How inflation can give rise to irregularities

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Discussion Overview

The discussion revolves around how inflation in the early universe can lead to both the isotropy and irregularities observed in the Cosmic Microwave Background (CMB). Participants explore the mechanisms behind these phenomena, focusing on quantum fluctuations and their implications during the inflationary period.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants express confusion about how inflation can lead to irregularities in the CMB, despite understanding its role in isotropy.
  • One participant explains that quantum fluctuations in the inflation-driving field are amplified by rapid expansion, becoming the seeds for temperature differences in the CMB.
  • Another participant elaborates that inflation causes exponential expansion, which drags nearby parts of the universe across the event horizon, freezing quantum fluctuations in place when stretched beyond a certain size.
  • A question is raised regarding the estimated values of primordial fluctuations in relation to the observed CMB, specifically asking for references or papers on the topic.

Areas of Agreement / Disagreement

Participants appear to agree on the role of quantum fluctuations during inflation but express varying levels of understanding regarding their implications for irregularities in the CMB. The discussion includes both explanations and questions, indicating that some aspects remain unresolved.

Contextual Notes

There are limitations in the discussion regarding the specific values of primordial fluctuations and their relationship to the CMB, as well as the dependence on definitions related to inflation and quantum fluctuations.

houhou.trad
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I can understand how can inflation give rise to the isotropy of the CMB, but that it can give rise also to the irregularities in the CMB...!?
Please, can anyone explain me this?
thanks.
 
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houhou.trad said:
I can understand how can inflation give rise to the isotropy of the CMB, but that it can give rise also to the irregularities in the CMB...!?
Please, can anyone explain me this?
thanks.
Well, the quantum fluctuations in the field that drives inflation get blown up by the rapid expansion to tremendous scales. These teeny tiny quantum fluctuations, then, become the seeds that grow to form the differences in temperature we see in the CMB.
 
Chalnoth said:
Well, the quantum fluctuations in the field that drives inflation get blown up by the rapid expansion to tremendous scales. These teeny tiny quantum fluctuations, then, become the seeds that grow to form the differences in temperature we see in the CMB.

What a nice and succinct answer!
 
Last edited:
Inflation is exponential expansion, and this expansion makes nearby parts of the Universe gets dragged across one's event horizon. Quantum fluctuations are no exception. They get frozen into place when they get stretched beyond the event-horizon size. Beyond that size, there is no way to communicate across the fluctuation's size.

When it stops, then distant parts of the Universe can return across one's event horizon.

Inflation and the CMB - C.H. Lineweaver
An Exposition on Inflationary Cosmology - G.S. Watson
 
Exclusive of later effects like baryon acoustic oscillations, what are the estimated values of primordial fluctuations in the fractional value of ρ that lead to the observed CMB? For example, over a distance equivalent to 10 Glyr now, was the early variation something like an abiabatic 1 part in 105? Any papers on this?
 
thank you every body
 

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