Crowds are essential to this moment — and, really, to opera as an art form. Choruses fill the stage; musicians cram into the orchestra pit; thousands of people sit shoulder to shoulder in the theater. The Metropolitan Opera, one of the world’s largest houses, seats an audience of nearly 4,000. And it would probably have been packed for the season’s opening night on Sept. 21, the premiere of a new “Aida” production. – The New York Times