The Black Hole War

My Battle with Stephen Hawking to Make the World Safe for Quantum Mechanics

By Leonard Susskind
Little, Brown. 470 pp. $27.99
Sept. 7, 2008

Chapter One


San Francisco, 1983

The dark clouds of war had been gathering for more than eighty years by the time the initial skirmish took place in the attic of Jack Rosenberg's San Francisco mansion. Jack, also known as Werner Erhard, was a guru, a supersalesman, and a bit of a con man. Prior to the early 1970s, he had been just plain Jack Rosenberg, encyclopedia salesman. Then one day, while crossing the Golden Gate Bridge, he had an epiphany. He would save the world and, while he was at it, make a huge fortune. All he needed was a classier name and a new pitch. His new name would be Werner (for Werner Heisenberg) Erhard (for the German statesman Ludwig Erhard); the new pitch would be Erhard Seminars Training, aka EST. And he did succeed, if not in saving the world, at least in making his fortune. Thousands of shy, insecure people paid several hundred dollars each to be harangued, harassed, and (according to legend) told that they couldn't go to the toilet during the sixteen-hour motivational seminars run by Werner or one of his many disciples. It was a lot cheaper and faster than psychotherapy, and in a way it was effective. Shy and uncertain going in, the attendees appeared confident, strong, and friendly-just like Werner-coming out. Never mind that they sometimes seemed like manic, hand-shaking robots. They felt better. "The training" was even the subject of a very funny movie called Semi-Tough with Burt Reynolds.

EST groupies surrounded Werner. Slaves would definitely be too strong a term; let's call them volunteers. There were EST-trained chefs to cook his food, chauffeurs to drive him around town, and all manner of house servants to staff his mansion. But ironically, Werner himself was a groupie-a physics groupie.

I liked Werner. He was smart, interesting, and fun. And he was fascinated by physics. He wanted to be part of it, so he spent wads of money bringing groups of elite theoretical physicists to his mansion. Sometimes just a few of his special physics buddies-Sidney Coleman, David Finkelstein, Dick Feynman, and I-would meet in his home for spectacular dinners catered by celebrity chefs. But more to the point, Werner liked to host small, elite conferences. With a well-equipped seminar room in the attic, a staff of volunteers to cater to our every whim, and San Francisco as the venue, the mini-conferences were lots of fun. Some physicists were suspicious of Werner. They thought he would use the physics connection in some devious way to promote himself, but he never did. As far as I can tell, he just liked hearing about the latest ideas from the characters who were hatching them.

I think there were three or four EST conferences altogether, but only one left an indelible imprint on me, and on my physics research. The year was 1983. The guests included, among other notables, Murray Gell-Mann, Sheldon Glashow, Frank Wilczek, Savas Dimopoulos, and Dave Finkelstein. But for this story, the most important participants were the three main combatants in the Black Hole War: Gerard't Hooft, Stephen Hawking, and myself.

Although I had met Gerard only a few times before 1983, he had made a big impression on me. Everyone knew that he was brilliant, but I sensed much more than that. He seemed to have a steel core, an intellectual toughness that exceeded that of anyone else I knew, with the possible exception of Dick Feynman. Both of them were showmen. Dick was an American showman-brash, irreverent, and full of macho one-upmanship. Once, among a group of young physicists at Cal Tech, he described a joke that the graduate students had played on him. There was a sandwich place in Pasadena where they served "celebrity" sandwiches. You could get a Humphrey Bogart, a Marilyn Monroe, and so on. The students had taken him to lunch there-I think for his birthday-and one after another ordered the Feynman sandwich. They had conspired with the manager beforehand, and the guy behind the counter didn't bat an eye.

After he finished the story, I said, "Gee, Dick, I wonder what the difference would be between a Feynman sandwich and a Susskind sandwich."

"Oh, they'd be about the same," he replied, "except the Susskind sandwich would have more ham."

"Yeah," I responded, "but a lot less baloney." That was probably the only time I beat him at that game.

Gerard is a Dutchman. The Dutch are the tallest people in Europe, but Gerard is short and solidly built, with a mustache and the look of a burgher. Like Feynman, 't Hooft has a strong competitive streak, but I am sure that I never got the better of him. Unlike Feynman, he is a product of old Europe-the last great European physicist, inheritor of the mantle of Einstein and Bohr. Although he is six years younger than I am, I was in awe of him in 1983, and rightfully so. In 1999 he was awarded the Nobel Prize for his work leading to the Standard Model of elementary particles.

But it wasn't Gerard whom I most remember from Werner's attic. It was Stephen Hawking, whom I first met there. It's where Stephen dropped the bomb that set the Black Hole War in motion.

Stephen is also a showman. He is a physically tiny man-I doubt that he weighs a hundred pounds-but his small body contains a prodigious intellect and an equally outsized ego. At that time, Stephen was in a more or less ordinary powered wheelchair, and he could still talk using his own voice, though he was very hard to understand unless you spent a lot of time with him. He traveled with an entourage that included a nurse and a young colleague who would listen to him very carefully and then repeat what he said.

In 1983 his translator was Martin Rocek, now a well-known physicist and one of the pioneers in an important subject called Supergravity. At the time of the EST conference, however, Martin was quite young and not so well known. Nevertheless, from previous meetings I knew that he was a very capable theoretical physicist. At some point in our conversation, Stephen (through Martin) said something that I thought was wrong. I turned to Martin and asked him for clarification of the physics. He looked at me like a deer caught in the headlights. Later he told me what had happened. It seems that translating Stephen's speech required such intense concentration that he was usually unable to keep track of the conversation. He barely knew what we were talking about.

