Chaotic space
From Memory Alpha, the free Star Trek reference
Chaotic space was the term given by the Borg to a parallel universe. The realm randomly overlapped regions of the Milky Way Galaxy, creating zones in space where the laws of physics were in a state of flux.
The spatial disturbance that was created, was an energetic trimetric fracture in space. It was several light years across, inside which the parallel universe intersects the prime universe at the eighteenth dimensional gradient. The fracture randomly shifts tens of thousands of kilometers throught space every few minutes. Fractures appear and disappear throughout the galaxy randomly and unexpectedly. Ships may remain trapped in the fractures. It was theorized that some of the Federation starships mysteriously lost in the Alpha Quadrant may have fallen prey to this phenomenon.
Changes in the gravitational coefficient cause graviton waves to form randomly into spatial sinkholes. The sinkholes inflict severe sudden graviton shear forces against the hulls of starships, eventually causing hull breaches. By 2375, only one Borg cube had ever survived an encounter with chaotic space. Subspace inside chaotic space was also in a state of flux. Traveling at warp would register on graviton wave displacement data, but woldn't register on subspace sensors, making it impossible to determine if the ship is actually moving or standing still. Using impulse drive inside the phenomenon was theorized by Tuvok to cause unexpected shifting and collisions to stars or asteroids. It was discovered that traveling a straight line at impulse resulted in the ship traveling a circle.
Normal starship sensors weren't designed to compensate for the changes to the physical constants. A basic recalibration of the sensor grid used on the USS Voyager, allowed scanning up to a million kilometers. But even a farther range would not have allowed a ship to chart a course out. It was possible to alter the warp field of a ship for a rentrillic trajectory to allow warp travel. Or to recalibrate the deflector dish to induce the paralateral rentrillic trajectory for the ship. Once activated at maximum amplitude, the sensor array routed throught the deflector could be used to plot a course out of the fracture for the ship to travel at impulse speeds.
A fracture encountered in the Delta Quadrant by Voyager in 2375 was home to an alien species. A signal on an isolinear frequency was used by an aliens reconfigure genes of some humanoids who became trapped inside the fractures, to communicate the instructions to find a way out. The aliens were theorized by Janeway to exist on a perceptual wavelength that normal humanoid senses couldn't detect. In a hallucination, Chakotay eventually saw one of the aliens who had a head with large ears and eight indents on a shoeprint like facial surface. (VOY: "The Fight")
