Terminator part 14:  fixed or replaced?

Over the course of the story of Terminator Salvation, we are several times confronted with the possibility that a change would occur in the future that would undo events in the past.  We noted last time that although these raise significant issues, everything ultimately works as it must.  That then raises the question, in what sense must it?  Is John Conner wrong when he says at the end that we make our own fate?  Is time fixed such that we cannot change the past, or the future, that even were we to travel to the past we would do, do, do what we did, did, did before, before, before?

If it is fixed time, then it becomes a somewhat less interesting story.  Kyle and John have to survive, not because we need them to and not because of plot immunity but because of something far more fundamental:  having lived in the future they really can't be killed in the past.  John then does not need to rescue Kyle to save his life, because Kyle was never in any danger.  Rather, John needs to rescue Kyle because that is what John is fated to do.  He thinks he is risking his life to save his father's life, but neither his nor his father's lives are ever at risk.  Of course the fact that it makes an unbearably dull story doesn't mean it's not the intended story.  It just makes it dull.

Distinguishing fixed time from replacement theory stories is not easy.  The final stable history of an N-jump will be completely self-supporting and internally consistent, just like a fixed time timeline.  They can be distinguished only if there is evidence of a different original history which cannot be explained under fixed time.  Terminator gave us a predestination paradox, which some fixed time theorists insist is plausible and others reject as impossible; no certainty can be obtained there.  Terminator 2:  Judgment Day gave us a grandfather paradox, postponing judgment day a few years, and thus when it arrived behind schedule in Terminator 3:  Rise of the Machines it forced the understanding that history had been altered.  Yet there are those who reject the third film as "not canon", who would insist that the first two must stand on their own, and as such are fixed time stories.  The first manages to survive only if you are willing to accept the validity of the uncaused cause in the predestination paradox; the second only if you conclude that Sarah's destruction of Cyberdyne was too late and Skynet went live that year anyway.  But the question is whether there are any hints in the fourth film, apart from the obvious predestination paradoxes, that there was a different history originally.

The problem is that given a particular resolved fact set the two theories are unfalsifiable and indistinguishable in their final histories.  That is, the final replacement theory timeline will have only those traces of previous histories that we call predestination paradox, and fixed time accepts predestination paradox as a viable event in history.  Thus if a film has a perfect temporal resolution, either theory will explain it.

This was disrupted in the Terminator series, because the acts of Sarah Conner at the end of Terminator 2:  Judgment Day were calculated to prevent that apocalypse, and Terminator 3:  Rise of the Machines gave us a story in which judgment day was delayed seven years.  However, Terminator Salvation has no time travel within itself, and creates no anomalies that are not resolvable by both theories.

Thus this film could be understood as a fixed time story, or as a replacement theory story.  The characters within it act as if it is a replacement theory story, that the past can be changed with devastating results for them.  They might be mistaken.  We cannot know just as they cannot know.  Terminator has its share of fixed time theory fans, but also has replacement theory fans.  Individually some of the films work under either theory, but for the series as a series, fixed time fails.

There is a more glaring issue with this movie, though, which will be our next problem.