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Heterogeneity Mapping of Protein Expression in Tumors using Quantitative Immunofluorescence
07:54

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Published on: October 25, 2011

Is the Universe homogeneous?

Roy Maartens1

  • 1Department of Physics, University of Western Cape, Cape Town 7535, South Africa. roy.maartens@port.ac.uk

Philosophical Transactions. Series A, Mathematical, Physical, and Engineering Sciences
|November 16, 2011
PubMed
Summary
This summary is machine-generated.

Cosmological homogeneity, essential for structure formation, cannot be directly observed. While cosmic microwave background (CMB) isotropy suggests homogeneity, proving it on large scales remains an open question.

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Area of Science:

  • Cosmology
  • General Relativity
  • Astrophysics

Background:

  • The standard model of cosmology assumes homogeneous surfaces for structure formation.
  • Homogeneity is crucial for interpreting cosmic microwave background (CMB) and galaxy distribution observations.
  • Direct observation of homogeneity is impossible on the past light cone.

Purpose of the Study:

  • To investigate the link between observable isotropy and spacetime isotropy.
  • To assess the implications of the Copernican principle for cosmological homogeneity.
  • To determine if current observations can prove large-scale homogeneity.

Main Methods:

  • Analyzing the relationship between isotropic observations on the past light cone and isotropic spacetime geometry.
  • Utilizing CMB data, specifically the dipole, quadrupole, and octupole.
  • Examining galaxy and cluster distributions.

Main Results:

  • Isotropy on the past light cone, combined with the Copernican principle, can imply spacetime isotropy.
  • The vanishing of CMB multipoles (dipole, quadrupole, octupole) is sufficient to impose homogeneity.
  • Current observations show near-isotropy on large scales, but proving near-homogeneity remains challenging.

Conclusions:

  • Direct proof of large-scale cosmic homogeneity is currently unattainable, even with the Copernican principle.
  • Observations of the CMB, galaxies, and clusters can be used to test homogeneity.
  • The question of whether large-scale near-isotropy implies near-homogeneity is an open research problem.