Canonfire! Forums-viewtopic-Oerth vs. Earth and planar/dimensional logic

Mon Feb 08, 2016 12:14 am Oerth vs. Earth and planar/dimensional logic

I’ve been thinking about Oerth and its relationships with alternate Earths in my campaign and I’ve come up with the following planar/dimensional logic.

A dimension is like looking at a shelf full of books. Each book is an alternate dimension.

The Great Wheel cosmology is in one dimension. It contains one Prime Material Plane that is home to all the TSR-settings we know and love. The Planescape/Spelljammer logic is that all these settings share the same Prime Material Plane. Each world sits within a crystal sphere which floats in the phlogiston.

So… where do all the deities that are based on real world pantheons come from? ie. Greek mythology, Norse mythology, etc. All these gods feature in the Manual of the Planes and Planescape. Well, in my campaign, these come from a fantasy Earth. This fantasy Earth will be the world of Aerth from EGG’s Epic of Aerth setting. Aerth will sit in a crystal sphere (Aerthspace) and will belong to the Prime Material Plane of the Great Wheel comsmology/dimension.

So, what about the modern Earth’s - like where Murlynd got his 6-shooter from? And where did the spaceships of S3 Expedition of the Barrier Peaks and the City of the Gods come from?

Well, in my campaign, they come from 2 Earth’s in alternate dimensions.

The Earth Myrlynd got his 6-shooter from will be Gothic Earth of Ravenloft’s Masque of the Red Death setting.

And the Earth the spaceships from S3 Expedition to the Barrier Peaks and the City of the Gods come from will be the Earth of the Gamma World setting. Let’s call this Gamma Earth for now. Basically, the Metamorphis Alpha wasn’t the only ship to escape the turmoil of Gamma Earth. Another ship, the craft we know as the City of the Gods, also departed Gamma Earth. This ship slipped through a dimensional rift and crash landed on Oerth. The spaceship in Expedition to the Barrier Peaks was another ship in the same fleet or a part of the City of the Gods mother craft that detached from the main ship.

This planar/dimensional model offers the opportunity to send my players off on some fun world-hopping. A planar hop to Aerth or a dimensional hop to Gothic Earth or Gamma Earth.

Tue Feb 09, 2016 5:24 am

I believe this is what EGG meant when he referenced "walking the lines of probability" in the description of the hierophant druid of the Unearthed Arcana. Basically the ability to walk from one version of Oerth to an Aerth to an Ayrth, perhaps to an Earth.

Tue Feb 09, 2016 4:46 pm

Good pick up, TregMallin.

Yes, I was struggling a bit to come up with terminology between planar and alternate dimension/probability and how they fit together.

The TSR settings - Oerth, Toril, Krynn, etc - all belong to the same Prime Material Plane and you can get to them simply be hopping in a spelljammer or planeshifting. So this means they are all in the same reality/dimension/probability.

I lumped Aerth in with them in my campaign as I wanted to explain where all the real world deities come from that we see in the Outer Planes.

As to Gothic Earth and Gamma Earth, however… it seemed silly putting them in the Great Wheel cosmology as the idea that these worlds are encased in something as fantastical as a crystal sphere floating in the phlogiston seemed silly. Because of the science in these worlds, I felt they needed a real world universe, i.e.. planets, stars, Milky Way and the galaxies beyond. So these worlds sit “outside” the Great Wheel cosmology in their own dimensions.

Tue Feb 09, 2016 7:21 pm

I wrote a post on this topic here.

Tue Feb 09, 2016 7:49 pm

Thanks for the link, rasgon. I remember that post. In your game, do Oerth/Yarth/Aerth/Uerth/Earth share the same Prime Material Plane? ie. like the Great Wheel model?

Wed Feb 10, 2016 5:13 am

No, more like the way things worked in the first edition Manual of the Planes, with multiple alternate material planes accessible through Astral color pools.

Wed Feb 10, 2016 1:54 pm

I thought Manual of the Planes had one Prime Material. So too the diagram in the back of the 1E PHB. I'll have to look at it again.

But the crystal spheres is a bit fanciful. A prime material plane for each world would make more sense.

Wed Feb 10, 2016 3:32 pm

Here's the diagram from the Manual of the Planes, first edition:

See also the 1st edition psionic ability Probability Travel:

Wed Feb 10, 2016 3:53 pm

Ah, I see. That makes sense. They must have changed it all up for Spelljammer/Planescape to all share the one Prime Material.

Would all alternate Prime Material planes in the MotP's model share the same Inner and Outer Planes?

Wed Feb 10, 2016 4:13 pm

Thu Feb 11, 2016 2:30 pm

Why the alternate ethereal planes? I know you didn't originate this, Rasgon, just thought there might have been an explanation.

Thu Feb 11, 2016 3:21 pm

Thu Feb 11, 2016 9:22 pm

I never noticed it before, but there should also be a conduit from the outer planes, to the alternate prime.

Tue Feb 16, 2016 7:26 pm

Probability Travel, now that I think about it, seems similar to the travel between worlds, or between "narratives" on the same world, that occurs in Neal Stephenson's novel Anathem.