This is an interesting scenario as I have traditionally sided with the Compendium's analysis of the Marle paradox.
At first when I was reading your post, I was thinking essentially what Zeality was and I further thought that what we have been discussing in the other thread about time and dimensional travel is a special case. What I mean by this is that the examples of TB working in an unnatural way, which we proved in the other thread about as thoroughly as we could, happens because of the dimensions being split and reunified and matter being created/combined so that a problem of duplicate matter caused TB to work in a different fashion than it normally does.
But then after reading your response to Zeality I am not so sure anymore. The Marle case is unique, to be sure. But I raise the following question:
Why wouldn't the atoms that composed Marle in 1000 A.D. just disappear as a person normally would due to Time Bastard?
In proposing your theory, Eske, you would have to explain this. But here, I'll help you out. If TB does indeed work by sucking an individual into a single "black gate", perhaps a single black gate could not TB away all the atoms which formerly composed Marle in 1000 AD, so instead the Marle in 600 AD was TB'd away to conserve matter?
But then, why did she disappear when she did and not immediately upon entering 600 AD? You would have to explain this as well. The Entity explanation still makes more sense to me.
So you have 2 questions then:
1. Why wouldn't the matter that was to be her composition in 1000AD disappear at Time X, mimicking Time Bastard?
2. Why did she not disappear immediately upon entering 600AD.
I have 2 answers:
1. Could the matter that formed Marle and her ancestors really be identified? No. So how does the system decide what matter to eliminate in 1000AD at Time X?
It doesn't - it takes the path of least Resistance and deletes the matter corresponding to Marle in 600AD.
Remember that with Time Bastard, the time traveller, as an entity, still exists up to Time X. At Time X that entity's original version entered a gate. If this new version does not, it will vanish because at this point it is extra information. If it does enter the gate it will vanish as well for the same reason.
2. Not just this, but why did the timeline not reset as soon as she travelled to the past? How did Crono and Lucca both travel from the same 1000AD even though 600AD is now completely different? Another member, Thought, once said that I "assumed time is brittle" and that every change in the past would erase the timeline immediately would be "wasteful". He was right. So I've changed my thinking a bit.
Let's look at how time is preserved despite changes to the past:
1. Marle goes back in time to change 600AD even the slightest bit. Nothing happens.
2. Crono goes back in time and finds Marle, perhaps originally Marle never saw Crono and there was some intermediate timeline. But wait.
3. While Crono is in the past, Lucca travels from the present. There is no Crono who lives out his life in the past, so we can conclude the same goes for Marle.
Time isn't so lenient with the items in the Northern Ruins: If you take them out in 600AD, they won't be there in 1000AD. That makes sense.
But looking at the Marle example above lets play out an event assuming that there is a gate in the Northern Ruins.
at Time X Persons A and B are in the Northern Ruins and Person A time travels to 600AD.
An Item is known as Item P in 600AD and Item F in 1000AD.
With the Marle example above we see that timelines aren't reset immediately.
Person A takes Item P out of the chest.
Person B is looking at Item F in the chest, the past isn't immediately changed as in the Marle example.
But at some point it must reset. Let's see:
If Person A (an immortal) waited out the 400 years would he still see Person B looking at Item F? No. Item F isn't there, the timeline has reset. But for Person B, this never happened. How can this be explained?
My idea is a different take on the 5th axis. Time Error is the idea that if you spend Time Error Y amount of time in an era or the EoT, your entrance to a different era will be the destination time (say 600AD) + Time Error Y.
I would think that the gates merely take us so many years into the past or future, from our point in the present. So if Crono said "screw it" and waited until 1001AD to enter the Millennial Fair gate, he would end up in 601AD.
I look at it this way: Every point on the 4D axis (time) is a snapshot of everything in 3D space. Every point on the 5D axis is a snapshot of everything in 4D space.
aka - an entire timeline. In another thread I used a flipbook analogy. 4D is like flipping through the pages of a flipbook one at a time, each page being a snapshot of motion -- while 5D is seeing all the of the pages at once, seeing all of the motion at once.
I propose that these "timecycles" explain why the future isn't immediately changed for Crono and Co. when Marle travels to the past, but if she were to travel back to the future, or wait out 400 years - the future would seem to be adjusted. She is at one point on the 5D axis, while Crono and Lucca are at another - they are totally unrelated right now.
Time Error isn't needed to explain why they don't reappear as they disappear. The gates need only take an entity back/forward a set timeframe. If they reenter a gate 10 minutes after they left it, they would emerge from the other gate 10 minutes later.
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So back to the Marle Paradox.
Using the above idea that at Timecycle N the matter that is Marle exists in two places in the same timeline, Time X. She doesn't disappear upon entry to 600AD because some event at Time Y in 600AD is what determines whether or not she is able to exist later on. This event at Time Y never occurs.
Crono and Lucca at Timecycle N-1 will not be affected by the changes into the past - that timecycle will carry itself out as normal.
I don't think we will find the answer or an answer that works until we shake things up a bit. I noticed awhile ago that I approach many of the puzzles here with TE. TB. and TTI on my mind right away. I'm sure many others do the same -- They work, but alternatives might be helpful as well. I mean, what if something in Chrono Break disproved TTI? We would have to retool many theories.