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Radius of the universe

  1. Jun 7, 2010 #1
    What was the size of the 'radius' of the universe when it started to expand acceleratingly about 6 Gyrs ago?
    Last edited: Jun 8, 2010
  2. jcsd
  3. Jun 8, 2010 #2
    Not quite sure what are you asking. You probably asking either about scale factor (a), or about radius of observable universe at the time. Or maybe about distance to the cosmological event horizon ?

    Can you be more specific about what you mean with 'radius of the universe' ?
  4. Jun 8, 2010 #3
    Thank you for clarifying the question before answering it :smile:

    If 'radius' of the universe is a, then cosmic scale factor is a(t), which is dimensionless. a has units of distance, which is presently ~10^29 cm. So I need to know how large was a when the universe started to accelerate ~6 Gyrs ago?
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