Denzel Washington departs from an experimental FBI-unit office in New Orleans, traveling through heavy city traffic in a Humvee.

At the same time — OK, actually 4 days and 6 hours ago — Jim Caviezel has departed the scene of a murder he’s just committed and is barreling his SUV down the same bridge.

How long will it take before Déjà Vu ends up miles away from its promising start as a sharp, compelling story about time travel?

About 15 minutes after this incredibly thrilling car chase between a good guy in the present and a bad man in the past that’s a rocking success for both the left and right brain.

This sequence earns its smirk of originality as one of a few bits when Déjà Vu doesn’t smear its science / philosophy plot with thick jargon or thin questions of whether actions are borne from freewill or destiny. As delivered during the movie, it feels like a kick to the head from a mule with a Ph.D. But by the end, it’s really a trick to make us think we’ve not seen time travel like this before.

Fat chance.

By now, some moviegoers might reasonably match wits with wormhole expert Brian Greene in speculative debates about chaos theory, causal loops and grandfather paradoxes. At the very least, they could name a better modern movie about the subject. That would be Frequency (coincidentally featuring both Caviezel and Greene), a more thrilling, smart, surprising and emotional tale about changing futures and preventing pasts.

Where Frequency revolved family around the science, Déjà Vu seems like it will, for a time, wrap a man’s personal and professional obsessions around the idea. For a time, this seems as if this might be Washington’s Vertigo. Instead, it becomes his Timecop, marrying time-travel tropes to blazing action in a climax that’s basically entertaining, but disappointingly conventional.

Washington starts the movie withdrawn, work-fixated and geekier than normal as Doug Carlin. He’s a forensics-guru ATF&E agent in New Orleans investigating the Fat Tuesday detonation of a bomb aboard a Mardi Gras party boat that killed more than 500 sailors and family members.

The blast is the jumping-off point for the first Tony Scott film in five years for which you need not pack Dramamine. Scott directs discreetly throughout and wisely backs off from his acid-trip visual kick of late in not playing up this opening blast for wows. There are daggers of screams on the soundtrack and quick-cut images akin to 9/11’s Falling Man photograph.

While casing the scene of this terrorist attack, Carlin comes across the body of Claire Kuchever (Paula Patton), whose corpse bears traces of accelerant and sliced fingers too neatly severed to have been from the bomb’s blast. Carlin determines she was murdered beforehand and placed near the site, but why? And why did she leave a message at Carlin’s office the morning of the explosion?

Amid jurisdictional preening, Carlin befriends on-site FBI agent Pryzwarra (Val Kilmer in egghead glasses and a nothing role), head of an experimental unit with a super supercomputer. The “Snow White” project allows a “time-window” view of exactly 4 days and 6 hours into the past from the present day.

The script finds its best strokes of fun, popular-science rhythm in explaining away “Snow White’s” limitations (its use can cause blackouts) and accessories (a “goggle rig” Washington uses in the car chase above to expand “Snow White’s” viewing area from initially typed-in parameters).

Leery of tinkering with the past, the crew just peeks back at Claire’s life to see where it may have intersected with bomb suspect Carroll Oerstadt, a blank slate of evil played by Caviezel. But tired of responding to horrific events, Carlin instills in the team a sense of can-do (or is that already-has-done?) optimism and travels back in time in an attempt to save Claire’s life and stop Carroll’s plan.

There’s a spiritual poignancy as Doug powerlessly watches what happened to his suspiciously missing partner in the past. But it’s a little bit eerie, the way he gawks at Claire as the team intimately peers into her home life, and if any actor is capable of heroes with questionable motives, it’s Washington. But he goes on action-man autopilot in the third act, and the notion of traveling in time to prevent death just becomes a gimmick to bring together the film’s leading man and lady.

Plus, for all its cautionary talk against Doug using the time-space fabric as a sort of snuggle blanket with Claire, Déjà Vu has a curiously linear storyline and ridiculously tidy resolution. The film is only relatively committed to being a scientifically feverish and fun time-travel ride, and the answer to its emotional equations is something the filmmakers can’t quite solve.