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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
When teaching the idea of expansion to my GCSE students, I would give them each a balloon, and they would draw galaxies on it. Then they would inflate the balloon and watch the galaxies separating. The most difficult concept for students, in my experience, is the idea that space itself is expanding. That's why galaxies further away from us are moving away from us at a greater speed. There is more space between us, and that space is expanding. Using the balloons allows students to reinflate their 'universe' as many times as they need to get their heads around the idea. Using tangible, hands-on methods like this aids understanding and also recall, because the memory of the knowledge (that space itself expands) is attached to a memorable event (the balloon activity).
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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