Shiftspace

The sub-shifted spatial medium, commonly shortened to 'shiftspace', is a realspace-adjacent dimension estimated to consist of less than 0.3% regular matter. Almost entirely empty, shiftspace nevertheless is full of colloquially named 'gravitational anomalies'. Though poorly understood, scientists theorise that due to shiftspace's superimposition upon our own universe, these gravitational anomalies bleed through and cause the effects which physicists previously attributed to unexplainable dark matter.

Shiftspace is now largely used as a medium of rapid, efficient transport between star systems, replacing the slow, bulky, and power-intensive Alcubierre Drives that previously led interstellar travel. Though much more advantageous than Alcubierre Drives in many ways, shiftdrives are reliant on the rare fuel known as Stardust to trigger 'flips'.

Properties
Shiftspace is a unique concept in astrophysics, being the only known dimension other than our own. Its very existence in accordance with Revised String Theory is an indicator of more possible dimensions, but to date, shiftspace remains the only one accessible or even detectable to modern humanity.

Cosmology
The sub-shifted spatial medium is not technically considered to be a 'true' alternative universe because of its inherent link to our universe (commonly referred to as 'realspace'). Shiftspace is instead considered an 'adjacent dimension', not truly independent but undeniably separate from realspace. Shiftspace is instead superimposed over realspace, with each point in the adjacent dimension corresponding to a linked point in our universe.

However, shiftspace is much smaller than the real universe, with two points in the medium being much closer to each other than the corresponding points in realspace. Because of this, it is commonly accepted among the scientific community that shiftspace must be a good deal younger than the main universe, as it appears to be expanding at the same rate. Therefore, youth is considered the only plausible explanation for its size.

Anomalies
Shiftspace is generally estimated to consist of no more than 0.3% ordinary matter by volume. The rest is largely composed of empty space and poorly-understood gravitational anomalies. These anomalies can bleed through the barrier between shiftspace and realspace, resulting in most of the gravitational effects of what was previously attributed to hypothetical dark matter.

Shiftspace gravitational anomalies are commonly theorised to be positions in shiftspace where graviton particles have collected in a singular area. This is entirely unverified, but implicitly supported by the discovery of graviton particles in realspace, where they account for what remains of the gravitational effects attributed to dark matter.

While having minimal effect on realspace, these gravitational anomalies can be incredibly destructive in shiftspace, ripping apart and destroying any ordinary matter within a certain range.

Interaction with Realspace
Evidence has shown that events and phenomena in shiftspace does affect realspace, and vice-versa. Though mostly comprising gravitational effects (such as shiftspace gravitational anomalies or realspace black holes), it also has been recorded to extend to limited electromagnetic fields, and of course, ordinary matter through the 'flip' phenomenon.

It is important to note that though ordinary matter can interact with shiftspace, it does not do so naturally, and can only interact through artificial manipulation of shiftspace negative energy fields.

Usage
The primary usage of shiftspace is as rapid, efficient transport. Using shiftdrives and Stardust, voidcraft are 'flipped' from realspace to shiftspace, where they must carefully navigate the dangerous gravitational anomalies of shiftspace.

Shiftlanes
In well-traveled regions of the Known Human Territories, charted safe routes through the gravitational anomalies are common, known as shiftlanes. Maintained by an cooperative effort between the international community and Stellar Industrial, the 'Shiftspace Beacons' use humanity's still-nascent understanding of shiftspace cosmology to indicate safe passage to navigational A.I. s.

The further one goes from the centre of the Known Human Territories, shiftlanes become sparser and less-maintained. In the Outer Frontier regions of the KHT, shiftlanes are practically non-existent, and any travelers frequently need to flip out of shiftspace to recalculate their routes.

Free-Charting
Exceptionally dangerous, free-charting is a method of shiftspace travel largely used by smugglers and criminals to avoid checkpoints; or by explorers in the Outer Frontier attempting to expand the Known Human Territories. Free-charting is done by flipping into shiftspace without a precalculated route and attempting to maneouver in real-time. Due to the relative size of shiftspace the common dangers of gravitational anomalies, this is nearly impossible for a human mind to accomplish, even with the assistance of a Tier 5 Sapphire-class Artificial Intelligence.

Free-charting can often lead to the destruction of the subject voidcraft and the death of its entire crew. Due to this risk, most exploratory expeditions use so-called 'dumb drones' to find possible routes and lay temporary guide beacons. Human crews then follow, finding the safest and most efficient of the possible routes and firmly establishing them with permanent Shiftspace Beacons before connecting them to the wider galactic network.

For many criminal groups, however, the risk is worth the reward, and smugglers often free-chart their wares to avoid customs inspections, border patrols, and general law enforcement checkpoints. The Rose Thorn Cartel and the Montessoir Families especially make large use of such smugglers, often several at a time due to the high mortality rate.