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I Exponential expansion of inflation

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  1. Apr 26, 2016 #1
    The expansion of the inflationary universe is said to be roughly exponential. Why is it called "roughly" exponential?
     
  2. jcsd
  3. Apr 26, 2016 #2

    PeterDonis

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    In what source? Please give a specific reference.
     
  4. Apr 27, 2016 #3
    It's mentioned in most cosmology texts, e.g. Cosmology by Steven Weinberg, in Inflation chapter.
     
  5. Apr 27, 2016 #4

    PeterDonis

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    Ok, so can you give a specific quote and page/section reference?
     
  6. Apr 27, 2016 #5
    ".....there was an earlier period of inflation, when the energy density of the universe was dominated by a slowly varying vacuum energy, and a(t) grew more or less exponentially." Pg. 201.
     
  7. Apr 27, 2016 #6

    PeterDonis

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    I would say the "more or less exponentially" is a consequence of the "slowly varying vacuum energy". As I understand it, only a vacuum energy that is exactly constant will lead to an expansion that is exactly exponential.
     
  8. Apr 27, 2016 #7

    Chalnoth

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    It's more that only in a universe with nothing in it but vacuum energy will the expansion be exactly exponential. It's not quite exponential because there's other matter around.
     
  9. Apr 27, 2016 #8

    PeterDonis

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    Is there, though? As I understand the basic inflation model, the Standard Model fields are all in their vacuum states during inflation, and all of these fields have zero vacuum expectation value for energy; they only get reheated to highly non-vacuum, high temperature states at the end of inflation.
     
  10. Apr 27, 2016 #9

    Chalnoth

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    Argh, sorry, you're right. I was thinking of the current near-exponential expansion. Never mind.

    Yes, expansion during inflation isn't quite exponential because the field that drives inflation isn't constant. The field just varies slowly enough that near-exponential expansion occurs.
     
  11. Apr 28, 2016 #10
    Thank you for clarifying the issue.
     
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