Worldgate

A means of access to other physical locations within a universe. Worldgates can be naturally occurring or artificial. In the second case, the simplest way to produce them is always via wizardry.

Worldgates tend to occur naturally, over time, in places of unusually high population concentration. The minds of living beings have an effect on the structure of the physical universe around them; the constant pressure and desire of their minds for things they want and don't have tends to "fray" universal and sub-universal structure in the area. The more beings that are packed together in one space, the more tightly they are packed, and the longer the packing is sustained, the more likely that the local structure of spacetime will fray sufficiently to tear open -- either temporarily or permanently -- and allow access to other realities. Odd disappearances of objects, or (more usually) of people, are normally the first evidence that gating is starting to happen in a given area. (This is of course something of an oversimplification of the actual physics and paraphysics, in which the population increase allows for both hyperstring "tonal frequency" shifts and the aggregation of higher-than-threshold amounts of exotic matter, sufficient to overcome the principle known locally as Hawking's chronology protection conjecture and its associated limitations on the manipulation of spacetime and "time-like curvatures".)

The population pressure required to spawn a permanently resident worldgate is normally expressed by an equation known as the demobaric formula or gating pressure formula, primarily involving two interacting varables: population concentration per square meter, and and percentage of population expressed as a function of planetary population. (There are other variables of much lesser importance in the equation which, for simplicity's sake, will not be discussed here.) The relationship between these variables is expressed in the threshold constant. Each planet has its own version of the formula and the constant: the relationship between them changes over time as the population of any given planet shifts. Once the threshold constant has been reached, and the resultant worldgate has persisted for an amount of time determined by an entirely different set of variables, it will normally remain in the general area for (at least) many decades unless accidentally deranged by local physical forces, or purposely extinguished by a wizard with the necessary expertise.