The Manhattan Project

Peter Galison's Interview

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Peter Galison is the Joseph Pellegrino University Professor in History of Science and Physics at Harvard University. The central component of Galison's work involves the exploration of twentieth century physics, including atomic, nuclear, and particle physics. In this interview, Galison discusses the two pillars of twentieth century physics, relativity theory and quantum physics, and how these foundational ideas played a role in the development of the atomic bomb. Galison also explains the basic principles of nuclear fission and the scaling up of this technology into a nuclear production reactor. Finally, Galison explains physics as a closely interconnected set of scientific subcultures based on experimenters, instrument makers, and theorists and how these played a significant role in the Manhattan Project.
Date of Interview: 
June 24, 2015
Location of the Interview: 
Cambridge
Transcript: 

Cindy Kelly: I'm Cindy Kelly. This is Wednesday, June 24th, 2015, and I'm in Cambridge Massachusetts with Peter Gailson. My first question for you is to tell me your name and spell it.

Peter Galison: My name is Peter Gailson, G-A-L-I-S-O-N. I'm a professor here at Harvard, Physics, a history of science.

Twentieth century physics has two great pillars to it. One of them is the relativity theories by Albert Einstein which had contributions by others, but in many ways he led the way. And then in Quantum mechanics, which was much more of a collective activity and drew on Einstein too, but also for Bohr and Heisenberg and Erwin Schrödinger and many others.

Those two accomplishments, the relativity theories of Einstein in 1905 and 1915, and then quantum physics, which really begins around the turn of the century, around 1900, with the first indications that nature may not be continuous up through Einstein's contributions. Showing that light was broken up into photons and into particles for example, and then eventually to a full blown quantum theory in 1926.

So you have these two aspects of physics, both of which play a role in the atomic bomb, and then go on after the atomic bomb to being very important in the rest of the development of modern science, up to and including the present. But those are the two foundational moments. They represent some of the greatest intellectual accomplishments of all time.

The aspect of relativity theory that has to do with the development of the atomic bomb is probably mainly the most famous equation of physics E=MC^2 that was a consequence and addendum to Einstein's special theory of relativity back in 1905. 

The basic idea wasand relevance of E=MC squared was that small amounts of matter could be converted into very large amounts of energy. Einstein realized that this could have an importance in radioactive phenomena. But never in his early work in 1905, or even the years after, suspected that it was really important for a possible weapon or the generation of massive amounts of electricity.

That changed in the period just before World War II where Lise Meitner and [Otto] Hahn and others began to understand this notion of nuclear fission; that you could break apart a big nucleus like that of uranium and turn it into two smaller nuclei generating immense amounts of energy.

One of the ways that those early reflections on nuclear physics invoked relativity was that they could see that there was a distance between the sum total of the masses of the smaller pieces of the uranium atom and the uranium nucleus itself. So that difference came out in energy. That was one of the ways that they understood what nuclear fission was. So relativity was important as one of the paths of understanding about what was going on when you split a uranium nucleus.

Quantum mechanics is relevant to the making of the nuclear bomb in lots of different ways. Quantum mechanics became the idiom, the language of modern physics. It was first used to understand how electrons would attach themselves and how they'd change their orbits. It was explaining much of chemistry and it was important for many aspects of physics. But in the years before the atomic bombs, people like Hans Bethe and others, realized that quantum mechanics could be used to explain what was going on inside the nucleus itself. So quantum mechanics really is the framework of the new nuclear physics and how it was going to be understood.

The people that were involved in creating this new science of quantum mechanics were the people who were at the very center of understanding what was going on theoretically in the possibility of building a nuclear weapon. Perhaps none more importantly than Hans Bethe, the person who eventually won the Nobel Prize for explaining why the sun shines. He ran the Theory Group at Los Alamos. He had working with him an astonishing group of physicists that included the very young [Richard] Feynman, and many, many others. But he was really the leader of that group.

