Richard Rhodes — The Making of the Atomic Bomb (#146)

Richard Rhodes is an American historian and the Pulitzer Prize-winning author of The Making of the Atomic Bomb.

Transcript

JOSEPH WALKER: Richard Rhodes, welcome to the podcast.

RICHARD RHODES: Thank you.

WALKER: So, Dick, you're best known for The Making of the Atomic Bomb, which, of course, I'd like to talk about. But I want to start with a scene from one of your more recent books, Arsenals of Folly, which was published in 2007. And the scene is the summit between Reagan and Gorbachev in Reykjavik in 1986. Because not many people know this, and I certainly didn't until I read your book, but the world came heartbreakingly close to getting rid of nuclear weapons once and for all. So, firstly, could you please set the scene for the summit, and then I'll ask you a couple of specific questions about it.

RHODES: People don't know that Ronald Reagan was actually an abolitionist. Ever since the end of the Second World War, he had believed that there must be a way to eliminate these terrible new weapons from the world. And he'd spent much of his political career quietly trying to figure out a way for that to happen. He saw it as a potential treaty, but he'd read a book by a Hollywood lawyer friend of his titled The Treaty Trap that basically argued that treaties weren't worth the paper they were written on unless they had some kind of guarantee. And the example that he always used was when poison gas was outlawed after the end of the First World War, nobody threw away their gas masks; they kept their gas masks. He told Gorbachev that at the Reykjavik Summit. Gorbachev would roll his eyes like, "Yes, so what?"

But in any case, when he was going to the convention to be nominated to run for president, he was asked by one of his staff, "Mr. Reagan, why do you want to be president?" And he said, "I'd like to get rid of all the nuclear weapons in the world." Nobody really took him seriously in Washington, because how would you do that and why would you do that? From the point of view of the leadership in Washington, nuclear weapons were kind of a prestige item in a way. I mean, of course there was a veneer of theory about deterrence and so forth, which had a certain elemental truth to it; you really wouldn't want to have a nuclear war with another nuclear power. But there was so much else built into the whole discussion of nuclear weapons, and one was the factor that it made you a big boy in the world.

So no one really wanted to get rid of nuclear weapons. Margaret Thatcher, for example, was horrified at the very idea, particularly because England was by then, of course, a somewhat vestigial former power. One of the things it had going for it was nuclear weapons. So Reagan had been looking for a way through all of this, and it came to him when heard about the idea of the Strategic Defense Initiative, which was sort of a dream of Edward Teller, the American scientist, and others, that somehow you could put up a shield in space that would use various advanced techniques, X-ray lasers, to shoot down warheads as they came over the horizon from the Soviet side, and thereby build what Reagan called a kind of umbrella over the United States. "To keep out warheads," he said, "as an umbrella keeps out rain." This is all very poetic, you see.

Reagan and Gorbachev had met once, and they had gotten along quite well, really. But then came a series of events that almost ruined the whole possibility of a discussion. A Soviet fighter pilot, with local approval, shot down a Korean airliner that had strayed over Soviet territory several hundred miles. He and his advisors thought that it was a spy plane, and without consulting Moscow for some reason — perhaps they couldn't connect at that hour of the day or night; I don't know — they shot it down. And that almost messed up the whole thing. But in a way, even more so, Reagan wanted to continue to talk to Gorbachev.

And Gorbachev, who had come to power in the Soviet Union as the Minister of Agriculture, he had grown up on a collective farm. His four year scholarship to Moscow University, the most prestigious university in the country, had come because in one summer he and his family had harvested more grain than any other family and any other person in the Soviet Union.

So from his perspective, he was desperately concerned about the decline of the food supply. This was a rich and bountiful country. It covers eleven timezones and it wasn't feeding its own people. They were having to buy wheat from other countries. He thought, "We've got to get rid of the Cold War with all of its vast expense." And from his perspective, the place to start was at the top, with nuclear weapons. So he was armed with the idea. He and Reagan were going to meet again in Washington in 1987, but they both thought maybe they should have a quick meeting, kind of a pre-summit, to lay out what they're going to be talking about at the big summit. And they settled on Reykjavik because it was more or less halfway between the two countries.

So here they arrive in this tiny little country. They are put up in a place called the Hofdi House, which had been the French ambassador's residence and was really quite small. I visited it when I was writing about it, and it's just a normal house. It's amazing that they squeezed all the staff into this little building. People were sitting in bathtubs having discussions behind shower curtains.

WALKER: And wasn't Reagan on the toilet in one of the discussions?

RHODES: Well, no, he got to sit in a chair [laughs].

WALKER: Okay [laughs].

RHODES: In any case, both men arrived. Gorbachev had managed to convince the politburo that if he proposed the complete elimination of nuclear weapons, that he really wouldn't be serious, he just would be doing some propaganda. And they believed him. But they stipulated that the limit of his authority would be: he had to get Reagan to agree not to test SDI in space — that would be too close to deploying it from their perspective. So if he continued to leave it in the "laboratory" (that was the word they used), that would be okay, and they could agree to whatever they wanted to agree to. So that was Gorbachev's remittance.

Reagan's staff were people who didn't take him very seriously. One of the key figures was a clever and very smart advisor named Richard Perle, who had been trying to sabotage every treaty the United States had written related to the Soviet Union, ever since he first moved into authority. And Perle was basically there to make sure nothing happened.

So here are both men, surrounded by people who don't really understand what their motives are. And these two men sit down together, and in the course of I think three or four meetings over two days, get to the point where, when they're talking about eliminating intermediate range ballistic missiles in Europe, Reagan says something like, "Well, why don't we just get rid of them all?"

And Gorbachev startles and says, "Wait, what? Get rid of them all? Is that what you said?"

"Yes. We don't need the damn things. Let's get rid of them all."

Gorbachev says, "Mr. President, you've just said something very historic. Are you proposing that all the nuclear weapons in the world, we should move to eliminate them?"

Reagan says, "Yes. I am."

And then he has this wonderful image. He says, "You know, Mr. Gorbachev, ten years from now we should be coming back here to Reykjavik to destroy the last remaining ICBM in the world."

"I would be so old," [Reagan] said, "you wouldn't even recognise me. You would still be a relatively young man. But we would tear the thing down, and then we'd open a bottle of champagne and toast the world."

It's really a very charming moment. But Reagan has in the back of his head this thing about, "I must have a backup to a treaty." So when he goes back to get a final nod, if you will, a final discussion with his staff, a kind of vote, George Schultz, the Secretary of State, says, "Mr. President, that's the best offer we've ever had. Take it."

But Richard Perle, clever man that he was and still is, I suppose, said, "Mr. President, if you agree to this deal, Congress won't want to support your SDI program. They'll cut the budget to zero, and it'll fall away."

And Reagan thinks and thinks, and goes back and says, "No, I can't agree."

And they're both, at that point, very angry at each other. You can see it in the picture of the two people coming out of the front door at the Hofdi House. Gorbachev is looking down, looking very sad, and Reagan is just red in the face, the Irishman that he was.

But everyone understood within a day or two that really this was the beginning of a real breakthrough. George Schultz told the President later, "This is more than we've had in 25 years of negotiating — eliminating all the nuclear weapons in Europe and so forth." And in Asia. Both. So it, in many ways, was the beginning of the end of the Cold War. There are a lot of markers that one could mention; the wall coming down in Berlin, and so forth.

But I think of this as the moment, because for the first time both leaders realised that they didn't need to chase each other around with nuclear warheads.

WALKER: Given how committed Reagan was to the Strategic Defense Initiative, was any kind of compromise plausible, and what would that have looked like?

RHODES: Well, the problem with the Strategic Defense Initiative, first of all, was that no one had yet figured out how to do it. Edward Teller's vision was that you would put some nuclear bombs attached to an X-ray laser when you were in space — because you needed a lot of energy to make an X-ray laser. The only thing that's small enough to put up in orbit would have been a nuclear weapon. So think about it: nuclear weapons circulating the Earth with all of these X-ray lasers attached to them, that when the time came, they would be exploded, and the energy would be directed into the laser, which would pump the laser to produce very powerful X-rays, and then a guidance mechanism would direct those X-rays at the warheads, heating them to the point where they would blow up in space and not reach the United States... I mean, that is really a bad science fiction movie.

So that wasn't going to work, and there were many other ideas along those lines. But when SDI was first proposed, the scientific community's response basically was, "Oh my God, a lot of new money from the Defense Department to do a lot of good science with." They understood that it would be generations, if ever, before you could come up with something that would actually work. From the Russian point of view it was even worse because they didn't know if the United States would ever do such a thing or not. But they did see that we were spending untold amounts of money on it. And from their point of view that was a sign that maybe there was something to it. Their science was never quite up to ours, particularly in terms of technology related to computers.

So they didn't know, but they didn't want to know, if you will. They didn't want to see it up in orbit, threatening them. Because as you reduce the number of warheads, what would not work when there were 1000 warheads flying around — because you couldn't possibly shoot them all down, and you wouldn't have to leave very many arriving to destroy the major cities of this country... But when you get down to ten or five, then maybe an imperfect strategic defence, even ground-based, which is what we have now, such as it is, might do the job and protect the United States from a counterattack from the Soviet side. So they saw it not as a way of reducing the threat, but actually as a way of increasing the threat to them from the American side.

Now, I don't think it ever would have gotten anywhere at that level. There are other ways to think about eliminating nuclear weapons, but having balanced defensive systems really isn't one of them.

WALKER: So about a week before recording this, I asked you a question that you described as sneaky. And that question was: "What's the best question you've never been asked?" And you replied that the best question you've never been asked is: "Why did America and the Russians build so many nuclear weapons?" And before I ask you that, I can't help but notice that a version of that question appears on page two of the 25th anniversary edition of The Making of the Atomic Bomb, where you write, "Why 70,000 nuclear weapons between us when only a few were more than enough to destroy each other?" So why do you think you've never been asked that question before?

RHODES: Well, maybe just in interviews I've done we haven't got that far into the weeds. But it's an important question because it points to the dual-use of nuclear weapons. There is, of course, the theory of deterrence, which I think is not a very strong theory. But at some deep level, it's pretty clear that nuclear weapons are a deep threat to another country that might be threatening us. And at that, if you will, existential level, I think they do deter. I think that's evident if you look at the gradual rise of the destructiveness of war from the 18th century to the middle of the Second World War. The most people killed in one year during any war in history was in 1943, when not only were combatants and the people who lived around them being killed, but also the Holocaust was going on at full throttle, too.

Then the number of deaths per year began to decline, and at the end of the Second World War, it began to level off at around one to 2 million deaths from war per year, and it's never gone above that since. I think you have to ask what cataclysmic change occurred, and I don't see anything else that explains it as much as the appearance of nuclear deterrence.

Once the Soviet Union got weapons, too, which was 1949, after that the wars that we've had and the wars the Soviet Union had have all been peripheral wars. I mean, of course we think of them as terrible wars, and they were. But to kill one or 2 million people a year in war worldwide... We lose about 6 million people a year in the world from smoking. So in a terrible way, we've kind of inoculated the world against world-scale war at the cost of potentially destroying the entire human world if there ever were a nuclear war.

So there's this Damocles' sword hanging over our heads, but it has had the effect of removing from national powers their ultimate sovereignty, which is the ability to make war.

WALKER: So why did the Americans and the Russians build so many nuclear weapons?

RHODES: One of the reasons that the United States and the Soviet Union built so many nuclear weapons was simply that we didn't know how many were enough, and they didn't know how many were enough. In a way, it was even worse on the Soviet side. They built twice as many as we did, and that was because of their traditional Soviet socialist program, which was every factory should produce 120% of its annual goal every year. Well, that's great if you're turning up lawn mowers, but they were cranking out nuclear warheads, and they followed the same rule: overproduce. Somehow the idea was always that would be a way of showing your Soviet spirit. That sounds trivial, but I think that really was most of the reason. Plus their sense — and it was true — that they were always behind us. Always behind us in the technology, not necessarily the numbers. We're the ones, we the United States, were the ones who invented multiple independently-targetable warheads one rocket. So you get four shots or nine shots instead of just one.

But then there's the prestige factor, and I think unfortunately that's a very big part of it on all sides. To give you a counterexample, China, following a theory of a British scientist, I think it was Patrick Blackett, a Nobel laureate in England, who had said a minimal deterrent was more than enough... If you can destroy the top five cities in another country, the capital and whatever, New York and Boston and Los Angeles and so forth, in the case of the United States, that's all you need. You don't have to destroy every bridge in the country or every railroad terminal, every telephone exchange. But the military in the United States and I'm sure the same thing was true in the Soviet Union and probably in every country that's built nuclear arsenals — China. The military saw very early on that if the army, for example, wanted to have a big piece of the defence budget, they were going to have to build some nuclear weapons and justify them.

After the Second World War, the only part of the military services in the United States that was authorised to have nuclear weapons was the Air Force. And the Air Force cleverly realised very early on that if you controlled the targeting that produced the number of weapons you needed, that in turn produced the number of bombers you needed to deliver the weapons, that in turn gave you a larger share of the defence budget.

So by the early 1950s, the US Air Force controlled 47% of the US defence budget. At which point the Navy discovered that they needed nuclear warheads, too, for nuclear submarines. And the army discovered that it needed nuclear warheads for nuclear cannon or whatever. So a lot of what was going on already was internecine struggle for political control of their share of the national defence budget.

All these reasons come together, along with the feeling that having a big arsenal makes you a big country and a big, powerful nation, which is true enough in a way, as long as people don't look too closely at the risks that are involved in potentially fomenting a full-scale war.

WALKER: Just so we concretely understand what's at stake here, can you describe the mechanics of a nuclear winter?

RHODES: Nuclear winter was first conceived by a group of scientists. Carl Sagan is probably the most famous among them. When they were studying Mars, of all strange things, they were looking at the effect on the surface of Mars of the big global windstorms that occur in that place, windstorms that blow up that red dust in huge moving clouds and actually block a lot of sunlight. And they noticed that the surface of the Mars during a dust storm would drop by 10 or 20 degrees in temperature. And someone thought, "Well, what would happen on Earth if we had a nuclear war and we put a lot of dust into the atmosphere? Smoke from burning cities. Smog from burning cities, burning forests. Would there be a similar effect?" And they did the numbers. And they discovered, to their considerable horror, that there would. In fact, a full-scale nuclear war, they calculated, would drop the average annual temperature worldwide about 30 to 40 degrees, which is enough to basically freeze the world and certainly stop all agriculture throughout the world, and therefore, 90% of the human population or more would die of starvation, if they hadn't already died from the blast and the fires and the radiation of the bombs.

This very careful science was vociferously repudiated by people who believed in building more and more weapons, like Edward Teller, the scientist who was convincing Reagan of the idea of the Star Wars system. Teller always believed that the more weapons we had, the better off we'd be. And he wasn't interested in hearing an alternative. He published papers arguing that the world would actually get warmer. I don't know how he figured that, but that was his argument. So once that was on the table, it becomes even more paradoxical that the leadership around the world would believe that we should have more nuclear weapons.

And again, the military was not innocent of its participation here. The military had concluded from the effects of firebombing in Europe and in Japan in the Second World War that you could, if you concentrated the bombing enough, with incendiary bombs, start a firestorm that would be like a tornado, a chimney, a fire billowing up over a city, and just burn the place down. We did that with most of Japan, even before the atomic bombings.

But because they were made with ordinary explosives, they were limited to times when there was a high wind blowing: basically 30 miles an hour or more, which was not all that often. So the military had the idea that you could start a firestorm, but it was very dependent on weather conditions.

They hadn't really done the numbers to realise that with nuclear weapons, the nuclear weapons make their own weather. You don't have to worry about whether the wind is blowing. They'll make the wind blow. The blast that comes off a nuclear weapon is moving for a mile or two at about 600 miles an hour. So there's plenty of smoke and dust that will be blown up from that.

So therefore, once they started calculating that if they had a good system, they could get more weapons and therefore more share of the budget, they started using only blast as their calculating formula rather than fire.

And nuclear weapons are really fire weapons. They start fires. The blast area is a certain radius, bigger or smaller, depending on the bomb and where it's exploded (up in the air is best). But the fire effect is instantaneous over a large area. For example, if you exploded a 300 kiloton bomb over the Pentagon at 1800 feet, let's say. You would, by blast effect, take everything out well beyond the capital and well out to the Pentagon. But the fire effect would start fires simultaneously all the way out to the perimeter belt that's ten or 15 miles away from downtown Washington and would burn out everything that was flammable throughout that entire area. These are fire weapons. The people who died at Hiroshima, Nagasaki, were primarily killed by fire. Those burns that people had were fire burns, with the exception of the burns that were like printed patterns on people's bodies from the dark part of their kimonos, which we've all seen. Most of the damage was caused by fire.

