If you are an academic historian writing about, say, St. Teresa of Avila, how do you write about her ecstatic levitations? In a new book, They Flew: A History of the Impossible, Carlo Eire acknowledges that certainty about such events is ultimately impossible to attain, yet entertaining the possibility that they really did happen leads to a startling conclusion: that the material reality we perceive is subject to the intervention of a much more powerful being, one not subject to the laws of physics. In other words, God.