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[Warhammer 40k] How do psykers work?

So anyone with strong souls or emotions whatever(specifically unlike the Tau) contributes to the Warp, which, as I understand it, is basically a sewer for psychic energy. Would that be right?

So do psykers tap into the Warp and channel it, or do they create the Warp energy they use themselves? What would happen to the average trained psyker who found himself in a universe without the Warp? What about the Emperor himself?
gpt
All living things (even the Tau) have a sort of 2-way connection with the Warp, referred to by Imperial Scholars as an Animus. This 'tether' links the physical body with the Warp, and develops over time along with the biological and chemical responses of the individual, reflecting their identity, personality and emotions. It is, accurately, described as a Soul, and slowly bleeds 'thought and emotion' out into the surrounding Warp. Upon biological death, this tether is severed and the Soul is released into the Warp, where it eventually disperses and fades into the background. 

In this way, living things 'power' the warp. The influence their thoughts and emotions has causes ripples in the background of the Warp, coalescing into strong energy currents and interactions. It's not that they collect Psychic energy, they CREATE it. Without living things, the Warp is calm and static. With living things, it is an infinite source of power. 

The strength of this connection varies, but all living things have one. Even the Tau have connections, though theirs is considerably weaker than, say, Humans, who are themselves far weaker than Eldar. The strongest connections aren't necessarily Psykers, though all Psykers have a strong connection. 

Psykers are different than normal entities in that some quirk of their biology allows them to draw power along these connections, opening miniature warp-rifts and channelling the Warp Energy through their own brains and bodies. Again, this is a biological process, and a lobotomy can actually sever a Psyker from the Warp (it's actually an extreme punishment considered a living death to the Eldar). Whatever quirk they have, the process allows them to harness and control Warp Energies, allowing them to influence the physical universe while basically ignoring it's laws. 

Those who lack this biological quirk CAN gain similar powers, however, if they are able to communicate with the things that dwell within the Warp. Though certain sorcerous practices, individuals can make deals with Daemons of various sorts who can either lend them their own power (by feeding it along that inherent 2-way connection) or force open that tether to unlock the individuals own potential. This is insanely dangerous however. 

If a Psyker were to be disconnected from the Warp, in any way, it would not kill them. However, they are said to experience a deep depression and feeling of detachment. Amongst the Eldar, such individuals often experience suicidal tendencies. 

The Emperor would, probably, suffer from a far worse fate. His immortality, knowledge and cosmic perspective is entirely because his Animus is formed of thousands of Psykers. Without the Warp, that connection doesn't exist, and he becomes a normal man. No Immortality, no Magical Powers, no Super Strength, and no special memories.