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 nothing, including light, cannot enter a universe via a rift, but objects can leave universes. Also, there are few resources available in the Slipspace world because there is little matter. No one inhabiting the THF universe knows that the Eternity Gate is also a gate to Slipspace. However, its destination will lead to a habitable, and inhabited area. An immense "World Machine" capable of fabricating entire worlds with their immense construction bays, and keeping the worlds they make tethered to itself to prevent them from drifting. 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 even to the Xadia 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 from the THF universe has the capability of jumping from the universes to the world machine.
The THF universe is protected by an exotic layer of ever-shifting matter, similar to the Progenitors' Void Sphere.
Each universe can have several sub-variants, such as the multiple timelines of the THF universe. These exist as various different 'echoes' of the same universe. The default echo of the THF unvierse is the main timeline, but other echoes could theoretically be reached with the correct technology, or perhaps the correct organ, if it was not for the THF's barrier, or membrane..
Although death in most other universes causes the person to depart their world as a ghostlike entity and join in Slipspace, the THF universe is a special case in that these souls are warped into The Void instead. They are unlikely to ever reach Slipspace because of this.
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