WALKER: Wow. So let's go back to the beginning of the story, or close to the beginning of the story, and then we can wind our way back today. In 1932, Leo Szilard read H. G. Wells's book The World Set Free, in which Wells prophetically describes the liberation of atomic energy on a large scale and the creation of atomic bombs, although I think in Wells's book they're more like grenades dropped from aeroplanes.

RHODES: I have to qualify that: they were atomic bombs as he conceived them. He didn't really know what they would do, so he had them continually exploding. But he forgot to upgrade the aircraft that would carry them. So he does have bombardiers in the backseat of a biplane, throwing them over the side.

WALKER: Yeah, that's right. So if Szilard hadn't discovered that book, how likely is it he would have conceived the idea of the nuclear chain reaction in 1933?

RHODES: It's very hard to say. He was following the developing science of nuclear physics almost from the beginning and clearly, having read Wells, had some idea of what would happen if nuclear energy could be released explosively. He also in that year — and maybe this is the clue — he read in a newspaper one day (he was in London by then), he read in a newspaper that the leading British scientist Ernest Rutherford had said at a scientific conference that the idea that there would ever be energy released from the nucleus of atoms in any useful way was moonshine. Because for Rutherford and everyone else at that time, the atom was mentally conceived as a kind of a hard little object, like a rock or something — a cannonball, if you will. So they couldn't see how you could split it apart. They hadn't figured out how to do it — yet.

But when the neutron was discovered, Szilard realised that this was something that could be used to bombard the nucleus of atoms that might cause a really big result. And one of the scientists I talked to who was alive at that time said, "You know, when a neutron slips into a nucleus of a uranium atom, it's almost as if the Moon hit the Earth." All sorts of things happen.

The big change had to come with the realisation that the nucleus of the uranium atom wasn't a hard little object. It was more like a water-filled balloon. It was barely held together because it had so many protons in it — 92. And they're positively charged, so they repel each other. And the only thing that holds a nucleus together in that situation is something called the strong force. And it was kind of at its limit as the uranium nucleus got so big. They had to realise that if you dropped a neutron into that kind of object, it was going to wobble much like a balloon would wobble if you were playing with it in your hands. And in some of its configurations, it was going to pull apart like a dumbbell, at which point the two ball ends of that dumbbell would begin to repel each other. And if they configured themselves just right by accident almost, they might pull the two pieces apart, and then those two pieces would configure back into nuclei of smaller elements.

But in the process, a certain amount of mass would have been converted into energy. E = mc^2. Energy equals mass times the square of the speed of light. So that's a lot of energy to come out of a very small object. So much, someone said at the time, that one atom fissioning, one uranium atom fissioning would be enough to make a visible grain of sand visibly jump.

And then you think about how many millions and millions of those could proceed in what's — Szilard also thought of this — called a chain reaction. If enough neutrons came out in the course of the splitting process to start some more atoms splitting, then you'd have one and two and four and eight and sixteen, thirty-two; in 80 generations, you have the Hiroshima bomb.

So Szilard saw all of this kind of, but he didn't think it completely through. He started experimenting at the wrong end of the periodic table. He started working on things like hydrogen and lithium. If he'd started with uranium, he would have been there right away, which he realised later would have been a real tragedy because Hitler took power in 1933 and the West wasn't really awake yet to the risks that were involved and the dangers that were involved of a Nazi Germany powered by nuclear weapons. Once that idea was clear, then everybody jumped on it and got busy working on a bomb to defend themselves, because deterrence was one of the first things the scientists realised.

WALKER: So the chain reaction insight was sufficiently obvious that if Szilard hadn't discovered it, someone else would have sooner or later.

RHODES: Would have and did.

WALKER: Yeah, yeah.

RHODES: So it was discovered accidentally by two physical chemists, of all things, in Nazi Germany in Berlin. Just at Christmas time in 1938, they were bombarding a solution of uranium nitrate with neutrons to see they were hoping they could make some man made elements beyond the uranium atom, up in the 93, 94, 95, 96 — something there. They thought that would be the way the reaction would go.

But instead, in their solution, they got two... As they did the chemical separation of what the bombardment had produced, they were finding krypton, which is about halfway down the periodic table from uranium. What on earth was that doing there? Previously, the best scientists had been able to do was maybe knock a couple of protons out of a nucleus and produce an element one step down the periodic table or two steps down the periodic table. But here suddenly was one halfway down.

How did that happen? They were puzzled, but they were chemists. They didn't know what the physics of it was. Their physicist who worked with them, Lise Meitner, who was an Austrian Jew, had just gotten out of Nazi Germany ahead of the SS and was harbouring in Sweden at the time when they wrote her telling her, "We've got this strange burst. We don't understand what it is. How can you find this stuff in here?" And I held this correspondence in my hand at a museum in Berlin. There were tears in my eyes. It's extraordinary to see it. She was vacationing at a little town in western Sweden called Kungälv with her nephew, who was also a theoretical physicist. It was Christmas time. They decided to go for a walk in the snow. They walked around a little while. They thought about Einstein's formula. They thought about Bohr's wobbly, water-filled balloon nucleus.

And they put it all together and they realised that what had happened is that the uranium atom had fissioned. And therefore they did the numbers and they saw the energy that was going to appear. So then her nephew went back to Scandinavia where he was staying at the laboratory in Denmark. She stayed in Sweden. He went to talk to someone and tried to think of a name for this new reaction. Talked to an American biologist. He said, "What do you call it when cells split in two?" And the scientist said, "Fission." He said, "Alright, I'll call this nuclear fission."

And they wrote up a paper — this was not a secret — they wrote up a paper that was published in the prestigious British journal Nature. And there were headlines all over the world. People today think it was a big secret. And it was, eventually. But at the outset it was something everyone had been hearing about. "One glass of water, properly set up, physically could power the Queen Mary back and forth across the Atlantic twelve times," and so forth. Big newspaper stories like that. "You'll have an atomic car that you'll be able to drive around forever." No, but that's the kind of thing that was out there. So the story made headlines all over the world for the next year or so.

In fact, the Soviet scientists, who had been kept in the dark about the possibility of a bomb, realised the United States must be working one when we started making these things secret and our physicists stopped publishing papers in scientific journals. One of the Russian scientists said, "Aha! All their nuclear physicists have stopped publishing. They must be working on a bomb. It's now a military secret." Which was right.

WALKER: It's funny they didn't anticipate that and just kind of put out some tokenistic articles anyway.

RHODES: Well, there was discussion of it, but it was not at all clear that you get a chain reaction. That's why before we could build a bomb, we had to build a nuclear reactor. We had to build a controlled nuclear chain reactor to prove that such a thing was possible.

WALKER: No, I mean, on the part of the American nuclear physicists who kind of disappeared from the publication record, why the American military didn't encourage them just to put out something to mask the fact that they were working on the bomb?

RHODES: Well, you know, it was a much less sophisticated world. Everything was done by correspondence, by mail, telephone at best, and they weren't very good. So telegraph was a common way to communicate. It just wasn't a kind of network.

When the first hydrogen bomb was tested in the United States, out in the middle of the Pacific, the first thing the sailors did when they got back to Hawaii was to run to the telephone booth, call mom and say, "I just saw the most incredible explosion you have ever seen in your life." And of course, now, how would you ever keep a secret about anything?

But then, it was possible. And if you think about it's quite extraordinary: there were, in total, about 600,000 people involved in the Manhattan Project to build a bomb during the Second World War.

WALKER: Astonishing.

RHODES: Counting construction people and so forth. They kept it secret. It was never revealed until the end of the war.

WALKER: It's astonishing.

RHODES: Yeah.

WALKER: So the German bomb project didn't get very far because of a crucial miscalculation around the purity levels of graphite. Was that an honest mistake? Or was perhaps someone on the German side trying to sabotage the project and prevent the prospect of a nuclear bomb?

RHODES: This has been debated. This question has been debated ever since the end of World War II. Let me just say what it was. Graphite is a low atomic weight material that serves very well as what's called a "moderator" in a nuclear reactor: something to slow the fast neutrons down so that they have a better chance of finding another uranium atom in the uranium slugs that are plugged into the blocks of graphite. You can do the same thing with the tank of water. And that's the way our reactors work today. But ordinary water has enough impurities in it that it soaks up enough neutrons that you can't make a reactor with natural uranium as it comes out of the ground. So our reactors that use normal water are all enriched to a higher degree of U-235 in the uranium.

There was no way to enrich uranium in the beginning of the Second World War. That's one of the things we built and the Germans tried to build. So the question then was: Is there any other material that we can use to moderate the neutrons? And graphite is pretty close to water in the periodic table, to hydrogen and oxygen, looked like a good material, but it had impurities in it that soaked up neutrons.

The Germans never figured that out. For whatever reason, they missed that. And therefore, when they tried to use graphite, it didn't work. And therefore they went to the next possible material which is a very exotic form of water called heavy water which has a neutron in the nucleus of the hydrogen atom instead of only a proton. That changes its nuclear characteristics enough that it can be used to make a chain reaction in ordinary uranium.

But heavy water is a very rare substance, and the only real supply in the world at that time, besides a couple of buckets full at a laboratory in Paris which the Germans tried to confiscate, but some of the escaped Jewish scientists from Central Europe who were working in Paris put into a couple of wine barrels or something and spirited out of the country and handed over to the British... The only other real supply was in Norway at a place called Norse Hydro where there's a huge hydroelectric system big enough to do the hydroelectric separation of heavy water from ordinary water. So they had a little side plant. The big plant was used to make nitrogen for fertiliser from the water. And then this little bit of side plant would make heavy water enough for scientific research. Once we understood that British send in a mission that worked with the Norwegians to blow up the heavy water plant, which they did.

What was left then was about 1500 gallons of heavy water, which the Germans immediately confiscated. But it had to be ferried across a lake to get from Norway to the continent. And the Norwegians blew up that boat even though there were Norwegian civilians on it, in order to sink that heavy water. So the heavy water never made it to Germany. And Germany never really had enough heavy water to build a reactor larger than about half the size it would need to be to chain react.

That's what was discovered at the end of the war: that they never really got started. And there were all sorts of political games back and forth. And Hitler didn't understand atomic bombs. He loved rockets. He really didn't realise that if you put a nuclear warhead on a rocket, you had the ultimate weapon. He was delivering rockets to England with high-explosive warheads that cost as much to build as a bomber, but they can only fly to the enemy side once. The British used to laugh that it was one of their secret weapons, the V1 and the V2. Because although of course they destroyed parts of London and killed about 40,000 people, they were nevertheless a waste of money from any military perspective.

So, didn't happen on the German side. But we thought it was. They had good scientists. Even though all the Jewish scientists had gotten out, or most of them, and were now in the United States and helping us build the bomb, they assumed that if they couldn't do it with their resources, that Americans couldn't do it with their resources. That's not true, obviously. We did, and they didn't.

WALKER: Right. So the motivation, at least the ostensible motivation for a lot of the scientists working on the Manhattan Project was: "We need to get to this before Germany does."

RHODES: No question. Absolutely.

WALKER: Okay, so I have a question following on from that, Dick, which is that Joseph Rotblat was probably the only scientist to leave the Manhattan Project, which he did in 1944 when it became evident that the Germans had abandoned their bomb project. And in an essay published about 40 years later in 1985, he reflects on why all of the other scientists but him stayed. And he offers three reasons. Firstly, and I think most commonly, was just pure scientific curiosity. People just wanted to see how this played out. Second was saving American lives by ending the war with Japan swiftly. And then thirdly was concerns that leaving would adversely affect a scientist's career. Do you agree with his assessment both of the set of motivations and also their order of importance, with scientific curiosity seeming to be the most important?

RHODES: No, I think that's rather cruel on his part. I talked to many of the people who worked at the top level of the Manhattan Project and they all said the same thing. And I don't think it was Monday morning quarterbacking on their part. One, for example, had a brother who was fighting in Europe who was killed in the Battle of the Bulge. He said ever after, "I realised that every day that we in any way delayed getting to the bomb was measured in American lives and in other lives as well. When my brother was killed, I realised that if we had worked faster somehow, if we'd had a little bit better luck on some of the decisions we made, my brother might still be alive today." I think it's kind of insulting to many of the people there who really did feel that they could put an end to the war.

You know, when Robert Oppenheimer, who, contrary to what the myth of history now says, didn't run the Manhattan Project — a big, powerful army general named Leslie Richard Groves ran the Manhattan Project. Oppenheimer ran the laboratory in New Mexico where the actual bombs were actually conceived and designed and built and tested, which was a big enough job, Lord knows... When Oppenheimer recruited staff for Los Alamos late in 1942, early '43, he went round to the laboratories and college campuses around the country and would call out the man he wanted. And they'd go for a walk across the sward, and he would say, "I can't tell you what I need you for — that's secret. But I can tell you that what we're working on will end the Second World War, and may well end all war."

A lot of them figured it out from that, because they, of course, were aware that uranium had been fissioned and that there was a lot of energy there. Some perhaps did not.

But the claim basically spoke to what Oppenheimer saw as what his mentor, the Danish physicist Niels Bohr, called the complementarity of the bomb, which is to say the dark side, which they were very much in the middle of. A weapon of unsurpassing mass destructive force. But at the same time, perhaps finally a weapon that was so big that countries could not safely use it to aggrandise national power because they would risk being destroyed by another nuclear power in the process. That was the double-edged sword of the bomb. And it was that that Oppenheimer was thinking about when he recruited the crew.

So they didn't come to Los Alamos just thinking, "By God, I'm going to build the worst weapon of all time and kill a lot of Japanese." (Because by then it was pretty obvious who the weapon would be for.) They came with the hope that they could save lives on all sides — and the larger hope that somehow they might at least reduce the destructiveness of war.

Remember, war starting in the 18th century had been almost exponentially increasing in the number of deaths until 1943, when 15 million people died in 1943, both from war and from the holocaust of the Jews. By 1945, deaths were down to a couple million a year, and after the end of the war, they dropped to about one to 2 million per year and have remained there ever since.

Something brought about an enormous change in human affairs. I think the evidence is pretty good that it was the introduction of nuclear weapons into the world, making it impossible for countries to have the scale of war they used to have for whatever purpose, for whatever reason. At the price, of course, of having this Damocles' sword hanging over our heads, risking a world scale war that would basically destroy the human world. So it's a very strange business with nuclear weapons, and always has been from the beginning. From Oppenheimer's first appeal to his potential staff to today.

WALKER: Right. I guess when Rotblat wrote his reflections on the motivations of scientists in 1985, I think there was a campaign for unilateral disarmament underway. So perhaps he had an agenda there.

RHODES: Well, I should say, of course, they were interested in the reaction. I'm trying to think when Enrico Fermi said something about it — it may have been later about the hydrogen bomb — but his phrase was, interesting. "This thing is superb physics," he said. Well, it certainly was, and I'm sure they were interested. But their primary goal, the reason they worked six days and nights a week and got drunk on Saturday night and recovered on Sunday and then went right back to work, for years on end, leaving their families behind — they were isolated up on the mesa in the middle of nowhere, in the middle of a national forest in northwestern New Mexico — was because they didn't want Germany to get the bomb first. They didn't want a thousand-year Third Reich powered by nuclear weapons. And when that no longer seemed to be a risk, there was still the terrible war going on in Japan.

WALKER: There was one nuclear physicist of great consequence, who also happened to be Oppenheimer's friend, who conspicuously never joined the Manhattan Project, and that was Julian Schwinger. Do you know why he never joined the project?

RHODES: It's interesting. I'm working on a book now about some of the work Schwinger, among others, did in particle physics. So I'm very aware of him. He didn't see the point in working on something that he wasn't at all sure would be finished before the end of the war. And of course, it barely was. There's still a debate today among historians about whether or not the Japanese would have surrendered without the bomb. And I don't think you can really answer that question. But Schwinger had that sort of thing in mind. He wanted to work on something that he thought could really change the war. So he worked on radar, which was simultaneously under development at the Massachusetts Institute of Technology, outside of Boston, in Massachusetts. And he did good work there, helped develop radar, particularly in the form of the proximity shell.

Before radar, to shoot down a plane, it took a minimum of about 3000 artillery shells. You had to hit the plane, of course, to make the shell fire. And it's very hard to hit a plane flying over at 300 miles an hour with a cannon on the ground. So it was pretty hopeless until they realized that if you could make a radar unit so small that it would fit in the nose cone of an artillery shell and rigid enough to hold together while a shell expired at faster than the speed of sound, the radar could tell you when it was just near a plane, near enough to damage the plane, and that would then detonate the warhead, the shell. So particularly in 1944 and '45, when the Japanese were sending suicide bombers, kamikaze planes, attacking the ships of the Pacific Fleet as it moved closer to the home islands of Japan, they were blowing up ships with these planes. They were just flying bombs, suicide bombers, basically... The introduction of the proximity shell saved a lot of lives and a lot of ships, because they were able to shoot the planes down before they struck their target.

