Charles tells us about his recent work with Camille Bonvin on the dipole anisotropy tension.

We expect there to be dipoles in most observables because of our motion through the (statistically) homogeneous and isotropic universe. However, there appears to be a 4.9σ tension between the magnitude of the dipole as measured from the CMB and as measured from quasars in the local-ish universe.

Charles and Camille have looked at the redshift evolution of the relevant physics that goes into the local-ish prediction for the dipole. They find that if both the magnification bias and the spectral index of the source change with redshift, the naive expectation for the magnitude of the dipole, given a particular velocity can change.

Therefore, they re-derive an alternative formula that is explicitly redshift dependent and more easily applied directly to redshift dependent observations

They look at a sample of quasars observed by eBOSS to see how the relevant quantities change with redshift. They do change and Charles and Camille show that *if* the larger observed sample of quasars did have the same redshift dependence then the tension would be substantially reduced.

It is more difficult to measure the full redshift dependence of the larger quasar sample used to measure the dipole as they haven’t all been measured with one telescope/survey. It is unclear what the actual tension would be between theory and observation were one to be able to take the effect C&C point out into account.

Time will tell with more detailed and larger surveys…

Charles: https://cosmology.unige.ch/users/charles-dalang
Paper: https://arxiv.org/abs/2111.03616