Big Dipper Cosmic Ray Hotspot Homogeneity question

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Discussion Overview

The discussion revolves around the implications of a cosmic ray hotspot in the Big Dipper region for the isotropic and homogeneous view of the Universe. Participants explore whether the concentration of high-energy cosmic rays from a specific location challenges established cosmological principles, particularly in relation to the distribution of cosmic structures and the Copernican principle.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • Some participants question if the concentration of 25% of the highest energy cosmic rays from one spot creates issues for the isotropic homogeneous view of the Universe.
  • Others argue that local anisotropies are expected and do not necessarily contradict the overall homogeneity of the Universe.
  • It is noted that the principles of homogeneity and isotropy apply on scales much larger than a galaxy, suggesting that smaller scale variations are permissible.
  • One participant mentions that ultrahigh-energy cosmic rays are primarily detected within 300 million light-years of Earth and are influenced by interactions with the cosmic microwave background radiation.
  • Concerns are raised about whether large-scale structures like superclusters of galaxies could affect the homogeneity assumption, but some participants assert that such structures do not pose a significant issue.
  • It is suggested that the homogeneous assumption is an approximation and that challenges to the ##\Lambda##CDM model would require evidence of more large objects than expected.

Areas of Agreement / Disagreement

Participants express differing views on the implications of the cosmic ray hotspot for cosmological principles. While some believe that local anisotropies are acceptable, others question the extent to which large structures might impact the homogeneity of the Universe. The discussion remains unresolved regarding the significance of these findings.

Contextual Notes

Limitations include the dependence on definitions of homogeneity and isotropy, as well as the unresolved nature of the relationship between cosmic ray sources and large-scale structures.

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The principles of homogeneity and isotropy [i.e, the Copernican principle] only applies on scales much larger than a galaxy.
 
Ultrahigh-energy cosmic rays stem from outside the Milky Way, but are weakened by interactions with the cosmic microwave background radiation — the leftover fingerprint from the Big Bang that kicked off the universe. As a result, 90 percent of the detected ultrahigh-energy cosmic rays originate within 300 million light-years of Earth.

According to Jui, a separate study currently in progress suggests that the distribution of ultrahigh-energy cosmic rays in the northern sky is related to concentrations of large-scale structures like clusters and superclusters of galaxies.



The article mentions superclusters of galaxies. Are these big enough to be a concern for homogeneity?
 
No. You are suggesting extragalactic sources which are not proven to be an issue.
 
Tanelorn said:
The article mentions superclusters of galaxies. Are these big enough to be a concern for homogeneity?
No. Why would they be?

Some level of inhomogeneity is expected at all size scales. The homogeneous assumption is only ever an approximation.

It is possible to challenge ##\Lambda##CDM if it can be shown that there are far more extremely large objects in the observable universe than we would expect given that model. But so far such challenges haven't held up under scrutiny.
 

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