The dazzling cinematic folly that is “Cloud Atlas” springs from the same idealistic impulse that has driven movies like “The Tree of Life,” “2001: A Space Odyssey,” even D.W. Griffith’s 1916 “Intolerance” — the urge to explain the mystery of existence, the whole ontological ball of wax, in one sitting with popcorn. At the risk of sounding cynical, it’s best to approach such projects with caution and, in this case, a sturdy pair of asbestos gloves. Unlike “Tree” or “2001,” “Cloud Atlas” offers more answers than it does questions, and by the end of its nearly three-hour running time — which flies by surprisingly fast, all things considered — it feels like the most feverishly expensive late-night college bull session ever. There are glories here, but they fade in the light of day.

Everyone on this project seems to be doing at least quadruple duty, from writer David Mitchell, whose multi-character, multi-epoch novel serves as the movie’s springboard, to writer-directors Tom Tykwer (“Run Lola Run”) and Andy and Lana Wachowski (“The Matrix”), to the all-star roster playing a complex variety of races and genders in six intertwined story lines covering six distinct time periods and genres. Their combined efforts are herculean, and without question “Cloud Atlas” is something to see on the largest screen possible. (The film’s not in 3-D, but it doesn’t need to be when it’s practically in 5-D.) You get your money’s worth in spectacle — but more change back than you might expect in vapid sermonizing.

The first thing we see is Tom Hanks as the Old Man of the Mountain: grizzled and growling, left eye drooping from the combined effects of age and high-quality studio latex. Speaking in a devolved pidgin English — half “A Clockwork Orange” and half Jar Jar Binks — he is the movie’s spirit guide (oh, yes), and we’ll spend quite a bit of time with the character’s younger self on a post-apocalyptic Earth many centuries in the future. The human race is divided into the elite Prescients, who still hold on to advanced technology, and various tribes fighting it out in the wilderness. Zachry (Hanks) is among the latter, a misfit mystic who’s approached by the white-clad Meronym (Hale Berry), a Prescient on a desperate mission.

Before you can settle into this comfortable rut of sci-fi-fantasy, though, “Cloud Atlas” switches gears. And switches again, and again. We’re on a three-masted ship sailing the Pacific in 1849, the young lawyer Adam Ewing (Jim Sturgess) gravely ill below decks while tended to by an islander stowaway (David Gyasi). We’re in 1973 San Francisco as intrepid journalist Luisa Rey (Berry) digs into the corruption behind a nuclear power plant run by the scurrilous Lloyd Hooks (Hugh Grant). We Ping-Pong to 2012 London, where the fubsy book publisher Tim Cavendish (Jim Broadbent) runs from gangsters and is imprisoned in an old-age home by his traitorous brother (Grant). Oops, back to 1936 England, where the young musician-hustler Robert Frobisher (Ben Whishaw) stalls his upper-class boyfriend (James D’Arcy) and cozies up to the nasty old composer Vyvyan Ayrs (Broadbent).

In the story line that forms the spine and most successful narrative reach of “Cloud Atlas,” Neo-Seoul in the year 2144 is the setting for a “Matrix”-y tale of insurrection, as the obedient “fabricant” clone Sonmi-451 (Doona Bae) rebels against her lowly station as a waitress-slave and joins the rebellion led by dreamy Hae-Joo Chang (Sturgess). These scenes let the Wachowskis play on home turf, with rocketing chases through holographic highways amid a vertigo-inducing post-“Blade Runner” dystopia. It matters (a lot) that Bae is genuinely touching as the factory model awakening to her own individuality.

Where Mitchell’s novel nested these stories inside each other, each character reading the tale preceding, “Cloud Atlas” intercuts continually between them. The effect is like watching transparencies laid atop each other to form a larger, more epic landscape, and it can be both exhilarating and frustrating. Tykwer and the Wachowskis, who shot the film on adjoining soundstages, use editing to find visual and thematic concordances between the narratives, echoes that give the film as a whole beguiling poetic shape and an elusive sense of purpose. But the big picture too often resists coming into focus, and when it finally does, it feels naively drawn.