I usually try to keep my spoilers mild, but I am irresistibly drawn to spoil Source Code, since the inventor of The Source Code in the movie explicitly says, “Source Code is not time travel. Rather, Source Code is time reassignment. It gives us access to a parallel reality.” But what does the inventor know? Go watch the movie (which I enjoyed) before passing your mouse over my take!

A common form of time travel is when the traveler goes back in time and a new reality branches off. That’s the form of time travel I see in Source Code, and from my reading of an interview, perhaps the director sees it that way, too. This view fits better than the parallel worlds postulate of the inventor, because each time the captain goes back, he is in exactly the same moment, with the same passengers, same comment coming from future girlfriend, same woman about to spill coffee, etc. If he were shifting to a parallel universe, then perhaps some things would differ before he arrives. So, I see it as branching-worlds time travel, with the twist that the mechanism to do the time travel is to pop the traveler’s consciousness inside the head of a dead person at about eight minutes before the death. I believe that the original world where the traveler came from (and usually returns to) continues along its original path (as evinced by the fact that after one return in which he saved girlfriend, there was no record of her being saved).