So Schwinger was right, the atomic bombs, whatever effect they had on the end of the war... And they did have their effect, to be sure, but they weren't very big bombs. They weren't any bigger than the fire bombing of Tokyo, which burned out about 18 square miles of downtown Tokyo. Neither the Hiroshima nor the Nagasaki bombs caused that much fire destruction. There was, of course, radiation involved, which was a different matter. But even not a lot of that in those two early bombs.

WALKER: That fire bombing, so I think that was April 1945.

RHODES: That's when it began. Yes.

WALKER: And that particular night in Tokyo, it killed something like...

RHODES: Half million people, total. Not that one fire bombing, but it continued. It was run by Curtis LeMay, who later was the head of the Strategic Air Command. Lemay was a tough engineer from Ohio in the United States, and when he got an assignment, he decided he'd make it work. We were trying to pinpoint-bomb Japanese factories, and with the wind blowing, B-29s flew at 29,000 feet, which is where the jet stream is. And no one really knew about the jet stream at the time, but they would be blown so far off course. There was one famous moment before the firebombing began when a B-29 dropped some bombs that were supposed to hit a factory about 20 miles north of Tokyo. They fell into the Tokyo Bay. And the Japanese, who could be very wry about the damage they were facing, joked for a while afterward that the Americans were trying to drown them.

So we just weren't doing the job with this supposedly pinpoint bombing. So they called in LeMay and said, "Figure out a way to bomb Japanese cities the way we did in Europe." And he noticed that the Japanese anti-aircraft cannons were designed to hit targets at 29,000 feet. They couldn't be cranked down low enough to hit something flying over at 5000 feet.

We basically destroyed the Japanese air force by then, so there weren't any fighters, much. He told the B-29 pilots and crews, "Strip out all the machine guns in the planes, take out all the armaments. We don't need them. We're going to fill our planes with high explosives to make kindling, and then with fire bombs to start fires." And once, he almost had a mutiny. They couldn't believe they weren't going to have any defensive weapons on aboard, but it worked.

And by that first raid, which I think was April 25, burned out 18 square miles of downtown Tokyo, killed at least 120,000 people, and seriously wounded another half a million from fire.

And thereafter, LeMay systematically bombed every city in Japan of more than 50,000 population, enough to destroy most of the central part of the cities. Three cities were set aside by the target committee in Washington for atomic bombing, because although were testing one of the bombs — the plutonium bomb was, of course, tested in New Mexico but in the desert, so you really couldn't see what kind of damage it would cause: knock down some cactus, kill a few rabbits. The Hiroshima bomb was never tested at full yield. We didn't have enough uranium to make more than one of them by that time. General Groves, who ran the Manhattan Project, wanted to see what the effects of the bombs were, and he chose cities that were deltas of rivers, so you could get a large flat area where the blast could run itself out as far as it would go.

And on that basis, Hiroshima was set aside for being bombed. Nagasaki had been partly fire-bombed, but it was also set aside. And there was one other city that happened to be covered with clouds on the day of the bombings, and the pilots had been instructed to use visual bombing only. So, in fact, the people in Hiroshima lived about three months longer than they would have had they been firebombed. Another one of those dark ironies of the war.

WALKER: So those cities were spared from firebombing simply because they needed a controlled experiment, basically, for the nuclear bombing.

RHODES: This sounds, by the way, really cruel. War is a very cruel business, as we know. And I think the evidence here is the only way you can call a war in any way justified at the end is if you stop when the enemy surrenders. Because there are other times and places where everyone has been slaughtered after the war is over. And we did stop.

WALKER: So I've seen various estimates, but the average age of the scientists working on the Manhattan Project seems to be mid to late 20s. There was even an 18 year old physicist who was recruited, Ted Hall, who later turned out to be a spy. How significant was the youth of the scientists working on the Manhattan Project?

RHODES: How significant?

WALKER: Yeah. In what ways was that fact important? Did it make them more psychologically malleable? Did it make them more energetic?

RHODES: Well, Oppenheimer once said, "We didn't do any physics between 1939 and 1945." And he meant basic science, of course. And there was a little bit of basic science at Los Alamos, but not very much. Most of the discoveries necessary to make these bombs had already been made. And what these guys were being used as is very high caliber engineers, scientist-engineers, if you will. Their job was to figure out... You have to get a certain amount of material. It's called a critical mass. The critical mass of U-235, an isotope of uranium, is about 125 pounds. And since uranium is an extremely dense metal, twice as heavy for the same size as lead, that would be a ball about the size of an American softball. Plutonium was even more reactive. You needed about 6 to 8 kg, which was a ball about the size of an American baseball.

But to get that, whole, huge factories had to be built. Giant reactors had to be built. The material had to be accumulated in very small quantities, step by step, as the machines got up to speed and started cranking out the material, the output from this huge collection of factories in Tennessee — one factory was a mile long; the supervisors rode around incited on bicycles, it was too far to walk — the weekly output was in a little suitcase, a briefcase that was handed to a member of the army intelligence who was in civilian clothes. He would take the train to Chicago, hand it off to another army guy who would take the train from Chicago to Santa Fe. Then it would be taken up to Los Alamos and put together with the other little tiny collections that were there, until finally they had enough for critical mass, which is the amount you need to start a chain reaction that will continue. Enough neutrons will stay inside the ball of metal to continue to find other uranium atoms and chain react. Smaller than that amount, and it loses enough neutrons out the surface that the chain reaction fails before it reaches any productive level.

There was a joke in the common room in Cambridge University early in the war, when the British were primarily working on the subject, that you would make a series of little cubes of pure U-235 and ship them over and have them delivered to Hitler as gifts wrapped in little packages, and he would be told to keep them all together. And when you had enough on his desk, it would blow up. So you have a sense you have to assemble this material. And the problem of assembling these materials was the main way that the bomb was a problem, if you will.

So [the young scientists] were the ones who had to figure out how to make these materials assemble rapidly enough that they didn't start a chain reaction prematurely, in which case they would melt down.

Famously, one of the problems that almost sunk the program occurred in 1944, in the spring, when the first big production reactors in Washington State started producing plutonium from the reactors. Before that, the only plutonium that they had to experiment with at Los Alamos came from bombardment in a cyclotron. Very small amounts, basically, but enough to work on the chemistry and so on. And plutonium has absolutely loony chemistry. Different phase states take different volumes. So you have to figure out how to keep it the same size or it gets fluffy and it won't go blow up. Anyway. That was a problem.

But when they got the first material from the reactor, they found out it was contaminated with an even rarer isotope of plutonium — 240, 241, 242 — that made it so reactive that if you fired a piece of plutonium up the barrel of a cannon... This was the way the implosion bomb worked. The Hiroshima bomb was a navy cannon, three inch bore. Some of the uranium attached to the muzzle of the cannon, the other, in the form of a kind of bullet, fired up the barrel. When the two pieces made it, you made a critical mass and it blew out. Very simple design, never tested full yield. The bomb went out as it was, because they knew it would work.

But the plutonium how are they going to assemble the plutonium? They couldn't fire it in the cannon. They didn't know. And it was really a problem. Oppenheimer almost resigned, he was so depressed by this new development. But they turned the whole laboratory around and developed another way. A whole new technology for taking a subcritical ball of plutonium, not quite enough to chain, react and surrounding it with high explosive shape charges such that when the charges went off, the explosive exploded inward toward a point instead of outward from a point and squeezed a small of solid metal to about half its previous size, which meant double, actually, four times its previous density, and that made it a critical mass and a smaller size.

And that worked, but it had to be tested. So thus the test in New Mexico before the bomb, the other one went off for Nagasaki.

So it was a very complicated business, and the scientists were superbly good at this sort of thing. They didn't work at computers. They weren't any computers yet. All the work they did in their laboratories involved the making of scale models of whatever they were building. If you wanted to build a cyclotron, you built a little tiny cyclotron first and you scaled it. You did the numbers slightly differently so that you got the same measures or a version of the measures that you would need to see if the experiment would work, then you built the full-size one.

So they were used to this. They had that set of skills in their hands, and they succeeded.

WALKER: It was John von Neumann who worked out the geometry of the implosion design with the plutonium bomb, wasn't it? Mostly him.

RHODES: Yeah, it was mostly him. It was a very complicated business. If you put an explosive charge, let's say one plug of explosive on one side of a spherical piece of metal, and you put a fuse in it and you light that fuse, the explosion wants to go out spherically in every direction from the point where the fuse ignites it. It's basically a very fast kind of burning, and anyone who's lit a log knows it starts in one place and then it spreads out. So how do you turn that around so that the blast wave, the shockwave, will go inward instead of outward?

What they did was use different kinds of explosives, some of which burned fast, some of which burned slow, and shapes that must have basically been hemispheres. I talked to the Soviets who worked on their bomb after the collapse of the Soviet Union. They said, "Well, we didn't make all that fancy stuff. We just took balls of high explosive, cut them into hemispheres, and stuck them on the outside of the bomb. And that gave us an idea of how to..."

Because if you see this explosion, there's nothing to blow outward. It's got to burn through what's there. What's there is shaped like a dome, so it starts to turn away. Then if you have another explosive sort of inside that other piece, the first piece being a kind of cap, then it can speed up the charge and make everything go in exactly the right way. And at the end of this, you have a converging shockwave. That's, in fact, what they did.

But how do you ignite 32 points around the sphere simultaneously? One of the scientists I got to know, Luis Alvarez, later a Nobel laureate, had to invent a whole new detonation system, because they'd tried fuses. They needed 1,000,000th of a second simultaneity on all these 32 different explosive starts. And you can't do that with chemical fuses. They don't burn that fast. We've all burned fireworks. We know how fuses work.

But Luis remembered that if you put a really big electric charge into a fine wire, that the end of the wire would just explode when you pump the charge in. So he invented a whole new technology for detonating explosives called exploding wire. It's standard now in the explosives industry. All these buildings that you see collapsing use explosives that are fired by electric wires. I wrote an article about the people who do those building constructions and watched them and got to push the plunger when they took down a building. But that was Louis technology that he invented for the purpose. That's the kind of thing they did.

WALKER: I think they had an eight month deadline for the implosion device, as well.

RHODES: Summer of '44 until August of '45.

WALKER: Yeah. I mean, it's an incredibly impressive achievement. It just strikes me as remarkable how young all of the scientists were, and here they were, charged with this enormous responsibility.

RHODES: Well, you know the joke that scientists all do their best work when they're young?

WALKER: Yeah.

RHODES: Here they were. I would mention, when we were talking about the motivation for what they were doing, one of their motivations and a primary one, was that they understood that if they were not working on this weapon, that they would be out in the front lines somewhere being shot at by the Germans or the Japanese. They appreciated the fact that they had been given protection from death, if you will, in order to do this other job. It was still a very dark time for them, and it was only Niels Bohr coming to Los Alamos with this vision that the bomb might be somehow a different world in a good way, as well as different world in a dark way, that gave them some hope. That's what they told me. That what they were doing wasn't entirely...

You know, physics before the war physics was a very exotic field. Luis Alvarez told me once that when he got his PhD at Berkeley in 1938, when he went to a cocktail party and people asked him what his degree was, he would tell them, "Chemistry."

I said, "Why did you do that, Luis?"

He said, "Because I didn't want to have to explain for half an hour what physics was."

Nobody knew what physics was. But after the war, the British novelist and physicist C. P. Snow famously said, "At the end of the Second World War, physicists became among the most important national security resources that a country had."

WALKER: Okay, some questions about Robert Oppenheimer.

RHODES: Yes.

WALKER: It's been said that the real tragedy of Oppenheimer wasn't that he lost his security clearance, but it was that he never became a truly great scientist. And some people say that's because he lacked Sitzfleisch, the German word that means literally sitting flesh. Basically, the ability to just sit down and focus on a problem for an extended period of time. So that's one view. But the other view is that he was just unlucky, because the work that he did on black holes was Nobel-quality work. It's just that it was experimentally verified only after his death, and obviously the Nobel Prize isn't awarded posthumously. So which view do you lean towards?

RHODES: It's interesting, I think both views have their relevance to who and what he was. He was someone who was very broadly based in physics rather than deeply based in physics. And I think that was a consequence of his childhood arrogance about needing to know everything. He never wanted anyone to one-up him about anything. He was invited by the geological Society of New York at the age of 14 to come and give a lecture. They didn't realize he was a teenage boy because, of course, he wrote superbly clearly and so forth. But that sort of thing, which was one of his signs of his deep insecurity as a human being. He really did have a kind of disordered identity, for whatever reason. I'm not quite sure I know why, except he grew up Jewish in New York and even though New York is a pretty welcoming place for Jews, there was still plenty of anti-semitism in America. He certainly experienced it at Harvard.

But there was also just simply the fact that, like many scientists, he did his best work as a young man. The work that would have led to a citation, probably, for black holes once they were physically identified, rather than simply theoretically proposed — which is what he and one of his graduate students did; they described a collapsing sun on such a scale that it would, once it finished collapsing, basically not release anything, including light... So there you are. That's the Black Hole. Named later by John Wheeler. That was 1939, when that paper was published. The glory days of quantum physics, if you will. And he was in the middle of all of that and did some very interesting work all over the place.

But he was someone who always had to be on top of everything. That was one of the reasons he could be so cruel to other people, because if anybody made the slightest mistake in one of his classes or in conversation, he would jump on them and rather coldly put them down for it. Hans Bethe told me that.

Hans Bethe was one of the great scientists of the 20th century. Bethe was the guy who figured out how the sun works, and it's a thermonuclear system of a certain kind. Bethe told me, "Well, you know, Robert could be so cruel."

"If you said something stupid, he would call you out on it," Bethe said. "And we all say stupid things. I certainly do," he said, "and he called me on it."

"But," he said, "[Oppenheimer] was like that before Los Alamos, and he was like that after Los Alamos, but he wasn't like that at Los Alamos."

And I think therein lies an interesting discussion of what made Oppenheimer such a great lab director.

But just to stay with this other part for a moment, he was someone who wanted to know everything. Rabi said that about him — Isidor Rabi, one of the other Nobel laureates in the story. Rabi said he wanted to know everything, which is why he taught himself Sanskrit in order to read the Bhagavad Gita in the original. He wrote poetry. He was widely knowledgeable about art. Not surprisingly, his family had original Impressionist paintings in the apartment where he grew up in New York, which is, when you think about it, really startling, to imagine that there would have been a van Gogh in Robert's bedroom.

So he tried to be on top of it all. And there, I think, the Sitzfleisch comes in. Rabi, who won a Nobel Prize, told me at one point, "He just couldn't sit down and focus on a problem as much as you need to do to solve it. He wanted to be sure no one would catch him out."

So, on the one hand, that probably kept him — that in the accident that black holes weren't really identified till after he died — probably kept him from winning a Nobel Prize.

But on the other hand, it made him a scientist of a certain kind, a very great teacher, even though most of his graduate students would take his course twice because they didn't really understand it the first time, the way he explained it. And he got a lot of the numbers wrong in the board, by the way, which apparently a lot of theoretical physicists do. And later, as the director of the Institute for Advanced Study in Princeton, New Jersey, which he ran as an institution that opened its doors to a much wider range of people than it had before. And as an advisor to the government he was superb, until he said the wrong things to the wrong people and got himself canned by having his security clearance lifted, which basically threw him out of government — because if you didn't know the secrets, then you didn't know what was going on. So a lot of different things come together.

But I think it's best to think of Oppenheimer as an actor, as many people with insecure identities can be. How many actors have we seen over the course of our lives who seem to be somewhat — what to say? — mousey, sort of fuzzy as human beings, but they're wonderful when they take on a role? He took on the role of being lab director at Los Alamos.

I interviewed Edward Teller early on in my work on this book, and Teller by then, was not talking to anybody he perceived to be potentially a critic. He had reached the point where if someone wanted to interview him for television, he would say, "How much actual airtime will my statements get?" And they would say, "Well, I don't know. Three minutes." And he would say, "Alright, you may have three minutes of my time," hoping that they wouldn't be able to edit him to make them look bad.

So he just about threw me out of his house. But he did say, "Ask me three questions." So one of the questions I asked him — and it was all I needed for that whole terrible experience of this old man shaking my very own book at me — was: "Was Robert Oppenheimer a good lab director?" And Edward Teller, probably Oppenheimer's worst enemy, said, "Robert Oppenheimer was the best lab director I ever knew." And I remembered something Eisenhower had written in one of his books. He said, "I always admired Hannibal among all the classical figures, because Hannibal's stories come down to us only in the works of his enemies."

WALKER: Wow. Yeah. So if Teller is saying it, there must be something to it.

RHODES: Exactly.

WALKER: That's fascinating. Okay, there are a few different questions I could ask at this point. So we'll come to the question of Oppenheimer as a lab director, but do you think if he had the right scientific collaborator, he could have been a truly great scientist? So maybe working with a partner who had Sitzfleisch, he could have done that great work? I guess I could think of maybe a couple of possible candidates. Freeman Dyson wrote a review several years ago for the London Review of Books about the Ray Monk biography of Oppenheimer. And Dyson pointed to Wheeler and Zwicky as two people who, whilst being close to Oppenheimer, were never really treated seriously by him scientifically, but whose ideas could have been very complementary to his.

