Isaac Newton thought that planetary orbits in our solar system were kept stable by God’s direct intervention; they were proof to him that God existed. The French mathematician and sceptic Pierre-Simon Laplace 100 years later described his new orbital theory to Napoleon and supposedly quipped of God’s role, “I have no need for that hypothesis.” In fact, it is bad theology to reduce God to a gap-filling hypothesis. Only recently, however, have we learned that planetary motions may sometimes not be so stable after all.One of the pioneers of studying chaos theory in celestial dynamics is Professor Jack Wisdom, of the Massachusetts Institute of Technology, who is visiting the Vatican Observatory this month. He’s working now on modelling the complex interaction bet