Edward Teller Interview

June 1996

Well, I can tell you, the beginning, I simply don’t remember. I know something that was said about me, which I very vaguely remember, when my grandfather, of whom it is said that I resembled him a great deal, was telling my mother not to be too unhappy that her son is apparently becoming an idiot. I was three years old, and I couldn’t speak. Well, I have an excuse. My father spoke Hungarian, and spoke German very poorly. My mother, her maiden name was Deutsch, German, and her first language was German. And her Hungarian was terrible. So, you know, I had, for every concept, two mutually exclusive – usually mutually exclusive – designations. I decided that these grown-ups don’t know what they are talking about, and I lost all interest in speech. The one thing in which I did not lose interest, in which I gained interest, was numbers. They made sense. When as a five- or six-year-old boy, I was put to bed, sleep, I did not feel like it, lights out, I played with numbers. Not terribly ingenious games. I knew how many seconds there are in a minute, how many minutes in an hour, how many hours in a day, how many days in a month, how many months in a year. I multiplied them. How many seconds in a year. I remember that very clearly. Incidentally, all this was secret. I never told anybody, at that time, about it. And game was very much more interesting because of circumstance, that every time I did it I got a different answer. But I somehow felt that this called for repetition, and that I enjoyed. This is my earliest memory, my playing with numbers, and it distinctly happened, before I was taught to read or write.

My other early memory is very much less agreeable. It is connected with the beginning of the First World War. I remember sitting at the table and hearing the discussion about the murder, murder of the Crown Prince, Franz Ferdinand, in Sarajevo, a terrible thing. But there will be no war. And you know, I used a privilege of children and I asked- Why? Why will there be no war? Well, because there is no reason that there should be war. But if there is no reason, then why do you say that there will be no war? I remember very clearly my confusion about the issue and in the course of years and decades, this confusion really did not change very greatly. I still don’t know why there had to be a First World War, but that lack of understanding is one of my earliest memories. Well, of course, as a six-year-old, I was born in 1908, I was just a little over six years when the First World War started. And seeing all these people with their equipment, even guns, marching down the main street in Budapest, was obviously very interesting. Also, my father – he was a lawyer – had a map in his office, in which the position of the armies was represented, so I learned geography. I don’t see why I should now repeat the sad and terrible story of that war. I want to repeat one little circumstance. In the early phases, the Russian armies got- occupied Lemberg, just north of Hungary, proceeded to a border of Hungary, the Carpathian Mountains, perhaps a little beyond that. Now, in those days, my father took my somewhat elder sister and me out for a walk every Sunday. And I remember on such a Sunday being see- being shown- having seen a model of a dug-out, you know, where- that you could hide from bullets. That, together with the knowledge that the Russians were not very far, made all things very much more real to me. So, the First World War was not a concept, was not something I understood, but was something that gave me a peculiar connection between the love of one’s country and having to fight. I won’t even say that that was a problem. I do remember the end of it. And I do remember, when crowds in Budapest demonstrated against the war, how that brought on a Socialist government that after a short time was thrown over by the Communists. By that time, I had started my high school education.

Of those years, till the end of the war, I remember my father was beyond the age that he had to join. He was a lawyer, and some of the people working in his office did have to join the army. So, I began to hear not so nice things about the way this glorious fighting was going on. I also remember my father’s office. The really interesting things in that were two typewriters. That was the first complicated machinery that attracted me, and that attraction was, of course, met by a strict denial – I shouldn’t touch them. That may have something to do with the circumstance that I did not become an experimental physicist. Another story of the same kind was my father brought home one day an extremely interesting toy, that was a mirror. And as the sun came in I could reflect the sun and throw it on various parts of the ceiling and, unfortunately, also out of the window. Now, at that time, you know, we had, had quarters just behind the Supreme Court.

And one day – I think it was at lunch, maybe it was at dinner – policemen appeared, and were going to arrest me. It turned out, and I claim it was unintentional, that I illuminated with my little mirror not only the general outside world but on the other side of the street, the bald head of a justice. As I already told you, my father was a lawyer and he said that I will get adequate punishment and they should- the policemen should go away. And that happened. And the punishment was that the mirror was taken away from me. So, there is another reason why I did not become an experimental physicist.

