Pocket dimensions have been an important element of my superhero campaign for decades. Over that span of time, the understanding of their origins and properties have evolved in richness and complexity.

Pocket dimensions were also much-sought-after magic items in my Fumanor campaigns, in the form of Bags Of Holding. And so I applied the conceptual dynamics from my superhero campaign, and gave them a fantasy “twist,” and all was well. The logical extension of that thinking led to a new view of the relationship between the Elemental Planes and the Prime Material Plane.

This in turn led to the creations of the various micro-planes of Zhin Tahn, an Ilithid scientist exploring this very facet of the universe in partnership with another Ilithid who seeded the resulting pocket dimensions with new life-forms of his own creation – some derived from existing species, some entirely original, all in his quest to understand life itself.

The time came when the two had a falling out – the next stage of Zhin Tahn’s experiment was to merge the quasi-stable micro-planes into a stable alternate material plane, but that would kill many if not all the life forms that inhabited these realms. To make a much longer story short, the two killed each other, leaving their mutual creations to fend for themselves until the PCs discovered them.

The “fire” micro-plane was featured at Campaign Mastery fairly early on, when I adapted the adventure created for the location into a standalone adventure – too big for one post at the time, it was split into three posts which collectively form the The Flói Af Loft & The Ryk Bolti series.

But – to the best of my memory – I’ve never actually explored the conceptual cosmology that led to that creation. That’s an omission whose correction is long-overdue – and so, here we are.

This illustration incorporates clouds-1835815, an image by Pexels from Pixabay. Click the image to see it full-sized in a new tab.

Creation by Nature

This depicts three important phenomena and three fundamental concepts – that’s a lot for one image, so it might be a little confusing at first. Nevertheless, it’s the right starting point.

Let’s start with the so-called “Real World”. This is a plane of existence that shares a common natural law. There is a dimensional boundary (in blue) that separates this plane of existence from the Interdimensional “void” – actually a misnomer, because it isn’t empty. The natural law of the void is a super-law or over-law of which the parameters that define the “Real World” are only one of many possibilities. Since it is not the only possible such solution, it should come as no surprise that there are other possible “Real Worlds” floating through the Interdimensional “Void”.

Energy from without can strike the boundary and reflect off it, in the process exerting pressure on the boundary. The n-dimensional space that comprises the “Real World” thus becomes momentarily smaller. Energy from within can also strike and reflect off the boundary, causing a brief protrusion, and causing the n-dimensional space to become momentarily larger. There is an inherent uncertainty as to the true size or position of anything because of this constant “quivering” of space-time, which is known as Heisenberg’s Uncertainty or the Planck Limit.

It can thus be shown that the more energy contained within a dimension, the larger it is, and the larger it is, the greater the likelihood of the boundary impacting with an energetic particle or wave at any given moment – there is an inherent resistance to growth that tends to force space-times to collapse into coherent structures.

Importantly, the boundary has an inherent elasticity. It will rebound from a deflection induced by an energy strike..

The effect on the energies concerned may or may not be detectable, depending on the form of the energy and on whether or not the dimensional boundary that was struck was expanding or shrinking at the instant of reflection. The near-certainty is that it will be one or the other. If the direction of motion accords with the direction of the energy, a little energy will be lost to the barrier when the energy is reflected; if the two conflict, the reflected energy will gain in energy. The energy-state of anything – be it radiation or electron-shells – is thus also knowable only within certain limits of accuracy.

Interesting things start happening when the energy density increases, however. Such impacts may be great enough that the dimensional boundary’s elasticity is overcome – it cannot deform enough, quickly enough, to prevent the energy passing from without to within in a momentary fracturing of the boundary. Once within the “real world”, it is just as subject to the natural laws that define that space-time as any other energetic phenomenon.

There is also a minute concussive effect that results from the dimensional boundary attempting to yield before it is overcome; this concussive effect ripples through the surrounding space-time and any matter contained within at that point. These concussive ripples can be detected, with the right equipment and conditions.

Of course, the same is also true of any energy of sufficient density that impacts the dimensional boundary from within. The larger the space-time, the more certain it is to be experiencing a simultaneous inflow and outflow of high-energy particles and waves at any given moment. Because the mechanisms of these are the same, the net average energy content remains fixed for the space-time being considered, but events within the “void” can cause local and temporary increases or decreases.

But there is also an intermediate outcome, and that’s the one that we are actually most interested in. If the incoming energy is just short of rupturing the space-time boundary, the rebound can be so strong that it carries a piece of the local space-time with it – a pocket world that contains a small piece of the “Real World”, plus the energy that caused the phenomenon in the first place – a pocket world.

If the energy of rebound is too great, the pocket world will become detached from the parent world, becoming a rogue micro-plane, sometimes called a planar seed for reasons that will become clear later.

When that is not the case, the pocket world remains embedded in the boundary that surrounds the main world. Now, natural laws function in a manner akin to gravity within the Void in that like attracts like; the natural tendency is for the pocket world to rejoin the source space-time and reintegrate itself. Opposing that tendency is the energy that was absorbed in the creation of the pocket world, which will make it just different enough that this reintegration will be delayed.

