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Measuring the homogeneity of the universe using polarization drift

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We propose a method to probe the homogeneity of a general universe, without assuming symmetry. We show that isotropy can be tested at remote locations on the past lightcone by comparing the line-of-sight and transverse expansion rates, using the time dependence of the polarization of Cosmic Microwave Background photons that have been inverse-Compton scattered by the hot gas in massive clusters of galaxies. This probes a combination of remote transverse and parallel components of the expansion rate of the metric, and we may use radial baryon acoustic oscillations or cosmic clocks to measure the parallel expansion rate. Thus we can test remote isotropy, which is a key requirement of a homogeneous universe. We provide explicit formulas that connect observables and properties of the metric.
Original languageEnglish
Article number048
Number of pages14
JournalJournal of Cosmology and Astroparticle Physics
Publication statusPublished - 28 May 2019


  • 1902.11298v2

    Rights statement: This Accepted Manuscript is available for reuse under a CC BY-NC-ND 3.0 licence after the 12 month embargo period provided that all the terms of the licence are adhered to.

    Accepted author manuscript (Post-print), 351 KB, PDF document

    Licence: CC BY-NC-ND

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