When I look at old black-and-white pictures of my ancestors, I search their faces, looking for clues. What kind of people were they? What had been their dreams and their ambitions? Had they ever read the philosophy of Plato or Descartes, the poetry of Milton, or learned about Newton's laws of physics? What lay hidden behind their eyes? They had left no record of their thoughts or their beliefs. They had left a void, an unsolvable mystery. I wanted...