The Universe filled with a "homogeneous perfect fluid"

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SUMMARY

The discussion centers on the concept of the universe as a "homogeneous perfect fluid," as described in Schutz's textbook. Participants clarify that this model replaces the outdated notion of ether, positing that the universe is filled with a uniform density and pressure of matter, dark matter, radiation, and dark energy, leading to the Friedmann-Lemaître-Robertson-Walker (FLRW) solution. The conversation highlights the limitations of the FLRW model, noting that while it serves as a good approximation at large scales, the universe exhibits significant local deviations from homogeneity and isotropy, necessitating more complex models for structure formation.

PREREQUISITES
  • Understanding of General Relativity (GR) principles
  • Familiarity with Friedmann-Lemaître-Robertson-Walker (FLRW) cosmology
  • Knowledge of the cosmological principle and its implications
  • Basic concepts of dark matter and dark energy in cosmology
NEXT STEPS
  • Study the derivation of the Friedmann equations from the cosmological principle
  • Explore the role of dark energy in the Lambda-CDM model
  • Investigate structure formation in cosmology using kinetic theory
  • Learn about perturbations in the context of cosmic microwave background radiation
USEFUL FOR

Astronomers, cosmologists, and physics students interested in the large-scale structure of the universe and the theoretical frameworks that describe it.

  • #31
Well, it applies in a very coarse-grained sense. You have to average over spatial volumes of some 250 Mio. light years:

https://en.wikipedia.org/wiki/Cosmological_principle#Observations

It's not a superfluid, but the "energy content" consists (according to nowadays "concordance model") of 30% of heavy particles ("cold"/"non-relativistic") (25% are "dark matter" made of yet unknown particles and about 5% is made up of the known standard-model particles). The remaining 70% is "dark energy", describable by a cosmological constant, which is the most enigmatic component.

https://en.wikipedia.org/wiki/Lambda-CDM_model
 

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