Immaterium

The Immaterium is the Warhammer 40,000 universe's solution to interstellar travel: an alternate dimension in which demons and magic spawn, agents of Chaos. This is also used as a way of faster than light travel much of an equivalent to the Star Wars Universe's hyperspace. This is achieved by the Warp being a domain of pure energy, with spacecraft navigating between streams, as in an ocean. Time also proceeds a great deal slower in the Warp than in the Material universe, creating a form of stasis. While an effective solution to generations-long trips across the galaxy, it is a far from perfect solutions. Long-distance journeys take months or even years, and the timing itself is unpredictable due to the very nature of the Warp.

The Warp is far from being safe place to travel through. Great currents and storms can blow starships into uncharted areas of the galaxy and make travel through certain regions impossible due to warp storms as they could last centuries. Ships could find themselves becalmed in the Immaterium, a terrible fate for its passengers as they become playthings for the dark creatures that inhabit that diabolical realm. Sometimes a ship will emerge from warp space centuries after they left yet only have lived a day onboard, many more just vanish without trace.

The Warp itself is home to a great many creatures, many of which are hostile to foreign objects from the Material universe. Ships travelling in the Warp are shielded against attacks from these creatures but Psykers risk danger when travelling the Warp. As the Warp gives Psykers their powers by way of channeling its energy, this makes them vulnerable to attack from Warp entities and Daemons.

The Warp is a dimension of the spiritual. The mind of every sentient creature leaves an imprint, an echo. Although the echo of one mind is almost indistinguishable admist the mighty presence of warp enities, when the imprints of an entire race are combined they have a huge impact on the laws of the Immaterium. When an emotion or faith grows strong enough in real - space, it becomes one of the denizens of the Warp. Many of these beings vanish when the emotion that creates them passes, but the strongest gain the ability to generate in real – space the thoughts and events that give them shape. These creatures are the gods of the 41st Millenium, be they Chaos, Eldar, Ork, or Human. (with the exception of the C'tan star gods)

The Warp is also home to the four Chaos gods; Khorne, Slaanesh, Tzeentch, and Nurgle.

There are conflicting accounts as to whether it is Tzeentch or the Emperor of Mankind which prevents the warp spilling out and completely engulfing the material universe. However recent canon seems to imply that necrons anti-psychic technology also contributes; it should also be noted that the warp seems to only be relevant to our own galaxy—potentially implying that there may be other warp shadows of other galaxies (assuming all life has not been obliterated by the tyranids in other galaxies).

A paradox of thoughts is apparent: The extra-dimensional entities of the warp are sustained by the minds and souls of living creatures within the physical world. So what would occur to the warp if all life was obliterated through the fall of the physical reality?