There’s an added sense of energy when an orchestra knows they are participating in something that is at the front edge of history,” says John Kennedy, resident conductor of the Spoleto Festival USA Orchestra. “When they’re among the first to perform a piece of music that might become legendary for generations to come.” Expect the Sottile Theatre to be vibrating with this energy on June 3, as Kennedy leads the orchestra in presenting a special program called “Orchestra Uncaged.” To celebrate the centenary of American composer John Cage’s birth, the concert features the premieres of Cage’s last innovative works yet to be heard in the U.S.: the 1991 orchestral trilogy Twenty-Six, Twenty-Eight, and Twenty-Nine. But they aren’t stopping there. The orchestra also presents two pieces by Jonny Greenwood, known for pushing the boundaries of rock—through the band, Radiohead, for which he’s lead guitarist, keyboardist, and electronic music organizer—as well as through post-classical composition. Hear Doghouse, an elegantly dark meditation, and 48 Responses to Polymorphia, a spirited wave of bubbling sonic intensity making its American premiere at the concert. Fans of Cage, an artist who once composed a three-movement work offering four minutes and 33 seconds of silence, and Greenwood, known for his mad-slashing guitar technique, will revel in the challenging works while others may wonder what they’ve gotten themselves into. And that may just be the point of it all.