DRAFT - SUBJECT TO CHANGE
The Detent Drive is the means of effectively faster-than-light travel used in the FE universe.
How it works it not known either by humans or by galactic civilization in general, and its behavior is understood by them through analogical models and empirical results. Traditionally, the Detent Drives of ships were operated by the Outer Priesthood, though since the beginning of the War of Religion, they have increasingly fallen under the control of others, including, recently, humans.
The key analogy to understand how the Detent drive works is to imagine that familiar four-dimensional space to be analogous to a notionally 2D flat piece of cloth which can be bunched, layered, and folded with recourse to the third spatial dimension. 3D space is found to be correspondingly "folded and layered" in higher spatial dimensions, and thus points which are extremely distant from one another in 3D space may found to be quite close when the higher-dimensional structure of space is considered. It is also found that things are normally attracted to the lower dimensions by a fifth fundamental force, which is why for example matter with higher-dimensional velocities is not seen to appear and disappear as it passes through areas of three-dimensional space.
(Why is it not possible to oscillate back and forth through 3D space, if the fifth force works like gravity or electromagnetism?)