
The most famous and mysterious phenomenon in the Star Trek universe has to be the Extragalactic Barrier. First encountered by the probeship S.S. Valiant in 2164 and rediscovered by the USS Enterprise a century later, the Barrier is observed to be a vast forcefield which at the least encircles the perimetre of the galaxy beyond the definiable edge of the spiral arms and may actually enclose the entire galaxy. According to sensor readings, the Barrier is composed of negative energy, has a negative density, and is filled with negative radiation (whatever that may be).
Starships encountering the Barrier at FTL velocities experience extreme sensory distortion and can suffer damage to various systems affected by the energy flux; also, the strange conditions of the Barrier can boost the psionic capacity of ESPer-sensitive individuals, or kill them through extreme sensory and neurological disruption. Ships can become lost within the Barrier, since there are no navigational fixes upon which to plot a course, and sensors cannot penetrate outward beyond its field effect. Furthermore, no ship travelling at sublight velocities can cross the Barrier from either side.
It goes without saying that there is no known natural explanation or theory which could conceive of such a phenomenon as the Barrier having a natural origin, and no observation of galactic space has revealed the presence of such a galaxy-encompassing forcefield. So the question is just what explains the Barrier? One fan-theory published in the Star Trek 25th Anniversary edition of Starfleet Dynamics suggested the theory that the Barrier is an artefact, the construction of a now dead race which was meant either as a defence against extragalactic intrusion (the Kelvans, the Old Ones, the Makers) or possibly as a cage to keep anything from leaving the Milky Way (perhaps a second-layer defence against the ShaKaRee Entity?).
If the Barrier is an artefact which exists physically in normal space/time, one possible explanation for our never observing the field from Earth-based telescopes would be that it was constructed sometime within the last 20,000 years and that the visible light from the forcefield has not yet reached Federation space. Or is the Barrier wholly a subspace phenomena? A boundary between "normal" subspace and the deeper layers of the hyperspace domain? This would account for the Barrier only ever being encountered by ships traveling at warp and for the lack of an observable forcefield envelope in normal space/time beyond the reaches of our galaxy.
Or is the Barrier simply that zone beyond which all the maps stop; denoted by the legend "Here be dragons"?





