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I Causally separated regions in CMB?

  1. Jul 12, 2016 #1
    So I have heard it mentioned that there are causally separate regions in the CMB. For instance a point A and point B that we can see here on earth, but are outside of each other's light cones. My question is then, how far apart are these points A and B at minimum to be causally separate in this way.

    Also, is this the motivation behind superluminal inflation theories?
  2. jcsd
  3. Jul 12, 2016 #2


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    Keep in mind the observable universe is the exact same size for all observers at any given instant in time. The size of the observable universe is essentially limited to the distance light has had time to travel since CMB photons were emitted. CMB photons we view today were originally emitted at a distance of 42 million light years from earth - and any other observer in the universe. That distance has since grown to over 46 billion light years for us, as well as any other observer in the universe. The light from remote regions of the universe have barely had enough time to reach earth, much less the opposite side of the universe currently observable from earth. Inflation is mainly motivated by the fact the CMB is in thermal equilibrium. This is difficult to explain if portions of the CMB were out of causal contact in the early universe.
  4. Jul 12, 2016 #3

    George Jones

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