Abstract
We have shown (Colin et al. 2019) that the acceleration of the Hubble
expansion rate inferred from Type Ia supernovae is essentially a dipole with
3.9$\sigma$ significance, approximately aligned with the CMB dipole, while its
monopole component which may be interpreted as due to a Cosmological Constant
(or more generally dark energy) is consistent with zero at 1.4$\sigma$. This is
challenged by Rubin & Heitlauf (2019) who assert that we incorrectly assumed
the supernova light-curve parameters to be independent of redshift, and erred
further in considering their measured redshifts (in the heliocentric frame)
rather than transforming them to the CMB frame (in which the universe
supposedly looks isotropic). We emphasize that our procedure is justified and
that their criticism serves only to highlight the rather ärbitrary
corrections" that are made to the data in order to infer isotropic cosmic
acceleration. This is a vivid illustration of the 'Cosmological Fitting
Problem' faced by observers who live in an inhomogeneous universe but still use
the maximally symmetric FLRW cosmolgy to interpret observations.
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