Slipspace

The space between universes, acting as a medium for the universes to exist in.

Slipspace is a vast, very cold environment similar to that of regular space. The laws of physics of the Slipspace world is different from that of the other worlds such as that with the Fortrais Galaxy Cluster. It is known to be reachable via Slipspace Bombs, but almost nothing more than that is known as light cannot enter a universe via a rift, but objects can leave universes. It is theoretically possible to enter, but the Slipspace dimension is so massive and empty that it would take even the most advanced of HF starships to cross a relatively small space. Also, there are no resources available in the Slipspace world. No one knows this, but the Eternity Gate is also a gate to Slipspace. However, its destination will lead to a habitable, and inhabited area. An immense machine capable of fabricating worlds and keeping the order between them, ensuring there is little interference between worlds. This is where the Xadia have retreated to, establishing themselves as an immensely strong power and essentially a utopia.

Slipspace is largely comprised of many of these worlds all orbiting various massive world machines, despite gravity simply not existing in Slipspace. Instead, other forces would need to be invented to allow life from Fortrais to exist in Slipspace. Slipspace has several fundamental forces that can replace gravitation, and the world machines make use of these forces to provide easier access to any life that reaches them. It is not known if the world machines were built or even if they are completely natural. They seem to remain in place no matter what happens, which prevents them from drifting into each other.

Leaving a world via a Slipspace rift will cause the object going through to end up in Slipspace close to the universe they left, which is very likely to result in death to anyone  on board because no ship has the capability of jumping from the universes to the world machine.

Every world is protected by an exotic layer of ever-shifting matter, similar to the Progenitors' Void Sphere.