Slipstream space is a specific set of eleven "non dimensions" existing in a very small bundle "above" the one temporal and three spatial dimensions perceptible to human beings. By moving matter from the three space dimensions and one-time dimension of normal space to slipstream space, one effectively changes the laws of physics for that piece of matter. This allows faster-than-light travel without relativistic side-effects i.e., the occupants do not "warp" time, despite their superluminal speed.
Slipspace is a tangle of intertwined non-spatial dimensions, comparably similar to a wadded-up piece of paper; rather like taking the classic "flat sheet" used to represent gravity and crumpling it up into a ball, thereby creating extra dimensions and shorter spaces between points. Our plane of existence is thought to have four dimensions (up-down, front-back, side-to-side, and time), but slipspace is an eleven-dimensional spacetime. Slipspace is entwined with the physical universe to the extent that phenomena in one realm can affect the other, and with sufficiently sophisticated equipment, transitions between the two forms of spacetime are possible
While faster-than-light travel is bound to generate chronological and causal paradoxes by nature, ships traveling through slipspace rely on a self-healing effect of space-time called reconciliation, more formally known as causal reconciliation or particle reconciliation, to eliminate any paradoxes that may otherwise occur. The severity of this effect, which scales in a nonlinear fashion, is determined by the amount of discrepancy in information transfer between locations, as well as strain on the local space-time brane, as opposed to the apparent length of the voyage alone. Mass, or size, is also a contributing factor, at least in the transport of abnormally large objects.
Reconciliation has a "budget"—extensive slipspace travel exerts strain on space-time on a large scale as causal paradoxes accrue a "debt". When these aftereffects build-up, it can impede with, or in extreme cases, entirely halt other superluminal traffic and communication. Slipspace returns to its normal state as reconciliations are allowed to take effect, gradually causing the space-time debt to disappear into the quantum background. This effect is noticeable if large amounts of mass are transported over long distances frequently, slowing down slipspace travel throughout the galaxy and requiring ships to perform more individual jumps during a journey.
The Shaw-Fujikawa Translight Engine used by the United Earth Government generates a resonance field, which when coupled with the unusual physics of the slipstream, allows for dramatically shorter transit times between stars. UNSC slipspace drives use particle accelerators to rip apart normal space-time by generating micro black holes. These holes are evaporated via Hawking radiation in nanoseconds. The real quantum mechanical marvel of the drive lies in how it manipulates these holes in space-time, squeezing vessels weighing thousands of tons into slipspace. The Shaw-Fujikawa Translight Engine itself provides no actual motive power outside slipspace, and ships equipped with such a device still require conventional engines for sublight travel.
Starships and their occupants are not directly exposed to the eleven-dimensional spacetime while moving through slipspace; instead, the ship is enveloped in a quantum field generated by the drive. The field acts as a medium between the ship and the higher dimensions, translating its presence as a normal-space object to the arcane physics of slipspace and enabling it to "squeeze through" the higher dimensions. This field requires an enormous amount of constant calculations to maintain, with the number of needed calculations increasing with the size of the ship. For example, the slipspace translations for a Phoenix-class colony ship require 4.3 quadrillion calculations of the quantum field per second. The vessel's mass is a noted consideration in the generation of this "buffer" as well as the energy expenditure of the drive-in general.
Before jumping into slipspace, human ships must first reach a Safe Slipspace Entry Point, or SSEP, where it can be ensured they will not drag anything from normal space into the slipstream as the ship initiates the transition. In addition, star systems have specific slipstream space transfer points known as "interstellar jump points", or IJPs, locations designated ideal for initiating a slipspace transition.
The plotting of slipspace jumps is known as astrogation, and is typically performed by a navigation computer or an AI, although humans are capable of conducting at least some of the calculations involved. The trajectory of a slipspace jump is already determined by the time the ship enters slipspace; thus, pursuing ships are able to follow the ship which made the transition. This also enables the pursuers, provided they are equipped with superior drives, to overtake the ship they were following through "slipspace supersession
(Source is taken from Halopedia)