This knowledge of fission and fusion is what the physicists in Berkeley had before them that summer. It took little time for them to conclude that a fission bomb (or A bomb, as it came to be called) was very probably feasible. By that fall, the Manhattan Project would be officially launched, and by the next spring work on fission bombs would shift into high gear—work that culminated, in the summer of 1945, in the successful “Trinity” test in the New Mexico desert and in the still-controversial decision to drop fission bombs on Japanese cities. (By that time, plutonium had been added to the roster of fissionable elements, and two of the three nuclear explosions in 1945 used that element.)
The Berkeley physicists were intrigued by the possibility of a fusion bomb, but much less sure of its feasibility. As a result, it was not accorded a high priority during the war years. As of 1945, work on the H bomb (as the fusion bomb came to be called[1]) had not led to a brighter prospect for its success. If anything, the work in the intervening years made the prospect dimmer. Nevertheless, work continued, for the H bomb, if it could be made to work, would be far more powerful than an A bomb, and might be less costly to make. For those concerned with “more bang for the buck,” it was an attractive option. For some others, it was almost too horrendous to imagine. Yet nearly all the physicists and policy makers agreed that work to establish its feasibility (or not) should continue.
As of 1950, when I joined the effort, there had been no breakthrough, and the likelihood of success in building an H bomb was at best clouded. Then, in the spring of 1951, came an idea that was a breakthrough. That is where my story begins.
Chapter 1
The Big Idea
On March 9, 1951, Edward Teller and Stan Ulam issued a report, LAMS 1225,[2] at the Los Alamos Scientific Lab[3] where they both worked at the time. It bore the ponderous, hardly illuminating title “On Heterocatalytic Detonation I. Hydrodynamic Lenses and Radiation Mirrors,” and it changed everything. Since it dealt with thermonuclear weapons (H bombs), it was, of course, classified secret. For some reason, it remains secret to this day. The highly redacted version of it that can be found on the Web{1} is mostly white space. Nevertheless, most of what was in it is well known.
Their big idea, which we refer to now as radiation implosion, was that the electromagnetic radiation (largely X rays) emitted by a fission bomb, if appropriately channeled, could compress and heat a container of thermonuclear fuel sufficiently that that fuel would be ignited and the nuclear flame would propagate, not fizzle. The expected result: megatons of energy, not kilotons.[4] History validated the Teller-Ulam idea. (In the end, it was even more effective than they first imagined.) On exactly who contributed what to that big idea, history is a little fuzzier. More on that below. (Here and in what follows, I use “Teller-Ulam” not to anoint Teller as the senior author but only to keep the authors in alphabetical order, as they are on the report’s cover.)
Stanislaw Ulam (always known as Stan) and Edward Teller (always Edward, never Ed) had some things in common. They were both émigrés from Eastern Europe—Stan from Poland, Edward from Hungary. They were both brilliant. They both had great curiosity about the physical world. And they were both a bit lazy. But oil and water also have some things in common. Stan and Edward differed more than they were alike. Stan, a mathematician with a gift for the practical as well as the abstract, was—to use current slang—laid-back. He had a droll sense of humor and a world-weary demeanor. He longed for the Polish coffee houses of his youth and the conversations and exchanges of ideas that took place in them. Edward was driven—driven by fervent anticommunism, by a desire to excel and be recognized—driven, it often seemed, by internal demons. Edward was too intense to show much sense of humor. Stan had an abundance of humor. Stan and Edward did not care very much for each other (which may help to explain why a “Heterocatalytic Detonation II” report never appeared).
I was a twenty-four-year old junior physicist on the H-bomb design team at Los Alamos when the Teller-Ulam report was issued. I saw Stan and Edward every day. I liked them both, and continued to like them, and to interact with them now and then, for the rest of their lives. Stan and I later wrote a paper together, on using planets to help accelerate spacecraft (the so-called “slingshot effect”). Edward and I later worked together as consultants to aerospace companies in California.
Not everyone at the lab had equal affection for these two men. Carson Mark, the Canadian mathematician turned research administrator who headed the Theoretical Division during the H-bomb period, could scarcely abide Edward. He liked Stan, even if Stan didn’t care much for bureaucratic nice-ties and even if Stan sometimes wanted to chat when Carson wanted to work. John Wheeler, my mentor, although a straight-arrow quintessential American (he was born in Florida and raised in California, Ohio, and Maryland), was Edward’s soul mate. They were completely in tune in their anti-Communism and their fear of Soviet aggression. Balancing their pessimism about world affairs, they shared an optimism that nature would, in the end, abandon all resistance and yield her secrets if they just pressed hard enough. They had done some joint research together back in the 1930s (on the rotational properties of atomic nuclei) and their wives, Mici (MITT-cee) Teller and Janette Wheeler, were friends. It was Edward’s persuasion, in large part, that led Wheeler to interrupt a sabbatical in France and take a leave of absence from his academic duties at Princeton to spend the 1950-51 year at Los Alamos. Wheeler didn’t exactly dislike Stan, he just didn’t resonate with him. (There were, in fact, very few people whom Wheeler didn’t like, and he tried hard to mask whatever negative feelings he had toward those few.) For Wheeler’s taste, Stan was just a bit too laid-back, a bit too nonchalant.
