Reality skimming (also known as rel-skimming is the faster-than-light solution for space travel which underpins the economy and culture of the Okal Rel Universe. In fact it is no accident that rel is derived from first syllable in English of reality skimming.
Real World Inspiration for Rel-Skimming
Special relativity equations become undefined (i.e. denominator becomes zero) as acceleration nudges an object toward the speed of light. In the ordinary 4d reality (3 spatial dimensions plus time) for which special relativity accounts, this means that the object become infinitely heavy and that time for the traveler in such a ship becomes infinitely slow relative to an outside observer whose inertial frame is at rest with respect to the ship. This makes the light barrier more challenging than the sound barrier, which was always known to be theoretically possible to exceed prior to its fall to supersonic aircraft.
Recent developments in cosmology suggest that the universe -- in some mathematical sense inaccessible to human intuition -- is actually 10 dimensional. That is, there is rather promising math that "works" if you assume 10 dimensions instead of 4. Whether true of not it makes for science fictional possibilities.
Reality skimming exploits the unknown properties of the unknown, "extra" dimensions. It is these dimensions which pilots experience as gap.
Mechanics of Rel-Skimming
A rel-skimming ship draws power from the binding force of the space-time continuum. Around jumps and large masses the space-time continuum can be turbulent, but for the most part the ship can use the energy of the universe itself to draw what may as well be infinite power. In fact the problem is taking only as much as you can stand. Pilots who lose their grip are boosted into an infinite future at infinite velocity -- in part to pay back the time debt of more successful space-farers.
A pilot rel-skims by phasing into gap using a combination of instinct (for guidance) and the distortion creation field referred to as a rel-ship's phase splicer.
Instinct is a key factor. Both entering gap and more particularly emerging from it again, are functions of self-conscious sentience matched with a good grip.
A pilot's grip is the intensity of his or her sense of being alive in a particular place and time. A willful, passionate, excessive person -- like your typical highborn sevolite -- is therefore apt to be a better pilot than someone even a little vague or apathetic about existence.
Acceleration (both thrust and direction) while in real space determines the displacement of a ship between phase-out and phase-in as it "stitches" its way through space. Think of the way that the steering wheel and gas pedal of a car determine its trajectory. This acceleration felt by the pilot is therefore proportional to the net displacement of the ship, although not itself sufficient to account for it. Since it is what the pilot (and any passenger) feels, real space acceleration is called the subjective acceleration of a rel-ship. Sevolites are made to sustain higher g forces than ordinary humans because of the demands of subjective acceleration.
Subjective acceleration sets the direction and net displacement of a rel-ship, but the mix determines how it is paid for. The coin paid is in exposure to either shimmer or gap.
Dangers of Reality Skimming
More gap means a greater distance is spanned in each manifestation of a rel-ship. The danger is to the pilot's sanity and grip. Overexposure leads to giddiness (space drunk) through depression, delusions, post-flight coma episodes or in-flight disappearances. Gap does not affect the physiology of the brain except through side effects. It corrodes the grip. Gelacks believe that soul is responsible for resisting gap.
Gap exposure can be reduced by increasing shimmer (and visa versa). Shimmer is the frequency of manifestations or phase-ins -- typically many times a second. A pilot does not experience shimmer as a strobe effect because gap is timeless. Hence the pilot cannot consciously experience gap exposure. The total subjective time of a trip is knitted up out of all the little stretches of time in real space between the phase-in of one stitch and the phase-out into gap again. But while the pilot experiences a continuous reality, in fact he or she is appearing in space briefly at some subjective velocity and then disappearing again. Good space lanes, then, must be particularly barren. The harder the vacuum the better. Since no vacuum is perfect,however, shimmer amounts to a constant, sub-molecular strafing of particles and the occasional bit of dust. Large objects can be repelled or dodged (depending on the size) but a pilot will sometimes be killed by a stray shard of something which was in exactly the wrong place at the wrong time. Fortunately there is an awful lot of nothing out in space for long, long stretches. Heavily traveled space lanes have been cleared over the centuries by the sweeping of passing ships repelling drifting dust as they materialize, and occasionally by purposeful effort.
Shimmer exposure is the primary reason for Sevolites being regenerative. Human pilots suffer cumulative damage to the nervous system and organs which results in early disability and death.
The most feared danger of rel-skimming is time slip.
strong>Warfare while Reality Skimming
Only Sevolites indulge in "shakeups" which are purposeful attempts to wrench another person's ship out of the reality skimming "medium" or cause it to break up. Since a pilot dominates any reality skimming unit traveling with exactly the same mix and skim factor as him or herself, pilots can throw one another off by "wake-locking". A wake-lock can be friendly if intended to pull you along or help you navigate a new jump. People don't "tow" each other using wake-lock, however, because it is too dangerous. And it is no good for dragging in a wounded ship because both ships must be skimming for one to capture the other.
