If death is one of the few certainties in life, what happens after a living being's heart stops beating is as inscrutable a mystery as any in the universe. There's no way of knowing what, if anything, is waiting on the other side, but writer-director David Lowery (2016's "Pete's Dragon") has imagined a provocative possibility as devastating as it is astonishing. Spare in its storytelling but incalculably profound in its suggestion, "A Ghost Story" may be as lonely as cinema gets, a sublime existential hymn of melancholic transcendence.

When any moment can be a person's last, often there isn't time to say proper goodbyes and tend to unfinished business. So it goes with C (Casey Affleck), a Texas-based musician who is killed in a freak car accident while backing out of his driveway. For bereaved wife M (Rooney Mara), she is suddenly left behind to pick up the pieces, living in an old house where constant reminders and memories of their life together call to her. She isn't, however, completely alone. Caught between this earthly plane and another, a ghostly C silently watches her, his spirit trapped under a flowing white bedsheet, two cut-out eyeholes the windows to his soul.

"A Ghost Story" is a cosmically connected masterpiece, deceptively simple in design yet awe-inspiring in its philosophical vastness. Lensed by cinematographer Andrew Droz Palermo (2013's "You're Next") in a boxy 1.33:1 aspect ratio with the rounded corners and slightly faded tones of a photograph from the 1970s, the picture's visual appearance remarkably emulates the beautifully forlorn remnants of years gone by. And go by do they ever, as C lives on in death, observing a world moving forward without him tangibly in it. As the barren trees and gently falling snow of winter make way for a rebirth of the flora and fauna of spring, the passage of time inescapably presses on. For C, days turn into months, and years feel like seconds. Isn't that, in its own way, what happens to all us as we age, our youth edging further out of reach? Meanwhile, he slowly but surely chips away at the paint covering a cracked doorframe, intent on reaching the enigmatic handwritten note his wife left behind.

It is difficult to pinpoint the precise origins of the simplistic, enduring image of a ghost covered top to bottom in a white sheet, but it likely had its birth in 19th-century European and Celtic traditions, a way to physically symbolize a spirit while providing an easy, inexpensive costume for trick-or-treaters. As it worked its way into American culture and popular entertainment—a famed 1920 Saturday Evening Post cover by Norman Rockwell portrayed a young girl in a bedsheet frightening her grandfather—one must assume this iconic representation was also a playful, palatable way for children to wrap their heads around the concept of death. Adopting this innocent spectral vision for a meditative adult drama proves exceedingly powerful, Lowery (also credited as editor) patiently living within his lush, observant frames. Each respective tableau is astounding and, dare it be said, haunting, an achingly intimate bridge between the viewer and C's uncertain yet presumably permanent condition of solitude and insight into the evolution of existence itself.

Casey Affleck (2016's "Manchester by the Sea") and Rooney Mara (2017's "Song to Song"), who previously collaborated with Lowery on 2013's "Ain't Them Bodies Saints," are the right actors for this introspective material, and certainly right as lovers whose life together is ripped apart in an instant. Much of Affleck's work is played effectively behind a shroud, resonating all the more in light of the private stolen moments between he and Mara scattered about. One such scene, as M listens to one of C's songs (Dark Rooms' glorious "I Get Overwhelmed") after his death and is transported back to her memories of the first time her husband played it for her, is shattering and true. That their relationship is imperfect and far from idealized—they are seen having disagreements over whether or not to move, for example (C is taken by the history of their home and wants to stay put, while M longs to be nearer to the city)—only deepens one's connection to them. These are complicated people, caught in crucial key glimpses illustrating their unmistakable love. The rest of their time together is not for us.

"A Ghost Story" is staggering in its ambition, its wisdom, and its unfettered humanity, a hypnotic eulogy to legacy and the ineludible epochal shifts which leave our mortal bodies behind. As the narrative develops in thoroughly unanticipated ways and composer Daniel Hart's ethereal score strikingly complements its voyage, Lowery continues to break convention and the heretofore laws of time and perception. Cyclical and nonlinear, an emblem to the conundrum of this world and the metaphysical next, the film manages the remarkable feat of capturing the visceral beauty of singular moments and the breathtaking enormity of everything at once. Having passed on and yet not, still seeing and yet not being seen, C has the answer to the biggest question of all which eludes the living. In so many ways, though, the afterlife and his purpose within it remain unanswerable. With or without him, the planet keeps spinning. For decades to come, "A Ghost Story" will be written about, fervently discussed, and amply deconstructed, but none of it will quite be able to live up to experiencing it firsthand. This is a miraculous achievement, an emotionally resounding supernova piercing through our hearts and minds—and, with any luck, those of future generations asking the same age-old questions long after we are stardust.