About halfway through Alfonso Cuaron’s astonishing “Gravity,” Sandra Bullock, playing a lost astronaut stranded 375 miles above Earth, seeks refuge in an abandoned spacecraft and curls into a floating fetal position, savoring a brief respite from her harrowing journey. Of the many sights to behold in this white-knuckle space odyssey, a work of great narrative simplicity and visual complexity, it’s this image that speaks most eloquently to Cuaron’s gifts as a filmmaker: He’s the rare virtuoso capable of steering us through vividly imagined worlds and into deep recesses of human feeling. Suspending viewers alongside Bullock for a taut, transporting 91 minutes (with George Clooney in a sly supporting turn), the director’s long-overdue follow-up to “Children of Men” is at once a nervy experiment in blockbuster minimalism and a film of robust movie-movie thrills, restoring a sense of wonder, terror and possibility to the bigscreen that should inspire awe among critics and audiences worldwide.

Opening Oct. 4 Stateside following its Venice and Toronto premieres, the Warner Bros. release offers in abundance the sort of eye-popping, screen-filling spectacle that demands to be viewed in a theater. Not unlike earlier triumphs of 3D and vfx innovation such as “Avatar” and “Life of Pi,” though conceived along less fantastical, more grimly realistic lines, “Gravity” is at once classical and cutting-edge in its showmanship, placing the most advanced digital filmmaking techniques in service of material that could hardly feel more accessible.

PHOTOS: George Clooney, Sandra Bullock Premiere ‘Gravity’

As scripted by Cuaron and his son Jonas, this tale of one woman’s expedition into the unknown is a nerve-shredding suspenser, a daring study in extreme isolation, and one of the most sophisticated and enveloping visions of space travel yet realized onscreen. It falls among that increasingly rare breed of popular entertainments capable of prompting genuine “How did they do that?” reactions from even the most jaded viewers, even as its central premise is so simple and immediately gripping that one might just as readily ask, “Why didn’t anyone do it sooner?”

The answer to both questions is that Cuaron, in another remarkable collaboration with longtime cinematographer Emmanuel Lubezki and visual effects supervisor Tim Webber (“Children of Men”), has pushed the relevant technologies to their limits in order to tell this story with the sort of impeccable verisimilitude and spellbinding visual clarity it requires. The long, intricate tracking shots the three devised for the earlier film were a mere warm-up act for what they unleash here, as is clear from the stunningly choreographed opening sequence — an unbroken, roughly 13-minute long take that plunges us immediately into the deafening silence of space. Specifically, we are in the atmospheric layer known as the thermosphere, the Earth’s massive form looming large in the widescreen frame as an orbiting shuttle gradually cruises into focus.

Three members of the crew have left the shuttle to help repair the Hubble telescope, though dramatically, the picture is concerned with only two of them: Matt Kowalsky (Clooney), a seasoned astronaut leading his final mission, and Dr. Ryan Stone (Bullock), a medical engineer on her first. The mood is relaxed initially, even humorous; radio music plays in the background as the astronauts exchange banter with mission control. Kowalsky, drifting lazily about in his harness, brags that he’s about to break the official record for longest spacewalk. The far less experienced Stone nervously tries to stay focused on her task, not the easiest thing to do for someone still adjusting to the woozy effects of zero gravity.

“Houston, I have a bad feeling about this mission,” Kowalsky quips early on. Yet all joking ceases when Houston (voiced by Ed Harris, in a nice nod to “Apollo 13”) suddenly reports that a cloud of debris, triggered by the self-destruction of a nearby Russian satellite, is headed their way. The camera, having gracefully bobbed and weaved around the astronauts without a single cut so far, continues to observe with unblinking concentration as the ship is pelted with shrapnel, killing the third astronaut, causing widespread damage and severing all communications with Houston. Amid the chaos, Stone comes untethered and finds herself spinning, alone and helpless, in the vast emptiness of space, an experience the audience will soon share to a deeply unnerving degree.

