The isotropic blackbody CMB as evidence for a homogeneous universe

Abstract

The question of whether the Universe is spatially homogeneous and isotropic on the largest scales is of fundamental importance to cosmology, but has not yet been answered decisively. Surprisingly, neither an isotropic primary CMB nor combined observations of luminosity distances and galaxy number counts are sufficient to establish such a result. The inclusion of the Sunyaev-Zel'dovich effect in CMB observations, however, dramatically improves this situation. We show that even a solitary observer who sees an isotropic blackbody CMB can conclude that the universe is homogeneous and isotropic in their causal past when the Sunyaev-Zel'dovich effect is present. Critically, however, the CMB must either be viewed for an extended period of time, or CMB photons that have scattered more than once must be detected. This result provides a theoretical underpinning for testing the Cosmological Principle with observations of the CMB alone.

5 pages, 1 figure

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• Inhomogeneous cosmology and backreaction: Current status and future prospects
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• How Problematic is the Near-Euclidean Spatial Geometry of the Large-Scale Universe?
• What if Planck's Universe isn't flat?
• Backreaction and FRW consistency conditions
• Quantum Newtonian cosmology and the biconfluent Heun functions
• Simulated reconstruction of the remote dipole field using the kinetic Sunyaev Zel'dovich effect
• Measuring the Homogeneity of the Universe Using Polarization Drift
• Evaluating backreaction with the ellipsoidal collapse model
• Spectral Distortion in a Radially Inhomogeneous Cosmology
• A Test for the Zero Mean Hypothesis in Cosmology