Exponential expansion of inflation

  • #1
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The expansion of the inflationary universe is said to be roughly exponential. Why is it called "roughly" exponential?
 

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  • #2
PeterDonis
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The expansion of the inflationary universe is said to be roughly exponential.
In what source? Please give a specific reference.
 
  • #3
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It's mentioned in most cosmology texts, e.g. Cosmology by Steven Weinberg, in Inflation chapter.
 
  • #4
PeterDonis
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It's mentioned in most cosmology texts, e.g. Cosmology by Steven Weinberg, in Inflation chapter.
Ok, so can you give a specific quote and page/section reference?
 
  • #5
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".....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.
 
  • #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.
 
  • #7
Chalnoth
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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.
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.
 
  • #8
PeterDonis
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It's not quite exponential because there's other matter around.
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.
 
  • #9
Chalnoth
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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.
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.
 
  • #10
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Thank you for clarifying the issue.
 

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