Slipstream space (Slipspace for short), otherwise known as Shaw-Fujikawa space or subspace by the United Nations Space Command or simply the void to the Covenant, is a collective term for the seven non-visible infinitesimal quantum dimensions used for faster-than-light travel. Making a transition from one place to another via slipspace is known as a "slip", or "jump".
Slipstream space is a specific set of seven dimensions existing in a very small bundle. While these dimensions are present in normal space, they do not have an effect on the physics of normal space. By moving matter from the three "normal" space dimensions to Slipstream space, one effectively changes the laws of physics for that piece of matter.
It is likely that the theory of Slipstream space existed prior to 2291, however Tobias Shaw and Wallace Fujikawa, in 2291, were the first humans to successfully implement a device that could transition normal matter into slipstream space, the Shaw-Fujikawa Translight Engine.
The Covenant Empire also utilize the same seven dimensions of Slipstream space for travel, though the means they use to make the transition are most likely different than those of the humans because of their markedly "faster" journeys from point to point.
The Forerunners had a far greater understanding of Slipstream space, with the abilities to travel nearly instantaneously over galactic distances, to disrupt slipstream travel from normal space, to create bubbles of Slipstream space such that time slows considerably inside (if not stopping time altogether) while keeping the contents of the bubble visible in normal space, to store considerable mass and volume in Slipstream space stably for thousands of years and potentially for all of time, and to transition matter from normal-space to the inside of a construct in Slipstream space without requiring the construct to transition back to normal-space.
Slipspace is a tangle of intertwined spacial dimensions, comparably similar to a wadded up piece of paper, which lie underneath the three conventional spatial dimensions of the universe. Because of this tangle of intertwined dimensions, objects in slipspace often group together in mass transit.
The Shaw-Fujikawa Translight Engine allowed human ships to tunnel into Slipstream space, called by technical humans "Shaw-Fujikawa Space," after the scientists who proved its existence. Slipspace is a domain with alternate physical laws, allowing faster-than-light travel without relativistic side-effects i.e., the occupants do not "warp" time, despite their super-luminal speed. But however fast it may appear, faster-than-light travel is by no means instantaneous; "short" jumps routinely take up to two months, and "long" jumps can last six months or more for the crew. The time it takes to normal-space observers, however, varies substantially - one cannot depend on the same amount of time passing in Slipstream space and normal space. These variations are typically measured in weeks or months, and are unpredictable. A fleet that transitions to Slipstream space at the same time may or may not transition back to normal space at the same time. Furthermore, if ship A and ship B both enter Slipstream space at the same time and exit at the same time, the crew on ship A could have experienced a longer journey subjectively, and the crew of ship A could, in fact, be a week older than that of ship B despite appearances in normal space.
Slipspace can be thought of as our detectable universe (which, technically, it is) but with a greater number of dimensions. 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 currently theorized (in 2552) as a "tangle" of our plane's dimensions, 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. The slipstream also possesses different laws of physics than our "normal" universe, although some basic ones, such as energy transfer and momentum, remain the same.
The Shaw-Fujikawa Translight Engine generates a resonance field, which when coupled with the unusual physics of the Slipstream, allows for dramatically shorter transit times between stars; however, scientists note an odd "flexibility" to temporal flow while inside the Slipstream. Though no Human scientist is sure why travel time between stars is not constant, many theorize that there are "eddies" or "currents" within the Slipstream — there is generally a five to ten percent variance in travel times between stars. This temporal inconsistency has given military tacticians and strategists fits, hampering an uncounted number of coordinated attacks. Shaw-Fujikawa engines allow ships to leave normal space and plow through Slipspace. 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 "magic" of the drive lies in how it manipulates these holes in space-time, squeezing vessels weighing thousands of tons into Slipspace.
The Covenant have a very finely tuned version of this technology, far superior to the UNSC Shaw-Fujikawa Slipspace Drive. Instead of simply tearing a hole into Slipspace, Covenant Slipspace drives cut a very fine hole in the fabric of space-time and slips into Slipspace with precision (much like a scalpel compared to a butcher knife). It exits with the same pinpoint accuracy, takes less time during travel, and is able to plot a course with error not exceeding an atom. This is why in battle Covenant ships are able to slip by human defenses by using slipspace. Standard Covenant tactics include using short Slipstream jumps to gain positional advantage and surprise other ships, in addition to avoiding incoming ordnance. The Covenant's superiority in drive technology (combined with differing weapon technology) allow a small number of Covenant ships to effectively engage a much larger UNSC force. Missiles, especially, can be defeated by a brief Slipstream jump, as they cannot track through Slipstream space.
