Was Dark Energy Dominant Over Matter in Early Universe?

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Discussion Overview

The discussion centers on the role of dark energy in the early universe, specifically whether dark energy was dominant over matter during that period and the implications for cosmic expansion. Participants explore theoretical models, observational data, and the relationship between dark energy and matter density at high redshifts.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants reference recent observations suggesting a dark energy equation of state parameter w < -1.3 for z > 1.5, questioning the dark energy density compared to matter density during that time.
  • One participant argues that the universe was undergoing decelerating expansion at that time, with the acceleration phase starting later, and suggests that dark energy density increased at early times before leveling out.
  • A participant estimates that dark energy density at z=1.5 was approximately 15% of the total energy density, compared to around 0.5% at z=7.5, implying that dark energy was not dominant early on.
  • There is speculation about potential interactions between matter and dark energy or systematic effects related to early quasars, as well as the impact of spatial curvature on observations.
  • Another participant expresses a view that both dark matter and baryonic matter densities decrease with expansion, while dark energy density remains constant, leading to an increase in its relative density.
  • A clarification was made regarding a misstatement about the comparison of dark matter and dark energy densities.

Areas of Agreement / Disagreement

Participants do not reach a consensus on whether dark energy was dominant over matter in the early universe. Multiple competing views and interpretations of the data remain present in the discussion.

Contextual Notes

Participants note potential limitations in their models and assumptions, including the dependence on observational data and the unresolved nature of discrepancies in measurements of the Hubble constant (H0) between different sources.

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TL;DR
Dark energy density w < -1.3 at Z > 1.5
Recent observations report w < -1.3 for z > 1.5. What was the dark energy density compared to matter density during that time? Was the universe briefly accelerating?
 
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At the time, the expansion of the universe was a decelerating expansion. The acceleration phase didn't start until later.

What this is saying is that according to their model, the density of dark energy seems to have increased at early times and then leveled out.

My guess is that there's something wrong with their model. My reasoning is as follows:
1) The dark energy density was much smaller before ##z=1.5## as a fraction of the total density compared to its value today. By my estimate, the dark energy density at ##z=1.5## would have been approximately 15% of the total energy density. At the start of the range, ##z=7.5##, the dark energy density would have been around 0.5% of the total.
2) Because the density of dark energy was much smaller as a percent of the total, a small misunderstanding of matter, which has by far the largest contribution to the expansion, would show up as a variation of dark energy instead.

There might be something interesting going on here, such as an interaction between matter and dark energy. But it might also just be a small systematic effect for early quasars. Or non-zero spatial curvature.

Whatever is going on here, though, it's probably related to the discrepancy in measurements of ##H_0## between the CMB and nearby observations.
 
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My impression of this picture (I may be wrong) is that dark matter and baryonic matter both decrease in density as the universe expands. On the other hand dark energy density remains constant, so that its relative density is increasing.
 
kimbyd said:
Because the density of dark matter was much smaller
As compared to?
 
Ranku said:
As compared to?
Sorry, that was a misstatement. I've fixed it. Should be dark energy was much smaller as a fraction of total energy.
 
Thanks for answering.
 

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