Aether

The world is part of a multiverse of parallel dimensions or universes. Running between and through them is a mysterious substance or medium called the aether. The aether is strange, with properties reminiscent of both a fluid and a solid as if they were interdimensional plate tectonics. Naturally-occurring cracks can appear it in, resulting in movement between dimensions. It is also possible for intelligent beings to figure out how to make artificial cracks, or schists. Our primary world is in one of these dimensions, but the Aether gives it a mechanism to connect to other worlds and draw material from them.

The aether creates strong aethereal fields between dimensions.

Behind the Scenes

The move that introduced the aether also introduced how travel between dimensions works, including an asymmetry in difficulty, and the temporal splits and slips between alternate dimensions. However, it was determined that such a move violated One Thing.