All of the 10'000 worlds are underneath this essential wall of protection. Well, not all of them. However, 99.9999% of them are enclosed within a Firmament. The massive clouds of Prima Materia leave no other option except for the abandonment of the universe to hide.
a Firmament will enclose the planetary system (the sun, occupied planet, moons, a few other planets) that the Gods want to be protected. The barrier has two mains means to keep it's occupants safe. 1) Each Firmament is far denser than conventional physics would allow, with the mass of a neutron star per square inch. While it can be shattered it would take something far stronger than a legion of gods for the smallest crack. 2) It constantly generates space and materials on both of itself at the speed of universe expansion to ensure that humans don't attempt to leave the world or the corrupted Materia can get close enough to breakthrough. So far, every universe with a Firmament as been spared the fates of those without.
How it works
the construction of a firmament requires pure Prima Materia, which means that no more can be made, as the last of the supply has been held in stasis in case the gods need to create something entirely new should the situation decline further than before.