The 'Huge-LQG' quasar 'structure' does not violate homogeneity

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Discussion Overview

The discussion revolves around the Huge-LQG quasar structure and its implications for the cosmological principle and the assumption of homogeneity in the Universe. Participants explore the validity of recent claims regarding this structure and its relationship to cosmological uniformity.

Discussion Character

  • Debate/contested, Conceptual clarification, Exploratory

Main Points Raised

  • Some participants express excitement about the discovery of the Huge-LQG quasar structure, initially thought to challenge the cosmological principle.
  • One participant cites a recently published paper that argues the quasars actually support homogeneity, suggesting that the Huge-LQG does not constitute a significant structure.
  • Another participant reflects on the need to adjust their understanding of homogeneity, indicating a shift in the threshold value from 100 Mpc to 130 Mpc.
  • There are mentions of historical challenges to the assumption of uniformity in cosmology, including phenomena like "dark flow," the Large Quasar Group, and the "Sloan Great Wall," which have sparked debates about homogeneity and isotropy.
  • A participant expresses a desire for a comprehensive review article that addresses various challenges to the Cosmological Principle, rather than focusing solely on the Large Quasar Group.

Areas of Agreement / Disagreement

Participants do not reach a consensus; there are competing views regarding the implications of the Huge-LQG structure on the cosmological principle, and the discussion reflects ongoing uncertainty about the nature of homogeneity in cosmology.

Contextual Notes

Participants note that challenges to homogeneity often fade into acceptance as statistical fluctuations, but the discussion remains open regarding the validity of these challenges and the overall acceptance of the Cosmological Principle.

Sesh
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There was some excitement a few months ago about the discovery of the Huge-LQG quasar structure, claimed to be the "largest structure in the Universe", which was said to violate the cosmological principle and the assumption of homogeneity of the Universe. Some previous threads on this topic on this forum are here and here.

Turns out this claim is wrong. A recently published paper (journal version here, free access version here) shows that the quasars actually support homogeneity as expected. A blog post explaining the issues at a less technical level is

Quasars, homogeneity and Einstein

A one-line summary would be "structures do not invalidate homogeneity; and the Huge-LQG is not really a structure anyway".
 
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Very interesting, thanks for the link
 
thats good news thanks for posting that, lol I will have to adjust my thinking on when Homogenous is considered. I used to use the value 100 Mpc. I'll have to adjust to 130 Mpc.
 
It seems that cosmologists like to challenge their own assumption of uniformity. From time to time some observations are found that seem to indicate significant nonuniformity and we hear doubts about homogeneity and isotropy (the roughly even distribution of matter at large scale).
Examples: "dark flow", Large Quasar Group (LQG), "Sloan Great Wall", "cold spot" or "great void".

After a while the excitement about a particular challenge quiets down and whatever it is seems to be accepted as understandable as a fluke or statistical fluctuation within the context of overall large-scale average uniformity. I don't know much about this at a detailed level, only a vague impression of general consensus that the Cosmological Principle still seems acceptable.

I wonder if there's a recent review article about this. Not just Large Quasar Group or anyone specific challenge, but giving an overview.
 

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