I have one other memory. And I don’t know why I should remember it. But you know, the King of Hungary and the Emperor of Vienna – Franz Joseph – died before the end of the war. His son was crowned. And we were invited- I was invited- on the balcony of my aunt who lived on one of the main streets where the procession would come by. And there it was pointed out to me that in the car that carried the new king, Karl, there was a little boy, smaller even than me, by the name of Otto. Very many years ago I met Otto, and I liked him a lot. But by- at that time, I immediately saw a very little boy. When the war was lost, the crowds in Hungary demanded an entirely different government, deposed the King, put in a Socialist government and then a Communist government. My father, as a useless lawyer, lost any job. We did not have terribly much to eat. In order to get something, we had to go out to the country to buy it because the peasants stopped bringing in food to Budapest. So, my memories of the Communist regime were not too favorable, with one exception. I just entered, at that time, high school, a little before the age of ten and my favorite professor was – I even remember his name – Ireneus Ynvans. He was an excellent mathematics teacher. He taught us the rule, the rule of nines. The point at if, for instance, you want to know whether eighty-five is divisible by nine, you had to add eight and five, which I think gives thirteen and then you have to add one and three, which gives four, and eighty-five, if you divide it by nine, gives four as a residue. And it’s divisible if the residue is zero. All of that was not only explained to us but proved to us, to kids ten years old. And therefore, I will not insult your intelligence by proving it. I suggest that those of you who are interested try to prove it. It was not too difficult.

Well, my excellent mathematics teacher was also an ardent Communist who occasionally told us- If everything is not quite all right in the regime, now listen, you build a new house. There are all kinds of difficulties while you are building it. In the end, what the Communists are building is right thing. Well somehow, I heard enough about my father losing his job and a few other things, that I believed his mathematics much more than his politics. But I also remember that all this was not a very big problem for me. It might have developed into one, but the Allied armies came, threw out the Communists. They had been in power in Hungary for only four months. At the end of that time, my mother’s darling children having lost some weight, we had to be taken down to the country, to my grandparents, for purpose of being fattened up. In particular, we were taken to my mother’s parents. My father’s parents had died long ago. My maternal grandfather, a very wonderful person. I must say so because it is said that I resembled him, and I don’t want to drive modesty so hard- so far as not to praise him.

But one of my very important memories of Lugos was connected with piano playing, with music. I started to be taught to use my fingers on the piano two years earlier and I don’t- didn’t like it very much. I just loved to listen to my mother, who herself intended to become a pianist. She was a good one. I remember the Beethoven sonatas, the ‘Pathétique’, the ‘Appassionata’, that she liked to play. Now, there in Lugos I got piano lessons that I started really to like. That was a Hungarian official who lost his job and I forgot to tell you why. During our stay in Lugos, that little town was taken off- taken over by the Rumanians. And the Hungarian employees of the state all lost their jobs. And there was – I now remember his name – a very wonderful man, Mr Willer, had no job, was quite willing to give me piano lessons. He was not a piano teacher, but he loved music. And he did much more than use my fingers. He started to explain both harmony and the way how, let us say, a piece like a sonata is constructed. Had I stayed with him, I might have satisfied my mother’s wish, I might have become a pianist but after a little while we came back to Budapest. We had stayed down there for maybe half a year or a little longer. And my next teacher did not tell me anything about theory, anything about harmony, but told me that to play a piece well you have to play it slowly a hundred times. And in the course of years, she proceeded very far, not all the way but very far, in spoiling all my interest in music. My interest in mathematics, that remained. My father knew very little about it. But he had a friend. I believe they had gone together hiking in the mountains, in a group of them. But the leader of that group, a Professor Klug, was a mathematician. And my father took me to him. Now, by that time, you know, I knew how to handle numbers, but I did not know what mathematics was about. I heard that there is much more to mathematics than handling numbers, but what that was, I did not know.

Now, Klug was a mathematician, and he did two things for me. One is that he told me about his specialist- about his specialty which was projective geometry. What is that? In geometry, at least a part in which we discussed at that time, we talk about drawings, about figures, a circle, a triangle, in a plane. Now, what happened if this plane was transparent with the figures drawn upon it and then light in- illuminating it and projecting it onto another plane behind? What are the properties of geometrical figures that remain invariant, that is, do not change in that operation? This is projective geometry, the part of geometry which remains valid when you pro- perform a projection. From Professor Klug I got problems which I usually could not solve. I remember one that I liked very much, I could not solve it, I could not prove it, but I’ll tell you what it is. In projective geometry, four figures, four kinds of figures, are declared to be the same. A circle, an ellipse, a parabola and a hyperbola. If you take any of the four in one plane and project it onto another plane, you will not get the same thing, but you will get one of the four. Projecting a circle can give a parabola. Now, here is a theorem in projective geometry. Take one of these four – in the simplest case, a circle – and inscribe into it a hexagon, so that the corners, all the corners, all the six corners, lie on the circle. Now, the six sides of the hexagon, select three pairs, each pair has the opposite two lines of the hexagon. Each of these pairs will intersect at one point. Out of the three points you get three intersections. Nothing interest- interesting so far. Now comes the theorem. The three points so constructed lie on a straight line. True for a circle and once you have proved it for the circle, you have proved it for the ellipse, for the parabola, for the hyperbola because that happens to the circle and straight lines remain straight lines; and the statement of three points lying on a straight line is again a sur- statement, invariant, not changing, on the projection. This was a group of new ideas wit- which I found very attractive.

