Speaker
Description
In the standard cosmological model, the expansion is expected to be statistically isotropic around any observer. Here, we test this prediction in the local Universe through an analysis of the expansion–rate fluctuation field reconstructed from the Cosmicflows-4 distance data.
We perform analyses up to redshift $z=0.1$ and examine not only the dipole, commonly associated with bulk flows in the standard model, but also the quadrupole component of the expansion field. This allows us to test predictions of the standard cosmological model directly, without assuming any of its ingredients in the definition of the observable being tested.
While the multipole amplitudes remain largely consistent with $\Lambda$CDM expectations, showing at most a marginal tension, the dipole and quadrupole exhibit a persistent coherence in both direction and polarity across redshift, a configuration with a probability $\lesssim 0.001\%$. This alignment hints at a possible violation of statistical isotropy, a cornerstone of the Cosmological Principle.