Gravitational fields of significant size, such as those generated by a planet, affect the superfine quantum filaments that the Shaw-Fujikawa Translight Engine must use to calculate an entry point to the slipstream, and UNSC calculations are unable to offset this effect. Covenant drives, in turn derived from Forerunner technology, have a much higher resolution of the filaments, and use more accurate calculations, and though the Covenant do not use this ability, are capable of making slipstream transition in and out of a planet's gravity well. Indeed, while using the captured Ascendant Justice to make a Slipspace jump within Threshold's atmosphere, Cortana remarked that "It was as if she was blind before." After observing this innovation, a Covenant AI managed to leak the data out to the rest of the Covenant in a transmission. During the first days of the Battle of Earth, the Prophet of Regret uses this newfound knowledge to transition into Slipspace while directly over New Mombasa in Earth's gravity well, damaging the city and causing the weakening and eventual collapse of the Orbital Elevator there. These events show that, while the Covenant often cannot innovate their own solutions, they are quick to adopt any practice that increases their battle prowess.
Slipspace travel is dangerous due to the high level of radiation encountered during the trip, which can be extremely hazardous to the crew. This is negated by the use of Lead Foil in UNSC ships, which absorbs the radiation. Fissile materials also emit radiation (specifically Cherenkov radiation, emitted when particles travel through a medium at a faster rate than light travels in that same medium. Named after the Russian physicist Pavel Alekseyevich Cherenkov) upon exiting Slipspace; this is not harmful to Humans, however it does make emerging from Slipspace very noticeable. It is not known how the Covenant deal with radiation, but it is presumed that either they also utilize a shielding material, or with their improved Slipspace technology and Energy shields, it does not affect them at all. During the beginning of the Civil War of the Covenant a Flood-controlled In Amber Clad entered slipspace and exited inside the dome of High Charity.
The concept of using an alternate dimension with different laws to travel faster than general relativity allows was first posited as the Minkowski Space Theory.
When ships jump into Slipspace, they need to reach a Safe Slipspace Entry Point, or SSEP, where it can be ensured they won't drag anything from normal space into the slipstream as the ship initiates the transition. Star systems have specific Slipstream space transfer points known as Interstellar Jump Points, or IJPs, where it is safe to initiate slipspace transition.
Slipspace velocities are generally dependent on the ship's momentum on transition, as the Slipspace drive itself does not generate thrust. As a result, ships that are faster in normal space, such as corvettes, usually travel faster in the Slipstream as well.
Human Slipspace velocities are far slower than Covenant versions, only able to carry a ship at a speed of approximately 2.625 light years per day [notes 1], while Covenant ships can reach 912 light years per day[notes 2], a vastly superior rate to UNSC Slipspace technology. The capture of a Covenant Slipspace drive by John-117 and survivors of the Battle of Reach and survivors of the events at Halo may have increased the capabilities of these Human Slipspace technologies.
One example of the differences between speeds is comparing the Covenant cruiser "Ascendant Justice" with the UNSC Halcyon-class cruiser "The Pillar of Autumn." It took several weeks for the Pillar of Autumn to get from Reach to Installation 04, yet the Ascendant Justice could get from Installation 04 to Reach within thirteen hours.
Though the Covenant use a modified version of Forerunner systems, true unaltered Forerunner slipspace technology has only been observed in the form of the Artifact transporting UNSC and Covenant vessels from Earth to The Ark. Additionally, while a Covenant Assault Carrier could reach Delta Halo from Earth in thirteen days, a distance of approximately 11856 lightyears[notes 3], the Forerunner Dreadnought took only five days to travel the same distance, giving a speed of approximately 98.8 lightyears per hour[notes 4]. given the fact that Covenant understanding of Forerunner technology is comparatively primitive, the ship may have been capable of much higher velocities. Without a slipspace portal the Librarian was unable to reach the Ark, though this may have been due to The Ark's coordinates being completely unaccessible even to all Forerunners due to the risk of being captured by the Flood, not due to inferior slipspace velocity.
