LOS ANGELES - "It's terrifying."

Will Smith talks with his hands, his eyes wide and smiling big as he describes the emotional impact of his new movie, "Seven Pounds," a romantic tragedy about a man putting his life right after a terrible mistake.

"What is the difference between depression and joy, in the face of loss?"

It's a serious idea the fun-loving Philadelphia native admits he's been exploring in his recent roles in "I Am Legend" and "Hancock."

For Smith, 40, the Ben Thomas character in "Seven Pounds" - the second film he's made with director Gabriele Muccino ("The Pursuit of Happyness") - is the most in-depth study of that idea.

"The revelation that I had, is that the difference is purpose. When you can wake up in the morning and feel that your life has purpose," he said. "Ben Thomas, as twisted as his purpose was, it got him out of the bed. Everyday. His life had value beyond himself."

The Fresh Prince of Bel-Air is sitting in a room at the Four Seasons Hotel, in Beverly Hills, part of a seven-city press junket promoting the film. It's mid-morning, and he's dressed smartly in an ice blue V-neck sweater over a pressed white shirt; cufflinks at his wrists, dark brown suede shoes on his feet. The only bling is sparkling diamond studs (the size of blueberries) that fill his ears.

"You have to be connected to something beyond the physical pain that you endure - and that idea exploded in my mind. If you remain in a narcissistic space, it's impossible to feel that sense of joy."

"The only true happiness is living in service to humanity," he said, summing it up. "Of all the films I've made, I'd say that 'Seven Pounds' changed my life the most."

In fact, Smith did change. He lost 15 pounds for "Seven Pounds," giving his emotionally haunted character a physically strained look. A new hairline was also created through make-up, to alter the shape of his face.

"We set it off a bit and no one's ever said anything, so nobody even noticed - a little movie magic." He gives that big Will Smith guffaw, to punctuate the thought, making everyone in the room feel at ease. "Seven Pounds" is serious stuff, but he's still Will Smith.

The actor's made 20 movies over the last 17 years, a body of work that has taken in more than $5.6 trillion at the worldwide box office. He's perhaps Hollywood's biggest and most successful star and even as he plugs "Seven Pounds," there are sequels to some of his previous hits in the works.

" 'I Am Legend' is a lot closer than 'Hancock,' " he says. "It's a fantastic idea for 'I Am Legend.' It's essentially the last stand of Manhattan; the prequel. The fall of the last American city."

Smith also teases another idea he's working on: A remake of the South Korean movie "Old Boy," with Steven Spielberg, to be written by "I Am Legend" screenwriter Mark Protosevich.

His production company, Overbrook Entertainment, just extended its multiyear deal with Sony Pictures - the studio where he's made four of his last five films (and most of the films in his career). Smith and his Overbrook partner James Lassiter also recently announced a groundbreaking deal to distribute American films in the Middle East.

He credits the idea to MTV, the music television network that launched his musical career and made Smith a household name.

"The conduit that MTV laid for the last generation between the inner city and the suburbs, and between America and the rest of the world, through art, was unparalleled. Every single day, 24 hours a day, black kids got to know white kids, white kids got to know black kids, Americans got to know Asian children. And I believe that connectivity destroyed the ability for misinformation."

"I want to start to lay that similar type of artistic conduit between the Middle East and the West," he added, "So the next generation of Middle Eastern children won't be able to be fed misinformation the way the current and previous generations were susceptible to."

That kind of truth, Smith believes, is what enabled Barack Obama to be elected president. Because the people had the information, Obama could be judged, as he quotes Dr. Martin Luther King, "by the content of his character."

An international plan for an international superstar, but Smith brings the conversation full circle, saying he still retains his connection to Philadelphia.

"My family still lives there. My mother and father are there, so I get back home. My sisters and nephews are there."

And what about the Phillies recent World Series win?

"Being in L.A. and being a Philly fan - it's almost dangerous," he says. Then that big laugh fills the room again. "But it worked out well." *