When science fiction decides to get all deep and philosophical, it always comes down to questions of free will. Do we choose our actions, or are they already totally predictable to someone who could glimpse the future? For example, Terminator 3 caused a lot of controversy with an ending that suggests John Connor can't escape his destiny as a post-apocalyptic leader. Are we just puppets of a future history engraved in stone? We settle these debates once and for all, and list the four different types of fate-vs-free-will stories in SF, below.
The whole idea that our actions are determined ahead of time is more metaphysical than scientific, although some have claimed that quantum mechanics proves our decisions have already been made. But the idea of "fate," or "unshakeable prophecies," really belongs more in the realm of mythology and gods than in a story about a rational, observable universe. As soon as you start talking about someone being unable to escape his/her destiny, suddenly there's a guy with a white beard talking for like ten hours. Like this guy:
(What I really want to know is, why hasn't anybody made an animated gif of the Architect doing a funny dance, with all his hand gestures?) So here's a list of the main types of SF stories about predestination, which I was always fated to write:
We're just following a program. That's what I think the Architect is saying at the end of Matrix: Reloaded. Neo is just the latest "One," acting out a program that leads to the Matrix and Zion being rebooted so that another version of the same cycle can happen again. Every choice Neo makes is just part of his program, except that this time around Neo actually saves Zion instead of rebooting it. I think.
Everything is ultimately predictable. If you have enough data about the present, you can make iron-clad predictions about the future. The only reason we don't know the future is because we don't have the raw data on every single factor that will lead to future events. In the first season finale of Blake's 7, the nearly omniscient computer Orac is able to make a dead-accurate prediction that a ship that looks like the Liberator (but isn't) will blow up. Orac never predicts the future again, for some reason. In another episode, "Weapon," a mascara-wearing psycho-strategist, Carnell, can predict everyone's future actions completely — but his predictions fail because he's lacking a crucial piece of info.
In Paycheck, Ben Affleck builds a machine that can absolutely predict the future. He uses it to witness his own fate (before his memory gets wiped), and gives himself a bunch of tiny items that allow him to
kill all suspense get out of every jam he gets into. But then, in our totally nonsensical clip from earlier today, he suddenly decides that the machine's predictions really only come true because people find out about them and inadvertently make them come true. (It makes no sense to us either.)
The vision of the future. Our hero gets a glimpse of a future event, and has to accept it or change it. It's usually something worse than just "You'll have a colostomy bag in a few years." Sometimes, it's only a possible future and we can totally change it, but sometimes it's presented as an unshakeable reality. In the Robert J. Sawyer novel Flashforward, physicists accidentally send everybody's consciousness twenty years into the future, and one of the physicists learns he'll be murdered. Sawyer has written that Flashforward is about the unsettling notion that "the future is just as fixed as the past."
But in Minority Report (the Dick book, and to some extent the movie), it's made clear that the precogs are only seeing one of a few possible timelines. Otherwise, even imprisoning the pre-criminals wouldn't be able to prevent them from committing the crimes they're destined to commit.
Time travel. Heroes actually takes a belt-and-braces approach to future predictions: Isaac paints his precog vision of New York getting toasted, but Hiro also travels forward and sees it first-hand. But Heroes also tries to have it both ways about whether Isaac's paintings are "fated" to come true: New York doesn't get toasted, but everyone still acts as though HRG can't possibly escape getting shot in the eye. Maybe predictions that include actual time travel are more mutable, because you're only visiting a possible future?
In Kurt Vonnegut's Slaughterhouse Five, Billy Pilgrim becomes unstuck in time, visiting his own past and future. He finds he can't change either one. He knows when he'll die, and can't change it. But he can announce the fact at a speech right beforehand, which seems like changing the future somewhat to me.
In most time-travel stories, the maxim "any future is only one of many possible futures" tends to come up, because an immutable future is a recipe for boring stories. At some point, the writers on Doctor Who realized that any story taking place in Earth's history must have zero suspense, because we "know" that Earth is fine in the twentieth century. So Robert Holmes inserted a scene into "Pyramids of Mars" where the Doctor proves that Earth in 1980 will be a barren wasteland if he doesn't stop the monstrous Sutekh in 1911. Similarly, in "The Unquiet Dead," the Doctor tells Rose that there's nothing stopping him from filling Victorian England with walking corpses, even though her "present" doesn't include that piece of history.
So here's the part where we settle the question of fate vs. free will once and for all. Ready? Okay. The bottom line is, in order to predict everyone's future actions absolutely, you would need an infinite amount of data. You would need a model of the universe the size of the universe. And you can't have time travel without the ability to change the timeline, or else you couldn't interact with the past at all. You'd be unable to touch anything or move anything, even minor things, because it's all part of established history. You couldn't even disturb the air molecules or step on anything. And if you can change the past, you can change the future. Any questions?