POCKET DIMENSIONS AND THE GATE BUILDERS

 

THE THEORY

Conceptually, creating pocket dimensions in hyperspace is rather simple.  Using complex n-dimensional geometry it is possible to twist and warp hyperspace so that it wraps around a bubble of realspace, creating a non-orientable object that is simultaneously inside and outside both hyperspace and realspace at the same time.  This is how a hyperdrive works.  It is also possible to use the same mechanism to make a hole.  This is ill-advised.  A hole made near a hyperspace mass shadow is an invitation to Gaunt and other creatures of baryonic matter living in hyperspace.  A hole in deep space is infinitely worse -- bad as the Gaunt are, they are made of the same stuff as people and operate on the same general principles (also, if you shoot them enough they'll die).  Higher hyperspace life (such as it is) is only detectable by its wispy interactions with this universe and even then only by indirect inference using sophisticated particle detectors and cutting-edge particle physics equipment.  

In any event with more processing power and a better understanding of exotic physics, it is possible to build metastable non-orientable structures in hyperspace.  In practice, the simplest of these structures is a tunnel or a sac (though these analogies do a great disservice to the mind-bending geometry involved).  The former is the basis for Tippler Oracles and can be created with state-of-the-art human technology.  Bigger structures resemble vast systems of non-orientable veins, twisting into, around, and through each other creating a pocket of realspace twisting and arcing through hyperspace without ever truly being in hyperspace.  

The most notable user of this geometry is everybody's least favorite human-derived superintelligence: MONARCH.  MONARCH's pocket dimension (or maybe dimensions) are relatively simple in geometric terms, the result of a mighty but ruthlessly pragmatic intelligence hobbled by its human ancestry -- if a competent scientific organization got a hold of ARTIFACT 97 (GD p. 63), they would likely be able to derive substantially more computationally efficient warp drive geometries from MONARCH's worked examples.  Without access suitable computing power, pocket universes would still be out of the question.

MONRACH is not the only intelligence that has played around with exotic hyperspace geometries.  Others have done so too.

THE GATE BUILDERS

The Gate Builders are a mysterious species, lost to the ravages of time for millennia.  It is likely that they made use of a DNA/RNA biochemistry very similar to that found on many worlds (including Earth) and were not inclined to create megastructures (other than the Gate Network).  The configuration of the gate network suggests that the Gate Builders embraced neoprimitivism and retained their carbon-based forms.

The Gates allow one to walk between worlds, covering lightyears in just tens of thousands of kilometers.  Gates show up intermittently, almost without exception on worlds with complex carbon-based life, usually in areas with considerable biomass.  Sometimes for minutes.  Sometimes for years.  Usually, multiple openings appear in close proximity.  Often, this leads to biosphere bleeds and may result in dangerous new invasive species.

The Gate Network supports a stable biosphere, has an internal surface gravity of about .62g, and most areas have a breathable oxygen/nitrogen atmosphere.  It's not obvious where a gate will lead until one gets there (the computing power required to model such a system is beyond that available to most true superintelligences).  Most explorations of the network have wound up on other life-bearing planets within or near Known Space.  If other explorations have strayed further afield, their realspace transmissions haven't reached a settled planet yet.  Luckily, most of the Network's documented destinations are reasonably suitable for human habitation.

In any case, the network seems to be intelligent -- gates appear and disappear with apparent intent but unknown motives.  It's quite possible that old Terran stories about the fey and spirit worlds were inspired by early humanity's contact with the gates.

Also notable is the fact that the Network's geometry, which is designed to create internal gravity, creates an external habitat for baryonic hyperspace life that depends on gravity.  Just as humanity crosses vast distances in the inside of the Network, the Gaunt do so on the outside, moving from planetary mass shadow to planetary mass shadow.  Sometimes things that should be outside slip inside (and vice-versa).  While the network does not tolerate sustained Gaunt infestations (and will seal off seriously compromised areas), small numbers of Gaunt have been reported by some explorers.

ADVENTURING IN THE GATE NETWORK

The Gate Network is a Big Dumb Object in the same way that a Ringworld is.  It provides a rich and diverse environment that can be traversed by explorers in an ordinary wheeled vehicle without the backing of a powerful corporation or research institute.  It also provides an excuse to introduce all sorts of wondrous terrain from fantasy OSR games into a game of MoSh.

The animating impulse for the Network is the chance to play a mega-scale Gardens of Ynn game.

The Gate Network could be connected to any number of other alien mysteries but probably shouldn't be.  It also provides a compelling in-universe justification for a large number of planets with a recognizable biochemistry.  That can be good for wilderness-type adventures.