RHODES: Wheeler especially.

WALKER: I wonder whether maybe he would have benefited from the right collaborator, and if so, why he wasn't able to find someone.

RHODES: These accidents of history. I don't know. Robert Serber, came very close in his work. I mean, many of these guys have told me stories about how close they came to getting a Nobel. Take that for what it's worth. But Bob told me about a particular scientific theory that was developed that he shared with the man who finally did put it on paper. And I asked Bob why he didn't, and that man got a Nobel Prize. I asked Bob why he didn't, and he said, "I wasn't quite confident enough." So although Serber might have been someone who could have worked with Oppenheimer, it's kind of hard to imagine Oppenheimer deferring in a way he would have.

On the other hand, Oppenheimer's primary work as a young man was with Ernest Lawrence, the inventor of the cyclotron and the developer of a number of very powerful particle accelerators that led to various discoveries. You'd like to think of a perfect world where something that Lawrence was working on might have been something that he and Oppenheimer could have done together. It just didn't happen that way. Who knows why.

It's such an almost accident. Science works by people noticing little side effects that no one else really noticed and thinking, "I wonder if there's something there?"

There's a famous story around the discovery of X-rays. There was a scientist who... X-rays were discovered when people were experimenting with cathode ray tubes, which are basically like the tubes that used to be in television sets. If you run a beam of electrons through a cathode ray tube and the electrons hit the glass front, typically that will produce a burst of X-rays. So if you're messing around with cathode ray tubes, you're getting X-rays out one end. All you have to do is have something that detects them.

So the assistant to this British scientist came to him and said, your cathode ray tube is fogging all the film we got in the closet in this room. And he said, "Well, move it," and therefore became someone who didn't discover X-rays. Someone had to have a piece of film, or some sort of screen across the room that would pick it up, and that's how it actually happened.

Or to give you another version, everyone I talked to who was present when the word about nuclear fission reached Berkeley, Alvarez and others all said to me — Glenn Seaborg was another one — they said, "I just kicked myself." It was, one of the scientists later called it, "an overripe discovery."

When they heard about it, Alvarez was getting a haircut. He told the guy, "Stop!" Pulled off the cloth, ran to his lab, pulled some equipment off the shelf, set it up, and as he told me, "I discovered nuclear fission." But two days late, unfortunately.

Glenn Seaborg, who later was the discoverer of plutonium, was in a funk. He was a very ambitious man, and that he missed it... He walked around the Berkeley campus for the next two days just with a grey cloud around him he was so unhappy. So sometimes it's just a matter of... I mean, it's amazing when you think about it, how many scientific discoveries, especially in the 20th century, have been made almost simultaneously in two totally different places at the same time. But it happens quite a lot, and it just tells you what a fine cutting edge there is to the moving frontier of new science.

WALKER: Yeah. And so many little, sometimes seemingly very mundane pieces kind of have to come together, and then suddenly something seems very obvious in hindsight.

RHODES: Oh, yes. Always.

WALKER: So. Oppenheimer as a lab director. I guess there are a few dimensions to this mystery. You've mentioned one, which is that he was a different person while he was lab director than he was either before or after that role. I guess another kind of dimension to the mystery is that you could view him as a very cerebral kind of person. He was theoretical. He wasn't a great experimentalist. He was in his ivory tower at Berkeley. And then suddenly he descends into this role that sees him leading thousands of people in this lab. So, okay, two parts to this question. One is, what made him such a great lab director? I'm sure he was smart, but was there some other unique attribute or set of attributes? That's the first question. And then the second question is, was there a period of transitioning, or becoming a great lab director? So how much of it did he have to learn, or was he exceptional almost from day one?

RHODES: I think Oppenheimer had two broad qualities that made him a very exceptional lab director, Edward Teller's "the best he ever knew." One is this breadth of knowledge that he cultivated in order to be on top of all things at all times. He would walk into a room and someone had just figured something out relevant to what they were doing, building bombs, and maybe they'd reached a point where they were stuck. Oppenheimer would just pick up from there and right off the top of his head, walk through what they just figured out, and then take it on forward.

I guess he must have read all the journals. He must have talked to everyone all the time about what they were doing.

I know even when Teller decided he didn't want to work on fission bombs at Los Alamos, that he only wanted to work on the hydrogen bomb — even though you couldn't make a hydrogen bomb until you made a fission bomb, you needed the fission bomb for a trigger for the hydrogen bomb... Oppenheimer just let him loose and said, "Fine, Edward, you do what you want, and every now and then come in and let's talk about it." So that's the way he kept on top of everything there.

That's one aspect of it, which is knowing what's going on, keeping your eye on the ball in terms of what the goal is, because it's really easy to wander off somewhere when you're doing all this science. And I'm sure there was a lot of that he had to rein in and pull back.

I know when Rabi, who was one of my favourite people, who was working on radar in Massachusetts, when someone would come in with a new idea, he would say, "How many Germans will it kill?" That was always his question. And if it wasn't going to kill Germans, he didn't want to hear about it. "Save that till after the war," he'd say.

So there's that aspect of being a good lab director: knowing what's going on and being able to phase that into the larger goal of the laboratory.

The other side — and Oppenheimer had this surprisingly superbly considering how difficult his own personality was — he really was psychologically astute. He was very good at reading people. He was very good at understanding what was the problem for a person who might come into his office and say, "Robert, I'm going to quit. I just can't take this anymore." That was the aspect of him that led him to be someone who read literature and studied Sanskrit and read the Bhagavad Gita and so on.

To give you a parallel example, when he arrived at Berkeley around 1929, 1930, he really didn't know anything at all about what was going on in the world. He just wasn't interested. And then his students started turning up with not enough to eat. One of them told me that he was living on canned cat food if you can imagine anything more disgusting to eat for your meals. But Oppenheimer discovered poverty, and he discovered the Depression, and he discovered the Nazification of Germany and Europe, while at Berkeley. He was a wealthy man. He had at least 100,000 a year income at a time when that was closer to a million a year. So he was able to spend quite a bit of money, which he did, helping get Jews out of Europe, helping his students in indirect ways, taking them out for big feeds at a restaurant over in San Francisco. They'd ride the ferry across. There was no bridge at the time. Just generally becoming aware... That's when he toyed with the Communist Party, his girlfriend, who was the daughter of a faculty member at Berkeley — anti-semite faculty member, by the way — his daughter was a member of the Party, and was having all these meetings at a time when communism in the United States was all intertwined not with the Soviet Union, but with the depression and with the sense that something was wrong with capitalism if 25% of all the people in the United States were out of work. So he got involved in all of that.

And as Rabi said of him later, "Robert was the kind of man who, when he got interested in something, moved right to the centre of it." And the centre of it was helping everyone. And that added to what he brought to his work at Los Alamos in keeping the thing together, in helping people through their problems. It's a deep irony because his wife Kitty was an alcoholic, and a mean and vicious alcoholic.

I asked Hans Bethe, who is one of the most equitable people you will ever meet in your life, a real sweetheart of a man — I asked Bethe if Kitty was as difficult a person as people said she was, and he looked at me and said, "Kitty was a bitch." I was shocked. Never heard Bethe say anything like that before.

So, despite his troubles at home, let's put it that way, he was able to play a role, something he always did. Rabi again, who was close friend of his, said, "Robert always played a role. Most people were bothered by it. I didn't mind. It was fun. It didn't get in the way of our friendship."

But Rabi was a very confident man. So he'd grown up in the Lower east side of New York and lived on the streets and really worked his way up to a Nobel laureate level, a brilliant scientist. And he helped Oppenheimer develop some of the big programs after the war that never got off the ground to eliminate nuclear weapons before they started into a big arms race. So Rabi was an important figure there.

But he understood Oppenheimer very well, and he was himself a practicing Jew. So for him, well, he said once of Oppenheimer — he said this at the security hearing — he said, "You know, Oppenheimer reminded me of a friend of mine from my childhood of whom it was often said that he couldn't decide whether he wanted to be president of the Knights of Columbus or B'nai B'rith." He said he was a certain kind of American Jew in that time and place.

They were German Jews who had come over in the 19th century, before the big population of shtetl Jews who came out of Eastern Europe early in the 20th century. They were polished. They had made money in Europe. And as I said, his father was quite wealthy. His father was wealthy because he manufactured linings for uniforms, and the First World War made him quite rich.

Oppenheimer was trying to find some way to contribute to the war, and one of the ways he discovered was to help General Groves understand the science. He became, he said, Groves's éditeur créatif or mon cahier. He was the one who Groves turned to for an explanation.

Groves was a brilliant engineer. He'd gotten his engineering degrees at MIT as part of the Corps of Engineers of the US Army. He knew plenty, but he didn't know physics. So he needed someone like Oppenheimer. And in those exchanges, I think Groves saw Oppenheimer's gifts.

Because no one in the scientific community agreed with Groves. They were sort of shocked and even horrified that Groves would think of Oppenheimer to run the laboratory where the bombs are going to be designed. I mean, he was a classic, they thought, theoretical physicist who, if he walked across a laboratory, would break some of the glass equipment.

WALKER: Well, let's talk about Groves then.

RHODES: Yes.

WALKER: Because I feel like he has become underrated compared to Oppenheimer in the decades since the Manhattan project. Without Oppenheimer, could the Manhattan Project have succeeded? And without Groves, could the Manhattan Project have succeeded?

RHODES: Without Oppenheimer, I don't know if the bombs would have been ready before the end of the war. Because the thing that triggered the final surrender of the Japanese was the Soviet forces entering the war on the Eastern Front, on what was supposed to be the 15th of August, 1945, invading Manchuria, where the Japanese still had about a million men on the ground with about a year's supply of ammunition. So if that had all fallen out, as it might have, as in fact it did, then maybe the bomb wouldn't have been ready without Oppenheimer.

But there's absolutely no question that without Groves, the whole thing wouldn't have happened. There was no one like Groves. Groves, when he was given the assignment in '41, I believe, by his superiors at the Corps of Engineers, interrupted the meeting and said, "I'm sorry, I have to get going," and walked out. The generals who told him what he was going to be doing thought, "Where the hell is he going?"

Where he was going was to Oak Ridge, Tennessee, to buy up the land to start building the factories that were going to enrich the uranium. He didn't even wait, and he would lay out a factory floor before he even knew what was going to be operated in that factory. He'd have the concrete poured. He'd sort of estimate how big a factory he needed and get going.

He, unlike, I think, almost anyone else might have done, decided that if there were four ways to go at making these materials, plutonium and uranium, and we weren't certain which one would be the most successful, then let's build all four.

He went to the guy who ran the industrial part of the Second World War and threatened him with oblivion if he didn't give him the highest priority for materials of any operation during wartime.

I mean, if they needed a ball of solid gold, which at one point they did, it would arrive the next day, from wherever it was manufactured. They needed an enormous amount of copper to make the wires for the electromagnetic separation system that made quite a lot of the enriched uranium for the bomb. Well, copper was being used to make bullets. There wasn't enough copper. So he thought about it and thought, "Well, this operation is not going to last after the war. We're not going to be building any more bombs after the war." (He was wrong about that.) And he thought, "What can I use instead of copper?"

He thought, "Well, there's a lot of silver at Fort Knox. It's just sitting in a vault up there." So he ordered tons of pure, coin-grade silver from Fort Knox and used it to make the wires and the bus bars for his isotope separation systems. And at the end of the war, he had it all pulled out and weighed by the troy ounce and shipped back to Fort Knox. And they were missing, I don't know, a kilogram or two.

An American writer who I talked to once said something about people who know how to get the spam to the front lines. I've quoted that line many times, and young people no longer know what that means since spam to them is something you find digitally. They don't know it was cans of spiced ham that was used as a common food stuff and still is in Hawaii. But my friend said, "He was the kind of guy who knew how to get the spam to the front lines."

WALKER: Got shit done.

RHODES: Groves was that kind of person. He knew how to make things happen, and he did. He simply did.

WALKER: What was the single most impressive project management feat that he pulled off? Was it the silver thing, or something else?

RHODES: I think in terms of just sheer sort of glory, sheer sort of chutzpah, it was that silver thing. Who else would think of that?

WALKER: That's a great story. The other really impressive thing about the Manhattan Project — and you alluded to it, Dick — but the impressive thing about the Manhattan Project from a project management standpoint was the parallel approach where they tried a lot of technological avenues in unison. But not only that, they were willing to combine those tracks or abandon them or even resurrect ones that they'd kind of tried and abandoned earlier. I think they call it the "parallel approach" in project management.

RHODES: They probably do. Groves was right to decide to try every method that the scientists had conceived of to make these materials. They were extremely exotic materials. Think about this: in natural uranium, as it comes out of the ground, one part in 140 is an isotope called uranium 235. All the rest of that massive material will be uranium 238. Physically, they're identical. The only physical difference is a very slight difference in mass, weight. Other than that chemically, if you tried to separate the two, you can't. They're both the same element.

So if you want to enrich the uranium in U-235, which by the summer of '39 had been worked out to be the actual chain-reacting material in natural uranium. Natural uranium, or I should say uranium 238, will fission with very high speed neutrons. So when we built our first hydrogen bombs, the casings for the hydrogen bombs were made out of U-238 because it would, with the kind of explosive neutrons coming out of a hydrogen explosion, it also would fission.

And you'd have what came to be called: fission (the trigger, a little bomb), fusion (the hydrogen reaction), fission (the casing). And later on they made the casings out of pure U-235. So you really had a bomb.

But how do you get these two things apart? How do you separate them in a way that allows you to enrich the natural uranium from one part in 140 to 90% U-235? That's a big transformation.

The only way you could do it was, well, you can do it electromagnetically. You could do it by diffusing a uranium gas through a very fine filter, and the heavier U-238 would not go through the filter quite as fast as the U-235. So the gas that emerged on the other side of the filter would be slightly enriched in U-235. And if you did that about 10,000 times, building a factory the size of an oil refinery, over and over again separating these two deliveries from the system, you could slowly enrich the enriched component up to where you wanted it.

And that was the mile long factory that people rode around in on bicycles.

Plutonium was such a gift once they discovered it because it's chemically different element, so you can chemically separate it from the uranium in which it is bred in a nuclear reactor and therefore make it faster. So we had two plutonium bombs by the 10th of August, and one uranium bomb. Well, that had already been exploded. So we had three bombs at the end of the war, basically.

So all of these different possibilities had to be explored in real time while you were building the factories to make them happen.

Glenn Seaborg, who was a great chemist, scaled up plutonium from his first almost invisible speck that he made by particles from a cyclotron bombarding uranium, kind of like a really miniature version of a big reactor. He did the chemistry using miniature equipment. I mean, a little balance that was made with a horse hair and two little tiny cups, things like that, where the balance was inside a glass container so your breath wouldn't blow it away. That's the kind of scale he worked on to establish the chemistry of plutonium, which has a really wonky chemistry.

And from that, they scaled directly up to these huge they called them "Queen Marys", because the separation plants, the uranium coming out of the reactors, was, of course, highly radioactive at that point, full of radioactive isotopes that had been created in the chain reactions so they couldn't be handled by hand. So they built these giant canyons made out of concrete and steel. And it was all done by remote control using television. They even trained the guys who built the chemistry systems inside these Queen Marys, by building the systems in the big building by remote control.

So they learned how to run the remote controls, and then they did all the separation, pouring the material in big buckets from one side to the next, and did their uranium separation to get their little bits of plutonium out. And once a week, this little bit of plutonium would be carried to Los Alamos in an ambulance just as disguise.

So, once again, they were getting little tiny bits of material out of this vast amount of material. And someone had to figure all that out and scale it at the same time. It's really quite remarkable what they did. I don't know if anything... I mean, it doesn't even compare to something like the moonshot, except in cost. Cost about the same: 2 billion in 1945 dollars, 20 billion in moonshot dollars. In the middle of a world war. It's really extraordinary.

That's how much everybody trusted the scientists to be telling them the truth. Stalin didn't start working on the bomb until Hiroshima. When heard about what happened at Hiroshima, that's when he said... Because before that, he didn't trust his scientists to be telling him the truth. He thought maybe the Americans were giving them disinformation, and since they didn't want to have to go get shot at, they were lying about it. So it was only when he had evidence that it really did the bomb worked. So they didn't get there. The Germans, similarly, never quite put it all together. We did, fortunately for us.

WALKER: I have some questions about the Manhattan Project generally. So Oppenheimer and Groves — well, particularly Groves — weren't designing a factory for repeatable innovation like Bell Labs. The Manhattan Project had a very specific purpose with a defined endpoint. So I'm curious, if you've thought about this, Dick, how much of the organisational culture and project management approach they created with the Manhattan Project was generalisable, and how much of it is just irreducibly specific to the contours of that particular project?

