Cracking the Einstein Code: Relativity and the Birth of Black Hole Physics , Fulvio Melia , U. Chicago Press , Chicago , 2009. $25.00 (137 pp.). ISBN 978-0-226-51951-7
Black holes have resonated strongly with the general public since the term was coined in the 1960s. In part, that fascination is because the defining characteristic of a black hole—it is so compact that nothing, not even light, can escape from its surface—is a powerful catalyst for the imagination (particularly of science fiction authors and Hollywood screenwriters). Not surprisingly, some think of black holes as super vacuum cleaners in the sky that suck in everything around them. That common misconception is at the root of the widely publicized but completely unfounded concern that the Large Hadron Collider would create miniature black holes that would destroy Earth in a fraction of a second.
Interest in black holes has proved a great opportunity for physicists to educate the general public about the nature of gravity and, in particular, Einstein’s theory of relativity. A recent addition to a long line of books that attempts to do just that is Fulvio Melia’s Cracking the Einstein Code: Relativity and the Birth of Black Hole Physics. What makes Melia’s book unique is that it focuses on the events and characters in the mid- to late 1960s when many of the fundamental properties of astrophysical black holes were elucidated. The hero of Melia’s tale is New Zealander Roy Kerr, then a young postdoc at the University of Texas at Austin’s new center for relativity. There, he single-handedly solved Einstein’s field equations for the general case of a spinning collapsed object, thus cracking a problem that had stumped relativists for more than four decades. His solution, now known as the Kerr metric, is the basis for all modern general relativistic calculations of spacetime around spinning black holes. Despite the magnitude of that achievement, Kerr’s story has been largely untold. All too often, non-specialist books on relativity refer to Kerr cryptically as the “New Zealand mathematician” and wrap up his contribution in a paragraph or less. In this book, Melia rightly brings Kerr back into the spotlight to ensure that his contribution to relativistic physics is celebrated.
The book reads well. It is the sixth book overall and third for a general audience written by Melia, a high-energy astrophysicist who specializes in astrophysical black holes. Melia adds a human element to a technical subject by including archival photographs of the participants from Kerr’s era. He also spent months interviewing Kerr, now 75 years old and living in New Zealand. As a result, the reader gets a sense of immediacy in the descriptions of Kerr’s struggle with the equations and the exhilaration of his success.
But the focus on Kerr and his achievement is also a weakness of the book. Because Kerr’s breakthrough was highly mathematical, Melia could describe the technical details in only the most general terms; his complete biography of Kerr, including the derivation of the Kerr metric, takes up less than half of his very thin book. To make the story more self-contained, Melia adds at the beginning of the book a few short chapters describing the history of relativity and, at the end, a brief summary of recent astrophysical black hole observations. Although the introductory chapters assume no previous knowledge of relativity, they also contain no diagrams to aid in the understanding of the theory’s difficult concepts. The author is in such a hurry to get to Kerr’s story that most general readers will be left floundering over such topics as time dilation and the equivalence principle. Therefore, it is difficult for me to recommend Melia’s popularization to those who have not yet encountered relativity in other books. It would be more appropriate for readers who have already encountered a more complete book on black holes and relativity, such as Kip Thorne’s Black Holes and Time Warps: Einstein’s Outrageous Legacy (W. W. Norton, 1995), but want more details on one of the unsung heroes of the field.
Perhaps the best audience for Cracking the Einstein Code would be current graduate students and postdocs. They would meet a man who, through the combination of luck, skill, and hard work, had that one insight to make an everlasting contribution to physics. Roy Kerr’s story should be an inspiration to young scientists to keep their eyes and mind open for interesting problems and to follow their instincts. After all, who knows when the next “young mathematician from New Zealand” may shape the future of physics?
