Nuclear Fusion, Episode IV: Teller’s Dream

The original episode, released in February 2019, can be obtained here.

One of the issues I have with trying to explain physics in a podcast format is that it’s difficult to explain it from a purely mathematical point of view. When I was a physics undergraduate, lectures usually consisted of starting with a set of equations or ideas that we already knew, going through the mathematical derivation, and explaining the consequences of these rules as you go along. It’s more rigid, methodical, and you get a better idea of how the mathematics allows the laws of nature to fit together. But this is impossible on a podcast, because I don’t have a blackboard — and also because I don’t want an advanced understanding of mathematics to be necessary to listen. Mathematics in audio is very difficult to keep track of.

So I tend to try to tell conceptual stories, and one of the best ways of doing that is going through the human angle. When I want to explain a particular part of physics, it’s often helpful to look at what people knew at the time, how they discovered or developed new bits of science, and fit them into the jigsaw this way. And it’s amazing, because there are some incredible stories and some incredible characters that arise in the history of science. And I think that human window — looking on science as this edifice of understanding of the natural world, constructed by the efforts of a great many *people* — as something that humans do and build to make sense of observations and understand the Universe — this is an incredibly important view. And we get to spend time with all of these remarkable people as they uncover extra corners of the tapestry for the first time.

But you can get too caught up in praising the beauty of science and conflating that with praising the individual. I think we should recognise and appreciate brilliance, but stop short of hero-worship. It’s reductive. It diminishes people. It removes important parts of who they were. It can, in its worst excesses, be downright dangerous.

Nevertheless, that’s not a problem I have today, even though I’m going to tell this story partly biographically. Because Edward Teller, for all his brilliance in physics, is not the kind of person you’d want to worship as a hero. Yet it’s Teller, for good or ill, rightly or wrongly, who is most associated with the first successful large-scale harnessing of the power of fusion by human beings: the hydrogen bomb.

If you’ve ever seen the film Dr Strangelove, or “How I Learned to Stop Worrying and Love The Bomb”, you’ll know something of the popular perception of Teller. If you haven’t, you should immediately find a copy and watch it. From the moment that Teller was brought onto the Manhattan project, he was pushing for it to expand — not just to create a bomb that would harness the power of nuclear fission, but a fusion bomb. A hydrogen bomb, that would — according to theoretical calculations — be thousands of times more powerful. It would begin a long career in physics and the military that would see Teller consistently and endlessly advocate for more and more powerful weapons — total nuclear supremacy over the Soviet Union. It was an obsessive quest that led some of his oldest friends and colleagues to turn on him, in the end. The physicist Isidore Rabi later said: “He is a danger to all that is important. I do really feel it would have been a better world without Teller.”

Plenty of historians have pointed to Teller’s background to explain his incredible hawkishness on the hydrogen bomb. He was one of those unfortunate people in the 20th century who brushed up against both Communists and Nazis. Born into a Jewish family in Hungary, at the age of 11 he saw Bela Kun launch a coup, throw society into chaos attempting to implement a Communist revolution, and then in turn be overthrown by a military dictatorship. The whole affair left him with a lifelong suspicion of Communism — something that reading accounts of others who lived under the USSR confirmed. He pursued his studies in mathematics in Germany, but as the persecution of Jews worsened, he emigrated to the USA in 1938 — and took with him a lifelong hatred of totalitarianism, and suspicion of Communism, that motivated his political views and work for the US military for the rest of his life.

It’s certainly true that he was used to being demonised, for reasons we’ll get to. When he was recovering from a stroke, a nurse asked him “Are you the famous Edward Teller?” He responded, “No, I’m the infamous Edward Teller.” And he’s famously quoted as saying things like: “I am proud to be called the father of the Hydrogen bomb. I have no regret that I spent my life working on nuclear weapons. If I contributed 1% to the defeat of the Soviets, it was 1% of a great deal. If it wasn’t for me, there’s a good chance we’d all be speaking Russian.”

But this was all in the future when, in the 1940s, Teller was a lone voice trying to pull the Manhattan project to work on a fusion bomb — which was nicknamed the Super. You’ll remember from previous episodes that fusion can release far more energy than fission per unit mass. This is because, for the first few nuclei building up to iron, the curve of binding energy is very steep — the nucleons in a helium are FAR more tightly bound than in a hydrogen nucleus. Because the changes in binding energy are so much greater, one fusion of hydrogen nuclei releases many times more energy than a uranium nucleus splitting in two. It makes sense: fusion of light elements forms entirely new bonds, whereas fission involves the energy changes associated with a slight reconfiguration of nucleons. In our episode on the semi-empirical mass formula, we described this landscape of nuclei — a very steep fusion hill on one side, and a much shallower fission slope on the other, with iron and nickel the most stable nuclei towards the bottom. When you roll down the fission hill — or plummet off the fusion cliff — you release that binding energy.

