New Yorker music critic Alex Ross’s new book is getting plenty of attention for its accessible style and innovative ideas about the state of classical music. He also delves into what happened to concert music in the 20th century: “Ultimately, all music acts on its audience through the same physics of sound, shaking the air and arousing curious sensations. In the 20th century, however, musical life disintegrated into a teeming mass of cultures and subcultures, each with its own canon and jargon.”