Just to be sure everyone's on the same page - I've only played the Twinning once, and I found three datalogs plus the recording played to us afterwards. Is that all, or have I missed anything?
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I also really dislike the implications of a "rewrite your own past without causing a paradox", with or without the effect of erasing the old timeline - particularly as erasing a future timeline (and all the souls within it) doesn't seem all that different to erasing a shard....
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I'm wondering if there might be a "hybrid version" of time travel theories in place, where time is perhaps "stable until irretrievably diverged"? Suppose that in most circumstances spacetime will simply reshape itself to accomodate any time-travel shenanigans and maintain a single stable time loop, but if something particularly impactful is changed then there's a chance it will break and split off into a second timeline.
Perhaps splitting it relies on very specific circumstances or abilities - like the reverse-engineered Alexander mecha that the Ironworks built (and we have now destroyed in the Twinning)?
For that matter, did the Exarch deliberately not explain the machine to us, and just sent us in there knowing we'd smash it and remain none the wiser about its workings?
The specific description of "The Twinning" does seem to suggest it's a one-off split.
(If you look closely in the deeper parts of the dungeon, we can see there are two versions of ourselves just slightly out-of-sync and snapping together again...)
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I'm also not certain the "bad timeline" has been averted yet, even if the exact circumstances leading to the Light-based calamity have been resolved. The Scions' bodies are still unconscious and vulnerable, and there was the scene of Elidibus counselling Varis to take advantage of this... which Zenos has made quite the mess of, but it's still possible that some kind of attack is in motion.
Black Rose is still a "gun on the mantelpiece" waiting to be fired.
The Exarch thinks that undoing the bad future (and himself) is what would release the Scions' souls back to the Source - but it seems to me that getting them back to the Source is probably a key to allowing it to be undone, if it's ever going to be.
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Patch 4.1, I think you mean.
Also he says his aim was off with the timing, but then also says the plan took decades to set up anyway...
It seemed to me that Alexander is only calculating probabilities - building its own theoretical model of the "4D time block" rather than actually looking at time itself. Though of course that should require a phenomenal amount of knowledge to have all the variables for correct calculation...
In any case, we're told that Alexander wasn't able to predict our future, presumably because we're "special" and the key to whether things will happen or not.
But if Alexander is actually looking at real spacetime (and not simply calculating possibilities of things happening) then did the Ironworks' time travel mechanism do something particularly spacetime-disrupting, or at least visible to Alexander, and this is the reason why it can't see what will happen to us?
Additionally, Alexander didn't conclude we were on the best possible timeline - just that it couldn't act to change it without causing other consequences that would be just as bad or worse.
I feel like the "optional-ness" of the Crystal Tower storyline is a barrier to getting young G'raha reinvolved. For story-structure reasons I think he has to remain in the tower until some point beyond the game's time bubble.
As I understood it, they were only predictions made by Alexander - not things that had ever actually come to pass.