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World 2 · The Expanding Universe · 12 min · PRO

The scale factor: a ruler that stretches

How to write expansion in one number

PRO · Cosmos: Big Bang to Now

World 2: The Expanding Universe is part of PRO

The first world of Cosmos: Big Bang to Now is free. PRO opens the other 25 lessons in 6 worlds — simulations, quizzes and all.

  • No centre, no edge: the raisin-bread universe
  • The age of the universe: running the film backwards
  • Accelerating: dark energy
  • Stretched light: Doppler vs cosmological redshift
  • Reading redshift in a spectrum
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