In April 1965, the Beatles were shooting a scene for their second feature film, Help!, in an Indian restaurant set built on a soundstage at Twickenham Studios. The set held instruments played by a real Indian ensemble — among them a sitar, a tanpura drone, and a tabla, the standard concert layout for Hindustani classical music, here pressed into service for the comic Indian-restaurant scene. George Harrison, twenty-two years old and bored between takes, picked the sitar up and tried to play it.

This is the official origin story for the most consequential cross-cultural collision in 1960s popular music. It is, of course, a story about an instrument that happened to be lying on set. Harrison knew nothing about it: nothing about ragas, the modal frameworks Indian classical music has spent many centuries developing, and nothing about the alap, the slow introductory section in which a performer establishes the mood of a raga before the rhythm enters. He held a sitar the way an actor holds a sword in a costume drama. Something nevertheless connected — and six months later it would end up on a Beatles record.

Six months later, in October 1965, the Beatles were recording Rubber Soul at Abbey Road. Harrison brought a sitar to the studio for a folk-pop song John Lennon had written about an affair, Norwegian Wood (This Bird Has Flown). The sitar part on the released record is brief. It doubles the vocal melody on the verses and adds a small instrumental flourish at the end. Harrison had been playing the instrument for perhaps six weeks. By Indian classical standards he was a rank amateur. By Anglo-American pop standards he had done something nobody had done before.

Norwegian Wood is widely regarded as the first major Western pop record to feature a sitar. Within eighteen months, sitars appear on records by the Rolling Stones — whose Paint It Black became the best-known of them — along with the Byrds, Donovan, and several dozen other British and American bands trying to sound modern. None of these recordings has any meaningful relationship to Indian classical practice. They use the sitar as a texture and, increasingly, as shorthand for altered, psychedelic consciousness. The connection is, in the strict sense, invented, and that invented vocabulary flowed straight into psychedelia's outer limits, into songs like Lucy in the Sky with Diamonds.

In June 1966 Ravi Shankar, by then the most internationally recognized Hindustani classical musician in the world, agreed to meet Harrison in London at the home of mutual acquaintances. He was a genuine inheritor of the tradition Western pop was only imitating. Shankar was forty-six; he had spent his boyhood touring the world as a performer in his elder brother Uday Shankar's dance troupe, had given up dancing around eighteen, and had apprenticed himself to the master Allauddin Khan, training for seven years in the gurukul tradition — living in the teacher's household to learn. Shankar and his brother-in-law Ali Akbar Khan were among the figures who introduced Western audiences to ragas tied to a particular time of day; Marwa, for instance, is an evening raga played at sunset. Shankar found Harrison earnest and humble, and eventually agreed to take him on as a student.

What followed is one of the stranger teacher-student relationships in twentieth-century music. Harrison spent six weeks in India in the autumn of 1966 — first in Mumbai, then, once fans had tracked down his whereabouts, on a houseboat on Dal Lake in Srinagar, Kashmir — studying sitar privately with Shankar and observing Indian classical practice as it is actually performed. He never became a serious sitar player — he himself said so freely — but he absorbed something deeper. The Beatles song Within You Without You, on Sgt. Pepper's Lonely Hearts Club Band, is the result. It uses Indian musicians from the Asian Music Circle in London, and is built on a raga-like framework in which the melodic line itself leads, rather than a chord progression. And it carries an actual tabla pattern in a long rhythmic cycle of a kind rare in Western songs. It is also, by any technical Hindustani measure, a beginner's attempt.

This is the sound Harrison was reaching for — a real, time-of-day evening raga. The next track is one.

By 1968 the sitar fad in British and American rock was already exhausted. Bands stopped putting sitars on records. The drone became unfashionable. Psychedelic rock as a commercial category began its decline. From the inside, the Indian classical detour looked like a brief misadventure — a few years in which white pop musicians had played with instruments they did not understand and then put them down.

From the outside, several things had permanently changed. Indian classical music had a Western concert circuit that did not exist before 1966 — Shankar's tours sold out the Royal Albert Hall and Carnegie Hall for the next forty years. Ali Akbar Khan founded a college in California in 1967 that is still training Hindustani musicians today. A generation of Western musicians had been exposed, however imperfectly, to a tradition that values a melodic line over a chord progression, and in which a single piece can take twenty minutes to begin. The drone and modal vocabulary turned up later in the drone-based minimalism of Terry Riley, who built whole pieces on a sustained tone, and in the late modal work of John Coltrane — and, more loosely, across everything called raga rock for the next decade. Music that trusts a sustained tone and a mode over harmony is hard to imagine without 1966.

The asymmetry, as always, is unflattering. Harrison became wealthy, famous, and posthumously revered. Shankar, immensely respected in the West and in India, never made comparable money. He spent the rest of his life patiently explaining to interviewers that the sitar is not, in fact, a psychedelic instrument, and that Indian classical music is not background music. He died in 2012, having outlasted his most famous student by eleven years, and having watched the music he spent his life on become a small but permanent part of the global pop vocabulary, sometimes credited, mostly not.