The Big Bang Theory and Red-Shift _ GCSE Physics

The big bang theory is currently the accepted theory for how the universe was created. The theory states that originally all the matter in the universe was concentrated into a single incredibly tiny point, which exploded and began to enlarge rapidly and is still expanding today. We know the universe is expanding because of the Doppler effect. You may have noticed that when an ambulance or police car goes past, its siren is high-pitched as it comes towards you, then becomes low-pitched as it goes away. This effect, where there is a change in frequency and wavelength, is called the Doppler effect and it doesn't only happen with sound. We can see it happening with light when we look at distant stars. The light is being stretched towards the red end of the spectrum because the object is moving away from us, just as it was with the police car. Evidence for this is shown by the location of these black lines in the spectrum of our Sun and in other stars. The black lines are where different elements such as helium absorb light. They are shifted towards the red end of the spectrum because of the Doppler effect. But be careful, just because things moving away from us are shifted towards the red end of the spectrum, doesn't mean they necessarily look red, they just have a longer wavelength.