I think that elements of Greyhawk and Forgotten Realms, as well as their various subsettings, can also give us additional information to infer about how other crystal spheres work (like the idea of crystal spheres being able to have "Overgods"). But sometimes Greyhawk, Dragonlance and Forgotten Realms do some things that are problematic for Spelljammer.
People can choose to ignore those problematic things (just like Greyhawk, Dragonlance or Forgotten Realms fans can easily ignore Spelljammer), but I'm in the camp of people who would rather find a "Ben Kenobi solution" (where something is "true...from a certain point of view").
I've been wrestling with Greyhawk, Dragonlance and Forgotten Realms all having alternative worlds, over the years. I thought it might be useful to have one topic, where we look at all three campaign settings, how their alternative worlds cause potential problems for Spelljammer and - more importantly - look at the overall situation, to see if there might be a single unified theory option (or options) that might help get all three of these crystal spheres to work with those alternative worlds. (A theory that would also work in other crystal spheres, would be especially useful.)
Lets go through the campaign settings in order, to see what the issue/s are:
Greyhawk/Greyspace: Alternate Oerths
Gary Gygax said that there were several "Alternate Oerths". These are Oerth, Aerth, Uerth, Yarth and Earth. I believe that the "laws of nature" are different on the various worlds and that magic works better or worse on some of them.
Dragonlance/Krynnspace "Takhisis steals Krynn"
There is a Dragonlance plotline (after the Spelljammer product line ended) where the deity Takhisis manages to move Krynn to another location, while the other deities of Dragonlance are distracted. From the point of view of people living on Krynn, the deities and even their moons, seem to vanish overnight.
Forgotten Realms/Realmspace The Sundering/Returned Abeir/The Second Sundering
The Sundering is something retconned into Forgotten Realms canon (after the Spelljammer product line ended) where the Overgod (Ao) has dealt with fights between deities and primordials by splitting the world (Abeir/Toril) into two and giving one world (Abeir) to the primordials and the other world (Toril) to the deities. The world was called Abeir-Toril during the 2nd Edition Era, but The Sundering is supposed to have happened in the distant past, with Abeir returning during the 4th Edition Era (or more like swapping some regions with Toril) and a Second Sundering happening in the 5th Edition Era.
The big picture
Looking at all of these things, the following elements jump out at me:
- Celestial bodies can be tied to alternate celestial bodies (Greyhawk, Dragonlance and Forgotten Realms),
- Celestial bodies can be tied to more than one alternate celestial body (Greyhawk),
- Celestial bodies can be split into two celestial bodies by Overgods (Forgotten Realms),
- Celestial bodies can be moved to alternative places by gods (Dragonlance),
- Lands on celestial bodies can swap with lands on alternative worlds (Forgotten Realms) and
- Deities are not able to see what is happening on alternative versions of their worlds (Dragonlance and Forgotten Realms).
Note that almost all spacefarers would not care about this sort of stuff. These theories are mostly useful as plot devices to deal with Spelljammmer campaigns that deal with alternative worlds.
Here are a few theories that sages might have to explain the above:
- Alternative worlds are located in Alternate Material Planes within the same crystal sphere,
- Alternative worlds are located in Alternative Crystal Spheres in different parts of the Material Plane
- Alternative worlds are located in Alternative Crystal Spheres that are somehow connected to the primary crystal sphere
Theory 1: Alternative worlds are located in Alternate Material Planes within the same crystal sphere
With this theory, there might be more than one world, but there is not more than one crystal sphere.
Alternative worlds will be located on Alternate Material Planes, and portals, gates or some other type of planewalking travel would be required to get from one world to the Alternate World.
- Ties in with the idea of Alternate Material Planes from Manual of the Planes,
- Existing phlogiston map can be used,
- Easy to ignore/retcon in/retcon out.
- More of a Planescape idea than a Spelljammer idea.
With this theory, any alternative worlds mentioned in Greyhawk, Dragonlance or Forgotten Realms canon are worlds that have their own crystal spheres somewhere else on the Material Plane.
As none of these worlds were mentioned in the original AD&D Adventures in Space boxed set, these crystal spheres would probably need to be undiscovered crystal spheres outside of the Known Spheres.
- Gives us an excuse to build up to seven clones of Greyspace, Krynnspace and Realmspace, based on the canon differences between these alternative worlds and Oerth, Krynn and Toril.
- Extra canon-inspired-fanon crystal spheres need to be placed somewhere on the map,
- Placement of the new fanon crystal spheres would be tricky, as discovery of phlogiston rivers to the alternative Oerths, "Takhisispace" and "Abeirspace" would give easy access to things that the designers wanted to handwave away
With this theory, Greyspace, Krynnspace and Realmspace are "cloned" and put in a place that is connected to the original sphere, but where spacefarers don't ever look.
I've thought before about phlogiston maps being two dimensional, and introducing a third dimension (a layer) above or below the layer of the Known Spheres, that nobody in the Known Spheres knows exists. There could then be "horizontal phlogiston rivers" on the ecliptic plane that spacefarers in the Known Spheres know about and "vertical phlogiston rivers" at the Zenith and Nadir of spheres that are lead to crystal spheres "above" or "below" those crystal spheres.
That could work for Dragonlance ("Takhisispace") and Forgotten Realms ("Abeirspace"), but would it work for Greyhawk and it's four alternate worlds ("Aerthspace", "Uerthspace", "Yarthspace" and "Earthspace")?
I used to think no, but now I'm thinking that a crystal sphere could have two, three or four different "vertical phlogiston rivers" that go to crystal spheres hidden above or below it. So if four rivers come out from Greyspace, and one river each comes out from Krynnspace and Realmspace, we could have a "Radiant Hexagon" above or below the "Radiant Triangle".
- Gives us an excuse to build up to seven clones of Greyspace, Krynnspace and Realmspace, based on the canon differences between these alternative worlds and Oerth, Krynn and Toril,
- Existing phlogiston map can be used,
- Easy to ignore/retcon in/retcon out,
- Placement of the new crystal spheres on an alternate layer has little impact on anyone using the original map or ignoring the alternate Radiant Triangle worlds.
- Obscure Greyhawk, Dragonlance or Forgotten Realms canon might cause problems for the other crystal spheres in the "Radiant Hexagon".
I had not totally decided, before writing this (I was thinking of a long string of crystal spheres above and/or below Greyspace at one point), but I'm now thinking that a "Radiant Hexigon" could be the foundation of an undiscovered layer of crystal spheres that does not include a single canon Spelljammer crystal sphere.
But it could also be a mixture of the different options, depending on what canon can be ferreted out for each crystal sphere.