Looking back, the odd thing to me now is that the Teller-Ulam idea, at the time it was advanced, didn’t shake the Earth under our feet. There were vibrations, but no earthquake. There was a new sense of cheer, but no parties or toasts or flag waving. We didn’t take the trouble to analyze, as so many have since, who exactly had what part of the idea and who deserves the greater credit. Years later, Edward said to me (I paraphrase), “Stan had a dozen ideas a day. They were almost all crazy. He himself had no idea which ones were valuable. It took me to pick out of the jumble the one good idea and exploit it.” Also years later, Stan said to me (again, I paraphrase), “Edward just couldn’t bring himself to admit, after his years of effort, that the idea on how to make the H bomb work was mine. He just had to take it and call it his own.”
The Teller-Ulam idea landed in the midst of numerous other ideas, of varying complexity and varying chance of succeeding. These included “boosting” (having a small container of thermonuclear fuel at the center of a fission bomb to “boost” the fission bomb’s yield); “Swiss cheese” (having numerous pockets of thermonuclear fuel scattered throughout fission fuel); the “alarm clock” (a name Edward Teller and Robert Richtmyer had coined in 1946{2}, {3} for alternating layers of fission and fusion fuel,[5] and which Andrei Sakharov in the Soviet Union, as we later learned, had separately envisioned and separately christened a “layer cake” in 1948{5}); and the “Yule log” (John Wheeler’s macabre name for a cylinder of thermonuclear fuel with no limit on its length or on its explosive power). Behind these lay the basic idea that had been around for nearly a decade and on which we were working assiduously at the time. That idea, known as the “Super” (and later as the “classical Super”) was simple in concept but maddeningly difficult to model mathematically, so that there was no sure sense of its potential. At the time of the Teller-Ulam idea, however, there were more reasons for pessimism than optimism about the prospects of the classical Super. Calculations[6] kept suggesting that igniting the fuel, even with a powerful fission bomb, and even with a good deal of highly “combustible” tritium mixed in, would not be easy, and that even if it were ignited, it would probably fizzle rather than propagate. A homeowner trying to get a fire started in a fireplace with wet logs and inadequate kindling can relate to the difficulty.
1
The H bomb, or hydrogen bomb, is also called a thermonuclear weapon, because its operation requires high temperature—
2
As an LAMS report (MS for manuscript), it was lesser ranked (or more informal) than an LA report.
4
A “ton” of energy is the nominal energy released when one ton of high explosive blows up (for the record, it is 4.2 billion joules). The energy released in nuclear explosions is measured in thousands or millions of tons (kilotons or megatons). The Hiroshima bomb, the first nuclear weapon used in war, had an estimated “yield” of 13 to 15 kilotons. The second weapon, dropped on Nagasaki, yielded about 21 to 23 kilotons. In subsequent tests, the yields have been measured with greater precision. To put all of this in human terms, a ton of explosive energy is about the same as a million food calories, enough to keep a human going for about 500 days. A kiloton would “feed” a thousand people for 500 days. A megaton, spread over that same period of time, would nourish a million people. But that same megaton, released in a fraction of a second in the right place could slaughter a million people.
5
Fitzpatrick{4} gives the specific date August 31, 1946, for the conception of the alarm clock idea, a date that Teller reportedly remembered because his daughter Wendy was born on that day. This is charming, and, with a bit of a stretch, consistent with Teller’s statement in his Memoirs that he and Robert Richtmyer devised the idea “during the summer of 1946.” Teller gives Richtmyer credit for the name.
6
Calculations at the time were carried out mainly by people wearing skirts and blouses operating Marchant, Monroe, and Friden calculators. They were called “computers.” Understandably, we often called them computresses. The nearest thing to a modern computer was a modified IBM accounting machine known as a card-programmed calculator (CPC). Computers as machines with internally stored programs came later—but not much later. I will return in Chapter 9 to a discussion of some of the “Super” calculations that were carried out when computers were still people and in Chapter 15 to calculations carried out on the true ancestors of modern computers.