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Old 2018-06-06, 17:42   Link #70
阿賀野型3番艦、矢矧 Lv175
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Join Date: Mar 2006
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Originally Posted by erneiz_hyde View Post
The world line theory Suzuha stated specifically says that paradoxes like the grand father paradox are impossible though. And she must have known that from SERN. If SERN knew paradoxes are impossible then they don't need to fear causing paradoxes.
Actually, the paradox is dealt with for world line change, but not time travel.
The world line shift prevents paradox regarding ongoing events affected by a change in the past. Basically, paradox cannot happen under such circumstances because the world line is shifted so the parameters of the world match the present based on the modified past.

But Paradox dealt by time traveler in their "present/current perspective" is "not allowed". It is the very reason why Suzuha was insistent about Okarin not to meet his past self during the very end of S;G, as it might lead to a severe paradox.
Likewise, in SG0 episode 9, Kurisu told Okarin that the attackers cannot go after the time machine because it would be a paradox: their research cannot be based on interference from the future.
So my conclusion is as follow: the future cannot alter directly the present which would change the origin/cause of that future action, as it would ultimately affect the present in an endless paradoxal state. Since the future didn't happen from the "present perspective" but still affect the present, it means that the required parameter doesn't exist yet but would be in such state that would recursively deny or confirm the future event, which is why it is considered as a huge time paradox in SG.

World Line shift is trickier but prevents paradox because the present is ongoing, but the past is settled. Since the past is changed from the perspective of the "present", then it means that the present must change to stay consistent, thus the world line shift. The fact the "previous world line" still existed makes the concept of world line shift "acceptable" in a sense that it "happened" already so there is that.

In other words, WL is acceptable in SG because the action affecting the present did happen and is in history. A time travel paradox is no good because it will recursively affect itself since it didn't happen yet. Of course, you may ask "but from the time travel perspective, the future is the present, and the present is the past, isn't it?".
Very true. However, the time traveler is really in a peculiar situation because they have their specific context of why they performed a time travel to begin with. They observe the world as it is, the "present". Therefore, they are in a unique situation where any change of the present would immediately affect them in return, which lead back to the "recursive" issue I was mentioning. The D-mail causing a WL shift is different mainly because the actor isn't obsering and acting directly on the change affecting the past itself.
Naturally, this also explains why Okarin must not undo the fact his past self witnessed Kurisu's "corpse" as it would immediately interfere with his current status. The scenarists pretty much abused some loophole in the time trvael paradox logic.

It sounds like a plot copout, but it explains why SERN cannot interfere in the present to secure their future domination: they cannot alter the present to be dependant of the future, since it would completely reverse the causality of such situation, and they probably knew about that since they worked really a long time on the time travel theory.
A World Line shift with a D-mail would be much more effective in this case, but as usual, D-mail are chaotic by nature since you cannot be sure if the result will be what you planned and there is the data limitation too. And I assume they weren't trigger happy with that kind of stuff, even though they did a hell lot of jellyman reports.

Let me say though that SG is not entirely perfect regarding time travel exactly because that "badge" issue is still an eyesore: the fact something fall in the "chicken or the egg" issue about the true origin of a certain event pretty much proves SG couldn't really escape the usual "paradox issues" with time travel stories. This only affect a minor thing like that lab member badge, but that's enough to tell you the writers were aware of their own limitations in their "time travel constraints". They are aware that certain paradoxes cannot be smoothen with the world line structure, but they unfortunately didn't avoid that with this peculiar story part.
In fact, Suzuha's presence is itself a rather large paradox for SG as a whole, but they presented in a way that "must be accepted" with the series premise because she is integral part of the world line shift in general, thanks to the status of the time machine depending on the attractor field.

Last edited by Klashikari; 2018-06-06 at 18:16.
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