Dune is set ~10,000 years in the future. Canticle takes up 1,200 of that. The "Butlerian Jihad", in which humans got rid of computers sounds a lot like The Simplification. While the two were not the same event, the history of Canticle likes repeating itself.
- Oddly enough, this makes sense...as the humans in Dune aren't aware of where Earth is anymore (possibly because the knowledge was lost/deliberately suppressed in order to give humanity a fresh start) and the Bene Gesserit, while being an exclusively female religious order, are run much like the Jesuits (possibly because their origins lie with the original church-sponsored colony ship).
It takes place before or during The Simplification. Either Alcatraz was eventually destroyed, or it managed to stay secret until after the first and second parts of the book.
- Chapter 24 of Canticle (bold emphasis added): "He spun the globe again until the axial mountings rattled; 'days' flitted by as briefest instants—In a reverse sense, he noticed suddenly. If Mother Gaia pirouetted in the same sense, the sun and other passing scenery would rise in the west and set in the east. Reversing time thereby? Said the namesake of my namesake; Move not, O Sun, toward Gabaon, nor thou, O Moon, toward the valley—a neat trick, forsooth, and useful in those times too. Back up, O Sun, et tu, Luna, recedite in orbitas reversas....He kept spinning the globe in reverse, as if hoping some simulacrum of Earth possessed the Chronos for unwinding time. A third of a million turns might unwind enough days to carry it back to the Diluvium Ignis. Better to use a motor and spin it back to the beginning of Man. He stopped it again with his thumb; once more the divination was wild."
- So...can we declare this confirmed at least as a Shout-Out?
The world of the book is simply too different from ours. There are immortal beings and mutated zombies, and what appear to be psychic powers. When the second nuclear war destroyed the world, the ship of refugees that was sent out to preserve mankind landed on a conveniently habitable planet which was then named after Earth That Was. Thanks to Eternal Recurrence, our present civilization ended up taking on more than a few features of theirs, minus the Medieval Stasis. Of course, history has become so muddled over time that our origins have been long since forgotten, but the story was preserved in a chronicle of the events by an obscure author who never wrote anything else.
Oh, and Benjamin? He's dead. Atomic blast hit him. Nothing could be done.
He is the Wandering Jew, destined to Walk the Earth until the return of Christ. Which is why he's still hanging around at the end. And while he claims that Leibowitz is a "distant relative," this is more to keep people from hounding him to the ends of the earth and partly to bury that part of his life with his long-dead wife, Emma/Emily.
While he likely long reverted to Judaism by the time "Fiat Homo" takes place, he knew that in order to guarantee the survival of both the Memorabilia he started and the abbey protecting it, he (as "Leibowitz") would have to be canonized by the Catholic Church. And what better way to ensure said canonization than to reveal to a young monk named Francis the location of a half-buried shelter containing his "relics."
It's also possible that he did this as well to confirm that the shelter in question really was where Emily, aka Emma Leibowitz finally died, and thus put one ghost of the past to rest.