Describing fundamental discoveries in physics, Nobel laureates rarely write with such evident enthusiasm that even the casual reader immediately understands the profound impact of their subject. Yet even with his calm demeanor, the great Indian astrophysicist Subrahmanyan Chandrasekhar could not easily contain his emotion when he wrote,
[I]n my entire scientific life, extending over forty-five years, the most shattering experience has been the realization that an exact solution of Einstein's equations of general relativity, discovered by the New Zealand mathematician, Roy Kerr, provides the absolutely exact representation of untold numbers of massive black holes that populate the universe. This shuddering before the beautiful, this incredible fact that a discovery motivated by a search after the beautiful in mathematics should find its exact replica in Nature, persuades me to say that beauty is that to which the human mind responds at its deepest and most profound.
So who is this Roy Kerr, whom one New Zealand journalist described as the "man of mystery"? In the summer of 2004, something quite remarkable arrived in my mail. It was an invitation to attend a fest in Christchurch, New Zealand, in honor of this man, whose name had by then become commonplace in physics, though with few knowing anything about him. The letter triggered an odd feeling, reminiscent of the time I first heard about Galileo Galilei turning down a professorship at Harvard.
Seizing upon the opportunity of attracting a major figure of learning, Harvard University set about recruiting him in 1638, but fearing the arduous journey in his old age, Galileo declined the offer, choosing instead to remain close to his daughters in Italy. The words "Galileo" and "Harvard" were never meant to go together in my view of history. Galileo was mythical, greater than life, and a giant of antiquity. In contrast, Harvard was young, founded by a band of scrappy settlers in the new world. Did they really overlap?
To the astrophysicists of my generation, the name Kerr is similarly iconic, perhaps even reaching mythical status, like that of Galileo. Kerr is not so much a person, we thought, but rather the designation of the most famous solution to Einstein's equations of general relativity, describing the spacetime surrounding black holes and other strong sources of gravity.
Yet the man Roy Kerr has been a complete mystery to the generation of astronomers and physicists that followed the golden age of relativity, from 1960 to the mid 1970s. His presence in the northern hemisphere diminished after his return to Christchurch, but his legend grew as the passage of time magnified the importance of his work. Like the story of the new world reaching out across history and the Atlantic ocean to touch Galileo and the antiquity he represented, the letter from New Zealand that summer connected me to one of the greatest mathematical physicists of the 20th century.
It brought into sharp focus the sad truth that although we know much about Einstein, considered one of the greatest physicists of all time, very little has been written about the story of how his theory of relativity has been made relevant to the physical world. Einstein himself was only partially successful in solving his own equations, of "breaking his own code" ? a measure of the difficulty of this task.
That is why getting to know Roy Kerr was an opportunity I could not pass up, and learning about how Einstein's equations were finally solved from the man most responsible for this remarkable feat has turned into a pleasure I could not have anticipated as a student. Roy and Margaret Kerr were exceptionally warm hosts during my many meetings with them, and the kind of accessibility they provided is what turns a simple story into an eye-witness account of a historically important struggle. Astrophysicists of my generation now have an opportunity to reach out across the decades and the Pacific Ocean to connect with Roy Kerr the man, and to share with him the dramatic progress being made in the study of black holes.
Yet with all its scientific drama, Cracking the Einstein Code is nonetheless a story always attuned to the human element. Ultimately, it is an excellent example of how breakthrough science gets done.