The idea of quantum mechanics begins with the notion that the world isn't continuous. Not every process can be smooth in its understanding. Sometimes matter and energy behave in little jumps in discrete packets, and you can't go any smaller than that. So if you break up light of a certain frequency, and Einstein understood this in 1905, say a certain color of light, a certain purple, that if you looked at it finely enough, light was made up of individual particles, photons as they've come to be called.

These photons always represent the minimum of light energy that you could have. You can't have half of a photon or two thirds of a photon. You might think that the world was always divisible in the way we imagine from our everyday life like carving up a bar of butter. You can carve it up into halves or into quarters or into sixteenths or into a thousand twenty-fourths. You could always find a smaller division of the butter, or so we imagine in our everyday experience.

Quantum mechanics says that that's not true. There are certain basic units of something like light energy and you never get less than that. This new understanding of matter and energy, of how even things that looked continuous like light could be ultimately understood in terms of indivisible particles, was one side of quantum mechanics. 

The other weird side was that every particle, for instance an electron, which you might think of as being a little like a BB only smaller, actually behaves in many respects like a wave. So we have this weird correspondence that everything that looks to us like a particle can also be a wave. And everything that looks continuous like a wave can be broken up into particles.

So understanding this aspect of matter, which was radically different from anything that classical physics had taught us, was the great revolution of the 1920's that formed the foundational understanding of our world even today.

One of the crucial and unnerving aspects of the history of physics in the twentieth century is that nuclear fission, the idea that you could break up something like a uranium nucleus and then have the parts fly apart within enormous amounts of energy, was discovered just before World War II. In a way the timing was extraordinary, but it meant that at the very outset of hostilities, many of the belligerent countries began to think, "I wonder if it might be possible that one of these breakups could cause another breakup of a nucleus and cause another one, cause another one, and cause another one?" This is commonly known as a chain reaction.

The physics behind that was that when a nucleus like the uranium nucleus breaks apart, it not only flies into two parts, but some of the constituent pieces of a nucleus, called the neutron, come out from there and can cause the breakup of other nuclei.

The uranium nucleus is very interesting, because it's the biggest nucleus that can hold itself together in an easy way. But it's right on the limit, because inside any nucleus are a bunch of positively charged particles, protons, and these neutral particles called neutrons. Positive particles don't like to hang out together. They're just like if you have like charges they want to fly apart.

So every nucleus has got these particles that are trying to fly apart inside of them. But they're held together by another force that's even stronger than the electric repulsion of positive particles for one another that we sometimes call the strong force or the strong nuclear force. Those are bound in together.

You could imagine for example a bunch of ping pong balls all positively charged. They want to fly apart and they've got little rubber bands attached to them that are very strong. They work terrifically to hold this thing together until you stretch them too far and then they snap. Once those bonds snap then this thing flies apart like the proverbial bats out of hell. So you can build up nuclei with more and more positive charges, more and more protons, until you get to about the size of a uranium nucleus.

The uranium nucleus is just balanced between the little rubber bands, the nuclear force that holds this thing together, and the positively charged particles that want to fly apart electrically. So it's just balanced and holding itself together. If you add another proton to it or another proton after that then it becomes more unstable, but uranium we still find on the earth in large quantities. That means that it's stable enough to last. If you go above uranium and add more protons, we tend not to find them naturally. This is very important for the nuclear weapons project, which I'll talk about in a moment.

Starting with the uranium nucleus if you could start this thing wobbling, imagine a kind of a ball that was flexible. If you hit it gently enough that it started to oscillate into a barbell shape, eventually the pieces of it would get far enough apart so that the nuclear forces, the little rubber bands I was talking about, can't hold anymore and then the sides fly apart with enormous energy. Once they're not bound by those rubber bands, the positive-positive electrical repulsion drives these things apart very fast, releasing enormous amounts of energy. 

That's what happens in nuclear fission. A neutron comes along. It starts this thing wobbling. The parts start to separate and start to look like a barbell with globs on the ends separated by a thinner middle. Then it flies apart. That's nuclear fission. That was what was discovered at the end of the 1930's, right before World War II. People could make uranium nuclei fly apart and they had the beginning of a theoretical understanding of how that took place.