The reason fusion is more difficult is, of course, is that you need a push to get off that cliff. The nuclei are all positively charged and repel each other. The electromagnetic force acts over all space, whereas the strong force only kicks in when you get nucleons incredibly close together. You have to provide nucleons with a hell of a lot of energy *and* simultaneously confine them — say, by putting them under the immense pressure and temperature conditions found at the heart of the Sun — so that they will collide and fuse together, overcoming the “Coulomb barrier” due to their electrostatic repulsion.

And, of course, the second you actually get the nuclei to fuse, confining them becomes all the more difficult; they’ll pour energy and heat into their surroundings, and whatever fusion fuel you have will attempt to blow itself apart. This was essentially also the problem with constructing the fission bomb: how can you prevent the fuel from just blowing itself to pieces before it can produce sufficient energy to create this nuclear explosion? But at least with fission the fuel can start relatively “cold”, and you can provoke reactions by bombarding the fuel with the appropriate number of neutrons. With fusion, you need to find some way to — even if it’s only for a few milliseconds — create conditions that are usually only found at the heart of stars.


Teller’s initial design involved detonating a standard fission bomb in a tank full of deuterium (hydrogen with a neutron in the nucleus.) The deuterium would be heated by the initial explosion to temperatures where fusion could occur. Teller, however, was pretty sure that it could be done — and besides, fission was a solved problem already, so fusion couldn’t be that tricky, right? His fellow Manhattan project workers began measuring scientific optimism in units of “Tellers”.

But it was a terrible kind of optimism. If anything, Teller overestimated not only the ease of the bomb’s construction, but also how deadly it would prove to be. You have to remember that this was in the early atomic era; no one had seen a fission bomb, let alone a fusion bomb. Teller was one of those who was concerned that the heat and pressure associated with a nuclear explosion might be sufficient to cause nitrogen atoms in the atmosphere to fuse with each other, leading to an unstoppable chain reaction — the entire sky catching fire and burning up the planet in an unimaginable inferno. Teller was, at first, concerned with how to make a bomb that would be powerful enough to destroy a city, but not all life on Earth.

If you want to know why Teller was considered to be the inspiration for Dr Strangelove, maybe this anecdote, from Robert Serber who worked with him, will help to explain:

“On Edward Teller’s blackboard at Los Alamos I once saw a list of ideas for weapons, with their abilities and properties displayed. For the last one on the list, the method of delivery was simply listed as “Backyard.” Since that particular design would probably kill everyone on Earth, there was no use carting it elsewhere.”

Teller’s calculations — both about his bomb design, and the possibility of igniting the whole atmosphere — were quickly dismissed by another physicist, Hans Bethe. Bethe showed that any fusion reaction would lose a lot of energy through radiation — sufficient that Teller’s bomb design wouldn’t even ignite a self-sustaining fusion reaction, let alone ignite the atmosphere. The atomic bomb committee would decide to scrap the fusion research: they wanted to build atomic bombs; hypothetical, world-destroying superweapons would come later. Combine this with Oppenheimer appointing Bethe to be head of the theoretical physics division of the project — which Teller was convinced would be his job — and a feud between Oppenheimer and Teller would start to ignite. Oppenheimer’s leftist politics were just another source of irritation for Teller, who blamed him for his bruised ego during the Manhattan project days.

It was this personal feud, growing over decades from this seed — that many have convinced led, years later, to Teller’s controversial testimony about Oppenheimer. When Oppenheimer was suspected of being a Communist, Teller testified:

“In a great number of cases, I have seen Dr. Oppenheimer act — I understand that Dr. Oppenheimer acted — in a way which for me was exceedingly hard to understand. I thoroughly disagreed with him in numerous issues and his actions frankly appeared to me confused and complicated. To this extent I feel that I would like to see the vital interests of this country in hands which I understand better, and therefore trust more.”

And this really stemmed back to the Manhattan project, because Teller’s testimony basically argued that Oppenheimer opposing the fusion bomb project was an error in judgement that could have allowed the Soviets to gain nuclear supremacy.

