Aether

Aether is the material that separates Dimensions. It is not matter in the conventional sense and is extremely difficult to study directly. The study of Aether is called Aetherology, and direct manned expeditions are called Aethernauts. The first scientific studies of the Aether began during the Golden Age, though progress was initially extremely slow. Aether cannot easily be reached in Finite Dimensions and locating the edge of a Flat Dimension can be extremely tricky. The simplest answer is to go up, where Aether can be found above the highest reaches of the atmosphere. Direct study of the aether is believed to be the primary mission of the G.S.S. Geomancer, though most speculators deny the ship has a scientific purpose.