It appears that the dynamics of the 3-space, in the presence of primordial black holes, essentially defects in the space emerging from the quantum foam, renders a homogeneous and isotropic universe
dynamically unstable, even without the presence of matter, resulting in a spatial bubble network.
A symmetric and isotropic universe
would have begun with a spherically symmetric explosion shaped like a basketball.
The expansion of a homogeneous and isotropic universe
is characterized by the expansion factor S (= S(t)) in the Robertson-Walker line element [3, p.
On the other hand, most cosmologists use the concept of a homogeneous isotropic Universe
wherein all points and directions are equivalent.