Playing in theaters across the United States is a film called ” Upside Down, ” about an alternate universe where twin worlds sit stacked like bread in a sandwich, separated by opposite gravities. If our world could somehow have a similar twin, last month would have marked the tenth anniversary of Saddam Hussein’s willingness to abandon his nuclear program without a shot being fired. Headline writers would have sung the praises of the sanctions regime imposed by the United Nations, which compelled Saddam to abandon his push for weapons of mass destruction. Abu Ghraib would still be a little-known, nondescript prison on the outskirts of Baghdad. And 4,808 American soldiers would still be alive to celebrate birthdays, weddings and Little League baseball games.