 But Klug did one more thing for, for me – he recommended that I read an old book, I forget, maybe 200 years old. The title was very simple – “Algebra”. The author was very famous, Euler, a great German mathematician; and with ten years or eleven, I read his book from cover to cover including the solution of equations of the first order – the unknown x occurs in the first power, up to the first power. It did not say in that book that high, high order equations cannot be solved, not by formulae. But the book had a lot in it.

Now I want to tell you what happened to me in high school, and I should say that this is a rather unhappy part of my life. My good mathematics teacher was fired. He was replaced by a disciplin- disciplinarian. Well, it turned out that what he taught us – from my answers he found out – I already knew it. He looked at me with sort of hostile eyes and said- What are you, a repeater? In the end, he was not unjust – he even gave me a high mark in the end but he spoiled my pleasure in mathematics. He taught me one thing, that formulae have to be written in a very clear, careful, beautiful way – which I am sorry to say I never, never learnt. But the main effect was, and this is one of my saddest memories, that for the time being I lost my interest in mathematics – not completely. I had a nice physics professor and a few years later when I was in the seventh or eighth grade – I think it was the last year, the eighth grade – I read or I should rather say I tried to read, a book by Einstein: relativity, explanation. Couldn’t understand it! So I went to our nice physics professor and asked him the question- Where did you get that question from?- That book. – Show me the book. I brought the book. He said- I’ll take it along. For a long time I did not see that book again. Then finally I ended my studies in the high school with good grades. My nice physics teacher Professor Tsiato came back to me, gave me the book and said- Here – now you can read it! It was a peculiar, a peculiar school. It had a beautiful past. It was founded by a Minister of Education, Secretary of Education by the name von Karman. His son who had studied there long before I did, had in the end come to the United States and was responsible for the early development of aerodynamics and flying, so that we entered the Second World War very well prepared. I didn’t know it at that time.

Actually, the high school, the gymnasium that I attended, had been founded by the Secretary of Education, whom I, of course, never have met. His son, I hadn’t met him at that time either, Theodore von Karman, became a very famous aerodynamicist. Another physicist about whom I have to tell you much more who studied in the gymnasium was Leó Szilárd, who in a very real bit- way has to be blamed for the atomic bomb, if anybody has to be blamed for it. There were, at that period, a couple of other very outstanding Hungarian scientists who did not go into that school: John von Neumann and Eugene Wigner. But my father, who, of course, knew very well my interests, did get me together, in my last year in high school, with these three: Leó Szilárd, Johnny von Neumann and Eugene Wigner. Their influence on me was very simple. In a way it was the same as the influence that Klug had on me and it was this: I found that many of the grown up people complained how hard they had to work. The scientists or mathematicians never complained. They quite obviously liked to work more than to do anything else. And that I clearly noticed at a very early age.

I wanted to go to stu-study mathematics. My father disagreed- As a mathematician you never will get a job in Hungary, you must do something more practical. After a lot of discussion, we settled on chemistry. But that was the second question, where? My mother wanted me to stay at home. My father thought I’d better go to a good university abroad. Compromise: I got my final examination done in June 1925. For the fourth semester that started earlier in Hungary than in Germany, I stay in the technical high school in Hungary. Then, by New Year, with the first term over, I go to a good university in Germany. That’s what happened and in that period I had one not so little challenge which had a very agreeable and fortunate outcome, that was the competition in physics and mathematics for a prize named after a famous Hungarian physicist by the name of Eötvös. I even want to tell you why he was famous. He looked into Galileo’s observation that all objects fall in an entirely similar way. A heavy one no farther than a light one, if you eliminate resistance of air or whatever. This, Galileo observed. This, Eötvös, quite a few years ago, measured with very, very great accuracy and this turned out to be the foundation of Einstein’s second great discovery, general relativity, which essentially says: if you put yourself and a falling object in a cage and you fall together, then you don’t notice at all that there is gravitation. And that is a way- the way how to approach the rules of gravitation. At any rate, the prize was named after Eötvös, and the mathematics prize was divided by three of us- between three of us. One of them was my good friend, Tisza, about whom I have much more to tell later. The physics prize I won alone.

