Quote Originally Posted by Wraith View Post
Argul Tal's visit to the Imperial Laboratory suggests a similar sort of thing, also involving a warp rift (which, when all is said and done, the Eye of Terror is). He wouldn't have gotten there without Lorgar, and there wouldn't be a Lorgar without Argul Tal.

That kind of seems to be 40k's take on time travel? No one truly has free will, everyone is tied to inescapable destinies and even skilled prognosticators like Eldrad Ulthuan can only change the future with logical cause-and-effect. There isn't a future where Sanguinious doesn't die at Horus' hand, he can only choose when and where it happens - if you time travel in 40k, it's because you have already done it and your own actions to change it are precisely what brought it about.
Yeah, it usually seems to be presented as an inevitability - by the time you realize that you've caused your future, it's too late to change it.

I remember the Ahriman novels having survivors from a Chapter that was declared traitor for no apparent reason... except that their fleeing to the Eye and turning to warp powers to survive ended up causing their Chapter's destruction in the first place, when they run into the Inquisition earlier in the timeline.