the beam of an observed source of size $\lambda_s$ if $M<2\times 10^{-23} M_\odot h^2 \left({\lambda_{\rm s}}/{1\,\text{AU}}\right)^3$. In the extreme case for which matter is composed only of macroscopic pointlike objects, then most high-redshift SNeIa would appear fainter than in a universe with the same density distributed smoothly, with some very rare events of magnified SNeIa [@Metcalf1999; @rauch; @HW97]. This makes explicit the connection between the Hubble diagram and the fluid approximation which underpins its standard interpretation.

The fluid approximation was first tackled in a very innovative work of Lindquist and Wheeler [@wheeler], using a Schwarzschild cell method modeling an expanding universe with spherical spatial sections. For simplicity, they used a regular lattice which restricts the possibilities to the most homogeneous topologies of the 3-sphere [@topos3]. It has recently been revisited in Refs. [@archipele] and in Refs. [@larena] for Euclidean spatial sections. They both constructed the associated Hubble diagrams, but their spacetimes are only approximate solutions of the Einstein field equations. An attempt to describe filaments and voids was also proposed in Ref. [@KM:2009].

These approaches are conceptually different from the solution we adopt in the present article. We consider an exact solution of the Einstein field equations with strong density 