RHODES: I think the scientists who were working in all these various places generally believed that when the war was over, they would no longer work on atomic bombs. I think it's abundantly clear that Groves did not think that was the case, that he, in fact, understood that the army was going to want some bombs after the war. He was an army guide. His father was an army guy. His grandfather was an army guy. So he understood the military perspective on this tremendous new weapon. Whatever else it was, it was orders of magnitude bigger than anything anyone had ever come up with before.

So there was a point where they had to make a decision about whether they were going to stop working on one kind of isotope separation long enough to switch to another kind at the price of delaying delivery of the material for a few weeks. And Groves made the decision to do so. I think, if I remember correctly, that was one of the reasons Rotblat realised that this was not going to end with the end of the war. At least one of the scientists did, and kind of backed away at that point. I don't mean they left the project, but at least they saw that this was going to be a plague to the world forever now that it was around, which they should have known. But I can't tell you how many of these guys told me, "You know, it was almost a spiritual calling to be a physicist before the war." That business about "nobody even knows what a physicist does." They felt that way, and they were the more shocked to find themselves working in weapons, particularly this weapon.

So it's hard to say how much. Certainly I know that the plant that separated enriched uranium, the big isotope separation plant, was the most automated plant yet built in America up to that time, probably anywhere in the world. That's why there were these few supervisors riding around on bicycles. But it ran itself pretty much. So I don't know. I really don't know the answer to that question.

WALKER: Your book's a lovely history of physics in the early 20th century, and as you describe in the book, it had this kind of character of almost being like a guild. I wonder how much of that was just imported successfully into Los Alamos. Which meant that they didn't really have to start from scratch. All those kind of like networks, those social networks, existed already.

RHODES: Well, they were cut off from communication to the outside world, to be sure. But they knew each other. The European scientists in particular were all old friends. I mean, until Oppenheimer and a few others came back from their graduate work in Europe around 1930, everyone went to Europe to learn physics. There was not any physics of consequence going on in this country at all. It was all British. And particularly German. Most of the great physicists of that era were in Germany. Quantum physics was Danish and German and French.

So they were used to working together. They were used to an international collegiality. And it was from that idea at the end of the war, in part, that people like Oppenheimer and Rabi and Bohr conceived of a possible way to have a world without nuclear weapons and without war. And that was to internationalise everything connected with the production of weapons, starting with the mining and going from there to the manufacture of the materials, going from there to the construction of the weapons themselves and so forth.

That was the proposal that, with Oppenheimer leading a committee called the Acheson–Lilienthal Committee, was prepared for the United Nations in late '45 and '46, which, unfortunately, was then taken over by a politician. And he changed it around a bit in a way that was unacceptable to the Soviet Union. I don't think the Soviet Union would have accepted anything that prevented them from getting the bomb, because the idea of the world with only one power with nuclear weapons was simply unsupportable. We wouldn't have accepted it for a minute. And neither did they. But once they had the bomb, then who knows?

Rabi made an effort in 1950 when the question came up of going for the hydrogen bomb, after the Soviets got the bomb. "So maybe this is a time when we could sit down with the Soviet Union and go through this once more, before we go to the hydrogen bomb. Maybe we could both agree not to build hydrogen weapons and go up another order or two of magnitude and destructiveness."

But President Truman was listening to his military guys and they said, "No, the Soviets got the bomb. The balance is thrown off. They've got two million men on the ground in Europe and the bomb now. We've only got the bomb. So let's build a bigger bomb. Maybe that will make balance things out again." And off we went.

WALKER: Were there any important scientific discoveries made by the scientists at Los Alamos in their spare time? So, the Manhattan Project is bringing a lot of scientists together into close proximity, and they have the opportunity to exchange ideas, which is kind of the lifeblood of science. Did any scientific fruits other than the bomb fall out of the Manhattan Project?

RHODES: They didn't have any spare time, first of all. They were working six days and nights a week. Saturday night was devoted to square dancing and getting drunk. Sundays were devoted to hiking around in those beautiful hills and mesas around Los Alamos, looking at old Indian engravings and kivas and so forth.

There were some cross sections measured. A cross section is a probability of something happening on a nuclear level. What is the likelihood that this material will fission if hit by a neutron? That's one of the measures they did.

But again, Oppenheimer said, "We didn't do any physics from '39 to '45." There was a war on. I don't know. I mean, I don't really know enough to know. But I've never heard anyone say, "We made a great breakthrough."

What did happen, and in a way set the stage for what followed, is that a lot of really wonderful machinery was put together, including in the radar world as well. They made it possible after the war when governments were grateful to the scientists for what they'd contributed to the war, they could go to Washington or probably London and say, "Can we have a billion dollars to build a new cyclotron?" And the answer was, "Sure, you can. You did a good job. You may have that money."

And really the whole development of the big machines of science came after the war. And until the 1960s, as far as I can tell (I'm writing a book about this right now), scientists were able to go to their governments and say, "Give us the money, and we want to play with it. We want to see if we can find X exotic particle." And the answer was, "Sure."

Then things got a little dicier, and science began to get a bad odour among the hippies of America and elsewhere, and the government kind of cut them off. But by then, they were rolling in it.

It's still an interesting question, and one I'm exploring right now. Why do we spend $20 billion on a giant machine 17 miles in circumference, in order to find something called the Higgs boson? Which is an interesting particle — it gives all the other particles their mass. But then what do we do with that? So I don't know the answer to that question yet, but I'm exploring it. Wait for my next book.

WALKER: Do you have a publication date yet?

RHODES: No, I have to write the book first.

WALKER: Okay, fair enough.

RHODES: Probably 2025, I hope.

WALKER: I want to quickly backtrack because there's a question I forgot to ask about Groves. And then we'll come back to the general lessons of the Manhattan Project. So I'm told that the new Oppenheimer movie does a good job of portraying the importance of Groves relative to Oppenheimer.

RHODES: Good. It's about time.

WALKER: So you didn't consult to the movie?

RHODES: No, the movie was based on a biography of Oppenheimer written by two guys, one of whom is dead. It was mostly one of those authors who consulted on the movie. It doesn't mean they didn't read my book and steal whatever they wanted. History, unfortunately, is in the public domain. You can't steal someone's actual words, certainly the information. And in fairness, that's why we write books, so people have that information. But no, I'm eager to see the movie, to see what's there and what isn't.

WALKER: Well, I'm told that they do a good job of elevating him.

RHODES: I'm glad to hear it. Groves deserves it. And I think they consulted a bit with Groves's best biographer, who's a friend of mine who has the same argument: Groves never got his due.

I have a lecture that I give a lot which says the Manhattan Project is fading into myth. It's devolving down to one city, Hiroshima. One bomb, Little Boy. One person, Robert Oppenheimer. And one place, Los Alamos. And it's true. Poor Nagasaki. Nobody ever goes to Nagasaki. They got hit just as hard. So there is that.

WALKER: Have you seen Turn Every Page, the recent documentary about Robert Caro and Robert Gottlieb?

RHODES: No. I know about it. But I haven't seen it.

WALKER: There's a really cool scene kind of in the middle where Caro describes taking Samuel Johnson, Lyndon's younger brother, back to their family home and sitting him down at the kitchen table, and Caro sits behind him. And up until this point, they've had an ambivalent relationship, because Caro doesn't think he's an honest source. He was a bit of a liar and a drunk. But giving him some space for twelve months, Samuel turns a bit of a corner, and so they reunite and go back to the Johnson's family home, which I think at this point is maybe a museum or something. Anyway, Caro sits him down at the kitchen table and sits behind him and then starts asking him questions to prompt his memories. But he does it by putting him in this physical setting.

And he asks, "Tell me about your childhood and how nice your father was." And finally, Samuel Johnson opens up about the fact that they had this incredibly abusive father as children. And that is an important element in the Lyndon Johnson backstory.

But the reason I use that story is it's a neat little illustration of how an interviewer or a researcher or a writer can employ some little tactics or strategies to try and get very hard-to-find information out of a subject. I'm curious, you spoke to so many scientists in the course of writing the book. What's your toolkit of tactics for conducting interviews? Was there anything special you did?

RHODES: These men — they were all men — had given so many interviews by then. They were pretty much in their old age, and there had not yet been one big book.

I started this book around 1975 and finished it 1985. It was a tough long haul because I had to raise the money to buy the time to write the book, and that's a story all of its own. But setting that aside...

All of the basic information about Los Alamos, for example, had not yet been declassified. So the only way you could write a book about the Manhattan Project, at least at Los Alamos, was — in fact, none of the material had really been declassified — to interview people. That's what Robert Jungk did, the German writer, for his book, Brighter Than a Thousand Suns, and it's full of mistakes because people don't remember things straight.

So when I went to them, fortuitously, the government had decided to declassify an enormous amount of documentation. I mean, literally a warehouse full of documents, so much documentation that no one could hope to go through it in a lifetime. So all of us who later on were writing about the subject drew on a select collection that General Groves, in writing his memoir of his experience, had pulled aside at the National Archives and used as the basis for his book. We figured Groves knew what the right documents were and that he was going to use them for his book. So they became the basis for my book.

But I wanted to walk the ground. That's why I went to Berlin to visit the place where nuclear fission was discovered, to see the actual workbench, which is in the museum there, to get a physical and psychological and emotional sense of what happened. It's why you have to do that if you're going to do a good job, I think, in writing.

And visiting these men sitting with them. They were, with the exception of Edward Teller, they were all very welcoming. They really wanted a good book about the story. And I guess I hope my reputation among them grew as time went on. I had done a lot of writing about science for magazines up to that time. But this was my first work of full-length work of nonfiction. Before then, I'd written novels. So they kind of had to take me on...

The only trick, really, in writing about science, unless you're a specialist in the field, then I don't recommend you write about it, because you don't know what people don't know... It's like the people who try to help you with your computer and forget to tell you how to turn it on. So, similarly, I'm not a scientist. I had one course in "physics for poets" in college.

But I also have done a lot of magazine writing about science just because I was interested, because I was eight years old in 1945 and was stunned by the bomb. All my childhood had been World War II. For the first half of the war, we weren't at all sure we were going to win. Most people don't realise that, but it was terrifying. And I lived in a boarding house with my father and a brother. It was run by a German couple, and he had been a prisoner of war from Germany in the First World War in America.

So I had a very intimate grasp of the sense of the war. Plus, on every block, even though it was kind of a nice time for kids because there weren't any cars in the streets — nobody could get gas or tires, so the streets were open as playgrounds, basically. But every block had at least one window with a black flag with a gold star on it hanging in the window, which meant that someone in that house, a father, a brother, a son, had been killed in the war.

So you had this sense of something ominous in the background. It was magnified by the fact that I heard Germans spoken all the time at home. By 1945, I was as impatient as the rest of America was for the damn Japanese to surrender. And then this one thing seemed to me, at eight years of age, to have done the job, this one thing called an atomic bomb. I was transfixed by science ever after, even though I didn't study it. So I was ready to pull together, and I think I brought that enthusiasm.

The other thing I think you need when you're interviewing scientists is the ability to use their language. And that doesn't take much. You just have to read some papers. By the time I saw them, I had already read the entire sequence of papers that constituted the history of nuclear physics, starting with the discovery of the electron in 1896, I think, up to 1939.

Because they were mostly experimental papers, you could read them, and if you knew the language, which I learned, you could understand what they were about. "I took this object and put it here on a bench, and I surrounded it with this box, which I then exhausted the air from." An experiment is a series of physical manipulations of objects or gases or whatever.

So if you understand the language, you can follow what they're actually doing. And so I had a pretty good sense of what was involved in the history of their subject, and at least now I'm knowledgeable when they discussed it.

Those things came together to make it possible for them to feel that I was a credible witness. And they told me their stories, which I then was able to check against the actual documentation — all of Oppenheimer's memos, back and forth, when he was lab director and so forth — to get a really, I think, rich sense of what actually happened, rather than the sort of vague sense that Jungk had put in his book.

That's why the making of the atomic bomb turned out to be such a rich stew of stories. I had some of these guys, Nobel laureates, write me later saying, "you described things that I never knew happened," or, "I remembered it so differently, but you got it right."

And then, blessings upon them, two of the Nobel laureates whom I sent copies of the galley proofs of the book to, hoping they would endorse it, give me a little puff on the jacket, wrote back and said, "Rhodes, you got some of your science wrong here. Can we fix it?"

So I have two copies of the bound galleys of my book with handwritten corrections of the science in them by two Nobel laureates, Luis Alvarez and Emilio Segrè. So I knew the physics was right.

I mean, a lot of things came together — partly luck, partly being in the right place at the right time, partly my own personal past in terms of being interested in science — that added up to a book that really tells the story.

And they're all gone now. You can't do it again. They've all died. The last of them, I think, was Bethe back in 2005. Maybe Serber.

WALKER: When you did that exercise of reading the chain of papers in the history of nuclear energy, did you develop a broad intuition for the process of scientific discovery?

RHODES: Having read so much science translated into popular writing in the past, I really did get a pretty good feel for what was going on. To give you just one example, there's something called a Cherenkov radiation that occurs under certain... You know when you see a water-filled reactor and it's blue light coming out of it? That's Cherenkov radiation, and it's caused by particles hitting a different medium that carries them at a different speed, and it's faster than the liquid can handle — I can't quite explain it — and it makes the liquid phosphorescent.

So I described it in my book as kind of like a sonic boom. And ever since, that's what scientists call Cherenkov radiation when they're trying to describe it: like a sonic boom. And I know they picked it up from my book, so I had some feeling.

I lectured at Harvard, to the Harvard Physics Department, after my book came out. One of my delightful moments. Because Harvard's a pretty stuffy place, and I was delighted to be able to tell them the story. Afterwards, one of their theoretical physicists came up to me quietly and said, "You have a good intuitive grasp of physics." That was kind of a damning with faint praise, to be sure. But given my background, I was delighted.

WALKER: Happy to take the compliment.

RHODES: Yes, thank you. I'll take your half-ass compliment. Thank you very much.

WALKER: That's funny.

RHODES: So, I mean, anyone who wants to write about science: read the papers. They're not that hard to read. Lots of people read them.

WALKER: I feel like the first stumbling block for laypeople is just the technical jargon. But once you actually understand the definitions of the words, everything kind of becomes 80% easier.

RHODES: Yeah. I think you do have to have some maybe basic feeling for what you're doing. My daughter is a molecular biologist, and she does not understand how I can like physics. She says it's so dead. After all, she works with molecular biology.

WALKER: I was going to ask about how the decision back in 1943 in Europe to switch from pinpoint to area bombing was in an important sense a more morally important turning point than the decision to drop atomic bombs. Could you explain that?

RHODES: When people ask me how could we have bombed those Japanese cities, which people do ask today, it tells me how far we are from war that people even ask that question, that they feel somehow that bombing civilians was an evil thing to do. And maybe it was. But that's the way wars end, unfortunately.

I always say that decision really was made in 1943 in Europe. And I say that because at a certain level, it was a technical decision. Again, people don't like to think of anything so bloody as war as being based on technical considerations, but the fact is, it is. Whatever the ultimate reason why one country surrenders, and there are good arguments that it has to do more with almost spiritual decisions than it does with technical ones, be that as it may, the United States and the British were trying to bomb specific targets — a ball bearing factory that made the ball bearings that went into the production of aircraft. If you could take out that strategic material, ball bearings, then you theoretically could put down the airforce of the enemy.

Well, how do you do that? You have to have a bomb site that is accurate enough to allow a plane flying overhead to find the target and close in on the target and drop the bombs at just the right time. Remember, they are flying with the plane at 300 or 400 miles an hour. They're not going to fall straight down, they're going to fall in an arc. And the bombsight has to be able to correct for all these things. Wind drift. How fast is the wind blowing? The bombsight has to have that information.

They were, in fact, the computers of the day. They were analog computers. They were made up of gears and switches and so forth. But they were computers and they were highly protected and top secret.

We had a bombsight that was supposed to be able to hit a pickle barrel in the middle of a desert from 30,000 feet. That was what they said, and it could in the middle of a desert.

But in order to line it up, to get all these different parameters fed into the computer and get it organised to be able to drop the bombs at just the right moment, the plane had to fly in a straight line for three minutes.

Now think about all the antiaircraft fire that's coming up from German cities to try to blow up that plane before it drops those bombs. No one in his right mind was going to fly their bombers in a straight line for three minutes. So what happened was they jigged and jagged and the Norden bombsight, as it was called — the bombs would drop in a cow pasture 5 km outside the city. Well, that wasn't doing the job, obviously.

So how do you do the job? Why did it matter? Why were we bombing the German cities in the first place? Because we didn't have any men on the ground in Europe until D-Day, until June 6, 1944, when we invaded on the coast of Normandy.

And there was great concern that Stalin, who was holding the whole war in his hands, who lost 20 million people in the Second World War just in the Soviet Union, civilians as well as combatants, might sign a separate peace treaty with Germany. And then the Nazis could pull all their fast forces out of the Soviet Union and move them to the west side and take over Europe, and then presumably move on to the United States.

