CERN insists its revolutionary experiment is perfectly safe, but a few scientists have raised doubts. They say the physicists are playing with dangerous forces that could have unintended consequences. Black holes, for example, are an intentional product of the collision the physicists are trying to bring about -- but the doubters say they could prove difficult to control. CERN says its project has been submitted to frequent safety reviews by independent scientists who say there is no reason for concern.