It
may have been left over from the Big Bang. Scientists also discovered extraterrestrial
noise. This noise is believed to be radiation left over from the Big Bang. NASA’s
COBE satellite found these cosmic microwaves too.
Will the Universe expand forever? There are two theories: The “Never-ending”
theory and the “Big Crunch” theory. The “Never-ending” theory says
that the Universe will continue to expand until the galaxies die away. This would be
similar to sparks dying out. The “Big Crunch” theory says that eventually
gravity will begin to pull the galaxies back inward until they crash into each other. It
should take about a trillion years for either theory to happen, so don't worry.
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