Spoiler Level: Atomic. There's really no way I can discuss my thoughts on this movie without giving away several key elements of the plot. And for once, I'm only a week behind when it was released. So only read on if you've already seen it or if you don't care what you learn! And if you do care-- this is a great movie. Go see it. Okay, you can go now.
Source Code is directed by the same guy who directed Moon?!? I didn't realize that until just now when I got the poster image. Well that explains a lot. Both are very human stories about one man whose life isn't what he thinks it is, who are being controlled by people without their knowledge, and who eventually take their lives into their own hands, irregardless of how overwhelmingly the odds are stacked against them.
Captain Colter Stevens is an unwitting participant in an experiment. He's being sent back in time, where he arrives in the body of teacher Sean Fentress on a doomed train in Chicago, a train that was destroyed by a terrorist earlier that morning. Colter's job is to figure out which one of the passengers planted the bomb. He only has the last eight minutes of Sean's life to accomplish this-- and if and when he fails, he'll be sent back to try again, and again, and again.
It's Quantum Leap meets Groundhog Day, but with a deeper twist. Because Colter isn't just going back in time. When his mind is linked up with Sean's, for those eight minutes he's creating an entire new alternate reality, separate from his home reality-- a reality that those running the experiment call the Source Code. Any changes he makes there have no effect on his original timeline, but since history is the same in both worlds, he can explore the world inside the Source Code in depth and bring back information on the terrorist so he can be caught before he strikes again in the original reality. But what about those other quantum realities he's created? Do they only exist for eight minutes, ending when he dies, or do they continue on without him?
The more time Colter spends on the train, getting to know the people on it-- especially Christina, the beautiful girl sitting next to him-- the more determined he becomes to find a way to save them all. It's hard for him to accept that even if he saves them inside the Source Code, they'll still be dead when he returns to his original reality. On his final attempt, he no longer cares-- he just needs to save them all in one reality for his own conscience's sake. And he succeeds beyond his wildest dreams, as that reality continues on, with him now getting to live out the rest of his life with Christina.
Except there's one person he didn't save-- Sean Fentress. Colter may not have meant to, but he's now quite literally stolen Sean's life. Now, sure, Sean was going to die anyway, but what about Sean's friends and family? One of the subplots of the film is about Colter trying to reach his father when he goes back in time, since he hasn't been able to contact him while he's been a part of the project, and it's a very moving part of the film. But what about Sean's father? Colter isn't going to know a thing about him or any of the other people in Sean's life.
The film also raises another intriguing point when it's revealed that since Colter came from the original reality (let's call it Reality A), in the altered reality he now lives in where he rescued everyone on the train (let's call that one Reality B) there's no need to send him. Therefore Reality B still has a Colter waiting to be sent. Now let's follow that for a moment-- Reality B now has two Colters. So when Reality B has a crisis where they can use Colter-B, Colter-B will begin creating new realities just like Colter-A did. Colter-B will be sent into a different person's body, since it will be a different crisis, and the odds of Sean Fentress being in both crises are unrealistic. So let's assume that, being the same man of ability, emotion and conscience, he succeeds in the same way that Colter-A did in creating a Reality C that continues on. This Reality C's divergent point would have started with both Colter-A and Colter-B in it, so Colter-B would now be living out his life in another person's body, leaving no need for that universe's Colter to have been sent... meaning there would now be a universe with three Colters! And so Reality-C wouldn't launch their program until a third crisis came along, resulting in the cycle happening all over again. And again... and again... and again. How long until there's enough Colters existing in one reality that he ends up meeting one of himselves? Would the Source Code Project even realize the full implications of what they were doing before they'd altered the entire human race into alternate versions of one man?
This is all the stuff I found myself thinking of after the movie ended. And that's what makes this movie great.