So we had a dilemma. And the only way we could think of to keep Stalin signed on was to keep bombing, to show him that we had a purpose and an intent. Even though we didn't have men on the ground, we were going to continue fighting until the two sides won the war. It was a close thing. Stalin, after all, had signed on with Germany in the late 1930s and signed a separate treaty for a while with Germany while they took over Poland and so forth. So he was not the most reliable of allies to begin with.

Well, if weren't able to bomb, then what could we tell Stalin about what were able to do? What would he think? He was a notably paranoid man anyway. Witness the fact that he never trusted the bomb program until there were actual bombs on the ground in Japan.

What we conceived and the British conceived — we, I must admit, somewhat more reluctantly than the British, but then they had been bombed themselves, we had not — was to area bomb.

The theory was this: if you're bombing a factory to get those ball bearings out of production, there are men in the factory and possibly women in the factory making those ball bearings, and you kill them when you destroy the factory. Well, they live in apartments around the factory, which was the way it was set up in Europe in those days. What's the difference between bombing the factory and killing them there, and bombing their apartments and homes and killing them there? Doesn't that do the same thing? Okay, so we can expand the bombing to a larger area.

And from there, well, we can't always hit the apartments, but there are other people in the city. They're involved in the war. You can see how it sort of smeared out until it was a target big enough to hit, basically.

And then what they did was fly pathfinder bombers, three or four ahead of the big fleet, and they would drop bombs in cross patterns and start fires on the ground and mark the target — big marked target, big fire, blocks and blocks wide. And then the fleet would come in, too many, overwhelming the antiaircraft fire and drop their bombs.

It was called carpet bombing because it was kind of like rolling out a carpet across the living room floor. You started at one end of the city, wing tip to wing tip, and you bombed straight ahead from there. If you had to jig and jag and so forth, fine, no problem, you're going to bomb everything anyway.

Then they discovered fire bombing and discovered that if you mixed in some incendiary bombs with your high explosives, in some cities with the wind blowing in the right direction at the right speed, you could actually start a firestorm, kind of an open chimney that would burn out everything in the city. And the first firestorms were started in German cities, burning out everything.

The most famous one came late in the war — Dresden, perhaps made famous by Kurt Vinegar's novel Slaughterhouse-Five. Because Kurt, 18 years old, was down in a meat locker seven stories below ground with his german guards and other prisoners of war in a bomb shelter, basically, and were protected from this horror that was going on up on the ground level until after the bombers went on. And then he and the other prisoners were made to clean out the bomb shelters full of dead bodies asphyxiated by carbon dioxide monoxide, without the benefit of schnapps, which the Germans were given to make them half drunk so it wasn't quite so horrible to do this horrible work.

So we made the decision basically on technical grounds in the middle of a war, so the war wouldn't get bigger with Russia joining the German side or just withdrawing entirely and not fighting.

And it was the obvious thing then to do in Japan when the same problem emerged. You couldn't drop bombs down a pickle barrel over a Japanese city from 29,000 feet.

So it's horrible when you think of it. I wrote a book about the early part of the Holocaust that found something very similar there. And I won't go into it now, but if you ever want to discuss it, the book is called Masters of Death. It's about the Bullet Holocaust. And it was the effect of mass killing on the people who were shooting people to death, that led to the invention of the gas chamber, not because it was more efficient but because there was less trauma to the perpetrators not to have to kill people face-to-face.

So technical issues determine a war. That's why I don't think it's ever going to be a moral issue if we're in a point where someone decides do they need to use nuclear weapons or not. When Vladimir Putin threatens to use nuclear weapons if he's losing rather than lose, I think I would take him seriously, although I'm sure we've given him many reasons to think that would not be a smart idea. There's certainly plenty we could do to his country if we had to with our nuclear weapons. Nevertheless, he's facing a dilemma that I don't think he knows the answer to at this point, short of being overthrown, which he doesn't want to be.

So here we are again.

WALKER: Here we are again. So I actually want to finish the conversation by zooming out and talking about non-proliferation, disarmament and some of the broader social and cultural consequences of nuclear weapons. So if World War II hadn't happened, the Americans never dropped bombs on Hiroshima and Nagasaki, would that have been better or worse for non-proliferation?

RHODES: It's hard to say, all these counterfactuals. I don't know. But I do think the bomb would not have been built on such a hurried scale or schedule. Obviously, they would not have had to rush.

WALKER: If World War II hadn't happened?

RHODES: Yeah, right. Why would it? And yet, given the destructive force that was clear at the very beginning... It's interesting, some of the earliest thinking about the bong was done by a couple of émigré German-Jewish physicists who were marooned in Manchester, England, because they were technically enemy aliens. So they couldn't work on radar. They had to puddle around and do whatever they could come up with. And they started looking at what would be a critical mass, which had not been figured out. And based on very rough calculations, they concluded it would be about a pound of uranium, which is like less than a golf ball.

And at that point they started thinking the whole thing through, what would happen if you had a weapon this big? And a report they then wrote to the British government that got this whole thing rolling on the British side said basically that a bomb of this scale would destroy... there would be no building that could be built or other defensive structure that could be protected against such a weapon.

The only thing they said that might prevent its use by an enemy would be having a weapon of similar scale that could be threatened in return. Deterrence had already been debated at length in England during the '30s with the bomber, because the bomber looked like something as it was originally intended to be: it could jump over these horrible trenches of the First World War, go back to the civilians, knock out the production of the infrastructure for the war and material for the war — and, theory was, would then cause the people of that country to rise up and overthrow their government and sue for peace. Good luck with that.

WALKER: Naive kind of theory.

RHODES: But with that idea in mind, here they came up with the whole system of deterrence in 1940, 1939. So the idea was there. And that, I think, in turn, would surely have led governments to realise that they better build some bombs, even perhaps the more ambitious governments, that they should get there first if they could.

Because the theory was at the outset, whoever controls the bomb controls the world. Which would be true, perhaps, in a monopolistic control of the bomb or ownership of the bomb, but it certainly wouldn't be true with more than one country. Once you have that, you have a standoff, as we've seen — until the match is lit, and then everything blows up.

WALKER: Yeah. Say the Americans develop the bomb, but they never end up dropping it. Russia invades Manchuria and forces a Japanese surrender. Could that actually have been worse for non-proliferation? Because maybe people needed to witness viscerally and visually the destructiveness of these weapons to take them seriously. Or I suppose, on the other hand, maybe the image of the explosion kind of contributes to the fetishisation of the weapons...

RHODES: Well, you know, whatever Stalin believed or didn't believe about his scientists, he had at least 20 or 30 spies in the Manhattan Project throughout the war. Plus, Fuchs delivered the actual measurements of each shell of the plutonium implosion device to Stalin, indirectly, through the KGB.

I found the document when I was in Moscow at the end of the Cold War after the Soviet Union collapsed in a public library. It had been published in a journal by the KGB to show how much they contributed to the war. And as soon as it was published, the atomic scientists, who had been Soviet scientists, jumped on it and said, "That can't be published. We are going to be signing the Nuclear Non-Proliferation Treaty. You're giving away some important secrets here."

So all the journals were withdrawn from circulation in June of 1992. But I was working with a very clever assistant who was Russian, who thought, "Wait a minute." He jumped on the night train to St. Petersburg, went to the science library there, and they said, "No, comrade, that's not available." And he walked across the street to the public library and found a copy of the journal, and copied the pages and sent them to me. I never published them. I didn't think anybody needed to know how to build the exact measurements of the implosion system.

So it was out there. And once it was out there, who would not think perhaps it would be the better part of security to build the thing? Especially given what we've seen in the way of the military-industrial complex making itself wealthy and powerful and the military playing games with different branches of the service to have their own arsenal of warheads. I mean, it's a mess. Even if there'd never been anything as a result of these weapons, there still would have been all this, I think.

And I think the odds of there having been use eventually would certainly have been very real, just because until you see what they can do... I've talked to scientists who worked on the bomb who said, "I know we're only testing underground now, but I wish every five years we'd take all the leaders of the world out to some island in the Pacific and blow one off for them so they'd know what they're playing with." And there is certainly that to be argued.

WALKER: Yeah, that's funny you mention that. I had a question about that. So I guess I'm a young millennial, and I have Gen X friends who tell me that they grew up with the fear hanging over them in the schoolyard of nuclear war, nuclear winter. And to me and my friends in our generation, there was literally none of that fear. It just seems like another world, a foreign concept. And it got me thinking maybe we should resume above ground testing just to remind people what's at stake. What do you think about that idea?

RHODES: I think a demonstration. I really agree with this particular scientist. A demonstration seems to me a very good idea. Once a year.

I've never seen a nuclear explosion except on film. One of the things about the Oppenheimer film that's going to be really interesting is that I think he's going to have some real ones. I know he didn't do digital reconstructions. So at least he's going to fake one with high explosives, which will be interesting in itself.

I heard stories when they tested the first hydrogen bombs. The fourth test, I think, yielded about twice or three times what they projected it was going to. They had missed one reaction with lithium, and the production of helium and hydrogen and lithium, that scared the hell out of everybody because it was so big. It was 15 megatons. It was supposed to be 5.

WALKER: Wow.

RHODES: And I've heard stories of one of the scientists literally panicking and crawling up the beach to get away from this giant thing because who knows, the cloud runs up into the stratosphere and higher. It just gets bigger and bigger and bigger, and it looks like it will never stop. And even though they were 20, 30 miles away, 15 megatons is enough for that to happen. It's a fireball several miles in diameter.

So I think it might be a good idea.

Your generation fascinates me because there are surveys that are probably still done in the United States every year asking people what frightens them most about anything connected with living in the world. And until the end of the Cold War, number one or number two was always nuclear war. After the end of the Cold War, when the Soviet Union collapsed, nuclear war dropped down to about number 25.

And you think about that, what does that mean? People think we don't have nuclear weapons anymore. There are a lot of people who think we got rid of them the end of the Cold War. It's logical. Why wouldn't we get rid of them? What would we need them for? Who are we fighting?

One of our Secretaries of State said in 1998, when Saddam Hussein was still around, he said, "I'm running out of enemies. I'm down to Kim Il-sung and Saddam Hussein." And when you think about that, that's where we were and where really we still are. Russia now is kind of stirring again, but not directly. And I think Putin is smart enough not to want to go to war with us, given how much we expend of our national capital on military every year.

So why haven't we gotten rid of them? I think the answer to that question is basically, in the case of the United States at least, domestic politics. Which is really sad, and really embarrassing ultimately.

Our two political parties took a stance long ago — it's not just because of the present Trumpian madness that's going on in this country — but long ago took a stance: the Republican Party were the hawks, Democratic party were the doves. And what that meant basically was the Democratic Party believed in negotiating, believed in diplomacy.

And in order to distinguish itself, and for other reasons as well, the Republican Party became the party of big military budgets. Throw more at the military, build more bombs. We don't trust... treaties are a trap — Ronald Reagan. We don't trust all that. So therefore we believe in armament.

And with that in mind, every time a Democratic president wants to sign a treaty, he finds out that he's going to have to let the Republicans spend 80-100 billion dollars to modernise our nuclear arsenal.

For what? I asked this at a conference a few years ago when a former member of the National Security Council was there and giving a talk and he looked at me and he said, "Yeah, you're right. We're speaking to the Russians in this strange alphabet of how many weapons do we have and how many do you have?" He acknowledged that there was no real purpose to it, that it was a kind of arcane, crude, dangerous kind of diplomacy, to play back and forth.

However, it worked during the Cold War. There were only two sides. And it turns out, according to some recent writing I've seen, that a dyad is a very stable structure, even mathematically. But when you bring in three powers instead of two, China, which is now arming itself with plans for about 1500 ICBMs — parity with us and parity with Russia — things get very unstable very fast. The combinations are much more complicated.

WALKER: Where did you read that, about dyads being more stable?

RHODES: I think the journal Science. The American Journal Science has some recent articles about it.

WALKER: Okay. I'll follow you up about that. I'm interested in that.

RHODES: Yeah. When I get home, I will find the reference for you and send it.

WALKER: Thank you. A lot of predictions about the proliferation of nuclear weapons have overestimated. So, for example, back in the 1960s, a lot of people thought that by the 1970s there'd be 20, 25, 30 nuclear weapon states. But today there are only nine nations with nuclear weapons. So what did those people miss? Why has non-proliferation been so successful?

RHODES: This is, I think, one of the really educational aspects of the whole nuclear arms race. To some degree, it followed from the Cuban Missile Crisis, where everything was so close to blowing up. And it was close — closer than we knew at the time, actually, because we didn't realise that Khrushchev had actual warheads on missiles in Cuba. We thought they were on their way or hadn't been put together yet. But they were. They were ready to go. Castro was even saying, "Use them. Let me use them. To hell with the United States. Blow us up. We don't care." It was really a fraught time.

I've looked at the correspondence between Kennedy and Khrushchev after the Cuban Missile Crisis. There was a flurry of letters back and forth that led pretty quickly to the decision that some kind of treaty had to be set up to prevent that proliferation from coming along.

And the Nuclear Non-Proliferation Treaty, which was finally, I think, tabled in 1968 and signed by enough parties to take effect in 1970, was a promise to non-nuclear powers that if they did not go nuclear they would be given support from the two major powers to work on peaceful uses of nuclear energy, nuclear power, basically. And another promise, which has not been kept, was that the nuclear powers would work on trying to get to universal nuclear disarmament. We haven't done that.

And for that reason, the other non-nuclear signatories are getting pretty restless and almost abrogated the treaty in 1995 when it came up for renewal. Most treaties are written for in perpetuity. Because nobody quite trusted the deal, the one signed in '68 was given a lifespan of 25 years, after which it would be reviewed and either renewed permanently or set aside.

And it was a narrow issue, which is another story. I know the man who made that happen. It was Australian diplomat Richard Butler. He went around to all the countries that might go nuclear and talk their governments out of it. It's a great story. Butler is one of your heroes. I don't know if you know that, but he is. He's a delightful man, too.

I talked to some of the people who were working on nuclear weapons in the 1950s in countries you would not believe. For example, I talked to Swedish scientists. They were well on their way to a bomb. And I said, "What did you think you were doing?" And they said, "Well, we were just going to build some small tactical warheads that would slow down a Soviet tank invasion long enough for us to put ourselves together and fight back."

And I said, "So why didn't you ever build them?"

They said, "Well, when they got hydrogen weapons, thermonuclear nuclear weapons, it would only take one or two of those to destroy an entire country. So we really didn't see the point in building nuclear weapons, so we stopped doing it."

But that sort of thing — Germany, Japan, South Korea, Sweden, Norway. I mean, you could make a huge list of countries that were looking at beginning to work toward thinking about all the possible stages of moving toward a nuclear arsenal. And mostly, I think, they decided that it was just not smart. That the proffers that were coming from the United States and the other nuclear powers, of something valuable...

There's been a general belief that once a country knows how to build nuclear weapons, it inevitably will build nuclear weapons. People to this day talk about that as one problem with eliminating nuclear weapons.

Well, no. Most of the countries that would have gone nuclear in a different set of circumstances decided, for various political reasons, not to go nuclear. So the 20 or 30 or 40 nuclear powers that President Kennedy famously said kept him up at night worrying in the 1960s never materialised.

That doesn't mean that all sorts of countries couldn't go nuclear very fast. I was in Japan some years ago. Japan has several tons of plutonium that it's separated out from its reactor material so that they could reuse the uranium.

A New York Times writer asked me in Tokyo, "Well, could Japan become a nuclear power?" And I said, "Yeah, it might take a year." So he checked in with a friend of his in the Japanese government who said, "Well, I'd say six months." So Japan is a nascent nuclear power, as many countries are.

But they don't see any political benefit, especially so long as they have the US nuclear arsenal as an umbrella for them. And we have treaties with many. South Korea kept trying to get to a nuclear point. Kissinger was sent over there by Richard Nixon in the 1970s, to tell the South Koreans, "Stop it, or we will withdraw all of our forces in Korea, and you will not have any protection whatsoever from China or anybody — Japan." The South Koreans did stop.

But then they tried again. There was a little flurry again around 2000. So they're ready to go if they ever feel they need to. And a lot of countries are. But it's politically not to advantage of most of these countries.

So what you see is those countries that have recently gone nuclear are the outlier countries, the ones that are basically world pariahs. I mean, North Korea has been working on nuclear weapons and then got there, primarily because nobody was paying attention to it. It wanted some help. It was hoping that its new benefactor would be the United States. And the only way it seemed to be able to find to get our attention was to keep moving toward a nuclear arsenal. And then, of course, when the Bush administration came in and made some very stupid decisions, called them part of the axis of evil and so forth, then they thought, "Well, what's to lose? Let's build some bombs.W Which they then did.