Crossing wakes is another way to shake an opponent up. The stress can crack a ship or dunk a pilot. Dunk is a slang term for succumbing to time slip and/or oblivion.
Skimming is only possible, at all, in clear space lanes of hard vacuum. The more dust or gas molecules around the worse the effects of shimmer. So driving an opponent into unknown territory can be a very hostile act.
Okal Rel forbids destruction of habitat, including space stations, on pain of being ganged up on by highborn Sevildom.
A pilot compensates for "cheating" special relativity by dumping time debt in gap. But if they lose their grip even a little, they will slip ahead in time relative to the stationary universe through which they pass.
Great pilots have an internal sense of time and space so accurate that they can make long flights without time slipping at all. Contests exist in which they try themselves against a space station clock, trying to make a round trip to a known destination and back in a fixed time. Pilots who can reliably do that are called clock setters, and help stations keep on court time.
Time slip, in keeping with the laws of special relativity, is always forward never back. So time travel in the Okal Rel Universe is still a one way trip.
It is common for pilots to time slip a little. Not to time slip at all is exception. Survivability drops off sharply as the amount of time slip expands though. A pilot might time slip up to a few hours or even a day or two and still arrive without making the history books on Monitum. The odds of coming back fall off very fast after that. Exceptional time slip cases are most likely to happen near a jump. Ameron time slips 200 years when his pilot dies making a jump. Ameron's grip -- although he is in other ways a poor pilot -- pulls him through that close call. Amel time slips 6 months during the Nesak War and is given up as lost after a week or two. The longer the disappearance, the weaker the odds of coming back.
Distance in Rel-Skimming Terms
Distance is spoken of in terms of a travel-time standard. This begs the question "at what subjective acceleration" since how fast you go determines how soon you arrive (unless you time slip). The standard used is 1 Earth gravity's acceleration for one hour. (Of course you will cover much more than you would if you were not rel-skimming, because subjective acceleration is merely proportional to actual displacement.)
Gelacks call the standard unit of travel time a skim'fac which is derived from the ancient English "Standard Displacement Skim Factor" still used by the Reetions although they tend to abbreviate it to "so many standards" or "SDs".
Here's how it works.
The distance you travel in one hour doing 1 g subjective acceleration (regardless of the mix used) is 1 skim'fac.
If you were to travel the same distance in 1/2 that time, you would be doing 2 skim'facs -- again, regardless of the mix. The gist of the usage is that you are going n times as fast as the standard if you are doing n skim'facs.
Tolerance varies between individuals, and may be better for one component of the "mix" than another as well. Horth Nersal prefers the tighter control and greater mental clarity of using high shimmer. Amel Dem'Vrel can tolerate record high gap when inspired.
Whatever the preference for how you take your lumps, there are upper limits on even exceptional individuals, set by birth rank.
Commoner pilots, including Reetions, are advised to fly at 1 skim'fac and not more than an hour at a time. Longer trips are taken in stages with rest stops on conveniently placed space stations. If they have to do more than that, nothing above 3 skim'facs is possible and that only for very short durations.
Nobleborn Sevolites are tougher than commoners and routinely weather 3 or 4 hour trips at 2 skim'facs. They can engage in space melees, called shakeups, and might do 5 skim'facs in a hair-raising maneuver.
Highborn Sevolites are the superstars in the cockpit, possessing the extreme adaptations to g-forces, shimmer damage and gap-stress which let them stay in flight 10 hours at a time and cruise at 4 skim'facs when they're feeling cocky. Traveling at 2 skim'facs for 3 or 4 hours would be tough going but not pushing the upper limits of survivability as it would be for a nobleborn. Doing 6 skim'facs in combat is not comfortable but possible for the better highborn pilots. Horth Nersal, the awe inspiring admiral of the Dragon Fleet, is notorious for pulling 8 skim'facs for short bursts in a real tight spot. Amel is reported as "pulling clear at more than 7 flat out" when he disappears in Holy War, fleeing highborn Nesak pursuers. Such things are not done except in dire circumstances.
Within birth ranks, the more sevolite you are the better but the net result is still a dice role. Pureblood Ev'rel hated flying although her sons excel as pilots. Whether she had pilot potential was never properly explored. Highlords Horth Nersal and Ayrium D'Ander are exceptionally good, tough pilots without being Pureblood.
See the article on sevolite physiology for the physical underpinning of the nobleborn and highborn distinction if interested. In a nutshell, although slightly less than half sevolite by genotype, a highlord can still have as sevolite a phenotype as a Pureblood.
Reality skimming is known to the Reetions by its the technical name trans-dimensional phase strobing
Although Reetions have many more safety precautions and rules surrounding TDPS than Gelacks do concerning rel-skimming, both are the same method of faster than light travel. It was the development of TDPS technology on Earth which led to the colonization of the Reetion Reaches. After contact was lost with the Reetion Reaches due to a natural disaster, Earth succumbed to the temptation to bioengineer a race of humans particularly well adapted to reality skimming before trying again.