DESC: Conspiracy theorists have come up with scenario after scenario to explain the events of September 11, 2001, and the Internet has helped spread many of them around and give them credence. In service to the ideal that reason must prevail, the editors of Popular Mechanics magazine (who are not funded by the CIA) test some of those more fanciful and widespread scenarios, 20 in all , with the aid of experts in various scientific fields. Their conclusions help dispel rumor and innuendo, allowing the truth to remain. Illustrated.