WALKER: So given the number of near misses, like the Cuban Missile Crisis, we've had — and I guess it's worth noting that even within the Cuban Missile Crisis itself, there were like multiple pathways for which it could have just ended in nuclear Armageddon. But given there have been so many near misses, does that mean we're in a world where we've survived only through sheer dumb luck? Or on the other hand, could it mean that, given we've got close so many times but nothing's happened, that's actually evidence for the fact that we're in a world where it's just really hard to make a mistake with nuclear weapons?

RHODES: I'm afraid the answer that I found is dumb luck.

There were some 13 possible nuclear exchanges that happened during the Cold War that were averted by luck and by pluck. The other thing is pluck. I mean, individual weapons officers risking their careers to stop something that had already been started.

The famous example is the nuclear Soviet submarine. We were dropping — we, the United States — was dropping depth charges on the submarine to get it to surface because we didn't know what it was and wanted to know. And they had nuclear torpedoes and control had been handed, as it tends to be in nuclear submarines because it's hard to communicate with submarine underwater, to the three officers who were in charge of the crew.

And two of them said, "Screw it, let's fire our torpedoes." And one of them said, "No." And fortunately, his wisdom prevailed. But that would have been like a bunch of matchbooks lined up one after the other, firing each other.

WALKER: Yeah, they needed a unanimous decision on that sub.

RHODES: Yeah. The worst one was during NATO exercise called Able Archer. We came very close to... well, actually, the Soviets came very close to believing that we were staging war games in Europe as a pretext for starting a nuclear war.

And they had planes on the runway in East Germany ready to go, loaded with bombs. And fortunately, Ronald Reagan understood suddenly that things had gotten out of hand and stood the whole thing down.

That's when he began saying a nuclear war could never be won and must never be fought. That's when he spoke to the Japanese dyad, to the United Nations, and started talking about his dream of eliminating all nuclear weapons.

So it's only by the sheerest thin film of luck and some bravery on the part of individual military officers that we have not already had a nuclear war. And anyone who knows anything about engineering knows that no machine is perfect, that it's going to fail sooner or later in some unexpected way.

We've had planes flying across the United States loaded with armed nuclear warheads and nobody knew they were on the plane. I mean, they was supposed to not be those. They were cruise missiles and they loaded them. They didn't realize they had nuclear warheads on them. They're flying around, nobody knows what they are. It's terrifying.

And yet, because they've been made so invisible... I say this a lot, because these are only machines. They're not the wrath of God — unless you're under one. They are simply machines. And machines can be taken apart. Machines can be put in separate places.

How do you eliminate nuclear weapons from the world? You walk them back. You start out by taking the warheads off the missiles and moving them to a building next to the missile silo. And then the next stage, if everybody's done that, and you've got inspectors everywhere or making sure they have, then you move the warheads down the street about 20 miles away. Then it takes an hour to launch a missile. We start out with a 30 minutes launch time to target. Now we're up to 3 hours.

You keep doing that with everybody cooperating in a totally open world — that's the requirement — and eventually you got six months. That means you've got six months for diplomacy, six months for a conventional war if necessary.

As Richard Butler (your countryman) said to me once, "Why, we could do this in a morning if we wanted to."

WALKER: Disarmament.

RHODES: Yes. By just moving everything.

In other words, delayed deterrence, but the deterrence is still there, until finally deterrence exists as it will always exist: as the knowledge of human beings about how to make these things. That's never going to leave us. That's often an argument for why we can't get rid of them.

But in fact we can. We can operate on the level of knowledge if you have what Bohr called a completely open world.

The reason he was so bent on talking to the guys at Los Alamos was to remind them that science is a model for an open world.

How does science work? Someone makes a discovery, they publish it. All the other scientists learn of it. That's a piece of a puzzle they were working on. So they work it into their research, and that leads to another discovery and they publish that.

So science works by gift exchange. I make a discovery and give it to the world, and then the world looks at it and takes the gift and uses it to make more gifts. And off we go into a world filled with magic. All the things that we take for granted, that we live with. Most of all the vaccines that keep us alive, from a time when people died in their tens and twenties and thirties in vast numbers because of epidemic disease.

So for many, many different levels, there is a way to eliminate nuclear weapons from the world. And it requires that everything be open to the world.

And that, believe it or not, is what the Acheson–Lilienthal plan that Oppenheimer worked on with a bunch of tough engineers and industrialists back in 1946 said, basically.

So the ideal is still sitting on the table waiting for people to get it. To stop, thinking, "Oh, we can get an advantage out of these things. Oh, we can build a factory and make a lot of money out of these things. Oh, if we have these, other countries won't push us around." It's just human veniality, ultimately, that has this Damocles' sword hanging over our heads. It isn't necessary.

WALKER: You mentioned Bohr, and he had this idea of complementarity, which was that the bomb represented a paradox in that it was the means of our own destruction, and then simultaneously that represented a solution for peace because of the fact that the threat of the use of such weapons would deter war. Is the Long Peace that we've enjoyed since the end of World War II a nuclear peace?

RHODES: I don't know what else you'd call it. I really don't. I know there are historians who have argued that's not true, but when you look at all the things that have happened over the years since the end of World War II, I don't see how you can argue otherwise.

For example, the wars that have been conducted since 1945 have, by and large, ended in either loss on the part of nuclear power — such as Vietnam. We lost that war. Why? We could have paved the place, wouldn't have been difficult, just dropped some hydrogen bombs all over. But we didn't. And we didn't because Vietnam seemed to have a patron in the form of the Soviet Union or China or both, and they had nuclear weapons.

So deterrence operated at a kind of secondary level, like deterrence squared. The same thing was true with the Soviet Union in Afghanistan. They lost that war. They backed off and went home for the same reason: because we were in the background, China was in the background by then. They simply couldn't take the gamble. They weren't prepared to take the gamble.

So I think if you look closely at the history of the last 80 years, you have to say, yes, nuclear weapons kept the peace. Now, could you keep the peace if there were no nuclear weapons in the world? Well, based on the notion of delayed deterrence, I don't see why not.

You'd have to have a lot of organisations and structures that maybe don't exist now, but that would be inevitable anyway. First thing that happens when some new invention is introduced to the world is everybody wants to build a bureaucracy around it. That's happening right now with artificial intelligence. I mean, our people, having made their great discoveries in artificial intelligence and monetised it, are now going to Washington and asking the senators, "Please save us from ourselves. Make some laws around this rampant technology, please. But by the way, don't make me shut down. I'm getting rich here."

WALKER: Yeah, there's some interesting possible parallels to the bomb there, which I'll come to in a moment. But just let me push back on you on the point of the Long Peace being a nuclear peace. We've spoken about how horrific conventional warfare can be with things like fire bombings. Isn't that a sufficient deterrent such that the marginal deterrence between conventional warfare and nuclear warfare isn't that much?

RHODES: But it is. The Italian theorist, I think his name is Douhet, who came up with the idea of strategic bombing, he was living in the trenches of the First World War, which a British poet once called "the long grave, already dug". The trench started somewhere up northern Normandy and ran all the way down as far south as Europe runs. It was a horrible place where millions of men died in ugly, ugly conditions.

And here is this Italian officer who thinks, "Jesus, God, how can we fight a war without having to go through this? How do you beat this system?" And he conceived that the idea of the airplane was very new then, right? 1916, 1917. How do you get around this? And his answer was, if we could fly over the trenches, if we could get back to where they make the material that's feeding this war, maybe in those circumstances we could avoid this horror that's killing all these young men.

And out of that, particularly in America where Americans who were gaga about flying, they love flying planes... The Air Force guys have always loved flying planes. It's the reason we still have bombers, truth be told, otherwise we wouldn't need them. So here they were, and they took up this cry and brought it into the military system in this country and in Great Britain and elsewhere, to Italy. Everybody started building bombers. Germany. They tested them out on Spanish Civil War, at Guernica and places like that.

So by the beginning of the Second World War, the system was in place, and it was believed generally to be enough. The question always was, could the bombers carry enough firepower to lead to the breakdown of an entire society? And the answer was, with World War II, no — not until the atomic bombs came along.

In fact, one of the reasons there was an arms race after the war is that a man who was very high up in the US State Department was sent, as part of the Strategic Bombing survey, to go into Japan right after the end of the war and see what the effect had been.

Well, he got on some general's plane in Tokyo, which was all burned out houses and broken grey roof tiles, and he flew down the green length of that beautiful archipelago, and he came to Hiroshima. Broken roof tiles, grey tile all over. And then he flew onto Nagasaki. Same thing. And he thought, "These aren't the decisive weapon that people are telling me they are. They're just another big bombing system. Just means we don't have to have as many bombers. We can use one instead of 400 to get the same effect. Well, that's good."

So when we were making policy against the Soviet Union in the late 1940s, guys like this guy were saying, "No, they're not decisive weapons. We're going to have to build a lot more of them, have to have a lot more bombers, going to have to fight a war." So the shift, the order of magnitude shift from conventional warfare to nuclear warfare was kind of missed.

And then it became clear, as we discussed earlier, that our military services saw the benefit of having some weapons. And then when the Soviet Union got the bomb and had so many men still on the ground in Europe, the balance was disrupted. You can sort of see the semi-accidental changes that followed that led to an arms race of truly holocaustal dimensions. It didn't have to happen that way. It could have happened another way. But that's the way it did happen. And it was largely because those first bombs, destructive as we think of them being, were actually what we would today call a tactical warhead. The Hiroshima bomb was about 15 kilotons; 15,000 tons TNT equivalent. The Nagasaki bomb was 22. But it was exploded in the wrong place, farther up the little canyon of that city's river, and so it didn't have as much destructive force, although the blast was blown up by the sides of the canyon.

So together, they didn't look any different from a typical firebombing city. And that had a big effect.

I'm always fascinated by how few people actually can turn everything around. Mr. Putin, or his chef, or one guy in a Soviet submarine in the Cuban Missile Crisis. It's amazing sometimes how the world tips around on just one little fulcrum and goes way off in another direction.

WALKER: To contrast that notion of contingency, I want to talk about some of the broader social and cultural consequences of nuclear weapons. So when there was all of the hype around Chat-GPT at the end of last year, I started buying a bunch of history books on how people reacted to new transformative technological revolutions at the time they were happening. Just to learn when the printing press happened or when electricity or telephones happened, how contemporaries actually perceived those new technologies. And I'm interested in the question of as a transformative new technology that was really sprung on most of the world, did the bomb change social structures in any interesting or unexpected ways?

So to give you an example of what I mean here, Neil Postman has argued in his book The Disappearance of Childhood that the printing press essentially spawned the concept of childhood. Because previously knowledge was transmitted orally. Both children and adults could understand that. But when knowledge depended on literacy, it created this barrier between children and adults because children needed to develop those skills to become literate to get the knowledge. And so it created this concept of childhood as this secluded time in your life where you're gaining the skills necessary to be an adult. Whether or not you agree with that theory, I provide it as an example of how technology can have kind of unexpected social consequences. So was there anything like that from the bomb?

RHODES: I must say, by the way, I'm not sure about the childhood argument. I've seen other arguments for when childhood emerged. But I'm thinking that my next book, after the one I'm currently writing, ought to be something called "Unintended Consequences". Because more and more it seems to me that technology's often most powerful effects are unintended consequences.

One of the things, for example, that I've noticed is that every time a new technology has come along, there's always a great cheering about, "This is going to bring world peace." The telegraph was thought to be something by bringing people closer together would bring world peace. The telephone was thought to do the same, and on and on, railroads, you name it. Whatever the technology, somehow the first thing is a great flushing out of hope.

But it never works that way. In fact, it's often the unintended consequences. Well, I mean, the bomb is an awfully good example because there's no question that an awful lot of people thought, "Wow, we're going to rule the world with this thing. This is the biggest thing since sliced bread." But of course it was too big. Ultimately it was too big. Maybe not at first, but it was eventually. Oppenheimer said that.

WALKER: He said that of the hydrogen bomb, didn't he?

RHODES: Exactly. There you have a weapon that destroys not only cities but entire states — and in many cases, as in the case of the Swedish instance, entire countries.

But on the other hand, and I remember when I was a little boy during the Second World War, there were in a world where we could play in the streets because there were not any cars on the streets anymore because they couldn't get tires or gasoline. And it was a kind of paradise. The bread man was now driving a horse drawn carriage again, so we could see horses walking up and play with them and talk to them. Automobiles, the whole internal combustion system, disappeared from the streets.

But in every block, there was a black flag with a gold star, meaning someone had been killed. There was a sense of — I mean, I remember it vividly — of some kind of weird impending doom hanging over everything. I didn't understand it, but I heard enough from grownups, and by then I was reading the newspapers, too.

So it was a very strange time to be a little child. And I think that sort of thing has seeped into the world ever since. And despite the fact that your generation seems to be la-di-da out the bomb, it's still there. It hasn't got away.

Something happened in 1999 that I find really terrifying, which is India and Pakistan suddenly realised that because they were nuclear powers, they could fight conventional wars and they wouldn't escalate because they wouldn't be prepared to escalate. But it didn't stop conventional war from their point of view. And they got very close in 1999 to having a nuclear exchange. Our people were all over them at that point saying, "Stop, stop, stop."

And at that point, they started actually talking to each other about how to control their two nuclear arsenals, much as the two sides had during the Cold War.

So that's an unintended consequence, and that's one that Putin is now relying on: that we won't stop him from having a conventional war, because he could go nuclear if we did stop him and if he was at a point of defeat. So that's the kind of thing that I think is still brooding in the background that maybe we've forgotten and maybe we will forget for a while, but it's still there.

And I think it will pop its ugly head up from time to time and remind us that it's still there. When I say there's a Damocles' sword hanging over our heads, there is. It's not going to go away until we get rid of the physical machines themselves. And then if we're running the world right, we really won't have to worry about that kind of war.

Will we have to worry about conventional war? I don't think so, because there will always be the possibility of a country going back to building nuclear weapons, of all the countries going back to building nuclear weapons, to deter large-scale conventional war. I don't think that's pie in the sky. I don't think that's irrationally exuberant at all. I think it's a very practical approach.

But it's going to take a long time for the political people to realise that they can't game it for their own advantage. There, I think, is where we are now. I mean, again, even North Korea started working toward nuclear weapons, not because they wanted nuclear weapons so much. It's because they wanted a patron. They'd lost their patron, which had been China, which was no longer protecting them, and they were ready for a new one, China or Russia. And they hoped it would be the United States, but we weren't paying attention. That sounds so ironic, but it's true.

WALKER: Many people have commented on the parallels between the making of the atomic bomb and the development of artificial general intelligence. And I assume you haven't spent much time thinking about AI technology.

RHODES: A little.

WALKER: A little. Okay, well, I was curious to hear from you in what ways you think that analogy holds and in what ways you think it doesn't hold.

RHODES: Right now, the analogy that I find pretty obvious is with people's response with moral panic to the introduction of new means of communication. And I don't mean telephones. I mean the novel, which was supposed to corrupt young women who read it because it gave them ideas about who knows what. The bedroom, basically. And then motion pictures were supposed to be evil. When I was a boy, comic books were supposed to rot your brain. You were constantly being told that you shouldn't read those terrible things. And eventually, in the early 1950s, some loony psychiatrist testified before Congress that reading comic books made people violent, which is nonsense. But he convinced Congress and the comic book industry decided they'd better hustle around and produce sweet, clean, G-rated comic books and just ruined them for us kids. They'd been full of all kinds of wonderful mayhem before that. It was all swept away. Now it's Archie and Betsy sitting at the soda fountain. I didn't want to read that crap.

And then after that, of course, it was television, and then it was video games, and now it's AI. So that's one level of response that I think is pretty predictable, and it will find its way. They'll settle down eventually, as all these other things have, more or less. People still are raving against the destructive power of movies and comic books to make people violent, which is not the way people become violent. You have to try violence to be violent. So of course you can't learn it out of reading a book or watching a movie. You have to risk your life. You have to see if you can be violent before you're violent.

But down the road, the process that's been going on now for some time, which is to make the seams between artificial reality and reality harder and harder to spot are going to cause some real dilemmas in the world.

There's a short story of Arthur Clarke's. This is when these devil looking creatures arrive on Earth to bring world peace. I can't remember the name, but he has something happen toward the end of the story. The creatures, who turn out not to be violent, they really do want to make things settle down on this crummy planet, they teach the children to be able to communicate brain-to-brain with thought. Pretty soon the adults are all noticing the children are gathering in parks, sitting together, no noise, no talking, just somehow communing with each other. And the adults realise that they're toast. Their version of the world is gone. These children have a new way to communicate to each other. And the point is, when you can read someone else's brain, you can't lie. So what would a world be like where there wasn't any lying anymore?

This is going to be a world where lies and truths are no longer distinguishable. So what happens then? I have no idea. But it's going to be tough. It's going to be hard to work out. Look how much the fumbling attempts of Putin and his gang and Donald Trump and others have had in trying to introduce fake news into the world. People are always around there sniffing around saying, "Wait a minute, that's not true." And they get the word out sometimes, not always. But it's going to get harder and harder.