Because the Slipstream is constantly shifting, and its laws of physics are different to our own, the magnetic coils of Slipspace drives drift out of phase when entering and leaving a Slipspace field, requiring constant maintenance. During the 2490's, technicians had to manually repair Slipspace drives, exposing themselves to the Slipstream and occasionally suffering injury, death or simply disappearing.
In addition, Cherenkov radiation is emitted by fissile materials, including a ship's reactor and nuclear armaments, upon entry and exit of the dimension, requiring all Slipspace-capable craft to be fitted with lead shielding as radiation protection. Slipspace drives can only be equipped on large ships, as the stress that the constantly fluctuating Slipstream exerts is considerable and can tear a small craft, such as a dropship or star fighter, completely asunder.
Direct exposure to the Slipstream is incredibly dangerous. People traveling on a Slipspace-capable craft can experience a range of symptoms, from nausea, to heart failure or even death. Even more uncommon, but still known to happen, is the total disappearance of a person while in the slipstream. In some rare cases, having a specific Forerunner object such as the Forerunner Crystal onboard may cause the ship to be in an anomalous dimension within Slipspace.
Prior to 2552, entering slipspace from the gravity well of a planet had never been attempted, either by the UNSC or the Covenant. The effect of gravity upon the creation of a slipspace entrance usually collapsed UNSC-generated holes, and was assumed to be the same with Covenant technology. The flagship Ascendant Justice, however, was able to escape from a gas giant's gravity well after Cortana realized that it had a far higher resolution of the quantum filaments that allowed a transition, and she was able to compensate for the gravity. Subsequently, the ability was transmitted by a Covenant AI, and the Prophet of Regret used an in-atmosphere slipspace jump to escape Earth, with the resulting shockwave dealing devastating damage to the city of New Mombasa. Slipspace jumping inside an atmosphere, however, is extremely dangerous to the surrounding people and objects. When a ship transitions into normal space in-atmosphere, the air that was there is pushed aside, causing a massive shockwave centered at the ship. If a ship transitions to Slipstream space inside an atmosphere, on the other hand, it leaves an empty space that air quickly rushes to fill, causing an implosion.
Entering and exiting the slipstream is normally only attempted by ships of large mass, their gravity wells stabilizing slipspace to a degree that allows safe passage. Small ships, such as dropships, do not possess the same gravity and are placed under considerably more stress than a warship, able to crack the hull and buckle reinforcing struts. It is not impossible, and UNSC slipstream monitoring probes make the transitions all the time, but require heavy reinforcement to survive the stresses, and are unmanned, having no need to protect internal occupants. Small objects like ODST SOEIV pods can be modified to make the transition, but are still an extremely uncomfortable ride.
The Forerunners were somehow capable of advanced message carrier waves in slipspace. This way, messages and memorandums could travel at great speeds throughout the Forerunner empire. Cortana was able to use this technology to declare codes Bandersnatch and Hydra during the Battle of Earth and The Battle of Installation 05 in close-knitted timing and symmetry.
The closest technology the UNSC has been able to create like this is the Slipspace COM Launcher. Even then this technology is limited as there were only three in existence before 2552: one on Reach, one on Onyx and one on Earth. As of the conclusion of the Human-Covenant War, both the devices on Reach and Onyx have been destroyed, with the fate of the Earth device unknown. Because all communications can take years or decades to travel the lightyears between colonized star systems, UNSC civilians use Slipstream packets. They use the slipstream to travel and to send communication signals significantly faster than otherwise possible, allowing faster communication between colonies.
Slipspace can be likened and very familiar to the recent discovery of matterwave transport without transit. In this process the 7 hidden spatial dimensions, 3 known spatial dimensions and the 2 time dimensions appear to collapse into a singularity to an outside observer. But in reality, this is only an illusion. In this type of field, relativity predominates, for instance the reality is dependent on the radial displacement from the source that generates the field. At small distances, reality is relatively intact. The further away from the field source, the less sense it makes to talk about reality; a cause can occur after an effect, time has no linear flow. Nothing has a definite momentum or velocity. Objects can occur at multiple positions simultaneously. When an object enters a field, it produces a burst of neutrinos, antimatter and other types of radiation.