The business buzzword of our era is “synergy.” Disney will have new ways to cross-market its movies, characters and theme parks. Westing-house-which last week announced plans to buy CBS if Ted Turner or someone else doesn’t make a higher bid-can milk its TV stations. But is synergy really nothing more than a fancy cover story for rich investors trying to dress up lucrative deals? Or is it the dawn of an era that seems as if it offers more choices but really doesn’t? “Synergy turns out to be a polite way of saying monopoly. And in the domain of information, monopoly is a polite word for uniformity,” writes Benjamin R. Barber in an important new book, “Jihad vs. McWorld.” Barber’s point is that the vertical integration that built the railroads, steel and other industries in the 19th century has taken on a more portentous cast. What happens when ideas are economically concentrated? Or when Ted Koppel reports to Donald Duck? We don’t really know. Entertainment is not just one of America’s largest exports, its’s also our culture gone global. It’s benign face, mostly, a moon face. But its beams rest uneasily on us all.