E-Space (also known as Exospace) is a smaller separate universe which can be accessed by portals from our usual realm known as N-Space. Locations within E-Space have their coordinates expressed in negative numbers.
Besides being much smaller than N-Space and with an unexplained green color that permeates the vacuun between stars; E-Space isn't tremendously distinct from its parent universe: it operates on the same laws of physics and seems to contain constellations, stars and planets which aren't fundamentally different from the N-Space ones. Species native to E-Space are able to survive without trouble if transported to N-Space and vice-versa. The planet Alzarius is located in E-Space and contains an Earth-like atmosphere and conditions.
Travel between the two universes is possible via a kind spatial anomaly known as Charged Vacuum Emboitment (CVE). The CVEs were actually constructed by the Logopolitans with the purpose of allowing entropy to be dissipated more efficiently between the two universes, rather than accumulating in N-Space to catastrophic levels.
Another way to travel between N-Space and E-Space is by means of a region of space known as "the Gateway", which takes the form of a white void with a gate-like structure within it. It is located at the intersection of spaces, coordinate zero, and nothing is known about its origins, which may have been natural or artificial, or neither. For millennia the Gateway has been used by the Tharils to travel between both universes.
- Doctor Who season 18 (1980 - 1981):
- Full Circle
- State of Decay
- Warrior's Gate