Why does the famous tower lean? Why is the lean accelerating? And can anything be done to stop it? QED examines one theory - that the tilt is caused by the sun; as it rises it warms the marble which expands causing the tower to move in the opposite direction to the sun. But whatever the reason, a solution doesn't seem to be any closer. Every year hundreds of remedies are put forward but so far bureaucratic delays have prevented any of them being put into practice. Time is running out. The rate of tilt has doubled in the last 50 years and just this winter it moved more in four months than in the whole of the previous year. Two years ago it was closed to the public. Now some predict its collapse may be imminent.