AQA GCSE Physics

Revision Notes

8.2.2 The Big Bang

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

universe-expansion, IGCSE & GCSE Physics revision notes

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

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