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I Reheating and the horizon problem - chicken and egg?

  1. Jul 25, 2016 #1
    One of the benefits of inflation often mentioned in beginner treatments is that it solves the horizon problem by taking a volume which was in thermal equilibrium and expanding it so much that it is now larger than the observable universe thus explaining how the CMB temperature is so uniform.

    Reheating says the majority of the particle contents of the universe were created as the potential oscillated around the minimum (the "true vacuum" value) at the end of inflation.

    This combination of descriptions appears to create a "chicken and egg" paradox, the matter was produced at the end of inflation by reheating but needed to have reached equilibrium before inflation in order to be solve the horizon problem.

    What is the correct timeline and dependency for these processes?
  2. jcsd
  3. Jul 25, 2016 #2


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    There is no need to reach global equilibrium before inflation. Inflation blows up the tiniest region to immense size and washes out any initial state. All that is left after is the inflaton field that will be the same everywhere in the observable universe.

    The point is that inflation creates a homogeneous initial condition for the remaining history of the universe.
  4. Jul 25, 2016 #3
    So are you saying that because the inflaton field when it started to decay had a homogeneous density when its energy was converted to matter through reheating, that resulted in the homogeneous observed horizon temperature? That makes sense to me, thanks.
  5. Jul 29, 2016 #4


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    As long as you keep in mind that reheating didn't cause the CMB ;)
  6. Jul 29, 2016 #5
    Well there might be a few interesting steps in between but I relate that to Edward Harrison's quote "Hydrogen is a light, odorless gas, which, given enough time, turns into people." :wink:
  7. Aug 4, 2016 #6


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    A waste of perfectly good hydrogen gas, in some cases.
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