Then people started contacting their governments. Werner Heisenberg went to the high officials in the German armaments establishment and said, "It's possible that a bomb could be made out of nuclear fission."

Albert Einstein was persuaded by a group of other physicists, including some of the other leaders in this field, and they wrote a letter to President Roosevelt under Einstein's name saying, "This could be very important militarily. The Germans have got control over uranium supplies from what was in the Belgian Congo and in other places. They've got very good physicists. This could be important in warfare and you, the Government of the United States should look into this, because it could turn out to be a decisive weapon." So that kind of conversation was happening all over the world as the world was tumbling into the dark hostility of World War II.

Many of the refugees from Europe were all too aware from personal experience, from family members, from everything that they were following about the development of what became Hitler's war in Europe, told them that this was an extremely dangerous possibility if Hitler could get control of nuclear weapons. Though nobody knew how to build an atomic bomb, there was a real worry that with sufficient uranium and the excellent physicists that Nazi Germany still had in its corner, that this was a real threat.

Some of the scientists who knew the Germany scientists and some aspects of the new developments in physics that might make this nuclear weapon possible went to Einstein. Leo Szilard, Edward Teller, and Eugene Wigner, who were some of the great physicists of the time, persuaded Einstein that he should put his name on a letter to the President of the United States, Franklin Roosevelt, warning about the possibility of nuclear weapons, and specifically warning that this might be something that Germany could do.

So they needed Einstein, because Einstein was then as now by orders of magnitude the most famous physicist in the world. Teller, Szilard, and Wigner might be well-known in physics circles, but they had no public authority at all. Whereas Einstein for twenty years had been not only one of the best recognized scientist in all of history, but had been somebody who had been in conversation with world leaders across the globe. So a letter from Einstein to Roosevelt would get read. And they thought that this was a way to the highest reaches of the American Government and perhaps as a way of getting the Government of the United States to put some resources into monitoring the situation and perhaps doing something about it. 

At first the response was rather lukewarm. This seemed like a rather speculative problem compared to the immediate war needs of the United States and how the war was actually going to be fought. Even some physicists were dubious that in the here and now that a nuclear weapon was going to be decisive for this war being fought at that moment as Hitler's armies crashed through Europe and threatened such enormous human and material destruction. 

There are people like I.I. Rabi, who's again one of the great physicist who when he had to choose between working on the atomic bomb and on radar said, "We have to win this war now, and that means radar." Whether the war would last long enough and there would be a possibility of actually building nuclear weapons was, for Rabi and others, a somewhat more speculative enterprise.

But the war lasted much longer than anybody expected. It lasted longer than the Nazi's expected. It lasted much longer than the Americans and the British expected. It was a war as many wars turned out to be much more destructive and much more long lasting than people thought at the beginning. And that made it possible for a project like the atomic bomb to actually lead to a weapon that was used in battle. It wouldn't have been if the war had ended in one or two or three years as people expected. So it wasn't crazy for people to be suspicious at the beginning of the war that this weapon might not be ready on time.

The United States Government eventually did give very high priority to the building of an atomic weapon. And its one of the extraordinary features of the war that a field that didn't exist in 1939, nuclear physics in some real sense, the nuclear weapons industry was nothing. It was an idea in a couple of people's heads. It went by the end of the war to be a multibillion-dollar enterprise in 1945 dollars, the equivalent of hundreds of billions of dollars in current currency.

So what had to happen was truly gargantuan. It would require, as Niels Bohr suspected, essentially transforming the country into an enormous factory from coast to coast, from Hanford in the northwest all the way to Oak Ridge in Tennessee and in Los Alamos and in universities across the country. It would take hundreds of thousands of people to build these plants at Oak Ridge and at Hanford. It was an extraordinary effort that required industrial scale plants the likes of which nobody had ever imagined. Some of those plants became the biggest factories in any industrial production practically overnight.

