The Materium, also called realspace, is the four-dimensional region of space-time where corporeal beings live; it is the physical plane of existence defined by the four basic forms of physical energy and the basic elements of matter, as opposed to the Immaterium, more often called the Warp or Warpspace, the hyperdimensional, non-Euclidean, psychically-reactive region of space-time that underlies the physical universe. The Materium abides by all the laws of physics and the natural world that we know today. The Warp, on the other hand, is another dimension where daemons and other Warp entities exist, created and maintained by the collective psychic unconsciouness of the sentient beings of the material universe, particularly Mankind since humanity is the galaxy's most populous and dominant intelligent species in the late 41st Millennium. These Warp entities lust to cross over into the Materium to create havoc and consume the souls of mortals. Travel through the Materium is relatively slow and the greatest achievable speed is that of the speed of light (lightspeed). Therefore, many intelligent species choose to travel through the Warp using Warp-Drives or similar technologies like the Eldar Webway or the far more limited Tau Phased Warp-Drive. Certain regions within the Milky Way Galaxy exist where the Warp and the Materium essentially bleed into one another due to an enormous trauma to the underlying boundaries of space-time, creating the permanent Warp Storms known as Warp rifts. The most infamous of these rifts are the Eye of Terror in the Segmentum Obscurus and the Maelstrom in the Ultima Segmentum in the galactic east.
- Warhammer 40,000 Rulebook (6th Edition)
- Codex: Chaos Daemons (6th Edition), pp. 6-17
- Codex: Chaos Space Marines (4th Edition)
- Codex: Chaos Daemons (4th Edition), pp. 4-13
- White Dwarf 139 (UK), pg. 139