Unified Cosmology

So, as I'm sure anyone who follows me is aware by now, I have my own personal D&D campaign setting. This article further expands upon the overall details of that setting on a cosmological scale. In general, my model follows something very similar to what you find in the PHB, but is quite a bit more detailed.

First off, I distinguish between planes which "overlap" and planes which "contact". A plane which overlaps another plane can be traveled to by foot. This occurs at points known as crossings, where the terrain in the two planes is nearly identical. Planes which contact each other are touching extradimensionally, and can be traveled between by magical means. Planes which neither overlap or contact each other cannot be traveled to directly. This is my control to try and slow potential planeswalkers from just walking to heaven.

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In the following diagram, the cosmos is represented by a system of overlapping color coded rings.

Mundus is my name for the material plane. It is shamelessly stolen from The Elder Scrolls, who in turn shamelessly stole it from Latin. My version of the material plane is significantly more complex than what the PHB prescribes, but I'll cover that after we explain the greater cosmos. Mundus is at the center of the cosmology, and is represented by an emerald green ring.

Mundus is overlapped by two important planes, the Feywild (a pale grey ring) and the Shadowfell, (A dark grey ring). In my cosmology, these planes exist as a consequence of energy flowing from the positive energy plane to the negative energy plane. The Feywild is the consequence of this cosmic energy reflecting back from mundus, which is in the way, creating the extraplanar equivalent of a rainbow. The shadowfell, conversely, is a void of negative energy left in the wake of mundus, an extraplanar shadow if you will. A crossing to the feywild is called a fey crossing, and a crossing to the shadowfell is a fell crossing.

All three of these planes are overlapped by the inner planes; the elemental planes of fire, air, earth, and water. While many other "elemental planes" exist, such as the plane of ooze, these are really border regions within the major elemental planes, and are the result of elemental crossings between them. In general, it is difficult to find an elemental crossing on mundus or its shadow/reflection, but they do exist in some extreme locations.

All of the inner planes are called that because they are collectively overlapped by a single plane, called the aetherial plane. Aetherial crossings are extremely rare on all inner planes. The aetherial plane prevents the inner planes from directly reaching the outer planes, as it repels the astral plane, which encircles the aetherial plane like a bubble. The aetherial plane and astral plane contact each other at this interior border, allowing magical passage between them.

Floating in the astral plane are the outer planes, so-called because they occupy the outer regions of the cosmology in the bubble-layer that is the astral plane. Crossings between the astral plane and individual outer planes are common, but because there are so many different astral planes to cross to. There are few crossings to any single specific outer plane. The outer planes organize themselves by energy density, forming a sort of vast cosmological compass divided along supernatural alignment. Good planes float near the top of the bubble, closer to the positive energy plane. Evil planes sink to the bottom of the bubble, close to the negative energy plane. Order and chaos polarize laterally.

Overlapping all of the outer planes and the astral plane is a plane called The Outlands, in which the city of Sigil is located.

Overlapping the entire top half of the cosmic sphere is a shell called the positive energy plane, or genesis to the beings that dwell there. All energy naturally flows from this point, and radiates down through the other planes to its ultimate destination: the negative energy plane, known as atropia to the few pseudo-entities that dwell there. Atropia has an infinitely negative force to it, and so is endlessly absorbing and cancelling out the energy that flows down into it from genesis.

Beyond this outer shell is the little-understood ordinal plane, which seems to lack any direct influence or interaction with the cosmic sphere.

Somewhere far beyond the ordinal plane is a region of the cosmos known as the far realm, which is almost completely unexplored because nobody can even figure out how to get there. Nobody knows anything about it except that it is home to horrifying nightmares which defy comprehension, and that some of these nightmares are nearly god-like.

Now, on to the material plane! Oh yes, we aren't done! While the greater cosmos is essentially my justification for including Planescape in my campaign setting, the lesser cosmos is my excuse for including Spelljammer! The lesser cosmos is that part of the cosmology that can actually be seen directly from a world.

It is much like our galaxy; worlds orbiting stars which in turn orbit a central mass forming a galaxy. My campaign setting occupies a dense cluster of stars with habitable worlds called "the tinderbox". It includes all of the past campaign settings for D&D and also all of the various "planes" found in Magic the Gathering's Multiverse.

The following is a star map of the tinderbox. Only habitable systems are included, empty stars are omitted. The lines between worlds represent the most commonly maintained cosmic trade routes; worlds which have cultures capable of interacting with each other, however rarely.

Because worlds do not overlap the same space, there are no world crossings. However, plane travelling magic, such as planar step, can be used to travel from one world to another. Likewise, teleportation magic, such as a teleportation circle, can also transfer you between world. While spelljammers are a more common method of cosmic travel, it is also possible to use extraplanar vessels, such as a Githyanki planar skiff, as they are generally capable of navigating the skyways as well.

Distances in the lesser cosmos are much shorter than those in our world. Gravity is a magical effect generated by large objects and does not follow the same mass-based laws of physics as our reality. In some systems the star orbits the planet, or there are other even more exotic or insane system structures.