Comment on "Hubble flow variations as a test for inhomogeneous cosmology"

Understand

Saulder et al [2019, A&A, 622, A83; arXiv:1811.11976] have performed a novel observational test of the local expansion of the Universe for the standard cosmology as compared to an alternative model with differential cosmic expansion.

• Their analysis employs mock galaxy samples from the Millennium Simulation, a Newtonian $N$-body simulation on a $\Lambda$CDM background.
• For the differential expansion case the simulation has been deformed in an attempt to incorporate features of a particular inhomogeneous cosmology: the timescape model.
• It is shown that key geometrical features of the timescape cosmology have been omitted in this rescaling.