“The preparation of the Olympic ceremony is a very complicated journey but also an exhilarating journey, because you get to meet all these volunteers, dance classes, normal people,’’ opening ceremony creative director Marco Balich told The Associated Press during a rare behind-the-scenes tour. The theme of this year’s opening ceremony is “Harmony,’’ an especially potent message as the world order is shaken and populations from Ukraine to Gaza to Iran are exposed to violence. Some moments of the opening ceremony have been announced: U.S. pop star Mariah Carey, crossover tenor Andrea Bocelli, mezzo-soprano Cecilia Bartoli, Italian singer Laura Pausini and concert pianist Lang Lang will perform. They include the unveiling of the Olympic rings, the parade of athletes and, in the final moment, the lighting of the Olympic cauldron. This is his second opening ceremony as a volunteer performer, after participating in the 2004 Summer Olympics in his native Athens as a 20-year-old.