And I would like to tell you one of the problems I solved, of which I am prac- I am very proud, because- not only my solution but the way how I solved it, I found to my great pleasure a few years ago, has become a legend in Hungary. The problem was this: you have a glass of water and you have an ice cube floating into it- flowing- floating in it. Question: If the ice cube melts, otherwise no change in temperature, by how much will the level of water rise? Now, I remember clearly I read this and within a couple of seconds I heard a memo – a melody. I will not do the favor to you of singing it, I could, but it’s a favor if I don’t. Unfortunately, I can’t even tell you the text because it’s Hungarian. It’s a famous Hungarian text and it is really a theorem. A body on the water will lose of its weight just as much as the weight of the displaced water, that is the melody. And of course, once you remember that, the rest is easy. Take out the ice cube, you leave a hole. Melt the ice cube, put it into the hole, the ice cube had floated, therefore it had to weigh just as much as the weight of the water that it has displaced. It became that water, and therefore it filled just that hole. And the answer to the question is: the level of water did not rise. That was, in a way, my first success as a scientist.

By the beginning of the new year – I was just a few days short of the age of eighteen – I left for a university in Germany, Karlsruhe, that had an excellent reputation for chemistry. And I studied chemistry. I even worked on experiments, I even am proud of an experimental idea that I had. One of the jobs we had was to determine what salt was discovered- was dissolved in water; sodium chloride or potassium chloride or lithium chloride or cesium chloride – difficult. You pour in this and you get a precipitate and they all behave very similarly. But here I had a splendid idea. In a corner of the laboratory there was a spectroscope. And I took a drop of it and I did not see the yellow sodium line. I did see the red lithium line. And so I had the answer sooner than anybody else. But you might almost say, not with complete justice, that as an experimental chemist I did well, but only by cheating, to a small extent.

Well, I studied chemistry as I was supposed to but I cheated, I really cheated – I studied mathematics as well and with great pleasure. I remember one vacation which I spent at home in Budapest by thinking about one set of problems in mathematics, which I love so much that I would like to mention it. I did not discover anything that people would not know but I essentially reconstructed the essential parts of it from the simple principles. The subject is called Set Theory. And set theory becomes interesting when you do not compare a set of five objects with another set of five objects but if you compare a set of infinitely many objects with another set and the remarkable result is that there are different kinds of infinity. I think I should tell you, without a proof, the kind of thing set theory is made of. Question: are there more points on a line than there are integers? The answer turns out to be yes – not very surprising. Second question: are there more points on a line than the number of fractions which can be written as one integer over another integer. The answer is again, yes. Continuous infinity, the infinity in a continuum of points, is greater. And these ideas can be defined precisely and a group of theorems can be deduced, which is what I dug into in one of the three weeks period that I was at home.

Apart from learning physics- from learning mathematics and chemistry, I also attended lectures by a visiting professor. His name was Herman Mark. A wonderful chemist. A chemist who is responsible for a new field of chemistry – long chain molecules, non-repetitive chains, chains of all kinds, which, for instance, are quite essential in understanding biochemistry. He founded that science and he lectured to us. It was a small group, but it was a wonderful one. And he noticed my interest and fed it. This really managed to make in me a big change, for an interest in mathematics, for an interest in physics. He told us about a young French physicist, Louis de Broglie, who wrote a paper, the content was this- if divide matter, then some components of all matter, no matter what, what kind of component you always find, are electrons. Nothing new. As a chemist, I knew that all along. What de Broglie added was- these electrons can be described not only as particles but also as waves. And he showed how the velocity of these waves, the practically measured velocities, can be brought into relation with the velocity of particles. Now, I had known from conversations, early conversation, with people like, for instance, Eugene Wigner, that there was a strange situation in physics. Light – that has been known for many, many decades, more than a century, as electromagnetic waves, a process in the continuum – light also does behave sometimes as though it consisted of particles. One little aside that you might know, one of the truly great physicists, Einstein, who discovered relativity and got the Nobel Prize, did not get the Nobel Prize for relativity. In fact, when he was informed that he got it, he was told very explicitly- It is not for that problematical statement of relativity, it is for your concrete arguments that light can be considered as particles or waves.

The same Einstein was also connected with de Broglie, in other very amusing story. De Broglie, in his French university, wrote a thesis and when the professors read that peculiar thing – electrons like waves – We can’t accept that. But there was a problem about that; they couldn’t refuse it either, because de Broglie’s father was a very famous mathematician – I am sorry – a very famous politician, prime minister or something. You could not throw out his son without very good arguments. So the French professors had a real dilemma and here was a fortunate circumstance – Einstein was visiting and they showed him de Broglie’s paper and Einstein got very enthusiastic. De Broglie got a Doctor’s degree and, incidentally, later the Nobel Prize. It would have been a spectacle for his not getting the degree but the Nobel Prize only. That almost happened except for Einstein. Einstein then showed the paper, sent it around among others to Schrödinger who then made a theory of the hydrogen atom based on de Broglie’s ideas. That was too much for me. This obviously was something I ought to be interested in. And I no longer wanted to become a mathematician. I did want to become a physicist, and told my father. Now, in the meantime, I had been a good boy and studied chemistry for two years. And my father didn’t want to say yes, but couldn’t quite say no so he decided to come out to Karlsruhe and talk to my professors. I wasn’t there at the talks. I suspect my professor might have told him something of the kind- A peculiar guy. If he would be my son I would let him do whatever he wants, it could be worse. At any rate, I got the permission to become a physicist.