The project really gets going in 1942 and is in full operation by '44. They test the weapon and use it in August of '45. It's a very accelerated project and it's why people sometimes refer to needing a Manhattan Project for this or that, meaning an all-out effort that takes essentially the resources of a country and directs them towards an extraordinary focused goal.

But that required a massive investment. The atomic bomb costs two billion dollars, which is roughly the same price as what radar costs the United States and roughly the price of what Nazi Germany put into their buzz bomb and their cruise missile and ballistic missile projects of the V1 and the V2.

These are world changing large projects of a scientific technical sort. And they brought together not just theoretical physicists, but new aspects of computation, theoretical work, chemists, metallurgists, and all sorts of resources including people who knew how to scale-up industry from thimble-sized processes to something in the world's biggest factories.

It required some of the biggest corporations in the United States. It required the U.S. Army. It required people like General Groves who had built the Pentagon, then the world's biggest building, to scale-up from what had been very small scale work in the nuclear physicists laboratories to something that would change the world.

You might ask what happened to the possibility of nuclear weapons in other countries. The United States was working very closely with Britain and Canada. Some of the plants that did fundamental work on the bomb were located in Canada. Especially early in the war, the British did extremely important work on the possibility of nuclear weapons, as they did on radar, which was then shipped over and expanded and developed in much deeper ways in the United States. The British played a very important role in this process.

In the Axis countries things were quite different. In Japan there was in fact a small and unsuccessful attempt to think about nuclear weapons, but it never had anything like the resources that they would need to actually convert this into an industrial process of a scale that could produce nuclear weapons. There were good physicists in Japan and they knew some of what needed to happen, but it never really got off the ground.

In Germany it went further. Heisenberg was a very well-known and recognized figure in Germany. He was not altogether considered trustworthy by the Nazi Regime. On the other hand, he wasn't considered an enemy of the State either, but he was in that sort of nether region. He had a group that began to think very seriously about nuclear weapons. They produced reports that went to the armament folks in Germany that showed the possibility, or advanced the hypothesis that it might be possible to build a uranium-based bomb. And even that there might be a possibility of making a plutonium-based bomb, which is another way of making a nuclear weapon.

But they never advanced for a couple of different reasons. One was that they made some mistakes. Heisenberg and his theoretical colleagues came up with a variety of different estimates about how much uranium of this particular kind you would need to actually make a bomb. It was much bigger than the amount that you actually require. So that created both the difficulty of manufacturing that much uranium of a special sort called Uranium-235, and also the possibility of delivering it by missile or air became almost impossible to imagine. It would be such a big object and that limited its potential use. That was one problem.

The second problem was that the German program building the reactors required what's called "heavy water," which is a kind of water, but with larger nucleus in the water than in the hydrogen that's in the H2O than normally found. They built a plant in Norway and that plant was repeatedly bombed and sabotaged by resistance fighters in a way that eventually destroyed the possibility of getting heavy water to build their reactors, which was a necessary precursor for advancing all kinds of nuclear research. So that was a second problem. Related to that, facilities in Germany by '44 were being bombed all the time and it was extremely difficult for them to continue building.

Then probably more important than anything else is that Hitler's top echelons and Hitler himself never wanted to invest the kind of resources that would have been needed to build an atomic bomb. They did for engineering projects: they built jets, which successfully flew in the war; they built cruise missiles; they built V-2 ballistic missiles. That kind of resource allotment was what would have been required to build an atomic bomb. The atomic bomb was never funded at that level.

It is related to a rather deep point that illuminates something about the Manhattan Project, which is that the Germans funded engineering very well. Rocket engineers, jet engineers, and radar engineers got a fair amount of money to do what they were going to do. Missile makers and airplane designers showed up in useable weapons during the war. Using slave labor and killing tens of thousands of concentration camp prisoners, they were able to dig into the side of the Harz Mountains to build protected sites in ways that couldn't be bombed. It paid off in terms of producing these revenge weapons that the Germans had made.

