9269_chap01

Chapter 1

The Big Idea

O -* where they both worked at the time. It bore the ponderous, hardly

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secret to this day. The highly redacted version of it that can be found on the Web[ ] is mostly white space. Nevertheless, most of what was in it is well known.

Their big idea, which we refer to now as radiation implo-

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energy, not kilotons.

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A ton of energy is the nominal energy released when one ton of high ex-

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.

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B U I L D I N G T H E H B O M B : A P E R S O N A L H I S T O R Y

use Teller-Ulam not to anoint Teller as the senior author but only to keep the authors in alphabetical order, as they are on

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They were both migrs from Eastern EuropeStan from

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, wasto use current slang

for the Polish coffee houses of his youth and the conversa-

Courtesy of AIP Emilio Segr Visual Archives, Physics Today Collection.

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T H E B I G I D E A

tions and exchanges of ideas that took place in them. Edward was drivendriven by fervent anticommunism, by a desire to excel and be recognizeddriven, it often seemed, by internal demons. Edward was too intense to show much sense of hu-mor. Stan had an abundance of humor. Stan and Edward did

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 pa-per together, on using planets to help accelerate spacecraft

Not everyone at the lab had equal affection for these

Courtesy of AIP Emilio Segr Visual Archives, Gift of Carlo Wick.

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liked Stan, even if Stan didnt care much for bureaucratic nice--

son wanted to work. John Wheeler, my mentor, although a -

-munism 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

Teller and Janette Wheeler, were friends. It was Edwards per-suasion, in large part, that led Wheeler to interrupt a sabbati-cal in France and take a leave of absence from his academic

Wheeler didnt exactly dislike Stan, he just didnt resonate

didnt like, and he tried hard to mask whatever negative feel-

just a bit too laid-back, a bit too nonchalant.

Ulam idea, at the time it was advanced, didnt 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

have since, who exactly had what part of the idea and who

took me to pick out of the jumble the one good idea and ex-

Edward just couldnt bring himself to admit, after his years

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T H E B I G I D E A

The Teller-Ulam idea landed in the midst of numerous other ideas, of varying complexity and varying chance of suc-

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-merous pockets of thermonuclear fuel scattered throughout

-[2] [ ] for alternating layers of

* and which Andrei Sakharov in the So-viet Union, as we later learned, had separately envisioned and

[5]

-monuclear fuel with no limit on its length or on its explosive

for nearly a decade and on which we were working assidu-

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sure sense of its potential. At the time of the Teller-Ulam idea, however, there were more reasons for pessimism than opti-

*Fitzpatrick[ ]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 Tellers statement in his Memoirs that he and

Richtmyer credit for the name.

and blouses operating Marchant, Monroe, and Friden calculators. They were called computers. Understandably, we often called them computresses.

-chines with internally stored programs came laterbut not much later. I

calculations carried out on the true ancestors of modern computers.

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kept suggesting that igniting the fuel, even with a powerful -

tible tritium mixed in, would not be easy, and that even if it

So the Teller-Ulam idea landed in our midst not as just another ideait was specialbut also not as a lone idea where there were none already. It was like a new sap-ling introduced into a nursery, not like a palm tree miracu-lously delivered into the desert. We thought, Now there is an idea with merit, and we started exploring its consequences at oncewithout immediately abandoning other ideas. As it turned out, the more we calculated, the more promising the new idea looked. Within three months, it had become the idea

with an idea about imploding thermonuclear fuel and Teller [ ]

bomb design in the United States assumed that the Super would have to be a runaway Super, a device in which the temperature of the material would have to run away from

radiation would soak up too much of the energy and there wouldnt be enough left to ignite the thermonuclear fuel and keep it burning. What could change this bleak prospect, Ulam and Teller realized, would be great compression of the mate-rial. It was this February meeting and its insight that led to the

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T H E B I G I D E A

that is, having the matter and the radiation at the same tempera-turecould be tolerated if there was enough compression.

the total energy. More energy would be left to heat the matter and stimulate its ignition and burning. Up until then, those of us working on the Super accepted the idea that thermal equi-librium would be intolerable because of the excessive loss of energy to radiation. And we accepted an argument Teller had made[7] that compression would not help. Teller had pointed out that although compressing the thermonuclear fuel in-creases its reaction rate, it also increases, and by the same factor, the rate at which the matter radiates away energy. So there was no net gain, he had argued, from compression. But that argument posits a runaway Super, which was our mind-

losing energy to radiation, it is just exchanging energy with radiation, gaining as much as it is losing. If you jump into the North Atlantic, you lose energy because your temperature is higher than that of the water, and you will soon be drained of

equally back and forth between you and the water as you re-main in equilibrium, and you can bask there all afternoon.

