I thought it was a damn good movie, too, based on concept alone. I believe they were manipulating a wormhole to somewhat "look back in time". Thing is they can only see like 4 days and some odd hours/seconds in the past, but even then the time keeps moving. They cannot stop, rewind, or fast forward because that would be on some ridiculous shit.
The idea seems believable only because of the limitations they put on the science/technology.
Denzel ends up sending himsdelf through the apparatus that does all this and ends up launching himself into the "past" in order to catch a domestic terrorist.