The Multiverse

The Multiverse is a book written by Sphen Corrun, Master Diviner of the Pollington Academy of the Arcane.

Think about your home. You are certainly familiar with it. But let's leave what you're comfortable with, and consider your village or city. Then beyond that, your Kingdom. And beyond that, the Material Plane. And beyond that, the world. Beyond that? More learned readers may already know. The planar system. Surrounding our own plane is the Feywild and the Shadowfell, and the Ethereal Plane linking all of them. Still somewhat familiar, somewhat similar to our own world. Then beyond them the Elemental Planes, then the silvery sea of the Astral Plane, then finally the Outer Planes. These planes are so alien, so foreign, they have to be the end, right? No, they are not. Beyond them is what we call the Far Realms. These Far Realms are beyond the understanding of even the most learned scholars. So surely this is it, right? There is nothing beyond this? Incorrect.
In a way, there indeed is something even further beyond this. Indeed, there is evidence that there are many universes just like ours, existing both in and out of reality. The concept can be difficult to understand. Imagine if you took our planar system and drew it on a piece of paper. Them imagine that there were many such papers with many such planar systems, all unique, compiled into a book. That book would be what we call the "multiverse".

If we refer to everything, including our entire planar system and the Far Realms as our universe, the multiverse is a concept of many such universes existing simultaneously, in parallel. This, of course, means there are other material planes, similar to ours with people and places like ours! Surely this is just a far-out theory, though, right? How could there be any proof of such a thing? No, the multiverse is real and we have proof. We know about the multiverse from someone who has explored it themselves.

That's right! Our universe was visited by a traveler from another! Our visitor was a powerful archwizard from a world called "Oerth", by the name of Mordenkainen. He traveled to our world briefly on his expedition of the multiverse, arriving in the Kingdom of Goldmask hundreds of years ago. It is through him that we know of the multiverse. He also significantly advanced our knowledge of the arcane. His visit was a significant one to the history of our world, and you can read more about it in my other book, Mordenkainen's Visit.

I'm sure the question you're asking at this point is, "how is interuniversal travel possible?" Well, the truth is we don't know. Nobody from our universe has yet figured out the secrets of interuniversal travel, and when Mordenkainen visited he left without revealing the secrets of how he got here. But don't despair, for the great arcane researchers of the Pollington Academy of the Arcane are exploring the intricacies of interplanar travel, and attempting to apply them to interuniversal travel. If Mordenkainen could figure it out in Oerth, we can certainly figure it out here, given enough time.