That's what you would have had to do to build an atomic bomb and the Germans never allocated that amount partly because they never really respected the scientists in the way that they respected the engineers. So German scientists—not Heisenberg and his inner circle of Nobel Prize-level scientists—they were not drafted and sent to the front. But a whole younger generation of physicists and chemists were sent off and were only recalled into a protective zone of war work rather late, by which time many of them were dead on the eastern front or elsewhere.

Even when there were scientists, they didn't work that well with the engineers. There was never a particular close relations between Nazi Germany's engineers and physicists, whereas in the United States that alliance was very deep. It was not without its problems. There were moments when there was tension, but the physicists, the engineers, the chemists, and the metallurgists worked in a concentrated and fairly focused way under the leadership of J. Robert Oppenheimer in a way that was absolutely undoable in Germany for all sorts of reasons of class, professional distinction, prestige, and their relationship to the military.

It goes deep into society, but engineers and physicists in the Manhattan Project worked together very well. The physicists ended up being utterly transformed by their relationship with engineers during World War II in ways that reshaped physics in the post-war period in the United States very profoundly and made possible the building of what eventually became the big particle physics laboratory, the big national physics laboratories like Brookhaven and later Fermi Lab in ways that were just impossible in Germany.

So that difference between funding, protecting the scientists, keeping them working with engineers, a harmonious and focused directed research effort in the Manhattan Project, all distinguished it from what was possible in Nazi Germany.

The Manhattan Project was important in the history of science in many ways. But one of them was that from early on J. Robert Oppenheimer, who was himself a very good theorist, brought in and put in important roles the best theorists around. The Theory Group was led by Hans Bethe, the physicist who figured out why the sun shines and played a very important role in developing quantum theory and applying it to the nuclear domain.

There were many others too. Edward Teller was involved in the project, who was himself a major contributor to theoretical physics. So was Szilard. So was Eugene Wigner, John Von Neumann played a very important role, Enrico Fermi. These are some of the great, great theoretical physicists of the twentieth century. They were there and they brought in even younger physicists with people like Richard Feynman, Julian Schwinger played a theoretical role on the radar side. The Americans brought in theoretical physics into the heart of these efforts to develop and understand weapons and countermeasures to weapons in a way that the way the Germans never did.

The second is that they brought in very good experimental physicists, and they of course in the United States especially had been absolutely dominant in physics. Theorists up until World War II in the United States didn't play the same role that the theoretical physicists had played in Europe. But that really changed with World War II, partly because of the homegrown theorists like Oppenheimer, who then had spent time in Europe studying with some of the greats there.

There was this extraordinary group of refugee theorists who fled Europe, many of them Jewish from Hungary, Germany, and from many other places within Europe. A large number of them converged on the Manhattan Project.

Surprisingly perhaps from our perspective, the Manhattan Project was considered less urgent as a secret project than radar. Radar was the one that was harder to get into in terms of security clearance, and many of these refugee physicists found their way more easily into the atomic bomb project than they did into the radar project. They wanted to serve the United States in any way they could. In some ways the security bar for foreign physicists was put in such a way that it was easier for them to work on the atomic bomb than it was on radar.

So there are a lot of reasons why theory was strong in this group, but it took the leadership of somebody like Oppenheimer to put theory in an important and in some ways a co-equal role with experiment.

The third side of the triangle so to speak that made this project possible was the material world of instruments and factories that had to work with the theorists and the experimentalists. Without the massive support of the group around DuPont for example, of people that had experience scaling up nylon from a thimble to a world industry, the physicists alone would have had no idea of how to scale-up. They had zero experience going from a tiny desktop process to factories much bigger than the biggest aircraft frame or car factories that existed in the United States. So that combination of industrial and instrument support, theory and experiment, made possible the Manhattan Project and distinguished it from any prior project in the history of science and technology.

E. O. Lawrence was one of the great American experimentalists. Under his leadership, the University of California Berkeley built some of the first cyclotrons and developed this new technology in extraordinary ways using the combination of private money, the state of California’s support and other means. They began to put together a series of larger and larger cyclotrons. So that by the time you got to World War II, this was a technology that Americans understood very well.

