I don't read the novels, they're just for the most part very inconsistent and mediocre. Some people like pulp, I don't, that's the end of my discussion on it.

Its not an assumption, its an educated idea based on what I know of various fields and we are talking about a field of some sort which I hypothetically figure is some mechanism based on quantum mechanics to stabilise reality around the ship, which is a little different to just pulling stuff out of my arse. Now if you where to weaken a field so some scrubby psyker can chuck his minor little powers around, you sure as hell can expect to have something eminently a lot more capable than him being able to hurl something back in... which you really don't want!

Dunno about it turning people into souless entities, I'd liken it to being near a Null, which blots out the majority of psykers powers with a much higher threshold or not at all in some cases. They dont enjoy being near such things, but likewise they can put up with it in preference to being made into a daemonhost and given the majority of the Imperium's knowledge of warp travel is based on superstition and supposition, its no wonder why they consider void born a bit weird.

As is, the Geller field was probably written down as an off-handed, quick explanation by some author without any basis of theory behind it. Most authors aren't engineers like most engineers aren't authors, its just the way it is.

MKX said:

How about this: if, as you say, the field is there to stabilize reality around the ship, then it would have to make reality the way reality is else it wouldn't be stable reality but something else, correct?

Now, in the reality outside the warp on any given typical planet, a psyker can reach out and grab a mental fist full of warp. At the same time, on this planet, a daemon is incapable of reaching out and grabbing a fist full of reality without someone opening a door for him (such as the psyker punching through and grabbing some of that warp or some drunk kids messing around with a ouija board or some such). So, if one wished to make a stable reality that functioned the way we would expect reality to function, one would have to make the gellar field semi-permeable. A bit of the warp would have to be let in and vis versa. Doing such would allow those aboard the ship to remain connected to their souls and the warp yet still prevent the daemons and various predators from getting it, just like the veil dose in reality.

As the gellar fields were designed back when the warp was a much safer place then it is in the 41st mil, it is very likely that this is how they were set up... to mimic reality as closely as possible for the comfort of the ships passengers. Some mechanicus might know how to "over clock" the field (I truly love that idea and it is definitly gonna get some use in my game) now, but such would be in no way common practice. Toss into this mix that, as pointed out in posts above, the fields might e weakening due to age and disrepair on a lot of ships. However, even in such a weakened state, they would still be enough to keep the horrors of the warp at bay. After all, in the real world, in areas with a weakened veil, daemons and various predators still have a god awful time breaking through without a helping hand from the other side. Perhaps it's not so much breaking through a barrier for them as it is perceiving reality. Like normal folks being unable to percive the warp, most creatures of the warp probably can not perceive reality without someone, say a psyker, making a bridge, and it's this inability to perceive it that prevents them from interacting with it.

Graver said:

That is a sweet bit of reasoning. I like it.

I know that when we were playing our DH campaign last summer and my character was a psycher I was told by the GM to expect that warp travel was more uncomfortable for psychers than for regular people. His reasoning was that the geller field was not perfect and so the psycher felt just a tiny bit closer to the edge of the madness than when in regular space.