Let's play a game: Save the Ancients!

[Iscah]

The events of Shadowbringers resulted in an entirely new timeline, not a mere branch. There is no conjunction formed for the 8UC with Elpis, and so Elpis is not tied to that timeline in the same way as it is in ours.

The reason it's not a mere branch is because the time at which the conjunction occurs is hundreds of years before the timeline split happens. The timeline split happens because the 8UC timeline sent the Crystal Tower backwards through both time and space, causing an entirely new timeline to form.

There is absolutely nothing to establish that as fact. There is no proof that the Crystal Tower's arrival split the timeline, because we have no prior knowledge of its state to say whether there was ever a version of events where the tower did not appear there.

Neither is there any proof that the split is an entirely separate timeline and not just a split.

And without any direct proof for or against, I would take "the interpretation that allows the game's story to make sense" as the one that is likely to be in place rather than the one that renders parts of it impossible or inconsistent.

[Vyrerus]

There is absolutely nothing to establish that as fact.

There is, and it's the 8UC short story they put up that established that an alternate timeline still exists where their own time machine had no effect on their own timeline (meaning their own time machine cannot interact with their own timeline). But I get it. It's a deeply convoluted mess, and you've spent a lot of time thinking about and seeing it a certain way.

[Iscah]

There is, and it's the 8UC short story they put up that established that an alternate timeline still exists where their own time machine had no effect on their own timeline (meaning their own time machine cannot interact with their own timeline). But I get it. It's a deeply convoluted mess, and you've spent a lot of time thinking about and seeing it a certain way.

The short story only establishes that the other future still exists, not that it has split apart all the way back to the dawn of time. It only needs to split as far back as whatever key event defined the beginning of a change that ensured the Calamity could not occur.

We have no proof that the earliest effects of the time travel did or did not take place in the history of the other timeline. They don't know the state of the First, they only work out later that it was the rejoined shard and that they need to go there, so the tower could have appeared in the history of their timeline and the Exarch's plan simply failed, resulting in a stable time loop from their perspective – not that they would know about it, as all sign of the attempt would be wiped out along with the First itself.

[Vyrerus]

the Exarch's plan simply failed, resulting in a stable time loop from their perspective – not that they would know about it, as all sign of the attempt would be wiped out along with the First itself.

No. If their plan could affect their own timeline, then the time where they made their time machine would cease to be, ergo, it had to go to a different timeline. If they had not written the short story, this would still be up in the air.

The proof that it's a different timeline all the way back to the beginning of time is literally what I just said. If the 8UC time machine could go back in time within the 8UC's timeline, that future would not exist, and the Crystal Tower would have faded from the face of The First once the 8th Umbral Calamity was made impossible.

I'll try to make it clearer.

If they could go back in time in the 8UC's timeline, then they could go back even further than just the 8UC's inciting event, and cause different outcomes. They could go back to before Black Rose was invented and stop its invention. There are many other possibilities, but I don't care to think of them at the moment, but do you understand?

The 8UC's Crystal Tower did not land in their past, because it could not. The short story made this the sort of time travel we are dealing with.

[Iscah]

No. If their plan could affect their own timeline, then the time where they made their time machine would cease to be, ergo, it had to go to a different timeline. If they had not written the short story, this would still be up in the air.

None of that makes sense, and the short story changes nothing except confirming whether we are in a "timeline is able to branch to support an old and new version of events" story or a "time traveller is exempt from the effects of a self-inflicted grandfather paradox" story, in favour of the former.

[Vyrerus]

None of that makes sense, and the short story changes nothing except confirming whether we are in a "timeline is able to branch to support an old and new version of events" story or a "time traveller is exempt from the effects of a self-inflicted grandfather paradox" story, in favour of the former.

It makes as much sense as anything you've proposed, and yes, the short story confirms exactly what I've stated. It creates a second timeline, not a branch. It's not a branch, because the traversal relies on going to a space time that no longer has a coordinates within their own universe. This exempts their machine from being able to affect their timeline, since it needs those spatial coordinates (and it remains a great mystery as to how they even got them, since they're also dimensionally separate from The Source's universe and space time). The short story is the proof that their timeline was completely unaffected.

Branches for timelines come from second to second instances of time, and are already infinite and chaotic. You don't need a time machine to cause branches. They will result from any variation or hesitation in choice or chance.

The choice to try to change causality by traversing time causes a separate and new timeline, when dealing with backwards time travel. This is because the impetus for your traversal is linked to your past. You can't change your past at all, because it will fundamentally alter the casual links that lead up to your motive for the traversal. Particularly true if there's no way to account or plan to reverse for the changes you make.

Even if that's not how you view time travel, the short story introduced multiple timelines by having the 8UC remain unaffected by their traversal. This means their machine went to a parallel past. Not a shared past. For it to be a shared past, the short story would have to not exist, much like how the 8UC would have to no longer exist.

In other words, SHB's use of time travel concludes that you can change other timeline's past, but you can't change your own timeline's past. Which, with regards to Endwalker and the thread, means that the WoL could change things in the past but it would be in another timeline entirely.

Which Endwalker then takes the stance that a conjunction between two time periods has formed, resulting in our beloved causal loop, while still trying to have its cake and eat it too by having the WoL rewrite the past by showing them influencing things through Elpis sidequests. (This is why it's just Writer Fiat, and there are no real rules. This is a repeal or willful ignoring of the SHB precedent(in order to have fun, because there is nothing concrete about time travel, it is all theoretical and quite paradoxical))

You like to say that the story operates under the rules that changing the past just makes it so that the timeline revision is what always occurred, but that is not what occurs when there are multiple timelines. It doesn't even occur that way if you allow for branches, because the revisions will just cause branches, rather than change the actual events.

I know you're not going to see things my way, but perhaps others will. That's all I've got to say on this.

[Iscah]

I know you're not going to see things my way, but perhaps others will. That's all I've got to say on this.

Right then, same back at you – I know you're not going to see things my way either, but perhaps other will want to listen to a theory that takes every part of the game and makes it all make sense together, over your theory that chooses to interpret things so they don't make sense with each other.

I came up with my theory to fit Shadowbringers' branching timeline together with Alexander's stable time loops, and then Endwalker came along and I didn't have to adjust anything in my theory at all. That tells me I was on the right track.