 But before going on, I want to tell you something about this wonderful man, Herman Mark, who is responsible for my becoming a physicist. He really was only a visiting professor. His main job was in the neighborhood, with what was called the Farben I.G, the ca- Interessen Gemeinschaft, the joint interest of chemists in the very remunerative practice of making coloring substances – Farben. He lectured as a side issue. When Hitler came a few years later he got fired, got a professorship in Vienna but wasn’t left there alone because a few years later Austria became a part of Germany and poor Mark was again exposed to Hitler. He did not have an offer from abroad, he had some money. He wanted to ta- take it along, to start a new life in the United States. You couldn’t take money out of Germany. As a professor, it was possible to- for him to buy platinum without being particularly noticed. That he did. He put that platinum into the pockets of heavy coats so that the weight difference should not be noticed. Then, when they were at a border leaving in the direction of Switzerland, I believe, the Hitlerite guards took a good and partly destructive look even at the coats. Fortunately, the Mark treasures were not discovered. Herman Mark came to the United States with his family, including a son who had not existed when Herman was teaching me. Hans Mark, an important figure in the United States, well, he and I got together years later. At any rate, as far as I am concerned, I had now the permission to study physics and one of the most famous professors who counted Pauli and Heisenberg and other famous students among his disciples was Sommerfeld, in Munich. So I decided to go there.

 I’m sorry to tell you I did not enjoy Sommerfeld. He was a bit on the high brow side and I can tell you one story about him that might explain my lack of enthusiasm. The story is about a very excellent American student who later got the Nobel Prize, van Vleck, who went as a young student to study in Munich. And there he was in the library, and in comes Sommerfeld. Excuse my German, I think you will understand it. Sommerfeld enters. van Vleck shows up and politely says- Guten Morgen, Herr Sommerfeld. He’s rewarded with a none-too-pleasant grunt. Next time it happens Van Vleck says- Guten Morgen, Herr Professor. This time, Sommerfeld smiled a bit. On the following occasion, he said- Guten Morgen, Herr Doktor. Now, this time Sommerfeld said- Guten Morgen. But the last time Sommerfeld came in and van Vleck said- Guten Morgen, Herr Geheimrat. Well, Geheimrat means secret councilor. A very high title in Germany. And Sommerfeld looks at him- Aber Ihr Deutsch ist jeden Tag besser! But your German is improving every day! Well, that was not the kind of improvement that was my ambition. I studied, I sort of liked it, I was none too happy.

  did go to hike with friends in nearby Alps and on one of those, of those occasions, I got into really bad trouble. I don’t know what I was doing. I took the tram to the railway sta- railroad station to get to the Alps and I missed the right place where the tram stopped. I suddenly realized the tram was going slowly off. I jumped off, by that time the tram was going a little faster.

 So, I got active, jump off. By that time the tram went too fast and I fell and I saw the tram, I think three cars coupled to each other, go by. And somehow, I don’t know for what reason, I remember looking back, before trying to get up and there I see my boot lying at a distance- My God, how will I go hiking without my boot? And then, several seconds later, it started to hurt badly. My foot was still attached to me, but barely. The car came to take me to hospital, as a student I would have free treatment. I remember the surgeon. An extremely nice person. All I wanted is that he should put me under anesthetic and get going. No. He said- What should we do? I could amputate you here or there. If I amputate you higher up, take more of you- of your leg off, then the prosthesis you get will look very much better but you will not be able to, to walk, except with very great difficulties. I could try to let- to leave on as much as ever possible. Then, it will not look so good, but you can walk. Which one do you want? I remember to have made the decision not objectively, or not quite objectively, but I immediately thought- Leave on more because if I’m sorry for it, I can change it later. There’s a point to the story. In fact, there are two points to the story. The name of that very nice surgeon, the name of that surgeon was von Lossow. We became good friends. Because of my use of some technical words concerning my condition, he started to call me – I was then, whatever, not yet twenty years old – Herr Professor. That, I liked. One day he disappeared. I heard he went to South America. He did not say good-bye. I was a little hurt. Years later, I found out why. He was a brother of General von Lossow, the general who arrested Hitler when he tried his first revolt in Munich. At that time, in 1928, the Nazis began to have more votes. If Hitler came to power, no von Lossow would survive. He left. Perhaps, in a way, that is the tragedy. If the right people could have found a way to resist, the world would be incomparably better. But I understand, of course I understand.

