So the plot is that Captain Colter Stevens (Jake Gyllenhaal) uses this device to go back and take over the body of Sean Fentress, a victim in a train bombing, and relives the last eight minutes of Sean's life over and over until he manages to catch the bomber (think Quantum Leap multiplied by Groundhog Day). In the process, Colter, wearing the body of Sean, asks out Sean's hot co-worker Christina (Michelle Monaghan), and the two live happily ever after, presumably.
Why can't Jake Gyllenhaal just travel through time like normal people?
The Creepy Implications
Except that there's one small thing Colter hasn't mentioned to Christina by the end of the movie: Namely, that the co-worker she's had a crush on for weeks is dead, and he's actually some other guy who possessed the dead dude's body.
Basically, Colter has stolen another man's life, and the end of the movie gives no indication that he'll ever tell Christina what's going on -- how could he? She'd probably just assume he had a psychotic break. This "happy ending" is actually a terrible situation for everyone involved: Colter is walking around in the body of a man he knows nothing about, and Christina is now dating a complete stranger pretending to be Sean. There's a name for that, by the way, and it's called "rape by fraud."
"We don't have those laws in the future. Uh, I mean Minnesota. Where ... I come from."