In the context of the 1950s, Teller arguing that Oppenheimer shouldn’t have a security clearance was as good as saying that he was a Communist. Not that Oppenheimer was suspected for no reason aside from Teller’s testimony — he had left-leaning views, and had been approached by Communist agents in the past. Ironically, one of the major things held against him in the trial was an episode in 1943 where he alerted security that one particular individual might be a security risk. The problem was that Oppenheimer lied about how he knew the man was risky: he knew because he had been told by his friend in the Communist Party. Without Teller’s intervention, it’s possible that — in the McCarthy era — Oppenheimer would have been forced out of nuclear weapons research. But many in the scientific community viewed this as a stab in the back from Teller towards someone who had always been a personal and professional rival. Oppenheimer’s security clearance was revoked, without that, nuclear research was very difficult to carry out, and he stepped down from prominent scientific and public life under a serious amount of pressure. But Teller too was ostracised from mainstream science.

The whole affair is deeply controversial. Some even see it as a turning point in how scientists were allowed to be seen in public life. Remember the historical context of these events. This is the Cold War. Nuclear weapons have existed for less than a decade. Two great superpowers seem to be on the brink of destroying each other in a war that would kill millions. Oppenheimer and other nuclear scientists who had worked on the bomb must have felt immense pressure to try and influence the process, guide the world towards safety in the face of this awesome new power. Oppenheimer had criticised the policy of the United States, arguing that they were too hawkish on the future development of nuclear weapons, that an arms race could lead to war. Remember the McCarthyism of the era, the fear of Communist revolution. This was a time when if you wanted to get security clearance, you’d have to answer questions about whether or not you’d “ever made statements regarding the poor or downtrodden.” Questions like: “There is a suspicion in your record that you are in sympathy with the underprivileged. Is that true?”

By denouncing Oppenheimer’s views as politically motivated — motivated by Communist sympathies — Teller helped push scientists out of the debate on nuclear weapons, and out of public life as intellectuals. The issue of a separation between science and politics is fraught, but many feel that Teller’s testimony against Oppenheimer meant that scientists were forced to be subservient to the military-industrial complex, and the politicians in power. Kay Bird and Martin Sherwin wrote:

“With Oppenheimer’s defrocking, scientists knew that in the future they would serve the state only as experts only on narrow scientific issues. The narrowest version of how American scientists should serve their country had triumphed.”

For now, though, we return to 1945. Oppenheimer and Teller’s feud hasn’t really kicked off, yet; they’re still bound together by this shared mission, creating the atomic bomb. The Trinity Test in July of 1945 was the culmination of their efforts. The physicists who watched actually bet on how big the bomb’s yield would be — how large the explosion would be, in terms of tonnes of TNT. Enrico Fermi, who was also there, offered to make bets about whether or not the atmosphere would ignite — a good gambling strategy, given that it would entail the destruction of all life on Earth. For the first-ever nuke yield sweepstakes, Oppenheimer guessed 300 tonnes. Bethe guessed 8,000 tonnes. Teller, ever the optimist, guided by the power of his weapons, suggested 45,000 tonnes. So convinced he was of the bomb’s power that he brought gloves and sun-tan lotion to protect himself, as well as sunglasses he wore behind the welding goggles the military had provided. So determined was he to see the explosion that he refused to follow orders to lie down on the ground, facing away from the blast, in military fashion, as it took place.

When the bomb exploded with the equivalent of 20,000 tonnes of TNT, Teller saw it. And the physicists knew that their work on the atomic bomb was as good as complete.

The question remained about what to do with it. And here, in fact, is one decision that Teller — the unapologetic, brash, paranoid, egomaniacal, staunch in all his views Teller — would admit to regretting.

Teller’s fellow Hungarian physicist, Leo Szilard, played a pivotal role in atomic history. Along with Albert Einstein, in 1939, and consulting with Teller, they had first warned the US government that an atomic bomb might be possible — and that the Nazis might be working on it. Szilard roped Einstein into the effort because he knew that the politicians would pay more attention to him, due to his worldwide renown — when he first approached the great physicist about the possibility of a nuclear bomb, Einstein said “I did not even think of that.”

The famous Einstein-Szilard letter kickstarted the beginning of the Manhattan project:

“In the course of the last four months it has been made probable — through the work of Joliot in France as well as Fermi and Szilárd in America — that it may become possible to set up a nuclear chain reaction in a large mass of uranium, by which vast amounts of power and large quantities of new radium-like elements would be generated. Now it appears almost certain that this could be achieved in the immediate future.

This new phenomenon would also lead to the construction of bombs, and it is conceivable — though much less certain — that extremely powerful bombs of a new type may thus be constructed. A single bomb of this type, carried by boat and exploded in a port, might very well destroy the whole port together with some of the surrounding territory. However, such bombs might very well prove to be too heavy for transportation by air.”[13]

“I understand that Germany has actually stopped the sale of uranium from the Czechoslovakian mines which she has taken over. That she should have taken such early action might perhaps be understood on the ground that the son of the German Under-Secretary of State, von Weizsäcker, is attached to the Kaiser-Wilhelm-Institut in Berlin where some of the American work on uranium is now being repeated.”

