Earth and Space Science / Unit 10: Stars, Galaxies and the Universe
10.6 The Big Bang and Expansion
Notes
The Big Bang theory: the universe began about 13.8 billion years ago as extremely hot and dense, and has expanded and cooled ever since. It was not an explosion into space; space itself expands.
- Hubble's law: distant galaxies move away faster in proportion to distance, shown by redshift (light stretched to longer wavelengths).
- Hubble's law: $v = H_0 d$. With $H_0 \approx 70$ km/s per Mpc, a galaxy 100 Mpc away recedes at about $7{,}000$ km/s.
- Redshift is like the Doppler effect: sources moving away have longer wavelengths.
Practice
Redshift of distant galaxies shows that they are:
Their light wavelengths are stretched.
The universe is about:
Estimated from expansion and cosmic microwave background.
Using $v = H_0 d$ with $H_0 = 70$ km/s per Mpc, a galaxy 200 Mpc away recedes at:
$70 \times 200 = 14{,}000$ km/s.
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