In one continuous shot, the film has not only introduced its central crisis — will Stone survive? — but also completely immersed us in the beauty and majesty of a dark, pitiless universe. While “Gravity” is hardly the first film to send characters into orbit, few have so powerfully and subjectively evoked the sensation of floating right there with them. As it glides nimbly around the action, the camera induces a deeply pleasurable feeling of weightlessness (the film might just as well have been titled “Dancing With the Stars”) that can suddenly turn from exhilarating to terrifying, leaving us gasping for oxygen alongside the characters.

The filmmakers’ technical command here is so precise that they’re able to shift perspectives at will; more than once the camera zooms in tighter and tighter on Stone until it seems to enter her helmet, sharing her frightening view of the great, black expanse before her. Exactly what she sees and endures over the course of her journey would be unfair to reveal. Suffice to say the script modulates the tension expertly, deftly preying on the claustrophobic and the agoraphobic alike, and maintaining an unflagging sense of peril as it carefully throws Stone one lifeline after another.

The most crucial of these lifelines turns out to be Kowalsky, who initially comes off as the film’s most obtrusive element, a glib smart-ass who’s there to help Stone and the audience find their bearings, and to provide a measure of comic relief. Yet while Clooney’s flippant leading-man charm may seem incongruous in this context at first, his tough-and-tender rapport with Bullock pulses with understated feeling, never more so than when the two astronauts are tethered together, trying to make their way to safety. Clooney gets one particularly audacious scene that perhaps only a star of his stature could have managed, pulling the viewer through various states of shock, disbelief and finally bittersweet understanding; it’s a haunting moment that firmly ties “Gravity,” for all its uncompromising realism, to the soul of classic Hollywood.

There are glimmers of artifice, too, in the script’s conception of Stone, who turns out to have a tragedy in her past, an unhealed wound that feels rather needlessly engineered to provide the viewer with a psychological entry point, as well as a deeper stake in her survival. It’s the one on-the-nose element in a screenplay that, given its rigorous intelligence in all other departments, might have done well to trust the audience to stay invested in Stone’s journey without the benefit of an emotional hook. (Providing a fascinating contrast is J.C. Chandor’s upcoming stranded-at-sea thriller “All Is Lost,” in some ways a purer, more radical storytelling experiment in which words, motivations and explanations have been almost completely expunged.)

Nonetheless, Bullock inhabits the role with grave dignity and hints at Stone’s past scars with sensitivity and tact, and she holds the screen effortlessly once “Gravity” becomes a veritable one-woman show. In a performance that imposes extraordinary physical demands, the actress remains fully present emotionally, projecting a very appealing combo of vulnerability, intelligence and determination that not only wins us over immediately, but sustains attention all the way through the cathartic closing reels.

The outstanding post-production 3D conversion enhances our sense of immersion in this foreign environment at every turn. Images of outer space give new meaning to the term “deep focus,” while the scenes set in enclosed environs provide a pleasing visual balance and contrast, with floating objects supplying a natural depth of field. As visual an experience as the film is, it would be far less effective without the exceptional sound work by production mixer Chris Munro and sound designer Glenn Freemantle, which makes especially potent use of silence in accordance with the laws of outer-space physics. Helping to vary the soundscape is Steven Price’s richly ominous score, playing like an extension of the jolts and tremors that accompany the action onscreen.

All in all, it would be impossible to overestimate the difficulty of what Cuaron and his top-of-the-line crew have pulled off, or to guess at the staggering number of decisions that were made regarding specifics of camera placement and movement; the motion-control robots that were used on the actors to plausibly simulate zero-gravity conditions; the marvelous scope and detail of Andy Nicholson’s production design; and the meticulous integration of visual effects, all-digital backgrounds, traditional lighting schemes and other live-action lensing techniques. But perhaps the boldest risk of all was the decision to combine these elements in a manner that would hold up under the prolonged scrutiny of the camera, in single-shot sequences of such breathtaking duration and coherence. Somewhere, one imagines, the spirits of Stanley Kubrick and Max Ophuls are looking down in admiration.