system
Given the following post, respond as if you're commenting on Reddit:
human
[Warhammer 40k] Help a Newb Understand Warhammer 40k

Hey folks:
I am running a pnp game set in the Warhammer 40k universe, but I feel like i don't know enough to really flesh out some of my plot points. Anybody want to set some things straight for me?

1) Did all of the primarchs know what chaos was and how it could change them? The wikis make it soubd like some were really naive or just ignorant of that threat.

2) Magnus broke into the webway when he was trying to contact GEOM. Is the webway now infested with daemons, or was it always like that?

3) Is there ever any lore about the two lost legions? Or is that just a thing gms can fill in on their own.

4) Do tech prayers actually work? Maybe like the orks rely heavily on the immaterium to make their stuff go.

5) How augmented are sisters of battle? Are they near Marine tier?

6) Is there any lore about what happened to the sisters of silence?

7) Do people ever make new things in the 40k universe? It seem like so much is about recovering old stuff, not making new advances.

8) Are the eldar trying to grow a God?

9) Are all the AIs wiped out? Why are AI vulnerable to chaos?

10) Are there gods of order, too?

11) The tyranids don't connect to the inmaterium, right? But how do they have psykers.

12) Can anyone clarify the difference between psykers and sorcerers? Also, are wards against chaos a real thing, or superstition.

13) If the emperor banned being a psyker why are there so many psykers, like the grey knights.

14) How did ftl navigation work before the emperor was placed in the golden throne?

15) Any suggestions on books i can read to get a good feel for the universe? I need like 2 or 3 titles, i cant read much more than that in the time i have to get this game running.

Thanks a lot, folks!
gpt
1. The Primarchs were semi-aware of Chaos, but only the Emperor knew the true danger it presented to anyone even having knowledge of its existence. Those that fell to Chaos were transformed over time, not overnight, and wouldn't've been immediately aware of what was happening no matter how cunning they were. Horus himself only fell to Chaos because he was shown a vision of the Imperium as it is now in the 40th millenium - he wanted to stop that from happening and save the future, with disastrous results.

2. The human portion of the Webway is under constant siege by daemons attacking the Golden Throne, the only entrance into the Materium that they remotely care about. The rest of the Webway is outside of Chaos's normal reach, and any daemons getting into it would soon find themselves under attack by Dark Eldar or Harlequins. If anyone hates Chaos more than humanity, it's the Eldar.

3. The two lost legions existed but were redacted by the Emperor for unknown reasons. It's not lore you can freely edit without spinning off from main 40k into your own thing.

4. Tech prayers and rituals are the result of 10,000 years of slowly forgetting how the machines actually work. A consecration ritual for a Leman Russ tank would involve lighting the incense and saying the prayers, but would also include the actual maintenance process it required. The Mechanicus has the blueprints and knows how to make its machines, but has forgotten what the specific parts do because of their complexity and the stigma against innovation.

Orks don't rely on the Immaterium for much at all. They have the Weirdboyz, which are their psykers, but all other Orks possess no psychic power besides the latent green energy, which affects probability more than it calls upon the Warp. A hundred Orks will slightly change the odds of a gun misfiring so it works properly. A million Orks will make it so a Gargant will run despite its engineering flaws. A full-blown WAAAGH! will let them build functional starships that rightly should fall apart when they move.

5. The Sisters of Battle are normal humans with better equipment than other normal humans usually have. However, thanks to their intense faith in the Emperor, in direst need a Sister of Battle may have a miracle occur wherein she channels the power of the Emperor himself and becomes unstoppable on the battlefield. This is an exceedingly rare occurrence, however.

6. Not sure.

7. Innovation risks taint by chaos and is frowned upon, but still happens. It may take centuries for a mundane invention to propagate through the Mechanicus before it's commonplace enough to be accepted, however.

8. When they die, the Eldar *should* reincarnate. However, their souls get devoured by Slaanesh when they go to the Warp, preventing reincarnation. To save themselves, Eldar carry spirit stones, which capture their souls on death and preserve them inside the stone. They hope that one day they'll have enough souls concentrated to form a new god to beat Slaanesh into paste, letting them return to their hedonistic ways.

9. AI is heresy in the Imperium. Eldar tech doesn't use it. Necrons aren't vulnerable at all, and are probably more dangerous to Chaos than humanity because one of their endgoals is separating the Immaterium from the Materium forever. The Tau don't have true AI yet but are working there.

AI, or at least human AI, are truly sentient and thus have a signature in the Warp. Any being that has a presence in the Warp can be affected by Chaos (the Necrons have no Warp signature which is why they're safe), and so the "machine spirits" in AI can be corrupted to turn against their creators.

10. The God-Emperor is the God of Order. Some of the Eldar gods are still around, and try to fight Chaos (it's a losing battle), with the only success coming from the Laughing God, who's too enigmatic to be defined as chaotic or ordered. The C'tan are godlike but not Warp gods, and fight Order and Chaos alike.

11. The Tyranids are all connected to the Immaterium, which allows for their massive communication webs and the presence of the Hivemind, which may exist only in the Immaterium. This creates the Shadow in the Warp effect where the Warp is so crowded with Tyranid psychic activity and the weight of the Hivemind that other races can't use it at all and Chaos is blotted out. Tyranid psykers are modified neural node creatures which act as routers from the smaller creatures to larger ones up to the Hivemind.

12. Stout and unwavering belief in the Emperor can hold off Chaos because Chaos needs doubt or fear to seed itself. If one is resolute against it, wards will hold. Also, belief can physically manifest, so if all humans believe wards will work, then they'll work since they have that cumulative power in the Warp. There's no difference between a psyker and a sorcerer except for how spiky they like their clothes, and Sorcerers can have a daemon in their head instructing them or loaning power.

13. The Emperor never banned being a psyker. The Emperor believed psykers could be used to great effect if they didn't fall to Chaos, but after he was placed on the Throne the Imperium started taking psykers on the Black Ships to the Terra, where they're either turned into Navigators or Astropaths so they can better serve the Imperium, or placed in the Choir where they constantly funnel their power to the Emperor, who amplifies it with his own and creates the Astronomican. The Choir is enormous and roughly 1,000 psykers die of the strain per day, but are constantly replaced.

14. Before the Emperor was placed on the Throne it worked the same as it does now. Ships travel through the Warp, protected by Gellar fields. The Emperor wanted to make a safer and faster way of travel than the chaotic Warp and started work on the human webway, but we all know how that went.

15. The Eisenhorn trilogy is pretty well-liked.