How it works

Dimensional Stability (name pending) is a concept I’ve had in my head for many years that I have spent a long time thinking about, but haven’t really polished. I’m writing it up here is a semi-finished state, and that’s probably where I’ll leave it.

There are two main questions this concept is trying to answer:

1. How do multiple planes of existence relate to one another?

2. What limits are there on magic?

These ideas sparked the premise for a short story, which I’m still in the process of editing. I’ll link to it here when it’s complete.

The multiverse

Already just reading that subheading you should be nervous. Multiverses are hard to design and run, which is why I haven’t put any real effort into explaining anything. As I said at the top: it’s a concept, and I’m going to use that as an excuse for as long as I can.

Often you’ll find “maps” of the planes that show the elemental planes of fire, earth, water, and air, with transitional areas between them. I don’t really like these maps, as they portray the planes as if they were a single plane that you could travel across. I prefer that each plane be its own thing, rather than a continuous spectrum. But the idea of having some sort of representation where the X axis is earth-air and the Y axis is fire-water with the prime material plane in the centre (guess who draws all the maps) is one that resonates.

I’m not calling these maps bad, just that they’re not personally satisfying.

Imagine extending that idea further, with more axes for quantities like “temperature”, “metalicness”, “the binding energy of a proton”, or whatever else you can think up (just not pi, which is constant in all universes). You can define (or imagine) as many axes as you like. It might be possible that our real-life universe exists in the setting, alongside any fictional universes of your choosing. Or maybe not.

Magic’s primary limitation

In the real world, we have these pesky things called the Laws of Thermodynamics. Of particular interest here is the Second Law, which introduces the concept of irreversability: heat flows from hot to cold, until reaching equilibrium, but not in reverse. The presence of magic fundamentally breaks this irreversability, with some spells in D&D explicitly having effects that reverse entropy (Mending comes to mind).

So how do we make magic follow the Second Law? One answer is to just not have the Second Law. I don’t like that, the Second Law is too elegant a rule to not afford it the respect it deserves. Obviously (obviously), there must be some other quantity that is monotonically moving in one direction.

This new quantity is Stability. Think of it as just another entropy except it decreases instead of increases. Stability exists throughout the world. It is, for the most part, undetectable on its own, but a lack of it has a profound effect on the local landscape. Whether this comes in the form of a small threat like a portal spawning monsters or a more existential threat is up to you. Either way, use of magic leads to a decay that is fundamental to reality.

In ye olde generic high fantasy settings, such as most D&D campaigns, this effect is probably not noticeable, maybe even to those closely attuned to magic. Gods battling may leave signs that something’s off, but it’ll take a long time before the effects are studied. It may be interesting to play soon after the discovery, as long-held positions of power have a threat that was always there, lurking in the unknown.

Increasing stability: merging

New fact to add to the facts list: universes aren’t inherently stable and the overall stability in a universe decreases over time. Some decay faster than others. In fact, most universes decay instantly into nothingness. Even a universe very similar to a stable universe might not be stable. Why? Because I needed it for this concept to work. If you want an explanation you’re going to have to come up with your own, but Chaos Theory might be a good foundation for it.

So if all the remaining worlds are doomed, what can a high-level adventuring party do about it? Why they can set off a chain of events that permanently merges two universes together, of course. Merging universes pools their collective stability together, but now there’s only one universe instead of two.

I don’t have any strict rules about how universes merge, but there are some points I’ve been considering:

• Merging can happen at any time, but is more likely in universes that are “close” to each other.

• Merges with very different universes are often catastrophic as two different versions of reality must reconcile their differences.

What does this lead to?

I’ve had a few ideas that might fit into a world that’s built using this idea. I’m not sure how well each would play out in an actual game, but I’m listing them anyway.

• A wizard casts a spell, causing a small anomaly.

• The aftermath of a holy war has left the landscape torn and devoid of magic.

• A town suddenly shifts or changes, as the equivalent town from another universe starts merging with it.

  • It’s up to you how the local residents handle this. Are they aware of what’s happening? Do their experiences/memories change?

• A terrorist attack where a cultist forcefully merges universes in the centre of the densest city. What happens?

• A civilisation bans the use of magic, citing the existential threat it poses to the universe.

  • How does healing work now? Is the nation technologically advanced enough to support healthcare needs?

• A universe is about to collapse without merging, but an outside group mounts the ultimate refuge mission to save as many inhabitants as possible.

• Two closely-aligned universes negotiate terms for merging.

  • In this scenario the players would be the delegation. How alien are the other side? What goals might the two sides of the agreement have?

• Inhabitants of one universe purposefully change its characteristics to more closely align with other universes, and starts consuming nearby realities.

• One universe uses a forced merge to mount an attack on an old enemy.

• The artifacts used to bring universes closer were designed by a long-since extinct or evolved species, and knowledge on how they work is lost.

• There’s only two universes left in the multiverse, what happens when the only option to continue existence is to accept your opposite?