Like many of us, Brit Marling has had the experience of being in a strange city, on another continent, perhaps, and spotting someone who looks exactly like a person - friend, lover, parent, sibling - she knows.

Of course, it isn't that person. Or could it be a mirror image of that person, moving through life on a separate track?

In Another Earth, the accomplished first feature Marling stars in and cowrote with director Mike Cahill, that idea of the mysterious doppelgänger is explored on literally a global scale. Suddenly, above the horizon line, a new planet appears, one that resembles the place we all call home.

"Our film, through intuition, is trying to approach what astrophysics is approaching from a mathematics and physics perspective - this idea of a parallel universe or multiverse," says Marling, who plays an MIT astrophysics major in the film. "And, of course, Another Earth makes this very literal, makes an actual visual representation of it in the sky."

The film, says the actress, is "getting at something that we all primally feel, which is, 'What if I had followed that girl that I fell in love with? What if I had taken that job offer? What if I hadn't left Rome?' And those are the big, weighty decisions, you know. . . . And then there are small, microdecisions you're making every day, and every time you make a choice you're sort of divesting a version of yourself that you could have been.

"There's something really haunting about that."

And there's something really haunting about Another Earth, which Marling and Cahill began with no money at all ("we both had negative account balances at the time"), and which emerged from the Sundance Film Festival in January with awards (including the Alfred P. Sloan feature prize) and a distribution deal (Fox Searchlight). Another Earth opened Friday at the Ritz East and Rave Motion Pictures at the Ritz/Voorhees.

Marling, 27, was an economics major at Georgetown, back in the early aughts, when she met up with Cahill - and another would-be filmmaker, Zal Batmanglij - and started collaborating. For a time, she stayed on her original career track, "out of fear," before realizing she had to find her passion and pursue it.

"There were a lot of people around me who were really good at what they did because they loved it, they loved the markets and they loved financial models and they loved bringing companies together," she says. "It got them high to do an IPO, and you could tell they were going to live a passionate, driven life.

"And I just wasn't inspired by the same things, so I thought I better go and figure out what it is that will inspire me."

It quickly became clear: Movies. Acting in them. Making them.

Marling, Cahill, and Batmanglij settled into a house in the Silver Lake district of Los Angeles. She started writing Another Earth with Cahill, and, at the same time, collaborated with Batmanglij on Sound of My Voice. In that film, which also premiered at Sundance and was acquired by Fox Searchlight, Marling plays a mysterious cult leader. It will be released this winter.

She would literally run up and down the stairs of the house, going from one screenplay project, and one imaginary universe, to the other.

"I was so desperate to work as an actor, I was willing to do anything," Marling says, laughing. "I was like, OK, I'll write four things at once! I just wanted to work so much.

" . . . And it seems like writing was really a way in which you could enter the conversation without having to compromise yourself. I think as an actor, and particularly as a girl in your 20s who hasn't done anything before, it's like, what are the choices available?

"Well, there aren't any choices. The movies you can get cast in, or even go out and read for, are, a lot of times, really just not substantive stories. So, for me, it was like 'OK, if I'm going to keep acting, then maybe trying to learn to write, trying to figure it out, would be a way to keep creating work for myself.' "

With the two low-budget indies under her belt, Marling landed her first big-deal gig. In Arbitrage, which is set for release late this year or early next, she plays the daughter of a Wall Street mogul. That would be Richard Gere. Her mother in the movie: Susan Sarandon.

"It's like a Faustian thriller," Marling reports. "Richard Gere plays a hedge fund manager who has the perfect life, the perfect family, and then all this dark stuff happens and his world unravels. . . . It was really cool. I don't think you normally see a father/daughter story where it's the progeny taking over the empire. He's sort of grooming the daughter to be the heir."

However, Marling says that working with the likes of Gere and Sarandon ("they really took me in - I felt so lucky") on a studio-backed project wasn't, in the end, all that different from working on Another Earth. At least, the differences didn't become a distraction.

"That part of it, the 'studio production' part, well, I feel like you acclimate to it actually relatively quickly," she says. "Because it doesn't really matter whether you're getting changed in Mike's mom's car in front of the location, or whether you're getting changed in a little trailer. At the end of the day, you're still faced with the daunting task of making a bunch of imaginary circumstances seem real to you, so that you believe them so the audience will believe them.

"And somehow, that is so overwhelming a concept that the setting where the process is happening, and what the catering is like, or even if there is catering - all of that sort of fades away, because that task is still so challenging to me.

"I don't think I'll ever get to the bottom of that well, that rabbit hole . . . that mystery of what these really talented performers do when they convince us to believe something that is as ludicrous as like Santa Claus coming down every chimney all over the world in one night."

And what if there's another Santa Claus, coming down every chimney in that other world?

Contact movie critic Steven Rea at 215-854-5629 or Read his blog, "On Movies Online," at