The Big Bang (AQA GCSE Physics): Revision Note

The Big Bang Theory

• Around 14 billion years ago, the universe began from a very small region that was extremely hot and dense

• Then there were a series of explosions, which we call the Big Bang

• This caused the universe to expand, cooling as it does so, to form the universe we currently observe

• Each point expands away from the others

  • This is seen from galaxies moving away from each other, and the further away they are the faster they move

• As a result of the initial explosions, the universe continues to expand

All galaxies moving away from each other, indicating that the universe is expanding

Evidence for the Big Bang

• By observing the light spectrums from supernovae in other galaxies there is evidence to suggest that distant galaxies are receding (moving further apart) ever faster

  • These observations were first made in 1998

• The light spectrums show that light from distant galaxies is redshifted, which is evidence that the universe is expanding – the galaxies are moving away from us - and, indeed, each other

• This is what happens in an explosion

  • Matter is first densely packed and as it explodes it, it moves out in all directions getting further and further from the source of the explosion

  • Some matter will be lighter and travel at a greater speed, further from the source of the explosion

  • Some matter will be heavier and travel at a slower speed, closer to the source of the explosion

• If you were to travel back in time and compare the separation distance of the galaxies they would become closer and closer together until the entire universe was a single point

• If the galaxies were originally all grouped together at a single point and were then exploded we would see a similar effect

  • The galaxies that are moving fastest would move the furthest - the distance they move would be proportional to their speed

  • The galaxies that are moving slowest would move the least