Great attractor and the CMB dipole

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Discussion Overview

The discussion revolves around the Great Attractor and its relationship with the Cosmic Microwave Background (CMB) dipole, exploring concepts of cosmic density variations, the implications of voids and overdense regions, and the potential challenges to existing cosmological models. Participants reference various papers and theories, contributing to an ongoing debate about the nature of cosmic structures and their implications for the universe's overall geometry and expansion.

Discussion Character

  • Debate/contested
  • Exploratory
  • Technical explanation

Main Points Raised

  • Some participants propose that the Great Attractor may not be a singular mystery but rather part of a broader cosmic structure, referencing the Dipole Repeller as a significant factor.
  • Others argue that the existence of dense regions implies the presence of voids, suggesting a balance in cosmic matter distribution.
  • A question is raised about whether the Dipole Repeller can be classified as a "supervoid" and if expansion rates differ between voids and attractor regions.
  • One participant expresses skepticism about the implications of the void/overdense model, suggesting it challenges the cosmological principle and the notion of an infinite universe.
  • Another participant questions the assumption that an infinite universe would necessitate a balanced average matter density in all directions, drawing a parallel to local gravitational influences.
  • References to various studies and papers are made, indicating tensions between cosmic flow measurements and the Lambda Cold Dark Matter (LCDM) model.

Areas of Agreement / Disagreement

Participants express differing views on the implications of cosmic density variations, with no consensus reached on the nature of the Great Attractor, the Dipole Repeller, or the overall structure of the universe.

Contextual Notes

Participants highlight limitations in current models and assumptions, particularly regarding the implications of local flows and the cosmological principle, without resolving these issues.

Chronos
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The Great Attractor has been a source of controversy since its discovery. Some think it is just a fluke, others feel it to be a clue to a greater mystery. This paper; https://arxiv.org/abs/1702.02483, The Dipole Repeller, offers a deeper look without necessarily resolving the enigma.
 
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I don't see an enigma or mystery.
If there can be regions in the cosmos which are unusually dense, there should be other regions almost devoid of matter.
 
Is this Dipole Repeller a "supervoid"? Would it be accurate to say expansion is accelerating faster in these voids than attractor regions?

Edit: I get the sense from this article that focus on the Great Attractor has been overtaken by the Shapley Supercluster (Concentration/Attractor) and the Dipole Repeller:

Arguably, the dominance of the Dipole Repeller over the Shapley Attractor is the main novel and surprising finding of this study.
 
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The void/overdense model has baggage. It certainly suggests, imo, the universe may not be infinite. In an infinite universe the average matter density should balance out in all directions. It's hard to imagine the scale at which a local flow of such magnitude is not highly improbable without creating tension with the cosmological principle.
 
Chronos said:
It certainly suggests, imo, the universe may not be infinite. In an infinite universe the average matter density should balance out in all directions
Why would that be the case? It's like saying that since we're accelerating towards the Andromeda, the universe may not be infinite.
 
At sufficiently large scales, our measurements of cosmic flows are in tension with the LCDM model. That sounds like the makings of a mystery to me. This issue is addressed here; https://arxiv.org/abs/1205.4627, Cosmic Flows surveys and CLUES simulations. Another potential solution is offered here; https://arxiv.org/abs/1607.07377, Frames of most uniform Hubble flow.
 
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