The control room of the Leaning Tower of Pisa is not very impressive, as control rooms go— just a handful of technicians and computers in a construction— site trailer. But if the tower ever decides to stop leaning and start falling, those technicians will be the first to know. Every five minutes the computers receive data from 120 sensors inside the tower that monitor its inclinations. The tower has its harmless daily moods. In the late morning it leans away from the sun, like some giant antimatter sunflower, tilting imperceptibly northwest as its southeastern side warms up and expands. At night the tower settles back to its current southward tilt of around 5.3 degrees.
It is that persistent angle that is alarming. It is bigger than it sounds or than it looks on postcards. When you walk the streets of Pisa, and the tower pops into view for the first ...
