Lesson 12, Topic 2
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Expansion of the Universe

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  • In 1922, Alexander Friedmann applied Einstein’s general theory of relativity to the universe and shows that its equations predicted a dynamic, expanding universe rather than a stable, steady state universe
  • Einstein tried to prevent his equations from producing a dynamic solution by adding a ‘fudge factor’ that he called the cosmological constant.
  • Using the world’s biggest telescope in 1923, Hubble observed that the Andromeda nebula (M21) was made up of a huge number of stars. Using the period of Cepheid variable stars, Hubble estimated its distance away from us and concluded that M21 was an island galaxy beyond our own. Hubble had discovered that the universe extended beyond the Milky Way.
  • Hubble then measured the redshift of the light from 46 galaxies and found that the further away a galaxy was, the more its light was redshifted, confirming that the universe was expanding.
  • Recent studies have shown that the rate at which the universe is expanding is increasing.