Stephen is an unusual sight. I am not talking about his wheelchair or the obvious physical limitations of his body. Despite the immobility of his facial muscles, his faint smile is unique, simultaneously angelic and devilish, projecting a sense of secret amusement. During the EST conference, I found talking to Stephen very difficult. It took a long time for him to answer, and his answers were usually very brief. These short, sometimes single-word answers, his smile, and his almost disembodied intellect were unnerving. It was like communicating with the Oracle at Delphi. When someone submitted a question to Stephen, the initial response was absolute silence, and the eventual output was often incomprehensible. But the knowing smile said, "may not understand what I'm saying, but I do, and I am right."

The world sees the diminutive Stephen as a mighty man, a hero of extraordinary courage and fortitude. Those who know him see other sides: Stephen the Playful and Stephen the Bold. One evening during the EST conference, a few of us were out walking on one of San Francisco's famous brake-busting hills. Stephen was with us, driving his powered chair. When we reached the steepest section, he turned on the devilish smile. Without a moment's hesitation, he took off down the hill at maximum velocity, the rest of us startled. We chased him, fearing the worst. When we got to the bottom, we found him sitting and smiling. He wanted to know whether there was a steeper hill to try. Stephen Hawking: the Evel Knievel of physics.

Indeed, Hawking is very much a daredevil of a physicist. But perhaps his boldest move ever was the bomb he dropped in Werner's attic.

I can't remember how his lecture worked at EST. Today a physics seminar given by Stephen has him sitting quietly in his chair while a disembodied computer voice lectures from a previous recording. That computerized voice has become Stephen's trademark; as flat as it is, it is full of personality and humor. But back then, maybe he talked and Martin translated. However it happened, the bomb fell with full force on Gerard and me.

Stephen claimed that "information is lost in black hole evaporation," and, worse, he seemed to prove it. If that was true, Gerard and I realized, the foundations of our subject were destroyed. How did the rest of the people in Werner's attic receive the news? Like the coyote in the roadrunner cartoon who overruns the edge of the cliff: the ground had disappeared beneath their feet, but they didn't know it yet.

It is said of cosmologists that they are often in error but never in doubt. If so, Stephen is only half a cosmologist: never in doubt but hardly ever wrong. In this case, he was. But Stephen's "mistake" was one of the most seminal in the history of physics and could ultimately lead to a profound paradigm shift about the nature of space, time, and matter.

Stephen's lecture was the last that day. For about an hour afterward, Gerard stood glaring at the diagram on Werner's blackboard. Everyone else had left. I can still see the intense frown on Gerard's face and the amused smile on Stephen's. Almost nothing was said. It was an electric moment.

On the blackboard was a Penrose diagram, a type of diagram representing a black hole. The horizon (the edge of the black hole) was drawn as a dashed line, and the singularity at the center of the black hole was an ominous-looking jagged line. Lines pointing inward through the horizon represented bits of information falling past the horizon into the singularity. There were no lines coming back out. According to Stephen, those bits were irretrievably lost. To make matters worse, Stephen had proved that black holes eventually evaporate and disappear, leaving no trace of what has fallen in.

Stephen's theory went even further. He postulated that the vacuum-empty space-was full of "virtual" black holes that flashed into and out of existence so rapidly that we didn't notice them. The effect of these virtual black holes, he claimed, was to erase information, even if there was no "real" black hole in the vicinity.

In chapter 7, you will learn exactly what "information" means and also what it means to lose it. For now, just take it from me: this was an unmitigated disaster. 'T Hooft and I knew it, but the response from everyone else who heard about it that day was "Ho hum, information is lost in black holes." Stephen himself was sanguine. For me the toughest part of dealing with Stephen has always been the irritation I feel at his complacency. Information loss was something that just could not be right, but Stephen couldn't see it.

The conference broke up, and we all went home. For Stephen and Gerard, that meant back to Cambridge University and the University of Utrecht, respectively; for me a forty-minute drive south on Route 101 back to Palo Alto and Stanford University. It was hard to concentrate on the traffic. It was a cold day in January, and every time I stopped or slowed down, I would draw the figure from Werner's blackboard on my frosty windshield.

Back at Stanford, I told my friend Tom Banks about Stephen's claim. Tom and I thought about it intensely. To try to learn some more, I even invited one of Stephen's former students to come up from Southern California. We were very suspicious of Stephen's claim, but for a while we weren't sure why. What's so bad about losing a bit of information inside a black hole? Then it dawned on us. Losing information is the same as generating entropy. And generating entropy means generating heat. The virtual black holes that Stephen had so blithely postulated would create heat in empty space. Together with another colleague, Michael Peskin, we made an estimate based on Stephen's theory. We found that if Stephen was right, empty space would heat up to a thousand billion billion billion degrees in a tiny fraction of a second. Although I knew that Stephen was wrong, I couldn't find the hole in his reasoning. Perhaps that was what irritated me the most.

The ensuing Black Hole War was more than an argument between physicists. It was also a war of ideas, or perhaps a war between fundamental principles. The principles of Quantum Mechanics and those of General Relativity always seemed to be fighting each other, and it was not clear that the two could coexist. Hawking is a general relativist who had put his trust in Einstein's Equivalence Principle. 'T Hooft and I are quantum physicists who felt certain that the laws of Quantum Mechanics could not be violated without destroying the foundations of physics. In the next three chapters, I will set the stage for the Black Hole War by explaining the basics of black holes, General Relativity, and Quantum Mechanics.


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