"Another Earth" opens with a conceit both horrifying and wondrous. What if it was discovered that there was another planet out there in the solar system, heretofore unseen, that was identical to Earth, right down to the same land masses, oceans, and people? The synchronicity between worlds may or may not have been thrown off at the moment it was publicly announced in the media, but, for all intents and purposes, there seems to be an exact double of yourself, your home, and everything else you've ever known. What would this mean in regards to your very existence? Is it a sign that what you do is meaningless, or not unique, since the same thing is being done somewhere else out there in the cosmos? Could it further prove that there is a greater power at work puppet mastering this big, enigmatic thing called life, what we know not even scratching the surface of the mysteries of the universe? Heavy philosophical questions permeate throughout "Another Earth," but they are not the focal point so much as supplement to a human study in grief and the possibilities of forgiveness. Fiercely independent but wildly ambitious in both resources and sensibilities, writer-director Mike Cahill and his co-writer/lead actress Brit Marling spill their hearts onto the screen, demanding notice even when they occasionally confuse arty affectedness for lyrical rumination. It is not surprising they made waves at the 2011 Sundance Film Festival and came away with the prestigious Alfred P. Sloane Award and a distribution deal from none other than Fox Searchlight. Now it's up to the studio to nurture the picture with delicate hands and find it the audience it deserves.

Moments after hearing on the radio that a second Earth has been discovered in the night sky, 17-year-old MIT student Rhoda Williams (Brit Marling) causes a fatal car accident that puts a man, music composer John Burroughs (William Mapother), into a coma and tragically takes the lives of his pregnant wife and young son. Four years later, a forever changed, helplessly sullen Rhoda reaches the end of her jail sentence, moving back in with parents Kim (Jordan Baker) and Robert (Flint Beverage) and college-bound brother Jeff (Robin Taylor). Rhoda once had all the promise in the world, but those opportunities have since been squandered on a terrible mistake that she can never take back. She gets a job as a high school janitor—she requests to her employment officer that she be placed somewhere where she doesn't have to interact with a lot of people—and, by chance, happens upon John visiting the site of the accident on its fourth anniversary. Posing as a maid for a cleaning service, Rhoda secretly infiltrates John's devastated life and begins a friendship with him as she tidies up his home. She wants to be honest with him, to apologize—he doesn't know who she really is—but as she starts to care about him on a more personal level, it never seems to be the right time. Then the unimaginable happens: Rhoda learns that her impassioned contest entry has won her a seat aboard the first voyage to Earth 2. Whether redemption or more despair waits for her on the other side, her mind has been made up. She wants to go.

There is potentially still a film to be made that more directly explores what would happen if a duplicate planet was out there in space and we were given the chance to meet a double of ourselves. Alas, if given that choice, it would likely be shot on a $100-million-plus budget and forego existential ideas for an onslaught of special effects and overblown action sequences. Created for a tiny fraction of that cost but indispensable in its thematic curiosity, "Another Earth" entices and challenges in ways that supersede its more traditional central storyline. Supporting characters, like Rhoda's parents and brother, aren't given the screen time or complexity necessary to fully develop as people whose relationship with Rhoda is anything more than roughly sketched. There also are a few too many shots of Rhoda wandering around in slow-motion, Earth 2 placed in the sky above her with contrived picturesque foreboding. The curious bond that forms between Rhoda and John is predictable, both in its details and how it ultimately plays out, yet there is also an authenticity to the way they begin to lean on each other and come out of their shells even as they both fool themselves into believing something that's not true.

Rhoda's and John's respective attachment is emphatic and would be potentially doomed in any other movie, but this is where the speculative, quasi-sci-fi subject of a replicated Earth changes said dynamic. When John comments on how presumptuous it is that we call the other planet Earth 2 when there is no reason not to believe our planet might be the duplicate one, he proves a valid point about how we, as humans, like to think of ourselves as more important than we are. In actuality, we are but a speck of dust in the grander scheme of everything there once was and will still be of the universe after we're gone. Ideas such as this, thought-provokingly intermingling with the reinvigorated notion of all that is possible and left to discover being infinite in nature, give Rhoda and John a slim but certain alleviation of their pain they otherwise would not experience. When there is so much left to learn about and know, who is to say that redemption isn't possible or that second chances can't be given?

In what should be a breakthrough performance, Brit Marling is eye-catching while remaining low-key and appropriately in herself. As an actress, she has what it takes to be beautiful, no doubt, but here, as Rhoda, Marling buries herself behind hoods and layers of bulky clothes to portray a young woman imploding with the constant psychological reminder that she has been responsible for taking others' lives. Marling has an almost otherworldly ability to express so much with only her body language, yet she never is anything other than intensely human in the dark emotional states she must embody. Every moment on the screen, the viewer can practically smell the guilt and sadness emanating from her pores. Rhoda is facing dire circumstances, but Marling avoids turning her strictly into a mope. There is a ray of light there, too, in the way she interacts with John and finds someone with even greater wounds than she. In the film's most astonishing scene, Marling finally finds the courage to make a searing confession she cannot take back and must face up to the consequences of. In her possession, however, is the ability to try and make things better for John. It's a long shot, but the only one she's got. As John, William Mapother (2006's "World Trade Center") falls not into the shadows of his co-star, but nevertheless plays second fiddle to her, essaying with quiet dignity and an underlying bitterness a man who has lost just about everything he ever cared about and needs to find something new to believe in.

When the first residents of our planet travel to Earth 2, what will they find? Will it put the dual globes into an uneven tailspin, or did that already happen the second one of the planet's populations learned about the other? If the two worlds no longer are in perfect sync, have we, as humans, broken free from our doubles to become, once and for all, a singular, one-of-a-kind being? The "what-if" questions could go on and on, and "Another Earth" is thoughtful and complicated enough to ably house these beside the personal drama playing out between Rhoda and John. When a scientist working for SETI, Dr. Joan Tallis (Diane Ciesla), makes first televised contact with herself from across the stars, it is a gut-wrenching moment with implications going far beyond even the shocked, dumbfounded faces of Rhoda's family as they watch it on their television. "What does that mean?" Rhoda's mom exasperatedly asks. What, indeed. The final scenes of "Another Earth," paving separate paths for Rhoda's and John's futures without needing to patly tie things up, head deliberately and assuredly to an unexpected conclusion that speaks volumes without a single word needing to be spoken. The last shot, answering many ongoing questions as it poses a few new ones, is especially staggering in its thematically and emotionally loaded inferences. The film, finally, locates a certain solace, a propensity for hope and empathy. In finding someone else, it finds itself.