I have not found in the written record any sure evi-dence that Stan Ulam had in mind this insight about equilib-rium when he came up with the idea that the thermonuclear fuel should be compressed. Nor do I remember him explicitly

did have

work on the runaway Super and knew its disconcerting inabil-

most likely knew, also, the Teller argument that for a runaway Super, compression would not help.

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Teller, in the now-famous conversation with Ulam, ap-parently did realize very quickly, despite his earlier arguments to the contrary, that compression could be a key to success. In his memoirs, written many years later [ ]

it.[ ]

given his previous rejection of the idea. In the same paragraph, in a further put-down, Teller says that Ulam did not actually understand why compression was a good idea.

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come in with a full understanding of why compression might

[ ] and also about Febru-[ ] These claims are dubious, especially in light of

his own account of the meeting with Ulam,[ ] and in light of my own recollection that no breakthrough idea occurred be-

meeting came the successful idea of the equilibrium Super, in which compression is so great that the huge amount of energy soaked up by radiation in equilibrium with matter is tolerable.

The second insight that came from the Ulam-Teller

is a substance with remarkable properties.*liquid and then push like a giant steel piston. No, not like steel. Stronger than steel. This is not the radiation emitted later in

ra-diation that can be channeled until it surrounds a container of thermonuclear fuel and then implodes it. There is at least

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T H E B I G I D E A

agreement that this idea of radiation implosion was Tellers. -

sion bomb could do the compressing. Teller saw that radiation

clearance,[ ] the radiation is indeed the agent of compres-sion, with most of the actual push being supplied by ablation

-nuclear fuel. The radiation bath also creates a plasma of elec-trically charged nuclei and electrons in low-density material just outside this container, further augmenting the push.[ ]

-monuclear fuel is and, in any case, is not publicly known. But it

reaction in the fuel while keeping the volume occupied by

within that volume cant soak up too much of the total energy. We tend to think of solid matter as incompressible

but it does in fact shrink and ex-pand. The girders of a steel bridge that together span a thou-

ten-fold compression in each dimension. The bridge would be a hun-dred feet long and a girder that was a foot across would be reduced to a width of little more than an inch. A cube of the original steel two inches on a side would weigh a little more than two poundseasy to hold in your hand. A cube of the same volume of the compressed steel would weigh more than a ton.

The physics of nuclear weapons concerns more than nuclear reactions. It also concerns the properties of matter at temperatures and pressures and densities light years removed from anything that can be tested in the laboratory. Edward

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Teller and Stan Ulam were among those theorists whose in-genuity allowed them to visualize and to calculate what would

The physicists knowledge that the laws of electromagnetism and of mechanics, both classical and quantum, extend to

that ultimately, no matter what the conditions, one is deal-ing with the same electrons and nuclei and photons as in the ordinary world around us.

Scientists and engineers in the Soviet Union were not far behind those in the United States in developing and test-

[ ]

the Soviets launched a serious program to develop an atomic bomb,[ ]

But perhaps not a great deal longer. The USSR had a comple-ment of nuclear scientists as competent as those in the United States. And not just competent. Some, like Andrei Sakharov,

best in the West.--

[ ] This was Sakharovs third idea. [ ] In his Memoirs, Sakharov avoids revealing secret information about the Soviet thermonuclear program by speaking enigmatically only of the

well known what these ideas were.[ ]

Sloika, or layer cake, a design much like the alarm clock that Teller and Richtmyer had pro-

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T H E B I G I D E A

help of espionage.[20] As initially imagined, the layer cake was [ ]

Sakharov and his team pushed hard on Sloika and indeed suc-

deliverable thermonuclear weapon,* The second idea, which Sakharov attributes to his col-

[ ] was advanced in the Soviet Union in

fuel by a particular form of the compound lithium hydride in which the lithium iseither wholly or in substantial part

or deuterium. I will have more to say about this compound

United States, it was proposed by Edward Teller as a thermo-[ ] Airdrops of weapons containing this

[25]

[ ] The two countries were never far apart in their developments of thermonuclear weapons.

same question of the Soviet scientists, where Sakharovs third

*It was a thermonuclear weapon in the sense that more than a token part of its energy was contributed by thermonuclear reactions.[22]

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a decade of work on thermonuclear weapons, including pe-riods both before and after Klaus Fuchs passed along some

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ity. The scientists in both countries were like horses wearing blinders. Each group was pursuing a particular path and could see ahead but not to the side. In the United States the view ahead was of the classical Super. In the Soviet Union it was of

when, in the United States, it looked more and more like the classical Super wouldnt work, and, in the Soviet Union, it looked more and more like the layer cake could never reach into the mega-ton rangeonly then did the scientists cast off their blinders and look in new directions.

And you the reader, could ask me, the once-young sci-entist, why I didnt come up with the idea of radiation implo-sion myself. Its a fair question. To be sure, I was a junior mem-ber of the team, but I understood all the relevant physics and I

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that the only hope of igniting and sustaining a thermonuclear

the temperature of radiation. That, as Teller and Ulam realized

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