A 0.002% perturbation to the flat FRLW metric is sufficient to model the observed universe granularity

We introduce a small perturbation term into the flat pressure-free FRLW cartesian metric. The derivation of the Einstein fields equations shows that this modified metric describes an inhomogeneous universe. Interestingly, the derived expanding rate equation is that of the flat isotropic pressure-free homogeneous FLRW model. A perturbation term modelling any galaxy distribution is provided and analysed. A maximal relative deviation of the modified metric from the original one smaller than 0.002% is sufficient to model galaxy bulge and inter-galaxy medium densities. This results from the fact that the Hubble constant is about 5 orders of magnitude smaller than the speed of light divided by typical galaxy diameter. This approached metric has the benefit to allow a direct physical interpretation of the coordinates. It also supports the validity of the Ia type supernovae distances assessments.