These pocket dimensions are naturally occurring, and tend to be microscopic in size, foam bubbles throughout existence. But there are ways of coalescing many of them into a larger construct – integrating multiple micro-worlds with each other. Because they have all derived from the one “real world”, they are fundamentally compatible with each other, which facilitates this coalescing.

It must also be noted that pocket worlds have thinner dimensional boundaries than major worlds, and thus have a lower threshold of escape. There is therefore an innate tendency for smaller micro-worlds to “leak” their extra energy, causing collapse back into the original reality.

It follows that worlds of less than a minimum size have a finite lifetime that is proportional to a function of their size and energy density. Perpetuating a pocket world is possible, but requires the constant infusion of energy to replace that which has leaked, a situation which is unlikely to occur through chance but which can be readily facilitated through artificial means.

These are the properties of Bags Of Holding, Portable Holes, and the equivalent; they are larger on the inside than on the outside, because the “inside” is actually a pocket world. They have a finite life that has been artificially extended by the “creation” process, and if you put more into them than you take out, that extension can be continued almost indefinitely. Depending on the age of the Bag, however, every removal from within risks taking it over the threshold and causing collapse.

At the same time, putting too much into such a bag at once increases the local energy density within the bag, increasing the likelihood of energy tunneling its way out of the bag spontaneously. Put 100 coins into a bag and you will almost certainly be able to pull all 100 coins back out; put 10,000 coins into a bag and you might only get 9.998 back.

It should be noted that magical energy counts in this regard as well – your wand may have had 50 charges going in, but only 49 coming out.

This illustration incorporates the-fjord-483189, Image by woong hoe from Pixabay. Click the image to see it full-sized in a new tab.

Creation By Intrusion

In the preceding section, I mentioned the possibility of micro-worlds being “blown off” a reality. These are attracted to the largest such micro-world that is nearby and traveling in a similar direction relative to the source space-time, creating a “foam” of micro-planes. When one “leaks” some of its’ energy, the micro-plane collapses into the only available space-time – the neighboring micro-world. This effectively lowers the energy density of the combined plane slightly, but reinforces the dimensional boundaries, which are now a two-ply layer (effectively). Multiply this process by tens of thousands of occurrences, and you can yield the apparently-spontaneous creation of a quasi-stable pocket world. This may be the size of a shoe-box or large enough to contain a city – though smaller is more probable. The median size will be about that of a room.

Eventually, inevitably, this pocket world will collide with another space-time. The more alike the two are, the more compatible with each other they are, the more they will attract each other, and hence the more likely this is to occur. It can be theorized that some are so unlike as to exert a repelling force upon each other, and equally validly theorized that there are only degrees of attractive force. No-one knows for certain.

Travelers within the void, by virtue of needing to carry a little of their native reality around them in order to keep them alive, are – by definition – pocket worlds, it should be noted.

The diagram that accompanies this section depicts what happens when the two realities intersect. The upper part describes the situation at the point of impact – note the deformation of the dimensional boundary of the “Real World” that results. The elasticity of the latter tends to absorb any directionality of the impact – note the change of direction in the arrow within the pocket world in the second panel.

The two dimensional boundaries coalesce once stability has been achieved. And that’s when interesting phenomena begin to take place.

One of the two worlds will almost certainly have a higher energy density than the other. That means that there will be a continual leakage from one into the other. This passage feeds enough energy into the remnants of the dimensional boundary that still separates the two to keep them from total collapse – at least for a while. (It’s hard to see in a small-sized image, but it’s there, I assure you!)

Their natural laws may be reasonably compatible, but are unlikely to be a precise match. The one with the lower total energy – almost certainly the pocket world – will thus find it’s internal natural law shifting toward that of the larger universe to which it has become attached. There will be a counterbalancing mingling in the other direction, but there is so much of the larger space-time that the effect is relatively diffuse; nevertheless, if you look closely at the “real world” in the two panels, you will notice a small shift in the direction of the pocket world.

When the energy densities match, the flow can no longer sustain the thin boundaries keeping them apart, and the pocket world will collapse into, and integrate with, the new “real world”. But this can take years or even centuries.

In the case of interdimensional travelers, this is akin to a process of “acclimatization” to the new natural laws before they are fully hostage to them.

One of the more spectacular applications of this process permits a room or area to be “invoked” from another plane. The wafer-thin boundary between the resulting pocket room is intentionally fed energy, slowing the flow of natural law across the barrier. The resulting space can literally be in two places at the same time – a room that is actually part of the elemental plane of Fire, or Hades, or someplace even more exotic.

Something of the sort is done on a smaller scale when magic mirrors permit communications across planar boundaries, or when scrying through crystal ball or reflective surface. Hence the strangeness of the points-of-view from which such scenes are often perceived.

This illustration incorporates castle-973157, Image by Jonathan Sautter from Pixabay. Click the image to see it full-sized in a new tab.

