Colossus Rex wrote:
On examination, I don't think the sci-fi premise holds up at all.  What Gyllenhaal is able to do on the train... and not just at the end... is counter to everything we've been told via the technobabble exposition the scientist character provides. 
I'm a little confused here.  In time travel stories, everyone is on their own; there are no "laws" regarding time travel.  This is another time travel story, and made up its own rule.  It even made up a rule that it then quite deliberately (and carefully) violated.