And what do you do then? Do we just all live in a world where the difference between a game and the real world is invisible? There's a short story by an English novelist where guys are out looking for someone who's gotten loose from wherever she's supposed to be locked up, who are taught to hunt down victims, hunt down criminals, by playing a video game. That's the form of their policing. And it's easy to see how that could be if somehow you had screens and all the rest where you're chasing someone down, he turns out to be someone who really needs to be arrested, but he's somehow a character in the game you're playing in your goggles, if you will.

So I don't know, but I think it's going to be a challenging world for the next hundred years or two while we do all the work of trying to figure out how to keep the planet from boiling away.

WALKER: Possibly the better analogy to the making of the atomic bomb is reverse-engineering of UFO technology, to the extent that that's actually happening. Not sure if you've seen these news stories, possibly disinformation.

RHODES: I've been reading up on UFOs lately because I'm writing a novel on the side which includes UFOs. So I wanted to know what the literature is about since I was a boy and I followed all those things. It's wonderful. There's a rich literature now of UFOs.

WALKER: Well, there's just been this whistleblower, David Grusch, and a lot of congressmen and women taking the issue seriously. I mean, who knows? Who knows? But just assuming that is actually something that's happened — there's been craft that have crashed or been retrieved and then the US government's been trying to reverse engineer that technology — to the extent that's actually happened (just suspending any disbelief you may or may not have with respect to that), given what you learned about the Manhattan Project, how plausible is it that such a secret could be kept hidden for so long? And how would you nest a project like that within the Department of Defense?

RHODES: Interesting questions. Well, I mean, what's the Department of Defense got in the way of secret programs? They had Area 51. And they had, what was it called where they built the U-2s? Black hanger, I forget what it was called. Anyway, small projects.

But as we said about the first hydrogen test, when the sailors got to Hawaii, they all called their moms. And that was long before you had a little magic box in your hand. There was a cartoon in the New Yorker a few months ago, showed someone holding up an iPhone saying, "Theoretically, I know everything." And if you think about it, and particularly now with the new AI systems that are available for searching things out... I asked an AI program recently to write a thousand words on something nuclear, and it did immediately. And I said, "Now write it in the style and voice of the historian Richard Rhodes." And it ended up with some gassy, vast summary of the whole thing that I would, I hope, never write. But anyway, at least knew what I was talking about.

So I don't see how that secret could be kept, frankly. I truly don't. Particularly when we now have 20 year old whistleblowers who are trying to make themselves look good with their fellow Army Reserve group in some place in Massachusetts, gives away deep nuclear secrets about our plans. Or a rogue president who thinks he should wave these documents around to impress the people at the dinner at his resort.

WALKER: But Harry Truman didn't even find out about the bomb until he became president.

RHODES: True.

WALKER: That's quite impressive.

RHODES: He was already sniffing at it as a senator. He made himself a specialist investigating war industries that might be pocketing a lot of money. And he was about ready to go look into Hanford, where the big piles were that made the plutonium for the bomb. He had to be told by someone he greatly admired, Henry Stimson, the Secretary of War, "Senator Truman, please don't go there. That's a project that I guarantee you is okay." And Truman admired Stimson and said, "Fine, I won't." So he was sniffing around the edges, in a time when communications were so much cruder than they are now, really. If went back to 1944, I think we'd be scratching our heads about, "Oh, my God, what is this crude place? How do people get anything done? You want to talk to someone, you write them a letter and drop it in a box and hope it arrives two weeks later?"

So we're in a different time, very much speeded up. And it's hard to see. But of course, what people do once they find out about something, that's another question, as it has been in these last years even with the increasingly open available communication systems. Some people want to use it to make money on their own. Some people want to tell the world so it won't happen. Some people want to do nothing because they think it's a secret and they shouldn't tell it. I mean, there are a million possible responses once you gain some information. So who knows about that.

But the idea that there are flying saucers buzzing around, I think, is really remote, particularly since they're attributed various technologies, wonderful technologies. I mean, antigravity sounds fabulous, but there are lamps you can buy that have a flying saucer at the top, like the shade, and then a plastic cylinder that has the light in it, and there's a cow being lifted up. I'm thinking of buying one of these. I think it's very charming. As I said, there's a rich, almost comic book-like lore around nuclear around UFOs.

It seems so unlikely that anything so interesting and complicated would have left so few traces in the world. You know that famous crash in New Mexico around Roswell, where there's now a Roswell museum devoted to the crash? Very much worth a visit. They give lectures about it and show you the remains. There's almost 95% certainty from what I've been able to see personally about the documentation that that was a balloon that were sending up in those days to try to find traces of a Soviet nuclear test. That like many balloons it blew up and dropped down and crashed on the ground and had some exotic equipment attached to it because it was sniffing for fission products that could then be sucked into a container that had a bunch of super-cooled material in it that would freeze them so they wouldn't blow away. Look, pretty alien, I think, to the people who first found it.

When we were moving toward building this huge machine called the Large Hadron Collider in CERN in Switzerland, the one I'm writing a book about right now, there was some concern among some American sort of scientists that this thing was powerful enough to make a black hole, in which case it would presumably suck the Earth into it and we'd all be gone in an instant.

They actually brought a lawsuit and the judge; they wanted a judge to enjoin CERN in Switzerland from starting this machine up and ruining the world. The judge asked some scientists and they said, "Nah, it's not that powerful. Take a lot more energy than we're getting in this machine to build to make a black hole." So it didn't happen. But that kind of thing is always floating around in the background in the world, about who's doing what.

I kind of trust the scientific community to be on top of it.

WALKER: Yeah. Last night, in preparation for this conversation, I was reading John von Neumann's essay 'Can We Survive Technology?' It was published in around 1955. And he worries about the dual-use nature of not just nuclear energy but a range of other new technologies as well. My last question, and this is a question about people, but when you were looking at the history of nuclear energy, in general, Dick, did you find the same people who were most concerned about the risks of nuclear energy were also the ones most excited by its promise? And I guess extrapolating from that, when you look at technology generally, do you see a lot of people with that schizophrenic kind of outlook where they're simultaneously the most worried and the most excited about a new technology? Or are those extreme optimist and extreme pessimist positions usually split out into different people?

RHODES: I think in general, people who develop new technologies are enthusiastic about them because, after all, they've invented them. They've devoted so much energy and thought and hope and dreams. I mean whoever invented the paperclip or anything, the famous Eddison quote, "Invent a new mass trap and the world will beat a path to your door." There's that aspect of technology that I think biases people in the field to believe that it's a good thing, whereas the people who think it's a bad thing typically think it's a bad thing because it's going to mess up something they value.

This is really obvious with nuclear power because people who are opposed to nuclear power well, let me step back a moment. The early people who developed nuclear reactors were scientists who'd worked on the bomb or around the bomb, and of course they saw it in part as a kind of a benefit to come from something that had seemed so dark at first. They hoped that nuclear energy would bring the world the benefits that they saw it could bring. I'm very much a believer in that myself at this point, after years of following all these arguments.

But nuclear reactors were first introduced as a private technology in the United States, basically by President Eisenhower in the early '50s with the Atoms for Peace program. The reason we declassified a lot of the technology and made it available for industrial development in this country was because it looked like the Russians were going to march on us and start selling power reactors in Europe and we'd lose a huge potential market. The guys in industry were saying, "Come on, let us build these things. We can do this." And so they started to do so.

That coincided with this particular moral panic that emerged in the 1960s — you can still hear its echoes today — and that is that overpopulation was going to reach the point where there were so many people in the world you couldn't feed them all.

There was a famous book that was published at that time that's still in print, the guy who wrote it is still alive, that basically said India and China are going to be so overpopulated that those people are all going to die, so what are we doing supporting them and feeding them with our food and our medicines? Why don't we just stop doing that and let them die off? They're going to anyway. They're just going to keep breeding and breeding and breeding. And eventually, the theory was, there would be 40 billion people on the Earth's planet and there wouldn't be room to walk around.

WALKER: You're talking about Paul Ehrlich's The Population Bomb.

RHODES: Yes, exactly. The Population Bomb. Ehrlich had been India before he wrote that book and had been horrified by all the people in the streets and how they smelled and so forth and came home. This was long before Rachel Carson came along. This was the belief that somehow overpopulation would never stop, we would just keep breeding. There were so many articles about it. I looked it up when I was writing about it.

The nuclear power people came along at that time and said, "Look, with nuclear energy, we can feed everybody. We can provide enough energy for all these people to live."

And those two big world visions, one of them very dark and one of them way over-optimistic, clashed.

And then a little later, Rachel Carson came along, and the whole Green movement came along, and picked all that up. The reason the Sierra Club became opposed to nuclear power when it had been pro-nuclear before was because the leader of the Sierra Club in California saw that were going to build a number of reactors up the coast of California. And that would mean more people could move in because there'd be enough electricity to support them all. And that would mean all these beautiful green wildernesses in California would be destroyed. And he thought, "My God, I don't want my wildernesses destroyed, so let's keep the people out. How do we do that? We go anti-nuclear." Honestly, that's the record. I know it is. I looked at the documents. So there was this clash between nuclear and overpopulation going on. And then some anti-nuclear group called the Club of Rome published a famous document that basically endorsed the notion of overpopulation. What everyone missed is something that was.

WALKER: Was that The Limits to Growth?

RHODES: I think so. Yeah, it was. What was going on at the same time that they missed but that Demographers understood was that when you reach a certain point in the development of a society, and that point is when at least a couple of your children that are born to you survive to adulthood so they can bury you when you die, that you don't have to have ten children anymore. You can only have four or three or even two.

In other words, the slow but brilliant development of public health, and the education of women, which was the other big part of it, brought about what's called the demographic transition. When suddenly it was possible to see that you didn't have to have ten kids, people immediately started cutting down on the number offspring they had. At the same time, vaccines, public health, brought in measures that enabled more children to survive infancy and childhood.

So even though we're still in that curve, but it's levelling off now, The World Health Organization predicts that by the year 2100, there will be steady-state population in the world: about as many children will be born as older people die, and we won't have any more increase to speak of after that. Because the growth of support for life, which is primarily a function of how much energy is available per capita — you can graph that, you can look at the countries that have high infant mortality rates, and you find they have low energy rates, production and so forth. The level seems to be about 3000 kilowatt hours person per year. At that point, enough people live to be 70 years old. If you go above that, you get places like Norway where it's dark all winter and you have to have more energy just to keep the lights on. Or the United States, where we're prodigal people, we spend a lot of time.

So the change, it was a moral panic on the part of the anti-human, I think, people. Really, imagine someone writing that we should just let all the people in India die, don't give them any antibiotics. That's Paul Ehrlich.

WALKER: That book directly led to those mass sterilisation campaigns. and India too, right?

RHODES: Sure, in China.

WALKER: And India.

RHODES: And in India, too. Right. That's over. But they haven't gotten the message yet. Some people have not yet got the message.

The United States, I think, is in the verge of renewing its commitment to nuclear energy, and it's because there's really no other practical solution to the problem of global heating, which is what I call it now, because it's past warming. We're getting up to 120 degrees in the Middle East now in the summer, which is truly almost unbearable heat.

You know, I've looked at a few technologies. For example, the introduction of the electric light. Before it came along in the 1860s, 1870s, the main form of lighting in the United States was natural, was gas, man-made gas made from coal or other products. It was not a very good source of light. First of all, it wasn't very bright. In addition, it was hot.; of course, a flame burning in your house, many flames. It made fumes, which were not healthy. It was not a great technology, but people were used to it.

And when electric light bulbs came along, a lot of people said, "I don't want that damn thing in my house. It's too bright." Honestly, I found that in the literature of the era. So what I turned to that generalises this question, was the work of an Italian physicist named Cesare Marchetti. He's a man of about 95 now, and he did most of his important work in the 1970s.

But he was interested in long-term waves of change in societies. And he got interested in how you go through an energy transition from one major source of energy to another. He looked at coal and oil and natural gas and nuclear power. He started in 1850. They did about 3000 punches into the documentation across the next 150 years. And he and his colleagues at a think tank in Austria discovered that it takes about 100 years to introduce a new technology for it to become the major source of energy technology. It takes 50 years for a new technology to get to the 10% penetration point, and then another 50 years to get from 10% to 50%, which is essentially a majority of all the sources that's been true consistently with all these sources of energy, one after another.

Wood was on the decline in 1850 and basically is gone now. Although it's come back a bit with Europe's decision to use pelletised wood to pretend that they're not producing carbon dioxide. The United States' forests are being stripped to make pellets for Germany to use so they don't have to use nuclear power. It's another sad story.

For example, let's take the introduction of the electric automobile, which Mr. Musk has done a pretty good job of. But the first problem that emerged when the Tesla came along was that there was no place to charge it. The only place anybody was buying Teslas at the beginning was in California, because he was putting charging stations around. I have an electric car and I only drive it locally. So I plug it into my house curtain on the weekend and it charges itself. That's nice, but if you want to travel any distance with the limitations of batteries, you have to find a place where you can recharge. He's now building charging stations with cooperation (I think General Motors), planning to all across the United States because until that infrastructure is in place, you're not going to have everybody driving an electric car. That's been true with every technology in some way or another.

So one thing is the infrastructure. Another very important thing is the sunk cost on the part of people who have invested in the previous technology. If you own a coal mine and everybody says, "We got to stop burning coal," all the money you invested in that mine is sunk. You don't get it back. It's in the ground. So it's called a sunk cost. They resist in every way they can, most particularly politically with going to the new technology. So that slows everything down.

And there's a whole list of this kind of thing that I wrote about in my book Energy, that slows down transitions.

Marchetti thinks of new technologies as social transformations, basically a learning process that societies go through. And since we learn pretty slowly, particularly as it kind of seeps out into the world with all the challenges the new technologies breeds. Edison used to tell people that the alternating current — because his system was direct current — he told people that alternating current was dangerous, that it would blow up in your house and burn your house down. He spread this word all over the place. He tried to make sure that the electric chairs that were being developed to electrocute criminals were using alternating current, which they did. He did everything he could to make people think alternating current, which was much superior for long distance transmission, was not as good as his direct current, which had to have another power plant about every 5 miles down the road. You couldn't transport direct current very well any distance.

So there's all these factors that play into the slow re-education of a society to accept and then welcome and use a new technology, and then another one comes along and you go through the same thing.

Therefore, one of Marchetti's really brilliant demonstrations, on these big millennial graphs that he's devised from the information he and his teams have collected, is that there were only two new technologies that were introduced in the middle of the 20th century, and therefore, anything that comes along now is already too late.

What were those two new technologies? Natural gas, mostly after the Second World War in the United States because pipelines had to be built to deliver the gas from Texas to the rest of the country. And nuclear power.

Whereas, coal was already on a decline and it's still declining. Wood had been declining for a long time. Solar power didn't even come along until almost the 21st century. Wind power the same thing. They have no chance of becoming a dominant source of energy in the world before 2100, if then. They've got a lot of other features that don't match very well with the large national grid, to be sure. But even if they did, there's still a big learning curve, a lot of resistance developing. You know those bald eagles that get chopped up by the [wind turbines], and so forth.

So Marchetti's prediction, and I think it will show itself to be true, is that the major sources of energy by 2050 will be natural gas and nuclear power. And they will represent a huge volume of energy around the world.

Because the problem in the world today isn't just global heating. There's a second problem of equal scale that people have only begun to talk about, and that is that all those people in what used to be the Third World, all those people that the anti-human people wanted to allow to die off, are reaching the point in the control over their lives and their prosperity where they want the same things the rest of us have — automobiles, television, air conditioning, and so forth.

That means that at the same time we have to deal with global warming by finding sources of energy that don't produce carbon, which are basically nuclear power — natural gas does, but not as much perhaps.

So you need to change the mix of energy sources to deal with global heating on the one hand. And you have to increase the energy supply with non-carbon sources for all the millions of people in China and India and Africa who are just getting ready to move into the middle class. That is a huge demand. And there's no way on earth the windmills are going to solve the problem, not only because the cells don't produce a lot of energy for the investment involved, but also because they just can't be introduced quickly enough.

So there's this double dilemma, and from Marchetti's point of view the answer is going to be natural gas and nuclear power. And I don't see how anybody can argue with that. Basically, I think that's what is going to happen and that's a really hopeful outcome when you think about it.

Other than that, the argument is basically everybody's got to cut down. We've all got to live in smaller houses with smaller cars, with less energy, burn candles at night. I don't know what the argument is, but it's a silly argument because human beings aren't built that way.

WALKER: I agree. I think that's very wise. Well, Dick, I've taken way more of your time than I intended. We've covered an astonishing amount of ground. Thank you for being so generous and thank you for writing these brilliant books. Probably characteristic of many people in my generation, I didn't take the nuclear threat as seriously as I should have. It somehow felt like it was in the past, very remote, something confined to the history books.

RHODES: Now you know better.

WALKER: I know better. And it's thanks in large part to you. So thank you.

Done. Thanks so much, Dick.

RHODES: Thank you. I enjoyed it.