Scientists believe the Universe began in a hot ‘big bang’ about 13,600 million years ago. The Universe continues to expand today. The evidence for the Big Bang theory includes the existence of a microwave background radiation, and red-shift. Stars do not remain the same, but change as they age.
The Big Bang theory
Scientists have gathered a lot of evidence and information about the Universe. They have used their observations to develop a theory called the Big Bang. The theory states that about 13.7 billion years ago all the matter in the Universe was concentrated into a single incredibly tiny point. This began to enlarge rapidly in a hot explosion, and it is still expanding today.
Evidence for the Big Bang includes:
all the galaxies are moving away from us
the further away a galaxy is, the faster it is moving away.
These two features are found in explosions - the fastest moving objects end up furthest away from the explosion.
Scientists have also detected a cosmic microwave background radiation or CMBR. This is received from all parts of the Universe and is thought to be the heat left over from the original explosion.