I healed slowly. In the end I healed and barely able to walk, I did not go back to Munich. I did not like the Herr Geheimrat. Anyway, he was on a trip around the world. I went where I belonged, to Leipzig where there was a professor only a few years older than  I don’t know, I think maybe six years older than I – by the name of Werner Heisenberg, a very wonderful man. And it was obvious that he liked me. He liked me, perhaps when he asked me what I have read; I told him the various works, including my study in Group Theory, which he appreciated. I am pretty much convinced that in part he liked me because of two somewhat strange circumstances. I hardly could walk and I beat him in ping-pong. In fact, we had the ping-pong evenings on Tuesday, I was the only one who beat him in ping-pong. I might tell you that my glory was great but not permanent. Next year, Heisenberg went around the world in the ship, really practiced up on ping-pong and after that I could not beat him. But here, I can tell you, that my studies in the gymnasium in Hungary were not completely wasted. My eigh- eight years of Latin and four years of Greek, I don’t think I ever could or will use again. But, outside the classroom, I learned to play ping-pong really well and that, I think, with Heisenberg, was the start of his appre- appreciation. He gave me a couple of jobs. I liked them both. One was to report, in his seminar, on group theory. I did not do it at that time but found out very fast that my friend whom I knew from way back in Hungary, Eugene Wigner, had studied the consequences of the symmetry of atoms and molecules.

 What Wigner has done was to find out the results, the consequences of the symmetry in the case of atoms and molecules. Hydrogen atom. One might guess the electron is somehow spherically distributed around the atom. And so it was, incidentally, in one particular state, the lower state of the hydrogen atom. But there were cases, most cases, where the symmetry was changed by the way the electron moved. And that had consequences for the behavior of the quantum states of the hydrogen atom, or any atom of the kind- any other atom of the kind. It has a consequence that the same energy, several ways belonged in which the electron could moved- could move. Indeed, by several we would mean infinitely many. If the electron would move on an ellipse around the – around the nucleus. No, you see, in classical theory, the ellipse could be in every direction, infinitely many states of the same energy. In quantum mechanics, there were only a few. And these few had to be in- interrelated in a very specific way which the mathematicians had already saw – had already studied – decades earlier. And this kind of a study was called group theory. I was asked to report on it. I cannot claim that I reported on it with full understanding. I can claim that I understood some of it. And I can say that when I reported on my semi-understanding, and that the questions that Heisenberg asked made me understand it very much better. It was a nice experience.

 But Heisenberg did another thing for me, he called me in, not much after I arrived, he said- Here are two papers, one by a Dane, one by an American. They are both about the hydrogen molecular ion. Two hydrogen nuclei, two protons, and one electron moving round both of them. The Dane, Buro, I think, was his name, Buro found the solution. The American has proved that Buro is wrong and no solution exists. Who is right? Well, on that one I did well. I went away, read the two papers, and in two days I was back and told Heisenberg in detail why the American objections were wrong. The American postulated a particularly simple behavior of the electrons when they got to- get very far away, at infinity. If you give this in a reasonable way, you got Buro’s result. All right, says Heisenberg- that is the lower state of the hydrogen molecule ion, and you say it’s correct. Now calculate all the other states. That was the origin of my PhD thesis: “The energy states of the hydrogen molecular ion”. I can tell you, I couldn’t do it. Nobody else did. Not in the form of definite known formulae. I could do it numerically, using a computing machine. Well, you know, what am I talking about? I am talking about the year 1929. The computing machines were sizable. They had a handle which you could turn and if you turned the handle, you made a lot of noise and you got one number out of it. In the meantime, as you all know, the computers made a little progress. But there I was, you know, not liking to get up early in the morning, I got in late. Each night I was turning the handle and got more and more of the excited states of the hydrogen molecular ion. Now, all this is relevant, because Heisenberg, at that time unmarried, tried, not always effectively, not always successfully, to sleep in the room right above the one where I turned the machine. So I noticed – I did not know it at that time – but I noticed that Heisenberg would come down and started to chat with me. And those were very amusing, very interesting conversations. I remember one when I had to contradict Heisenberg. He said- Now everything is done in physics, what will I do next? I sort of said, not quite in these words- Damn it, aren’t you satisfied? And he said to that, very explicitly- No. I think I’ll go into music. Well, on another occasion, he came down and asked- When we will be through? I said- I think in one or two years I could finish it. Heisenberg said- I really think you have done enough. I think these are nice results. Just write them up and it will make a good thesis. Now look, I very clearly claim that I got my Doctor’s degree because I did not let Heisenberg sleep. I wrote it up, it was published, my first publication. In spite of what I’m saying- what I said, I am even slightly proud of it, not very proud. But I didn’t have my Doctor’s yet, and that is another story I want to tell you.

