Probably the single most important was the revelation, near the beginning, that there's a recalcitrance of the universe - or at very least, life on Earth - which resists changes in history brought about by time travel. If you have to kill someone who was on some higher level meant to live, then that death won't happen - one way or another, that person will live. Or, someone else will do what the deceased was supposed or meant to do.
The problem, of course, is knowing what this ultimate, unchangeable course of world history really is. Presumably not just what some character claims it to be. That leads to excitement and dramatic tension, even in a universe in which changes in time can be meaningless.
We have all kinds of incidents in which this principle is well expressed in 12 Monkeys 2.1. Cole can't just kill Jennifer point black, even to stop the plague from being released. Is this because he knows or senses on some level that the universe doesn't want the plague to happen, and will stop it by some other means? Ramse can't bring himself to abandon Cole in Cole's attempt to stop the plague, even though no plague means no son for Ramse in the plague-torn future. Is this because Ramse feels deep down that his son will somehow be born, anyway, without the apocalypse?
Railly presumably has not gotten this message - she is, after all, a scientist, not a metaphysician - and this leads her to confront Cole, gun drawn, in her single-minded intention at the end of the episode to kill Jennifer. The confrontation is a great touch, not only because we last saw Jennifer in the 2040s, with Jones and her estimate that the time machine could take as long as a year to repair, but because the guns-drawn confrontation is symbolic of the conflict between philosophy and science that runs through the series.
Railly's sudden appearance is also nice because it exemplifies another underlying truth of time travel - one which I use in many of my time-travel stories - to wit, it doesn't matter how long it takes for something to happen, including building a time machine in the first place, or anything else before the actual time travel, because you can arrive a split-second, if you like, before or after the time you want to travel to, in the past or the future. You can do this, in other words, however long it took you to make the decision and attain the means to do it.
Ain't time travel grand? Indeed it is, and it's good to have 12 Monkeys back at it in such good form again.
See also this Italian review, w/reference to Hawking and my story, "The Chronology Protection Case"
And see also 12 Monkeys series on SyFy: Paradox Prominent and Excellent ...12 Monkeys 1.2: Your Future, His Past ... 12 Monkeys 1.3: Paradoxes, Lies, and Near Intersections ... 12 Monkeys 1.4: "Uneasy Math" ... 12 Monkeys 1.5: The Heart of the Matter ... 12 Monkeys 1.6: Can I Get a Witness? ... 12 Monkeys 1.7: Snowden, the Virus, and the Irresistible ... 12 Monkeys 1.8: Intelligent Vaccine vs. Time Travel ... 12 Monkeys 1.9: Shelley, Keats, and Time Travel ... 12 Monkey 1.10: The Last Jump ... 12 Monkeys 1.11: What-Ifs ... 12 Monkeys 1.2: The Plunge ... 12 Monkeys Season 1 Finale: "Time Travel to Create Time Travel"
podcast review of Predestination and 12 Monkeys
three time travel novels: the Sierra Waters trilogy
What if the Soviet Union survived into the 21st century,
and Eddie and the Cruisers were a real band?
The Chronology Protection Case movie
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