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Testing the Cosmological Principle

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In the ΛCDM cosmological model it is assumed that the universe is statistically isotropic and homogeneous when averaged on scales >100 Mpc. That the CMB has a large dipole anisotropy is explained as due to our ‘peculiar motion’ because of local inhomogeneity. There should then be a similar dipole in the sky distribution of high redshift sources. Using a catalogue of 1.4 million quasars we find this standard expectation is rejected at 4.9σ. This calls into question the usual practice of boosting to the ‘CMB frame’ to analyse cosmological data. In the heliocentric frame the acceleration of the Hubble expansion rate is also a dipole (at 3.9σ) aligned with the CMB . It can no longer be argued that boosting to the CMB frame makes this acceleration look isotropic, so it can be interpreted as due to Λ.

This talk is part of the Theoretical Physics Colloquium series.

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