'The universe is expanding and that matter and space expanded violently and rapidly from a very small initial point’. This is what many scientists believe and then went on to the 'big bang' theory. The 'big bang' theory is about how the universe stared. According to this theory, all matter in this universe started in an amazingly tiny point, and then started to get bigger and expand so quickly in a hot explosion. This was the big bang. It is said that the universe is still expanding today.The Big Bang happened around 13.7 billion years ago.
Astronomers have found a cosmic microwave background radiation (CMBR) that is apparently the heat left over from the original explosion.
The Doppler effect is where there is a change in both wavelength and frequency.For example, when a police car goes past, the siren is high-pitched when it is driving towards you and low-pitched when it is away from you. This is because when something moves towards you, the frequency increases whilst the wavelength decreases. When it is moving away from you, the wavelength increases and the frequency increases.
When an object moves away from an observer, its light is affected by the Doppler effect. When we look at the spectrum of a star, we still see an absorption spectrum. But, the pattern of lines has moved towards the red end of the spectrum. The lines are shifted towards the left and right ends of the spectrum.
The further from us a star is, the more its light is red-shifted.