Pressure
Density and compressibility
Viscoelasticity
Surface and surface tension
We will examine each of these in detail later, but for now, it’s worth noting that viscoelasticity is the property that gives rise to gravity and inertia and is what allows for all relative motion. As mass accumulates, it begins to displace the spacetime membrane, which thins beneath the object. This is gravity. Likewise, the membrane resists change, which means it takes time to displace when force is applied. (The viscousness of spacetime results in friction between boundary layers, which is the reason for the Lense–Thirring effect, aka: frame-dragging).
Since subluminal and superluminal space are physically separated by the spacetime membrane, STL mass and FTL mass can occupy the same coordinate points simultaneously, although this arrangement would be short-lived as (a) all matter in superluminal space moves at some speed faster than c, and (b) the shared membrane means that the spacetime displacement from mass, which is to say gravity, has an equal and opposite effect on the opposing realm.
An example to illustrate: in STL space, a planet will press down upon the fabric of spacetime to create the sort of gravity well we are all familiar with. At the same time, that depression will manifest in FTL space as a gravity “hill”—an equal and opposite prominence in the spacetime fabric. And the reverse is also true.
This has a number of consequences. First of which is that mass in one realm of space has a repulsive effect in the other. Stars, planets, and other STL gravitational bodies no longer act as attractors when one transitions to FTL. Quite the opposite.
The same is true of mass in superluminal space. However, since FTL contains a lower net energy density (a natural side effect of tachyons possessing a base speed of >c), and given the radically different laws and particles that exist in FTL, what happens is that the gravity hills produced by the denser, subluminal matter scatter the tachyonic mass, forcing it out and away. As confirmed by Oelert (2122), the majority of our local superluminal matter exists in a vast halo surrounding the Milky Way. This halo provides positive pressure on the Milky Way, which helps keep the galaxy from flying apart.
The gravitational effects of superluminal mass on our own subluminal realm were long a mystery. Early attempts to explain them resulted in the now-obsolete theories of “dark matter” and “dark energy.” These days, we know that the concentrations of superluminal mass between the galaxies are responsible for the ongoing expansion of the universe, and that they also affect the shape and movement of the galaxies themselves.
Whether or not tachyonic matter coalesces into the superluminal equivalent of stars and planets remains an open question. The math says yes, but so far, observational confirmation has proven elusive. The rim of the galaxy is too far away for even the fastest drones to reach, and our current generation of FTL sensors aren’t sensitive enough to pick out individual gravitational bodies at that distance. No doubt that will change in time and we will eventually be able to learn far more about the nature of superluminal matter.
Another consequence of the well/hill caused by mass-induced spacetime displacement is the effect commonly known as the Markov Limit. Before that can be explained, it will be helpful to conduct a quick review of how FTL travel and communication actually work.
In order to have unlabored transition from subluminal to superluminal space, it is necessary to directly manipulate the underlying spacetime membrane. This is done via a specially conditioned EM field that couples with the membrane (or rather, with the constituent TEQs).
In gauge theory, ordinary EM fields can be described as abelian. That is, the nature of the field differs from whatever generates it. This is true not only of EM radiation but also electron/proton attraction, and also repulsion within atoms and molecules. Nonabelian fields would be those such as the strong and weak nuclear forces. They are structurally more complicated and, as a result, display higher levels of internal symmetry.
The other, more relevant, nonabelian fields are those associated with the surface tension, viscoelasticity, and internal coherence of the spacetime membrane. These arise from the internal motions and interactions of the TEQs, the details of which far exceed the scope of this section.
In any case, it has proven possible to convert ordinary EM radiation from abelian to nonabelian by modulating the polarization of the wave energy emitted from antennas or apertures, or by tuning the frequencies of alternating current to the toroidal geometries through which the currents are driven (this is the method used by a Markov Drive). Doing so results in EM radiation with an underlying field of SU(2) symmetry and nonabelian form, as described in Maxwell’s expanded equations. This couples in an orthogonal direction with the spacetime fields via a shared quantity: the “A vector potential.” (Orthogonal, as tardyons and tachyons exhibit opposite motion directions along their packet lengths, and the conditioned EM field is interacting with both the subluminal and superluminal surfaces of spacetime.) This has often been described as traveling in a straight line along a right angle.
Once the EM field is coupled with the spacetime fabric, it becomes possible to manipulate the density of the medium. By injecting an appropriate amount of energy, spacetime itself can be made increasingly thin and permeable. So much so that at a certain point the energy density of subluminal space causes the affected area to pop into superluminal space, like a high-pressure bubble expanding/rising into an area of lower pressure.
As long as the conditioned EM field is maintained, the encompassed subluminal space can be kept suspended within superluminal space.
From the point of view of an STL observer, everything within the bubble has vanished and can only be detected by its gravitational “hill” from the other side of the spacetime membrane.
From inside the bubble, an observer will see themselves surrounded by a perfect, spherical mirror where the surface of the bubble interfaces with the outer FTL space.
From the point of view of an FTL observer, a perfectly spherical, perfectly reflective bubble will have just popped into existence in superluminal space.
Mass and momentum remain conserved throughout. Your original heading will be the same in FTL as in STL, and your original speed will be converted to the superluminal energy-equivalent.
Once the EM field is discontinued, the bubble will vanish, and everything inside will drop back into subluminal space (a process no doubt familiar to many of you). Often this is accompanied by a bright flash and a burst of thermal energy as the light and heat that built up inside the bubble during the trip are released.
A few points on the specific features of Markov Bubbles are worth mentioning:
Since the surface of the bubble acts as a perfect mirror, it is nearly impossible to shed waste heat from a spaceship during an FTL flight. This is why it becomes necessary to put crews and passengers into cryo prior to the trip.
Given that, it is impractical to run a fusion drive while in FTL. Thus, Markov Drives—which require a not-inconsiderable amount of power to generate and maintain a conditioned EM field of sufficient strength—rely upon stored antimatter to produce said power. This is more efficient and results in the least amount of waste heat.
Although a Markov Drive and the spaceship around it contain a large amount of compressed energy by FTL standards, the only energy that superluminal space sees is that which appears via the surface of the bubble. Thus, the more efficient a Markov Drive (i.e., the less energy it uses to generate the conditioned EM field) the faster you can travel.