John D. Norton
Department of History and Philosophy of Science
University of Pittsburgh
Einstein's early discoveries were made by thinking physically and reflecting on special cases of clear physical meaning, as in his famous use of thought experiments. He contrasted this method with one based on formal or mathematical naturalness. In a remarkable notebook of private calculations, written during his discovery of general relativity, we can observe Einstein as he tested both approaches and failed to get them to agree. In his later years Einstein turned to formal-mathematical methods exclusively, proclaiming that "our experience hitherto justifies us in believing that nature is the realization of the simplest conceivable mathematical ideas."