Apparently, Philip Glass’ life is a lot like the old joke his music inspired: “Knock knock.” “Who’s there?” “Knock knock.” “Who’s there?” “Knock knock.” “Who’s there?” “Philip Glass.” Knock as you might in all the conventional ways, the composer isn’t going to give you easy entry into his soul, let alone a punch line that pegs him just so. He’s an interior figure, and Scott Hicks’ documentary Glass: A Portrait of Philip in Twelve Parts reveals just what an unrevelatory fella Glass can be: “I have so few secrets,” he declares, going about his work and spiritual practices with quiet devotion rather than confession. The film provides unprecedented access to the man’s world—to the creator of, according to Quatsi-trilogy director Godfrey Reggio, “a musical language that is an acoustic door to the unknown”—but follows closely the habit of Glass to craft “an ever-ascending score that never reached to the heavens.” Come along to see God at work, but if you expect deep questions and big answers you’ll find yourself just knock-knock-knockin’ on heaven’s door. The film shows at 3 p.m. Friday, July 4, and 4:30 p.m. Saturday, July 5, at the National Gallery of Art’s East Building Auditorium, 4th St. & Constitution Ave. NW. Free. (202) 737-4215.

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