Near-death experiences, or NDEs, are controversial. Thousands of people have had them, but many in the scientific community have argued that they are impossible. Dr. Eben Alexander was one of those people. A highly trained neurosurgeon who had operated on thousands of brains in the course of his career, Alexander knew that what people of faith call the "soul" is really a product of brain chemistry. NDEs, he would have been the first to explain, might feel real to the people having them, but in truth they are simply fantasies produced by brains under extreme stress.