 I also had to be examined, not only in physics, but two auxiliary subjects which I, of course, selected to be mathematics and chemistry. No trouble, except that a good mathematics professor – I forget his name – was absent. And the one who was to take the examination, and that I remember, was named Professor Kobe. There was a story about him, rather generally known. In a company, the question was asked- Which one of those here thinks more highly about himself? And everyone wrote Kobe, with the only exception of Kobe. He wrote- Kobe and rightly so. Well, I went to see him, he looks at me- I never see you in my lectures. I don’t quite know how I blushed, how I excused myself. – Well, let’s see anyway, what shall I examine you in? Shall we say non-Euclidean geometry? Shall we say this, shall we say that? Shall we talk about the theory of functions? And I more or less, modestly said, in every case- I know a little about it. That went on for maybe five or ten minutes. Then Kobe says- Here you are, you haven’t taken one of my lectures. You know a little, a little, a little of this, and of that. And you want to pass your examination? Maybe you even want a good grade. At that point, I clearly remember, I interrupted him and I said- Yes, sir, I would like to have a good grade. Well, that sort of stopped the questions. He said- Well, it doesn’t seem to make- make much of a difference for you- to you. I’ll examine you in the theory of functions. That was just as well with me, I liked the subject. And then, next time, in the next Tuesday evening, when we part with ping-pong, I told all this to Heisenberg. And Heisenberg laughed and laughed and then he stopped laughing and he said- Now listen. If I say anything to Kobe about you, it’s an absolute certainty that you will fail. You’d now better prepare. So I did.

How do you prepare? Well, a very important part of my preparation was that I talked to students who took that examination from Kobe on earlier occasions. And then I also talk- read a very nice book by Bieberbach on the theory of functions, which I greatly enjoyed. And, at the proper day, I went to see Kobe. And he started by asking me one or two trivial questions, not much more difficult in the theory of functions, how much is two and two? That, I knew. Then, Kobe says- Now, talk about whatever you like. And for that, I was prepared. Because I found out by talking with others who took the examination, that he almost always asked that question. I know precisely what I talked about. The theory of functions really works in the complex plane, where a number is given. For instance, like 5 + 7 x i, where i is the square root of -1, which in a common sense of the word does not exist, and is defined like i- as i. And what a function in the complex plane does is to transform the complex plane, the points in the complex plane, from one configuration to the other, all right? I talk of a function, f(x). Then x has a position in the complex plane, and f(x) another position. And in this way, a region in the complex plane, by the function, is transformed into another region. Now, I set out to prove a theorem that if you have any simply connected region in the complex plane, essentially one without holes in it, then you can find the function – an analytic function – a function that satisfies certain simple criteria, which tram-transforms that complex system without a hole in it. Transforms it into the interior of the unit- unit circle. Beautiful proof. I talked and I talked and I talked, for much more than half an hour. And Kobe sat there and listened. And he asked- Where did you get that proof? I said- I got it from the book of Bieberbach, the common textbook. – Ah, you got it from Bieberbach. I suppose you know that I was the first one to prove that theorem? I said- Yes sir, I know that. I did not add- and that’s why I talked about it. I won – I got my good grade.

Well, that was not the only thing I learned from Heisenberg. The main thing that there was to learn was something about which I want to talk and to talk and to talk at the risk that maybe nobody will understand because the number of people who don’t understand it right greatly exceeds the number of people that do, and that is Heisenberg’s main work, his wonderful work on the Uncertainty Principle. The Theory of Waves and Particles is so constructed that if you know that the hydrogen atom is in its lower state, then you can calculate, without any doubt, the energy. But if you ask another question: the hydrogen atom is in its lower state, where is the electron? Is it at such a distance from the nucleus or at such a distance or at such a distance. The only answer that is furnished by the standard theory is: maybe this, maybe this, maybe this distance, with probabilities that we can predict. Some very important people, like Einstein, did not like this. His remark was- I can believe that God governs the world by any set of laws, but I cannot believe that he’s playing a dice. Now, this is an important question. And it is perhaps the most interesting thing I learned in my life. And I want to talk about it. They are abstract ideas, but not complicated ideas. Einstein’s statement, his remark, was really something to the effect- I can not imagine any science without causality. What the rules of the causality is, that we can develop, that we can learn. We don’t know all of them. But without cause and effect there can be no science. To that question, in the theory not only of Heisenberg, but of his teacher, Niels Bohr, there are two answers. The first answer is this: if you look at a situation and ask all possible questions about it’s past, you will find that these questions, without any exception, are consistent with the principles of causality. Ask the same question, not about the past but about the future and the answer about it is- the answer to it is: the future is uncertain. Heisenberg’s uncertainty principle. There are many situations, not all but many, where it is impossible to know the present sufficiently accurately to predict the future in a complete manner. The discussion of this uncertainty principle by Heisenberg involves ideas of this kind.

