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How big do we need for comsological principle?

  1. May 21, 2012 #1
    When we say the universe is homogenous and isotropic . How many Mega PArsecs are we talking about? Preusmably we all agree its not homogenous or isotropic on small scales. So where is the border and how when was it established? Is the current estimate, whatever it is, as recent as Sloan Digital Sky survey or much older than that?
  2. jcsd
  3. May 21, 2012 #2


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    There's a diagram on Ned Wright's site. It's a gradual transition - the larger the scale, the more homogeneous.
  4. May 22, 2012 #3


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    Roughly 80Mpc or so.
  5. May 23, 2012 #4
    Agh thanks for that, wanted it for my cosmology exams which was yesterday ,think I aced it and you guys have been enormous help in general, Physics forums rock
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