The novel posits that space around the Milky Way is divided into concentric layers called Zones, each being constrained by different laws of physics and each allowing for different degrees of biological and technological advancement. The innermost, the "Unthinking Depths", surrounds the galactic core and is incapable of supporting advanced life forms at all. The next layer, the "Slow Zone", is roughly equivalent to the real world in behavior and potential. Further out, the zone named the "Beyond" can support futuristic technologies such as AI and FTL travel. The outermost zone, the "Transcend", contains most of the galactic halo and is populated by incomprehensibly vast and powerful posthuman entities.