A few months later, it became clear that the amount of fissile material required for a dangerous chain reaction was far less than had previously been calculated — that an atomic bomb that could be mounted on a plane, or perhaps a missile, might be possible.

Einstein, as a lifelong pacifist, was considered a security risk and had very little to do with the American bomb project. As early as 1947, he said that the only reason he’d sent the letter was out of fear that the Nazis might develop the atomic bomb first, and that “had I known that the Germans would not succeed in developing an atomic bomb, I would have done nothing.”

Szilard was not done with trying to change the course of history through influential letters. In 1945, after the Trinity test, he circulated the Szilard petition. It warned the US against using atomic weapons to end the war in Japan, arguing:

“The development of atomic power will provide the nations with new means of destruction. The atomic bombs at our disposal represent only the first step in this direction, and there is almost no limit to the destructive power which will become available in the course of their future development. Thus a nation which sets the precedent of using these newly liberated forces of nature for purposes of destruction may have to bear the responsibility of opening the door to an era of devastation on an unimaginable scale.

If after this war a situation is allowed to develop in the world which permits rival powers to be in uncontrolled possession of these new means of destruction, the cities of the United States as well as the cities of other nations will be in continuous danger of sudden annihilation. All the resources of the United States, moral and material, may have to be mobilized to prevent the advent of such a world situation. Its prevention is at present the solemn responsibility of the United States — singled out by virtue of her lead in the field of atomic power.”

Szilard was also an advocate for a demonstration of the nuclear weapon, and signed the Franck petition:

“If the United States would be the first to release this new means of indiscriminate destruction upon mankind, she would sacrifice public support throughout the world, precipitate the race of armaments, and prejudice the possibility of reaching an international agreement on the future control of such weapons.

Much more favorable conditions for the eventual achievement of such an agreement could be created if nuclear bombs were first revealed to the world by a demonstration in an appropriately selected uninhabited area.”


Teller faced a decision whether or not to sign either petition. He says that he originally intended to circulate the petition for signatures — but Oppenheimer talked him out of it, arguing that scientists had to leave their political decisions to the wisdom of the leaders. Regardless of what happened, Teller and Oppenheimer didn’t sign. Szilard’s petition, after collecting around 70 signatures from those who worked on the Manhattan project — still top secret — was given to a General in the hopes that he would pass it to Secretary of War Henry Stimson, and then to the President. But the petition never made it to either of those people. In fact, most of the signatories lost their jobs in weapons research or were moved to other departments. And Szilard himself was investigated for potential criminal activity — the General made efforts to see if he’d ever discussed classified information so that he could be tried with Espionage. In the end, the petition made sadly little impact on world history except to perhaps deepen the mistrust between the military and the scientists who worked on the bomb.

After some deliberation, the atomic bombs were dropped on Hiroshima and Nagasaki. Loyal listeners will recall from our earlier nuclear weapons episodes what the consequences were like on the ground. And, in the aftermath, the Second World war finally over, the Manhattan project disbanded.

Only years later did Teller talk of his regret:

“I have regret connected to Hiroshima. We should have dropped the bombs not on Hiroshima but in Tokyo Bay. Ten million Japanese would have seen the blast and nobody would have been hurt. With the Japanese seeing that, we could have ended the war without killing. Or we could have dropped the atomic bomb over Tokyo at an altitude of twenty to thirty thousand feet, at eight o’clock in the evening, so they would have seen it and felt the shock. Hirohito would have seen the bomb and used it to surrender.”

He also said that the scientists should have worked on making any necessary modifications to the bomb to allow it to be dropped at high altitude, in a demonstration over Tokyo — a warning shot, so to speak.

This is a moral and ethical question that will probably be debated for centuries to come. For what it’s worth, I think that the further we get from that episode of history, the more unjustifiable the decision seems to be. Whether that’s because we aren’t living through the alternative that they felt they had at the time — a far bloodier land war — or because our emotions are cooler and we can judge things more rationally — who can say.

After Hiroshima and Nagasaki, the Manhattan project was disbanded. There was little interest amongst the scientists or the military, at this stage, in developing Teller’s “Super” weapon. But a few years later, the USSR’s atomic bomb project — that thing born of Sharaskhi and Atomgrads, Beria’s threats, and the brilliance of Soviet physicists… as well as a little bit of espionage — had borne fruit. And, in the new atmosphere of a Cold War, the heat was turning up on nuclear fusion. Teller would get his chance to build his bomb.

Next time, we’ll talk about that bomb.

Thanks for listening etc.