CMB: How Was Matter Distributed Before Photon Decoupling?

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Discussion Overview

The discussion centers on the distribution of matter in the universe prior to photon decoupling, as described by the hot Big Bang model. Participants explore concepts related to density perturbations, inflation, and the implications of cosmic microwave background (CMB) observations.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants assert that before photon decoupling, matter was almost perfectly evenly distributed, with early density variations serving as seeds for later galaxy formation.
  • Others clarify that inflation is thought to be responsible for density perturbations, with quantum fluctuations during inflation leading to small density variations in the early universe.
  • One participant questions whether the observed perturbations could arise from chaotic or statistical events, suggesting an alternative perspective on their origin.
  • Another participant notes that while evidence supports the inflation model, it does not conclusively prove it, indicating a level of skepticism regarding the interpretations of the data.
  • There is mention of baryon acoustic oscillations as a line of study linking the CMB and galaxy distributions, which some participants argue correlates well with theoretical predictions.

Areas of Agreement / Disagreement

Participants express differing views on the origins of density perturbations, with some supporting the inflation model and others proposing alternative explanations. The discussion remains unresolved regarding the definitive cause of these perturbations.

Contextual Notes

Participants reference statistical distributions of density variations, specifically mentioning Gaussian and scale-invariant characteristics, but do not delve into the mathematical details or assumptions underlying these concepts.

orricl
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According to the hot Big Bang model, about 380000 years after that violent explosion, the universe was transparent to radiation but before that moment photons were trapped in the soup of ionized plasma. And my question is how does the matter distribute in space before the photons decouple from the ionized plasma?
 
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orricl said:
According to the hot Big Bang model, about 380000 years after that violent explosion,
There is a very common misconception here. The Big Bang was not an explosion in the common meaning of the word. Throughout the history of the Universe, matter and radiation have both been relatively evenly spread in it. This is not and have never been a problem for the Big Bang model.
 
orricl said:
According to the hot Big Bang model, about 380000 years after that violent explosion, the universe was transparent to radiation but before that moment photons were trapped in the soup of ionized plasma. And my question is how does the matter distribute in space before the photons decouple from the ionized plasma?
Before decoupling, the matter was almost perfectly evenly-distributed. We can see the photons that resulted from that decoupling, and the temperature variance is approximately one part in 100,000. This roughly correlates to a density variance.

Those early density variations became the seeds of later galaxy clusters and galaxies, and by measuring the statistical distribution between later galaxies and the CMB we can show that the two match to a high degree of accuracy. This line of study is known as, "baryon acoustic oscillations".
 
I want to clarify something:
Is "inflation" the reason of the density perturbations?
 
ChrisVer said:
I want to clarify something:
Is "inflation" the reason of the density perturbations?
Inflation does have the property that quantum fluctuations during inflation become small density variations in the early universe, variations that eventually grow to become galaxies, galaxy clusters, etc.

Those density variations are currently the primary piece of evidence we have for inflation, as their statistics are precisely what was predicted.
 
It's good to know that the evidence incriminates the suspect we thought it was.
That does not prove much though, other than humans seek patterns.
 
Last edited:
rootone said:
It's good to know that the evidence incriminates the suspect we thought it was.
That does not prove much though, other than humans seek patterns.
Huh ?
 
Couldn't e.g. those perturbations happen due to chaotic/statistical events?
 
ChrisVer said:
Couldn't e.g. those perturbations happen due to chaotic/statistical events?
They are, but from a very particular random distribution (Gaussian, scale-invariant).
 

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