'21 Grams' (R) (out of four popcorns)

"They say we all lose 21 grams at the exact moment of our death ... everyone. The weight of a stack of nickels. The weight of a chocolate bar. The weight of a hummingbird."

So begins a disturbing, bleak and stirring story of how just one brief moment can change the lives of many people who don't even know each other.

But what is that 21 grams? Is it the weight of a soul? Is it lost bodily fluids? Is it the release of air and gases after death? Or is it the weight of the world we have been carrying on our shoulders?

There are no easy answers in the English language film by Academy Award-nominated director of "Amores Perros," Alejandro González Iñárritu. But there are plenty of gritty performances by powerhouse actors like Sean Penn, Benicio Del Toro, Naomi Watts, Melissa Leo and Charlotte Gainsbourg.

In two of the three initial stories, the characters have overcome incredibly bad choices and their lives seem to be on the right track. In the third story, a couple is hoping for a miracle.

Their lives intersect in the wake of a gruesome and heartwrenching accident in which a man and his two children are run over by a car.

Penn is Paul Rivers, a mathematician whose heart is failing him and desperately needs a transplant to survive. His wife, Mary, (Gainsbourg) is desperately trying to hang on to any part of him she can by trying to get pregnant.

Watts is Cristina Peck, a former addict who finally has everything she has dreamed of -- a husband, two young daughters and a cozy home. But then comes the call we are all terrified of getting.

Del Toro is an ex-con who has escaped his past by clinging to religion and strictly using its precepts to run his life and the life of his family. But his past can never be put behind him and he loses his job because of prejudice over ex-cons. His despair is the catalyst that changes the lives of everyone in the movie.

"21 Grams" is the kind of movie you need to pay close attention to. It is a patchwork quilt of scenes, alternating between several different time periods. A scene that may be confusing at first, later makes sense in context. But the connections are not always clear and even when the screen fades to black, you will probably have questions about what really happened.

The washed out cinematography adds to the sickly unease you feel as the stories unfold. Iñárritu is a director who has his own distinctive style and just seems to get better. When a director's first film is nominated for an Academy Award, you know he is a creative force to watch, and "21 Grams" reinforces that idea.

You may not be entertained if you decide to see "21 Grams," but you will be witness to a challenging film that makes you question how much guilt, love and revenge weigh in your own life.