The Black Hole War: My Battle with Stephen Hawking to Make the World Safe for Quantum Mechanics by Leonard Susskind, Little Brown and Company. Hardback ISBN 9780316016407, $27.99.
Despite appearances, you will not encounter Stephen Hawking in an armoured wheel chair, Lenny Susskind wearing a short spade and a net, or Gerard ’t Hooft with a spear and a shield; all three in the gladiator’s arena. This book contains a lot of drama, but most of it happens in the heads of these physicists and in their discussions. All three, the main characters of the book, are good friends and respect each other profoundly.
In the 1970s Hawking studied quantum mechanics near black holes and made the remarkable discovery that they are not black after all. They radiate energy with an apparently thermal spectrum, the temperature of which is inversely proportional to the mass of the hole. For the black holes that occur in nature at the centre of galaxies, or as the final products of the deaths of supermassive stars, this radiation is completely negligible. So, what was the point? Elaborating on his computations, Hawking concluded that in this process, if some information is gobbled up by the hole once it passes its event horizon, it will be forever lost. There is no way to retrieve it.
This was the starting shot in the war, and what a shot it was. As Susskind explains in great detail, it rocked the boat of physics so badly that it almost caused it to sink.
The claim was made in the late 1970s but ’t Hooft and Susskind learnt about it in a special meeting in 1981, in the attic of Werner Erhard (of "est" fame). Many physicists at the time dismissed the problem, but our two heroes recognized the mortal blow that it represented to the heart of quantum mechanics. A basic feature in the quantum description of nature is the conservation of information. In more technical terms, we believe that no matter how complex a process, it will never violate the unitarity of quantum evolution in time. The formation of a black hole out of ordinary stuff – and its subsequent evaporation – should not represent an exception despite its complexity. Hawking put his finger on a fundamental issue that hindered the possible unification of general relativity and quantum mechanics, which was a major preoccupation of Albert Einstein and many after him.
Hawking had clearly won, by surprise, the first battle. This we learn at the beginning of the book. The rest describes Susskind’s strategy of attrition until he could claim victory a quarter of a century later.
In sharing the author’s path to victory you will learn a lot of deep physics: the basis of quantum mechanics; the fundamental characteristics of black holes; the need to use string theory and some of its tools developed in the 1990s – arcane notions such as the principles of black-hole complementarity, the discovery of D-branes by Joe Polchinski and, above all, the holographic principle that appeared first in the study of the problem by Susskind and ’t Hooft, but that was masterfully formulated in string theory by Juan Maldacena. There are many other heroes in this story: Strominger, Vafa, Sen, Witten, Callan, Horowitz, Giddings, Harvey, Thorlacius and Russo etc. – who all provided the ammunition necessary to demolish Hawking’s edifice, to the point that he surrendered by around 2003.
In parts three and four of the book, the going gets necessarily rough. The ideas are deeply unfamiliar and one may from time to time feel some form of mental saturation. Being a consummate storyteller, the author punctuates the more difficult passages with a good deal of irreverent and iconoclastic humour. Read the chapter "Ahab in Cambridge". His description of life and academia in Cambridge, England, is hilarious. Indeed, throughout the book you will get a good number of laughs.
In all, the book presents a fascinating and intellectual adventure in accessible terms where you can learn some of the more challenging ideas in modern theoretical physics. The author follows to the letter Einstein’s mandate of making things as simple as possible, but not simpler. It is original, honest, profound and fun. You could hardly ask for more.
Luis Alvarez-Gaume, CERN.
Mémoires d’un Déraciné, Physicien, Citoyen du Monde by Georges Charpak, Odile Jacob. Paperback ISBN 9782738121844, €23.
Eighty-five years and at least three lives’ worth of living unfold in the three sections of these memoirs by Georges Charpak with the contributions from François Vannucci, Roland Omnès and Richard L Garwin.
Uprooted as a child from his native town on the Polish–Ukrainian border during the anti-Semite persecutions of the Russian civil war, he narrates the tribulations of a central-European immigrant in the first part of the book, entitled "Déraciné" (Uprooted). This is the account of his incredible early destiny, from his arrival in France at the age of seven, through his brilliant secondary studies in Paris to his engagement in the struggle against Fascism and subsequent imprisonment, and finally his survival of deportation to Dachau.
Charpak’s career as a physicist "started at age 24 and was more complex than that of most young French scientists". This sets off the second part "Physicien", which is entirely devoted to physics and – through the account of his career – a golden age of physics. After liberation, he first joined the Ecole des Mines ("not the right choice," he says on p24) before finally moving to the laboratory of Frédéric Joliot Curie at the Collège de France, where he specialized in particle detection. A detailed account follows of all the steps in the invention of the multiwire chamber, from Curie’s lab through Charpak’s career at CERN to applications in medicine. This is all complete with images, anecdotes and original documents. "One of the ambitions of the book," Charpak writes on the back cover, "is to show the extraordinary construction of particle physics in the space of one century". For this reason he asked Vannucci to write an in-depth but accessible explanation of the meaning of the Standard Model, which is included in this section.
Another objective of the book is to "throw light on the imminent threat to all the treasures accumulated by civilizations over thousands of years, if we do not change radically the way that mankind manages its material and spiritual richness, its creativity and the education we give to children". The last part, "Citoyen du monde" (Citizen of the world), written with Richard Garwin, details another chapter of Charpak’s life, devoted to the teaching of science to the young and towards the cause of total nuclear disarmament – "le danger toujours plus pressant … non seulement pour la paix mais pour la survie même de l’humanité" (the most pressing danger, not only for peace but for the survival of mankind).
Personal anecdotes provide another enjoyable feature of the book. As Charpak says, he "did not hesitate to describe … his short-term dreams", such as his research on fossil sound in ancient objects and his attempts to sell a comedy scenario inspired by Dr Strangelove to Hollywood.
Paola Catapano, CERN.