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Horizons in Cosmology

  1. Oct 21, 2009 #1
    What is the difference of cosmological horizon and particle horizon in cosmology?
  2. jcsd
  3. Oct 21, 2009 #2
    Nobody knows the answer?
  4. Oct 22, 2009 #3
  5. Oct 22, 2009 #4
    Thx Chronon! I benefited a lot from your website, which is really cool! lol!

    I have two more question: the cosmological horizon people often talk about actually means the the cosmological event horizon, doesn't it?
    You said:"for particle horizons to occur the rate of expansion of the universe (the derivative of the scale factor with time) must be infinite at time zero.", why?
    Last edited: Oct 22, 2009
  6. Oct 23, 2009 #5
    I think that 'people' are sometimes confused about the issue, but that would be the most reasonable interpretation of cosmological horizon.
    Well a freely coasting a universe without large scale gravity or cosmological constant - the (0,0) universe, also known as the Milne universe - doesn't have particle horizons. If you transform to conformal coordinates (See http://www.astro.ucla.edu/~wright/cosmo_03.htm#MSTD) then the conformal time goes back to minus inifinity.
  7. Oct 23, 2009 #6
    But in the Milne universe we still have the boundary of the observable universe, do we? Can we refer to it as a particle horizon? thx
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