Lawrence was really the master of building these things. The cyclotron was one of the ways that you could accelerate uranium nuclei and uranium atoms and separate them to the useful kind for nuclear weapons and the useless kind. You had to take less than one percent of uranium that you dig out of the ground and that less than one percent was what you actually needed to isolate to make a nuclear weapon. That's called "enrichment."

It's much in the news over the last decades because it's one of the paths that you need. There are different ways to do this. You can have centrifuges that spin gaseous uranium around and separate the heavy part from the light part the way you do with the light parts and heavy parts of blood in a medical office. But you can do that or you can use these cyclotrons. Someone like Lawrence was therefor crucial to the atomic bomb project. He was one of the people who really had to be enlisted into scaling up into this factory-sized outfit.

But Lawrence was never in any stage of his career a master of the theory of this new nuclear science. So from early on he relied on theorists to help focus on what the interesting questions might be. Although he and Oppenheimer never got along particularly well, they worked together on this project. Lawrence threw himself body and soul into building these separation facilities, these racetracks as they were called; the cyclotrons in the Manhattan Project. He worked so hard on it that he practically drove himself into a nervous wreck at one stage.

It required taking the country's whole reserve of silver and throwing it into making these plants. Nickel was brought in in enormous quantities, which is why we have war nickels. Copper was brought in. That's why we were using steel to make pennies in that stage. It required the resources of America to build this thing, but it required understanding these processes at a very basic level to be able to design the right experiments, the right processes to getting this right, to not blow yourself up in the process of making a nuclear weapon.

Those sorts of concerns required the theorists who could calculate how much of this enriched uranium could you keep in one place before it became dangerous. It was always going to be dangerous making a bomb, but you didn't want to blow yourself up in the process of making a bomb. So those sorts of questions preoccupied people and required a harmonious interchange, or at least working together even if not always harmonious between the experimentalists and the theorists.

Then you needed the people that knew how to scale-up industrially. They had to be brought into this too. There were some real moments of tension. There was a time when Eugene Wigner was so anxious to create this nuclear weapon, he felt like the industrial side of things at DuPont was not moving fast enough. He wrote a letter to the President of the United States and said, "We're going to lose the war if you don't get these industrialists to listen to us theoretical physicists. They may know how to tan leather or do this or that industrially, but they don't know how to make a nuclear bomb and we do."

But in fact he was wrong. Without the industrialist who knew how to make semi-plants, how to scale-up gradually from a desktop process to a mid-range process to a large industrial process without understanding the problems of engineering at larger and larger scales, the big plants at Hanford never would have worked. It was only industrial knowledge about building excess capacity and contingency planning, building mid-sized plants, and testing things—it may have driven someone like Wigner crazy, who in fact had some engineering training—without it there's no doubt the project would have failed. As many of the physicists like the great John Wheeler later recognized, they learned how to scale-up to a large project by paying attention to these industrialists. 

There are many ways in which the physicists really learned to respect the industrialists' sense of design and scaling. John Wheeler is one of the great theorists and was one of Richard Feynman's teachers. John Wheeler was the guy who proposed the name "Black Hole" for that extraordinary object that we are learning about today. They calculated how big the reactor should be to do what they wanted to do.

The industrialists said, “No, you have to build some excess capacity. We should add some excess capacity.”

The physicists said, "No, we've calculated what it should be."

It turns out that there are all sorts of things that went wrong that they didn't expect. For example when you break apart uranium nucleus into smaller nuclei, one of the things you produce is Xenon, another element. Xenon just loves to absorb neutrons. It just sucks it up. If you want to make a chain reaction so that each breaking apart of uranium nucleus causes some neutrons and they cause more reactions and more reactions, which you need to make a reactor work or eventually make an atomic bomb work—in order to make the reactor work, you had to have enough neutrons around. If something was scooping them up and absorbing them that wrecked things. So having that excess capacity, because of this unexpected Xenon that no one knew would absorb neutrons like all get-out, really saved the day.

