The history of opera as we knew it changed when Einstein on the Beach premiered in France in 1976, and made it to Hamburg, Paris, Belgrade, Venice, Brussels, Rotterdam, and New York City by the end of the year. (Fat chance of that happening today with a new work.) Here was an intermissionless, five-hour, music-theater piece comprising nine connected 20-minute scenes and five “Knee Plays” (interludes) at which the audience was free to come and go. The current revival tour, which began this year in France, heads to Italy, London, Toronto, and Brooklyn before reaching Berkeley. Catch this radical work while you can — you may not get another chance.