Time Traveler's Immunity has other ramifications; namely, the Emergence Preservation Corollary. Imagine that you go back in time to 999 A.D. and murder Crono a full year before he can travel through time. What occurs at 1000 A.D.? Does the ruined future magically come back into place now that Crono cannot conceivably go back in time to 600 A.D.? It would not; under Time Traveler's Immunity, a time traveler's actions are preserved in the past. Think of it like this -- when Crono enters a Gate to 600 A.D., it does not take him to a specific timeline, but merely deposits him somewhere spatially at the time of 600 A.D. in the current timeline.
Ah, I see where you are coming from now. But I still am not following you in how TTI is just "a guarantee that the same person/thing will come out of a gate or whatever at the right time." It is a protection of events in the past being in the past, but wouldn't a Traveler still need immediate protection as well? Marle, for instance, could undertake an action that results in her never being born. The action gets preserved in time, but after that action wouldn't she then disappear (thus not giving us the grandfather paradox, true, but still resulting in a time-traveler not realizing their own changes to the past, which seems to be in contradiction to the games). On a lesser scale, let us consider the Mayor of Porre. Crono goes back in time to give the ancestor Jerky. In doing so, his action is preserved in the past, via TTI. However, as you seem to indicate, Crono himself would not be protected. Thus, the Crono that leaves 600AD would have been changed by his own actions (though those actions still occurred), and as such he would have no idea why he needed to give the ancestor the Jerky, or that the Mayor of Porre was ever a bastage (or would even memories be covered under the "same person" bit?)
Perhaps you might better understand where I am coming from (and thus better see my confusion) if I explain why I think this is an important question.
The grandfather paradox is a paradox because the effect alters the cause in such a way that the effect itself would change (thus negating the effect that altered the cause in the first place). We can represent this by the following (where C represents cause and E represents effect)
If C=1, then E=1
If E=1, then C=0
If C=0, then E=0
If E=0, then C=1
repeat
We get a paradox that just can't be resolved. TTI solves this problem in the following manner (where T represents TTI):
T=1
If C=1, then E=1
If T=1, Stop
If T=0, then
>If E=1, then C=0
>If C=0, then E=0
>If E=0, then C=1
>repeat
This nicely solves the Grandfather paradox; it should never occur in the game. However, the question is if T may sometimes = 0. This relates directly to the Marle Paradox, as she is effected by the Grandfather Paradox even though it would seem like TTI should prevent it. If T can toggle, then the Marle paradox might be resolved through the following
T=1
If C=1, then E=1
If T=1, Stop
If T=0, then
>If E=1, then C=0
>If C=0, then E=0
>If E=0, then C=1
>repeat
T=0
Run line 2
Or, to put that in less quasi-code-y terms; the Marle Paradox may easily be accounted for
if TTI protects the individual and
if TTI is not permanent. That is, Marle travels back in time and is protected by TTI, so that the Grandfather Paradox (her causing herself not to be born) doesn't affect her. At some point, she looses TTI, thus she suddenly
is affected by the Grandfather Paradox, thus she disappears. However, her actions in the past are still preserved by TTI, so the Grandfather Paradox doesn't cycle; she stops herself from existing, but the action which caused her not to exist persists. Meanwhile, Crono and Lucca time travel and gain TTI, so that when the action which sparks the Grandfather Paradox occurs, they are not affected.
As Marle is no longer protected by TTI (and as such, ceases to exist), Crono, Lucca, and Frog are able to undertake actions which restore Marle's existence, allowing her to come back. She then time travels again and regains TTI.
Of course, for such a theory to work it would 1) need to be in line with established TTI theory (thus, why I asked if it is permanent, and thus my subsequent attempts to confirm that I am understanding TTI), 2) and one would need to establish a specific means for one to loose TTI (as just saying that it was randomly lost is little better than claiming that the Entity Did It).
The first issue is still at hand, however I believe I can provide an answer to the second issue.
Consider Chronopolis and El Nido, as indicated in a previous post. The residents of El Nido, though they do not Time Travel themselves (and thus are not protected by TTI), are able to change their own future (by bringing back the apocalypse). The original scientists from Cronopolis would be protected (as they have TTI), but not subsequent generations. Thus, the original scientists would have their actions be preserved, but not the long term results. Unless, that is, TTI is maintained. How might it be maintained? A simple refusal to reintegrate into the timeline; FATE prevents El Nido from truly being a part of the times that it lives through, thus TTI is maintained.
Marle, on the other hand, integrated herself into the time that she found herself. I would claim that this is what caused her to loose TTI. We see the same with Melchior, Belthasar, and Magus; they find themselves in different times and make their lives there. They cease being time travelers and become time immigrants. Thus, they loose TTI. Even though their "actions are in the past," those actions are not preserved and can be changed. Belthasar's actions (in particular, dying) can then be changed when the timeline changes (which indeed is necessary for Crono Cross to even happen... or else Belthasar in the game is a very vibrant corpse).
But it would seem that I am incorrect in some manner on my understanding of TTI. Not sure where, though.