In examples like that, and there are many of them, John Wheeler and others began to respect the way these engineers thought. And even though these industrial engineers hadn't had experience building an atomic bomb or a reactor, nobody had that experience, they nonetheless came to respect this process of going from small scale to large scale. That was what happened all over the Manhattan Project.

How do you make plutonium? Plutonium had been only known shortly before the war in quantities of millionths of a gram. How were you going to make tens of pounds, twenty, thirty, fifty, a hundred pounds of this stuff when you'd only had a millionth of a gram earlier? So those sorts of questions—scaling up on the plutonium production, scaling up on the separation of uranium to the useful part and the useless part—those were all a process of industrializing a process that only existed at the test tube desktop scale. For that, it really required this triple coordination of industrial engineering, theoretical science, and experimental science.

There are two kinds of legacy that you might see to the atomic bomb project. One is the legacy of nuclear weapons themselves. That's been an extraordinarily dangerous history and we're not done. So there is the proliferation aspect of it in terms of the numbers of weapons, the kinds of weapons, and the number of countries that have it. We've been pretty lucky so far. We haven't had a post-World War II atomic war, and things have gotten scary many times over the course of the Cold War and even outside of that framework.

There have been moments when heavily nuclear-armed countries like Pakistan and India have come close to confrontation. There have been moments in the Middle East where it was considered. There was a time in Korea when the United States considered the possible use of nuclear weapons. There have been accidents where nuclear weapons have been dropped and not exploded, but fell out of airplanes. Airplanes have crashed carrying nuclear weapons. It's a precarious technology. And the idea that it would only be held by one or two or three or five countries was never very realistic.

Even during World War II people thought that it would be four or five years before the Soviet Union would build an atomic bomb. In fact more or less on schedule in 1949 the Russians did detonate their first atomic bomb. And then a huge arms race followed in which the country spent trillions of dollars and built numbers of weapons that no one imagined. The scientists might have thought in the years after World War II that people will build dozens and maybe a hundred. But nobody thought that the United States and Russia which each be fielding around thirty thousand nuclear warheads each, or that they would build, depending on how you count, somewhere around seventy or eighty thousand nuclear weapons over the course of the Cold War. Or that so many countries would eventually have it and that it would become cheaper and easier to get the equipment to make it.

Over time it's going to be possible for many countries to have nuclear weapons. And the gamble has always been that we come to some kind of political understanding eventually that would make it not worthwhile for countries to continue to build and to develop nuclear weapons. But I think it's been more luck than skill that we've not had the use of nuclear weapons over the last sixty or seventy years outside of World War II, which is really the first atomic war.

Then there's the side of legacy of the atomic bomb project that has to do with the whole relationship of science, technology, the military, the coordination of large-scale efforts and scientific work. And that's a deep legacy of a different sort and one that in some ways can be thought of as very hopeful. But out of the atomic bomb and then the hydrogen bomb that followed quickly on its heels were fundamental developments in computers that became very crucial.

For example simulations were developed first to understand the atomic and hydrogen bomb, and then computer simulations now play a role in almost every branch of modern science. Modern astrophysics is unimaginable without the ability to simulate the complicated processes involved in the early moments of the universe or the development of stars or galaxies. It's really foundational to our understanding of modern physics.

Everything that's done in particle physics uses simulations. That's just one example. The National Laboratories and the International Laboratories like Cern that sits on the Swiss-French border and they bring scientists in from all over the world, is a scale of engineering theory and experiment that really has its direct antecedent in the atomic bomb project.

So you have a fantastic, splendid history of science that grew out of funding models and a scale of work that came out of nuclear weapons that really has nothing to do with nuclear weapons, but has been very important. Then you have the history of weapons research in general and the role of science, technology, and the military in many countries that was transformed by this as well. Not just for the building of atomic bombs, but for many aspects of military technology. So that's another aspect.

The whole funding model, the way the government funded contract work in the United States through the universities or through government-owned, company-operated plants, these are all structural industrial economic relations that were founded and transformed the universities, and transformed the relationship of science and technology in the modern world. It came out of the atomic bomb project in various ways.