There have been several possibilities proposed. There's Idran's notion that the effect would ripple back by undoing future acts of time travel that in turn affected the past -- much like what happened in "Yesteryear."
I personally can get behind this one. In fact, I kind of assume that the differences in Khan's cyro tech in
Into Darkness compared to "Space Seed" (TOS) is because of the likely possibility that Henry Starling never got the 29th century time ship and created his advances, meaning that the '90s computer revolution from real life that Cronowerx explained in "Future's End, Parts I and II" (VOY), never happened, which arguably would affect all '90s tech, including cryonics.
The catch is that I think there might be a few instances where without a specific predestination paradox or time travel incident, the 23rd and 24th century Federations would be vastly different from what we know and the Kelvin timeline shows, but since a lot of time travel shows are about fixing a changed future, then in most cases, if the event never happened, then the timeline would just follow the same correct history as the "repaired" timeline did.
There's my notion that the red matter wormhole (which we know opened in both 2233 to deposit Nero and 2258 to deposit Spock) could've opened at other points in the past and that the energy, matter, or gravitational effects it emitted could've caused some past phenomena to happen a bit differently.
I can see the logic to it, although I'm honestly not sure how many changes in the movies could be explained by extra radiation and the like. Also, I think the '09 movie is pretty clear that the red matter wormhole only opened twice (in 2233 and 2258), so I'm not sure I buy the idea of it opening at random (although if there is evidence or ways it could happen, I'd be curious for further explanation/discussion).
And there's the Okuda/Pegg notion that it's some kind of retrocausality effect we haven't seen before -- which seems vague, but there is a theoretical-physics basis for the hypothesis that quantum causality could progress both forward and backward in time, specifically John Cramer's
Transactional Interpretation of quantum mechanics. Cramer's idea is that there are always quantum waves propagating both forward and backward in time, and in most cases they cancel out, but not always, so that there are instances where an event in the future can influence an event in the past -- which could explain the quantum paradox of how a photon in a slit experiment seems to "know" in advance what slits it will or won't pass through. Cramer's model hasn't been experimentally verified yet, as far as I know, but it's certainly solid enough theory to use as a basis for fiction.
I don't really like this idea, and I'm not sure how well it works with what we know about
Star Trek's quantum mechanics, but it's really hard to argue with, esp. given that the gist of it seems to be: "This happened somehow." Maybe when the
Encyclopedia comes out, it'll make more sense.
Really, it's contradictory to allow for the idea of time travel in the first place, yet resist the idea that causality can go backward. The very existence of reverse time travel would prove that we have to throw out our conventional assumptions of cause coming after effect.
I think that depends. Does only what the time traveler and his equipment do in the past affect history, or is there extra radiation and stuff, like you've suggested, that can do crazy stuff? At the end of the day, I think this can only be answered by the laws of time travel that the story uses.
Now, you've said repeatedly that
Star Trek temporal mechanics vary so much by story that (going on canon alone) there's no unifying theory. (I think that there's just enough consistency to make a couple rules of thumb, and the rest can be -- mostly -- chalked up to special circumstances, but that's another topic.) So, are there any other
Star Trek time travel stories that have worked with causalities like this before that we can compare to this model? (For the sake of discussion, let's allow examples from non-canon stuff, too.)
Like I said -- it's a fundamental mistake to assume it has to happen the same way in every instance. The outcome depends on the specific conditions of the interaction. The gravitational forces that hold you against the Earth's surface right now are the exact same forces that would stretch you into a strand of spaghetti if you fell toward a black hole. Same physics, wildly different conditions, wildly different outcomes. So it's completely possible that "normal" time travel events would only have forward-propagating effects, but some specific types of time travel event, occurring under unusual conditions, could also have backward-propagating effects.
Good grief, time travel itself is already an enormous exception to the normal operation of physical law. It's a solution that arises out of the equations of general relativity, but the variables that have to be plugged into those equations to get that result are staggeringly improbable at best. The normal operation of relativistic physics just does not produce closed timelike curves (i.e. backward time travel), but they might rarely occur in extremely unusual circumstances.
Poor choice of words. What I was trying to get at was, are we assuming that that the "total timeline" re-write has only happened with '09 movie incursion, or are there other time travel stories in the franchise that we could or should assume could've also used the same rules? (I'm not counting "Year of Hell, Parts I and II" [VOY], since that was already explained as a unique form of time travel.)
So since time travel is itself an exception to the norm, why should it be hard to believe that there are also exceptions to the way time travel normally happens?
That's a fair point and I agree with it. Let's just say that, based on the movies themselves, I don't think there's enough evidence to support the suggestion that this case is an exception to the "normal"
Star Trek time travel rules.