Think big.Kurt Andersen and composer William Bolcom explore the grand ambitions that drive artists to work on a vast scale. We’ll visit with Christo and Jeanne-Claude as they prepare “The Gates,”a massive art installation that takes over New York’s Central Park with orange fabric. And we’ll check on the progress of the Sagrada Familia church in Barcelona by architect Antonio Gaudi. Started in 1884, it’s still not even halfway complete.