The Black Hole War

There is an unfortunate idea that many people have about science, that it is cold and dry and that there is no room for disagreement or debate. Of course this is far from reality. While the hope of most scientists is to eventually settle on a consensus that will answer any given question, there is often quite a bit of disagreement and fighting to get to that point. From questions about the processes by which evolution works to the question of whether Pluto is a planet, the history of science — and mathematics — is littered with examples of disagreements.

One recent example of such a debate in the theoretical physics community can be simply stated as "Can information escape from black holes?" According to general relativity, there is no way that anything can escape from a black hole including any amount of information. But according to quantum mechanics, that cannot be the case, as everything must be reversible and therefore it must be possible for information that falls into a black hole to be able to come back out. Trying to reconcile these opposing views perplexed physicists for more than two decades, and has pitted some of the luminaries of the field against one another, with Stephen Hawking leading the charge of the relativists and Leonard Susskind and Gerard 't Hooft on the side of quantum mechanics. In 2004, after many developments in such areas of physics as string theory and quantum gravity had weighed in on the matter, Hawking conceded that he had been wrong. Proving the adage that winners get to right the history, Susskind has recently written an account of the struggle entitled The Black Hole War: My Battle with Stephen Hawking to Make the World Safe for Quantum Mechanics.

Susskind's book is a wonderful contribution to the popular physics literature, as the author does a very good job of explaining what seems like very difficult physics while assuming very little background. (I suppose I should note at this point that, while I am certainly more mathematically sophisticated than the lay reader, I have not taken a physics course since I sat through lectures on mechanics during my freshman year of college nearly two decades ago).

I will not recap all of the details of the physics here — the 500 pages of Susskind's book barely does justice to the material, so I am not even going to attempt to do so in 500 words — but he does begin at a very elementary level, describing how gravity affects the tides and what is meant by the speed of light. He even describes what scientific notation and 10¹⁸ means. The material gets more complicated rather quickly, as even describing what the underlying question is involves descriptions of noneuclidean geometry, entropy, and quantum physics, while describing the eventual resolution involves issues such as the holographic principle and even a bit of string theory.

While the physics gets a bit hairy towards the end, Susskind always keeps his exposition light, and constantly reminds the reader that understanding this material is hard and that the history of physics has shown again and again that advances typically come along with a need to 'rewire' our brains to understand the new ideas. Unlike some authors of popular books, Susskind isn't afraid to use equations and variables when the situation calls for it, but he does so sparingly. Many of his descriptions of technical issues in physics rely on metaphors and simplifications (and even a short work of fiction!) which would probably drive the specialists in the field crazy, but which gave this reader a sense of what was going on, even if I know that I don't actually understand the details.

Even more impressive than his description of complicated ideas in simple language, Susskind has a great story to tell and he tells it very well. The chapters covering the technical details of the physics are interspersed with a fascinating narrative of how the debate evolved over time. We see its beginnings at a conference in San Francisco in 1983 and we hear about Hawking's "concession speech" in Dublin in 2004. Along the way, Susskind takes us to conferences in locations such as Cambridge and Santa Barbara and introduces us to characters such as Juan Maldacena and John Wheeler — Richard Feynman even makes a cameo appearance. Susskind clearly has a great deal of fondness and respect for the other physicists on both sides of the so-called war, and throughout his story he shows how scientists can disagree strongly about their theories while still working together to come to a common understanding and without resorting to vicious attacks — perhaps there is a lesson in here for other disputers, such as politicians or (even worse) string theorists.

If it isn't clear from the above, I truly enjoyed this book. I learned some physics and I feel like I got a real sense of what the world of theoretical physics, or at least the world of the bigwigs in the field such as Hawking and Susskind, is like and what it is that physicists do. I think that authors of popular math books could learn a number of lessons from Susskind's book, in terms of the clarity of its exposition, its willingness to embrace metaphors as an explanatory tool, and (most importantly) in the balance between technical exposition, engaging characters and story, and a willingness to give readers a peek "behind the curtain" and explain how the profession wades through both correct and incorrect theories to discover the underlying truth. I hope that we see similar books about debates in mathematics show up in bookstores in the near future.

Darren Glass is an assistant professor of mathematics at Gettysburg College whose mathematical interests include number theory, cryptography, and Galois theory. He can be reached at dglass@gettysburg.edu