The 8th umbral calamity

[Cassar]

It's important to note that no one, not even Venat, knows exactly how time travel works. G'raha knew that he wouldn't be able to save his timeline, but he didn't know what would happen to him afterwards, if he would perish or if there would be a branch. Even Emet-Selch was very surprised when he found out that G'raha found a way to time travel. Based on that, I think it can be said that Venat's comments on time travel are merely speculative, that's why she says things like "You may find your world to be very different...".

Now I do firmly believe that there is a time loop involved, since Venat kept her memories and tried to steer the future of Etherys to meet with what she knew. I think that the whole reason why the writers decided to make her keep her memories and, therefore create this loop, is because they wanted to make this neat little parallel of us, the player, fighting our fight in the present while Venat is fighting the same fight in the past. I think the "convergence" of timelines she refers to could be, just as Iscah said, a way to say that the loop is now closed, and from this point forwards everything is unknown.

Also one last note, I have a theory that Pandaemonium doesn't involve time travel. That would imply that the ancients somehow did find a way to travel through time, but somehow Emet-Selch never heard of it? I find it hard to believe. What I think happens is that the Pandaemonium we see in the present has actually always been there, but it's only visible to us now, perhaps due to Hydaelyn not being there anymore. (Although I will say, it's a little weird how it appeared right after we came back from defeating Hephaistos.... It's a working theory.) I also say this because, based on how time travel was established in this world, it shouldn't be possible to change the present by actions done in the past, doing that should create a time branch like it did with G'raha. I say should because the writers could always change that and mess everything up, which I hope they don't.
Something else that's very interesting is that even though Elidibus saw us in the past, he sent us to a different time from that which he saw us in. Remember, he only saw us during the events of Pandaemonium, but instead decided to send us to a time where Hermes and Meteion were there. How did he come to that conclusion? Wouldn't he want to send us to the time when he saw us, to ensure that the loop is fulfilled? These are interesting questions to think about, but I think we'll need to wait for the conclusion of Pandaemonium to get our answers.

Time travelling in the FFXIV world, as much as it seem confusing, actually makes sense and they have been following their own rules so far.

[KariTheFox]

It's definitely an interesting question from a societal perspective. Given that the societal definition of a Calamity is essentially 'big damn disasters that enormously fractured, destroyed, or changed society as it was at that point', and it just happened that they lined up exactly with the Ascians' Rejoinings, you can definitely make a claim that the End of Days is a functional Calamity for how badly it hit everyone, especially Garlemald, who like it or not was an enormous influence on Eorzean civilization. Hell, it's debatably even more of one than the Seventh, which was actually pretty localized all things considered.

I wouldn't be suprised if future historians of the world end up conflating every event from the fall of Dalamud to the Final Days as a singular "calamity" that resulted in a lot of political reshuffling of the world and the destruction of the Garlean Empire. After all, the time between Calamities is usually measured in thousands of years.

[Cleretic]

I wouldn't be suprised if future historians of the world end up conflating every event from the fall of Dalamud to the Final Days as a singular "calamity" that resulted in a lot of political reshuffling of the world and the destruction of the Garlean Empire. After all, the time between Calamities is usually measured in thousands of years.

That I could definitely believe being an approach gaining traction in-universe. Hell, it's happened with real-world history a few times, particularly with wars, as conflicts once digested as separate eventually get seen as basically the same conflict spread over a longer span and region.

[Iscah]

it's a little weird how it appeared right after we came back from defeating Hephaistos....

The more likely trigger is whatever Claudien discovered in Azys Lla. (I'm not really sure why we haven't been sent there to check if anything obvious has happened.)

Perhaps it's been hidden in a pocket dimension all this time and drawn out by some kind of signal from the crystal.

I also say this because, based on how time travel was established in this world, it shouldn't be possible to change the present by actions done in the past, doing that should create a time branch like it did with G'raha. I say should because the writers could always change that and mess everything up, which I hope they don't.

It's still entirely possible for it to involve time travel without breaking the rules, if the Aitiascope hasn't changed to house Pandæmonium all along, but rather the facility itself was transported through time – departing some time after where we left it and arriving in its new location just now, potentially drawn to this particular temporal point by whatever happened with Claudien.

[Iscah]

An additional thing with Pandæmonium is that it seems very difficult for it to not be a time travel plot while still involving the established cast so far, because two out of those three people* need to be present for the Sundering, so can't be permanently relocated to the present.

Either we're going to spend time back in the past trying to decipher what will happen to the facility from there – and perhaps even trying to tweak things to our advantage (hiding keys in the past where we need to find them in the present, and such) – or we need some way for the key characters to find their way to the present and back to the past again.

* There's some possibility that there'll be a switchabout and the Ascian Lahabrea is actually Hephaistos, leaving the real Lahabrea unaccounted for, but it would seem to defeat the emotional point if Themis turns out to not be the Elidibus we knew.

[Cassar]

It's still entirely possible for it to involve time travel without breaking the rules, if the Aitiascope hasn't changed to house Pandæmonium all along, but rather the facility itself was transported through time – departing some time after where we left it and arriving in its new location just now, potentially drawn to this particular temporal point by whatever happened with Claudien.

Ah I see what you mean and yes, I suppose it would still make sense within the game's rules considering the Aitiascope itself hasn't really changed, although that concept in itself is a little hard to understand.

The main issue really that I have with Pandaemonium involving time travel is that, like I said earlier, they would've had to achieve this without Emet-Selch ever knowing about it. And, you know, time travelling is a pretty big deal - something that should definitely be brought to the attention of the 14 or at least of Emet-Selch. All of that plus the fact that Emet, Lahabrea and Elidibus became pretty close to each other after the sundering, being the only unsundered left, surely they would've brought that up at some point, right?