Subspace

Subspace is the theoretical mathematical construct used to describe the extra-non-euclidean time-space structure upon which the framework of normal space is built.
In order to explain subspace to laymen without the use of tensors, manifolds and eigenvectors, physicists typically describe subspace as a two dimensional plane in a three dimensional space. Large mass bodies in normal space translate as plateaus in subspace. The larger and more massive the body the higher and larger the plateau. The faces of the plateaus form a massive shear plane easily capable of ripping apart any object which attempts to traverse them. The only safe place is on the surface of subspace which corresponds to the space between worlds and on the plateaus.
These gravitational shear planes extend out from any object in real space. That is a stellar or planetary body will create an area in real space in which it is dangerous to try a shunt into subspace. As a rule of thumb this area extends for a volume approximately 100 diameters around the body. Any vessel shunting into subspace in this volume will be torn apart by the shear plane caused by the body. It takes a mass equivalent to a small planet, or very large asteroid to produce a large enough shear to create this effect.
The surface of subspace changes as a function of the density of stars or other matter in real space. Where stellar density is high travel is faster and easier. Where it is low, such as between the stellar arms or at the edge of the galaxy it is slow and difficult.
Normal matter can exists in subspace in the same way that it exists in real space. To an observer in subspace it appears as though one is immersed in a glowing cloud of color. The shear plane of gravitational plateaus appear as rugged discontinuities. Other normal space objects, such as other ships, beacons and portal gates appear normally, though speed and distance don't always seem to correlate properly to the human mind.
As might be expected there is no air in subspace. Research has shown that, while sensory input from looking too long as some subspace topological structures, such as shear planes, can cause headaches, generally observing subspace results in no adverse physiological or psychological effects.
Subspace Ghosts are unexplained objects and sometimes people which have been reported by observers. Many times such objects are merely ships of unknown or unusual designs. Sometimes such objects do not appear to be solid and some physicists have postulated they are the reflections of objects located in real space or in a hyperspace separate from subspace. Some believe they are either the souls of the damn or angelic messengers, although the Church has been silent on the matter.
Topological features in subspace are not always stable. Gravity producing masses in real space move in their relation to each other and sometime this causes shifts in the underlying topology of subspace. Such topological shifts are called subspace storms, and they can be very destructive as shear planes move through subspace causing havoc to objects from normal space.