Aether refers to the environment in which all planets and astronomical bodies are suspended in Project Aetherium, replacing the cold empty space of real life. It consists of breathable air at comfortable temperatures, though this may vary depending on the location. A gas called Aetherium is found all throughout the Aether which can be used to create Aetherium fuel. This fuel is the primary source of power in the setting, used in voidships, settlement power plants and even as a weapon.

There are no universal directions in the Aether due to the absence of a solid ‘up’ or ‘down’. Planets and astronomical bodies have gravitational pulls, but in places far from such bodies the sole source of gravity is often the artificial ones generated on board traveling void ships.

Astronomical formations still occur, such as planets, stars and solar systems, but all take place on vastly closer distances than in real life. Voidships travelling from system to system can take days or weeks depending on the density of Aetherium on the route which shifts from time to time, creating a phenomena where routes of high Aetherium density are used for faster travel by void ships. The routes may vary due to the shifting densities, but some routes are more volatile than others, with the the stable areas becoming strategic centres of trade and commerce.

A variety of resources can be obtained from the Aether and its creations. Metals can be mined from asteroid fields, solar crystals from bright stars and even crops can be planted on stray landmasses in the void. The rich environment of the Aether also causes wondrous results on flora and fauna, such as the ever migrating Flotilla of Comet Jellyfish, humongous Space-whales, and the moon tree of Carran.

The major factions of the setting live on planets and moons, but many others have chosen to build independent settlements, oftentimes with exotic results. Asteroids can be linked together to form floating communities, people living on the backs of giant space whales, and a church sprung up orbiting a black hole.