Creation By Extrusion

It is clear that those with sufficient expertise and capability can take a part of their “Real World” and project it outward from that space-time, as depicted in the diagram – creating a space that is larger within that it seems – thought that is the least-significant of the potentials of such acts. Because there is certain to be a leakage of the energy used to achieve this extrusion, the pocket world inevitably has a higher energy density than the base space-time, which ensures that it is self-sustaining (for a time) and quasi-stable for decades if not millennia.

Because this act of separation of one part of a space-time from its primary existence is being performed deliberately, there are a number of parameters of natural law that can be varied. In particular, a resonance may be created with a different space-time or even a different protrusion from the same base space-time, linking the two and permitting easy passage from one to the other. The less adept the architect, the more limitations and restrictions that will define the connection – it may only function at certain times of day, certain days of the month, or after certain conditions have been met. These do not have to make sense from an objective perspective – they are accidental in nature.

For example, one could create a room in which time passed more slowly, permitting days of work to be achieved within hours – or in which time passed more quickly, permitting an occupant to survive long past their allotted span of days.

Such acts of creation tend to be extremely complex, and many result in failure. Even when successful, there are usually unwanted complications in the form of Anarchy Foam. Fractures in reality, these can be considered emergent micro-worlds – refer to the inset in the diagram – containing the “discarded possibilities” that have not been adequately controlled during the extrusion process. Prone to collapse without warning, these have been known to inflict drastic-but-temporary changes to local natural laws – some of the consequences of which last longer than the causative triggers.

Everyone in the vicinity may be transfigured into some other life-form – even if that life-form had not previously existed. Magic may run wild, or be snuffed out like a candle. The air may become toxic, or a swamp transformed into a garden. Temperatures may change wildly – igniting forest fires, causing unexpected flash flooding, or plunging a desert into the heart of an arctic snowstorm. Mountains may rise – or fall.

Since most beings dislike these consequences, they oppose the creation of reality extrusions – if given a choice. But the benefits of rapid transit from place to place, even plane to plane, are too useful; those with the capacity will keep using it, or trying to.

It is also worth observing that some applications of Creation By Intrusion are also acts of Creation By Extrusion from another plane of existence.

Unstable Meta-pockets

Some planes of existence are simpler and more elemental in their structures and natural laws. It is possible to create a pocket reality that both mimics those planes and have the potential to combine with others to form a completely stable new reality, an Alternate Material Plane.

However, the potential for unity comes at a price: the pocket realities that result are inherently incomplete (you need somewhere for the natural laws deriving from the other pocket realities to hold onto during the integration process), and this makes them more unstable. This instability can cause them to “mutate” in undesirable ways, or explode, or implode, or simply collapse into a torrent of energy.

Applied correctly, this can bombard an existing reality with enough energy to split it in two – at least in theory.

Greater Collisions

There were two great planes that were going to pass quite close to one another in the interdimensional “void”. A resident of one migrated to the other for reasons too complicated to go into at the moment. That personage created a pocket world by extrusion and resonated it with her native world, continually feeding the pocket sufficient energy that there was virtually no leakage of natural law across the boundary; the resulting “room” was effectively a set of chambers from their native world.

At the time, it was not appreciated that like attracts like when natural laws are concerned; the resulting chambers exerted a slight but definitive influence on the trajectory through the “Void” of her native space-time, locking the two major realities into a collision course.

And that is how Ragnarok came about in my superhero campaign. The two realities collided and merged, releasing enough energy to destroy both – but that energy was captured and expended in a reordering of the newly combined reality. There were all sorts of beings – some friendly, most not – who wanted to take command of that reordering. Other realities that had been linked to one of the two, such as the Asgardian Nexus of Planes, were thrown adrift in unpredictable ways. The oceans heaved, nations were destroyed, and new ones erupted. Life forms that had not previously existed in one of the realities took possession of real estate int he combined world – substantial effort was expended in ensuring that as many survived as possible, emerging into an environment that was satisfactory for their needs, and even transfiguring some to ensure such suitability.

The game universe survived – was even, superficially, almost unchanged in some respects – but the instant you look beneath the surface, the more different things became.

The repercussions of these events are still being discovered by the players, 14 years (real time) after the fact. Every time they think they have a handle on things, I pull another one out of my hat – where it has quite obviously been lurking, undiscovered, for all that time. What’s more, the collision was discovered and found to be inevitable more than 5 years before it actually happened – and there was a naturally quite intensive effort to learn what that would mean, in advance.

The Power Of Deep Pockets

And that’s the real power of having a deep understanding of some aspect of your game reality – pocket dimensions, in this case – you can find applications of the theory that are trivial, but add depth to the way things work, and you can find applications that are quite astonishing in the scope of their impact.

It facilitates big ideas – while anchoring those ideas in a small-scale conceptual framework of plausibility. They permit effects that are not understood by others but that are simply “Cool” – leaving the deep thought in back of those manifestations to be discovered the hard way at the moment most satisfactory for the delivery of entertainment.

And, on top of that, it’s always fun in and of itself to discover how the world works!