"Smithsonian World," never faint of heart, tackles the formidable topic of quantum mechanics this week and does its best to make the subject more accessible. Understandable. User-friendly.

After all, we're talking about the nature and structure of the universe. But since no one -- not even scientists -- can see what we're talking about, it would be nice if we viewers understood what's being said.

Not so easy, it seems. "Ask 10 physicists what quantum mechanics is really talking about, you'll get at least eight different answers," physicist David Mermin of Cornell tells viewers.

So although she's obliged to toss around off-putting terms such as "quarks," "leptons" and "gluons," "particle physics" and "quantum theory," producer/director Sandra Wentworth Bradley also uses often-exquisite photography, includes passages from Tom Stoppard's play "Hapgood" starring Roger Rees, and ties it together with the soft, careful narration of 11-year-old Heidi Brown, her daughter.

"The topic is one that doesn't strike you as being human at all," acknowledged Bradley. "It also strikes you as being not involved with your everyday life, because you're talking about the microworld, the subatomic world. I think most of us let go of that world when we finished science in elementary school. It isn't part of our everyday existence.

"What the film tries to do is use visual elements that are part of our everyday world, but viewed in another world. The yellow blossom you see at the beginning is a tiny forsythia. It's simply that we don't see things that close and, of course, you can't see them on the subatomic level."

So you may find yourself smiling when physicist Martin Perl, talking about subatomic particles, says casually: "I see them as little, and that may be a problem because they may have no size at all."

Little? Seems almost inadequate a word.

Even Burton Richter, who directs the Stanford Linear Accelerator Center, says that "it's possible that there is no minimum, there is no smallest thing. It's possible that {the universe} is like an infinite onion that you can keep on peeling layers off, and every time you probe to smaller distances using a higher-energy tool, you'll discover still another layer of the onion."

When Bradley took on the task of "The Quantum Universe," she realized that "there is no way that you can teach the rules of quantum physics in 54 minutes, nor can a whole series do it."

But, curious to know whether people had even the slightest familiarity with atoms, she set about doing interviews outside the Smithsonian's Air and Space Museum. It didn't take long before she saw that she would get no useful footage for her film.

"I didn't think most people would know about quantum mechanics, but I thought some people would know what atoms were. But many, many people did not even know what I was talking about. One person thought I was talking about John Adams. The only ones who knew something immediately were school kids.

"It struck me that we don't think about things that are difficult to contemplate. What the film tries to do is just give a taste of something that's a phenomenal world and that affects our lives, because how far science goes is important to us."

Sometimes, however, what is important isn't always easy to film. This same season, Bradley was assigned "Tales of the Human Dawn," about evolution. "Adrian {executive producer Adrian Malone} gives me the ones no one else will do," laughed Bradley. "I tried to trade 'Human Dawn' with Dave Gruber, who did 'Zoo.' Gruber loves evolution, but he wouldn't trade."

Doing a film about animals in the National Zoo, they both knew, would be a lot easier than making one about quantum mechanics.

Setting into her task, Bradley found photographer Berenice Abbott, 92, who had become science's "friendly interpreter," and sculptor Kenneth Snelson, whose work appears at the Hirshhorn Museum of Modern Art, both of whom are fascinated by physics. British playwright Tom Stoppard said she could use passages from "Hapgood" if they featured actor Roger Rees.

She talked to a clutch of scientists ("extremely intimidating, they're so brilliant") including Nobel laureates Richter and Sheldon Glashaw of Harvard and Rev. Robert Russell, who received his Ph.D. in physics and was ordained on the same day.

"There's a surprising number of people who deal both with theology and physics," observed Bradley.

Glashow agrees. "Many scientists are deeply religious in one way or another, but all of them have a certain, rather peculiar faith. They have a faith in the underlying simplicity of nature, a belief that nature is, after all, comprehensible, and that we should strive to understand it as much as we can. Now this faith in simplicity ... is completely irrational and completely unjustifiable. It is, therefore, a religion."

She also interviewed Bruce Gregory, director of the Harvard-Smithsonian Center for Astrophysics, and his colleague, astrophysicist Margaret Geller, who talks about "a special gift ... of being the first to discover something, to see something that has never been seen before."

She was particularly pleased with Geller, calling hers "astounding, groundbreaking work. And it was nice to have a woman in a field that is very much dominated by men. I felt lonely at times out there."

When she traveled for shoots, Bradley, mother of daughters 11 and 8 and a son, 2, missed her family. So sometimes she incorporated them into the film. The child at the beach building a sand castle is 8-year-old Kimberly. And the narrator (also the cellist) is her daughter Heidi, a student at Sligo Creek Middle School in Silver Spring.

"They're cheap, torturable labor," laughed their mother the filmmaker.

When Bradley considered having a child narrate the film, to bring the subject down from the chilly ivory tower of academic research, Heidi came in handy. She helped her mother with a scratch track {trial narrative}, proving that she could pronounce the words and speak with inflection.

"Then I tested professional child talent in about Heidi's age range, both boys and girls, and I gave them to my editing staff," said Bradley. The editors decided that Heidi Brown would be fine as narrator. But like all adolescents, Heidi wanted to do it herself.

"I figured she wouldn't know how to enunciate, or how to say the sentences," said Bradley, who presumed to coach her. "Finally she said, 'Mom, just let me do it. If I do it wrong, you can tell me.'"

Being the producer/director's daughter turned out to be a mixed blessing.

"The whole thing was a game with her -- it wasn't just work, because she knew and liked all the people she had to work with," said Bradley. "So I had to keep it serious. It really did involve being very hard on her. At one point later I went to her and said, 'Heidi, you really did a very good job,' and she smiled. I know she's proud of it."

Sandra Wentworth Bradley, daughter of a geologist who worked for the United States government, grew up in the Middle East. Her parents, whom she described as "adventurous," had taken their son and three daughters first to Baghdad, although Iraq was thrown into the tumult of revolution shortly after they arrived and the children and their mother were evacuated to Rome. Later the family lived in Amman, Jordan, and Sandra and her older brother Rod went to boarding school in Beirut.

Eventually, the family moved to North Dakota, where Bradley recalls enjoying science and being the only girl in her analytical geometry/trigonometry class. She completed high school in three years, did a year at George Washington University, then worked for 18 months before switching to UCLA to major in film. She finished three years of college in 1 1/2 years largely because she disliked Los Angeles, she said, then headed "home" -- her parents were living in Washington, D.C., at the time.

"I came back here and they went off to Austria," she said, "so I lived in their house and took care of their dogs. Eventually I said, 'I can't keep following my parents around,' and I bought a house here. And they moved off to Long Island."

Today Bradley lives in Silver Spring with her husband, Stevens Brown, and their three children. She has been a Washington filmmaker for more than two decades and has been associated with "Smithsonian World" since its inception in 1983. Stepping into Adrian Malone's shoes as executive producer, she is already working on two films for next season, one on gender, the other on drugs, addiction and obsession.

Her more than 50 documentary films have earned her the DuPont-Columbia Award for Outstanding Journalism, the Ohio State Award, the International Film and Television Festival Gold Award, several CINE Golden Eagles and two Emmys for "Smithsonian World."

"You make them in the hope that they will stimulate thought -- that's the purpose," she said. "They can't work perfectly for everyone, but if they provoke some thought, that's a triumph."