Dimensional Split (Timing of)
In Viper Manor, Belthasar declares that the split of the dimensions happened ten years ago.
Prophet: Serge... This world is not the world you grew up in. 10 years ago, something happened that put your very soul teetering on the balancing scales of fate... with a fifty-fifty chance of life or death! This is when your future was split in twain. Prophet: In your home world, you survived to live a happy and prosperous life. That is how you made it to the present point in time. However, here in this '"alternate"' world, you are, in fact, very dead and buried. You died 10 years ago, but this world's time line has flowed on regardless. You have no place in this world... Here, you are but a ghost brought back from the past! Prophet: I do not know what happened 10 years ago... Nor can I guess what triggered your entrance into this world.
Later, Lucca alleges that it occurred in 1006 A.D. when Serge was injured and Schala reached out across time.
As Schala fell through the time gate in this condition, she heard your crying echoing through time... That is when her story and yours began to intertwine... It is also when the past and the future began to intersect, and when the world became divided into two... Led by the pitiful crying the young Serge made as the panther demon's poison took hold of him... Princess Schala traveled ten thousand years in time to try and make contact with this dimension!
Which account is correct? Is Belthasar lying? He obviously is faking it when he notes that he does not know what happened ten years ago; could he be misguiding Serge in preparation for the real truth as delivered by Lucca? Did it happen even earlier?
1010 A.D. Support
The 1010 A.D. timing was originally chosen by the Chrono Compendium for sheer weight of evidence. This is when Kid rescues Serge from Lynx and his life truly diverges from the past. This is the date several people in the game allude to as the point at which their lives diverge (such as Mojo and the Arni fisherman each). Miguel states that the Dead Sea was formed in 1010 A.D., which is consistent with the repercussions of splitting the world in twain with the consequences of Home World's future being fated to an apocalypse. Crono even suggests it at the same point in the game with Lucca by noting that the false reality of Serge's living stemmed from ten years ago:
[Crono] Where even angels lose their way... Ten years ago, you died at this very spot. There's no mistake. You drowned. The truth is, this world, in which you are still alive, is the irregularity... This is the false reality!
Also, we know that Kid is sent to the world by Schala as her mind tottered on the brink of being completely consumed by hatred. If the split occurred before 1004 A.D., two Darkness Beyond Times would have to exist for two copies of Kid to be sent to each dimension. This is a strange and troubling possibility, and this would mean there are two Time Devourers (with only one defeated), something we know to be false by ostensible game presentation at the nature of Time Error regions. However, this problem does not occur if it happens after 1004 A.D. If the split is truly retroactive (going backward as well as forward), problems for Chronopolis arise as well. Chronopolis came from a future in which the split hadn't happened; if it traveled back in time to 12000 B.C. with two dimensions, one of them (presumably Home) would never receive Chronopolis, and we know this to be false.
What causes the plot hole and flies in the face of all 1010 A.D. evidence is the statement by Chronopolis researchers that World 01 existed before this date.
An instruction to the young girl in Arni 01 to give up going to the main continent as a poet. An instruction to the man in Arni 02 to give up becoming a fisherman. A plan to avoid any point of contact with the main continent, so as not to affect history. However... Ever since the formation of the Dead Sea 10 years ago... FATE has been unable to intervene directly with World 01. The best FATE could do was cross the dimension and receive data through the Records of Fate. And with much difficulty, FATE succeeded in binding Miguel to the Dead Sea as a watchman...
Chronopolis even seems built in mind with watching a second dimension. This completely shatters the internal logic of having the split in 1010 A.D. by establishing that Home World existed before the split. It directly contradicts everything, including Crono's statement and all supporting evidence that a new reality -- an irregular one -- was created when Serge lived.
Gate Effect Modification Theory
Perhaps the Gate Effect is not a solid 'dome' encompassing Chronopolis, but a dome-shaped barrier taking entrants ten thousand years into the future always to the same Chronopolis, the one that came back from Keystone T-1. Assuming Home World does retroactively get its own history (albeit a carbon copy of Another's before 1010 A.D.), when the split of dimensions occurs and time traveler's immunity is preserved, so too is the Gate Effect. This means that those who would enter the Dead Sea from Home World would merely be accessing Chronopolis, just as there are distortions allowing dimensional crossing in Home World after the Dead Sea is dissolved. With this in mind, there is one Chronopolis for both dimensions until 1010 A.D. Now, perhaps Belthasar foresaw that the history of Home would extend back, and planned for Chronopolis to be equipped to control it or at least know about it from their perspective in 1010 A.D. onward.
- Whether Chronopolis cares or not, Home World's history is automatically a carbon copy of Another's. It wouldn't need to be equipped to control it.
- The Dead Sea is treated as its own future separate from Chronopolis. If the Dead Sea is accessible in one world and Chronopolis in the other, then the Gate Effect is either dissolved in 1010 A.D., or each Sea of Eden retains its own effect.
1006 A.D. Theory
The original timeline was split into two due to Schala's unstable contact with it in 1006, but the two resulting futures remained largely unchanged thanks to FATE until a another new change was made (saving Serge in 1010) to one of the dimensions, this time by Belthasar and Kid. Thus the game can say that "the world became divided into two" in 1006, but "[Serge's] future was split in twain" in 1010.
The volatile nature of Schala making contact with the modern era divides time into two separate timelines. Chronopolis, which until now only had to monitor one dimension, recognizes that it now has to monitor two, and limits both to a small amount of variety so as to ensure the saved future's continuance in both. And part of FATE's plan was to use its vessel Lynx to kill Serge in 1010 to break the lock on the Flame - I guess in both dimensions now that they have split. However, Kid is sent back in time to stop this from happening in one dimension (Belthasar's got it all figured out). So in that dimension, Serge lives, and this somehow negates the saved future and transforms Chronopolis into the Dead Sea. (I know this contradicts the "Armageddon-Branch Theory" within the "Salt for the Dead Sea" article. I'm merely trying to harmonize the explicitly stated facts from the game itself. Besides, just how Serge's existence negates the saved future is not in itself a contraction, merely a mystery - we don't have a conclusive, in-game explanation. So I'm not attempting to explain that one...)
Okay, so Chronopolis - which has been able to control both worlds from 1006 to 1010 - now can only control one, as stated with these words: "Ever since the formation of the Dead Sea 10 years ago... FATE has been unable to intervene directly with World 01." My aforementioned explanation allows for this fact. And this would explain why other people's futures start to diverge so greatly from this point on - FATE is no longer able to keep them so limited in variation. Based on these things, I believe (for now...) that the Dead Sea was formed, not merely because one world split into two, but because a relatively big change was made in one of them - a human who originally is eliminated from both timelines is now reinserted into one. This could potentially change the world, so to speak...
At the end, this theory just leaves the question, "what caused the Dead Sea to form/Home World to end in ruin by Serge's hand?" It also leaves the question, "How was Chronopolis able to set up a room to monitor two dimensions, given the nature of it workers (ghosts) and their seeming caught up in temporal loops?" The second question is another part of the overall plot hole.
From: Plot Inconsistencies