GCSE Physics · Edexcel 1PH0 · Topic 7C
The Big Bang and red-shift
Key points
- Red-shift: light from distant galaxies is shifted to longer wavelengths, showing they are moving away.
- More distant galaxies show greater red-shift, so they are receding faster. This suggests the universe is expanding.
- The Big Bang theory says the universe began about 13.8 billion years ago from a very hot, dense, small region and has expanded and cooled since.
- The Steady State theory said the universe is expanding but new matter is created so it always looks the same.
- The cosmic microwave background (CMB) radiation, found everywhere in the sky, is left over from the early universe. It is explained by the Big Bang but not by Steady State.
- The Doppler effect: waves from a moving source are stretched when it moves away and squashed when it moves towards you.
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The universe is expanding, and it once was very small, hot and dense. This sub-topic explains the evidence for that conclusion and why the Big Bang theory replaced the Steady State theory.
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