 So, to summarize: if you look at the past, we find nowhere any contradiction with causality, with cause and effect relation. But – here comes Heisenberg’s contribution – in regard to the future, it’s different. We never can know enough about the present to predict the future, in every case, except for predicting probabilities. Let me repeat the usual form in which this is set. I have a particle, I know it’s here now. I want to know where it will be in a second. For that purpose, I have to know the place of the particle and the position of the particle. And Heisenberg points out that in the formalism of quantum mechanics, because of the particle’s behavior, in some cases as a wave, you cannot do- know both the position and the momentum or the velocity, at the same time. Now, I want to talk about this in a little detail. Because the idea has not been as generally accepted. I already mentioned that Einstein was not happy about it. Two of my Hungarian friends have not been either. Wigner objects to Heisenberg’s reasoning, because Heisenberg says- In order to have enough knowledge about the future, I have an observer, the observer disturbs the state, and that gives rise to difficulties of quantum mechanics. Wigner says- That is no explanation, because I don’t know what an observer is. An observer, I am an observer. I don’t know myself. Having explained something you don’t understand by something else that you don’t understand, is not a great feat. I had the same discussion – Eugene would not listen to my answer – I had the same discussion with Johnny von Neumann. And he listened to my answer, and I am glad to say, he agreed with me. And to explain this, I’d better tell you the sharpest objection that has been made to the uncertainty principle, that is connected with the name of the physicist who made the first good Wave Function, good description of the hydrogen atom, Schrödinger. And the story is famous and known as the story of Schröding- Schrödinger’s cat. We have the following arrangement. Here we have a radioactive substance that emits, on the average, a particle – an alpha particle – once every second on the average. Now, here I have a counter, and I close that counter, so it won’t count, except that I open it for half a second. If, in that half a second, a particle arrives – the probability is one half – then the same apparatus that I have already used can be coupled into other apparatus that will open a horrible door, which will let out some poison, which will kill the cat. So, the quantum mechanical description is, a velo- a probability distribution, after an hour, with the cat, the probability of cat being alive, one half, being dead, one half. And the correct description is that I don’t know. Now, here comes our observer, and looks. And his looking will either result in killing the cat for good, or for reviving it. And this finishes, Schrödinger, I can’t believe. This is an ob- an objection published, generally quoted, my scientific listeners will know that this is age old and not forgotten, very well known. I have no objection to any of this except that I say- I don’t need to look.

 The essential part, the real novelty in quantum mechanics, I describe by talking to you about a phenomenon called Interference. Assume you have an original state and a final state, and you can get from the original state to the final state in two different ways. For instance, the original state is a particle – an electron – here, the final state is an electron there. In between, I have a screen which stops the particle except that it has two holes in it and the particle can go from the original state to the final state through one of the holes or through the other of the holes. In the interaction of the particle with the screen, allows the particle to move not quite on a straight line. Now, the very peculiar thing in quantum mechanics, the phenomenon called interference, is this: that there are situations where the fact that an electron can go that way or that way will lead to a high probability of the electron arriving. Or, under other conditions, it can lead to the more peculiar result that the fact that it can go this way or the fact that it can go that way, will make it certain that it never arrives here. That the possibilities how the thing can move can cancel each other. That is called interference. And the part of the quantum mechanics which explains the connection between wave description and particle description is precisely this study of Interference Phenomenon. Now, if I do anything, let an alpha particle be emitted or not be emitted, and I do anything with it I like, I can calculate the consequences. With one special remark; if you make a measurement which defines the position precisely, this measurement does not require an observer. Indeed, it is entirely independent. Something might happen a billion years ago and I can find in the geological remains that this or that has happened, no observer. What happens in a measurement is what is called – excuse me for introducing a new concept, which I will explain – something must happen which is called an Irreversible Process. And I will show you an irreversible process right here. Here is this hopefully empty cup and I drop it. Now, what happens in physics forward can also happen backward. The equations are so constructed that everything that happens one way can happen also the opposite way. So therefore, having stopped this- dropped this cup, I stand here with my hand open and wait for the cup to rise again, not as I do it, lifting it, but of its own accord, redoing the whole thing and landing in my hand. You all know that if that can happen at all you have to have a lot of patience, a patience greatly exceeding the age of the universe which is about as good as saying it never can happen. And the interference phenomenon, a peculiar thing in quantum mechanics, will show up its consequences in whatever else I do with this object. Because from the end state, I can reconstruct the initial state, except if there is an irreversible process. A measurement is not defined by Eugene Wigner knowing about it, or anybody else, it is defined by an irreversible process which does not allow the original state to be reconstructed from the final state. It is in this sense that Heisenberg should be understood. And he’s talking of it- about an observer. It’s simply justified as a didactic device, as a device to explain things, so people understand more easily what an observer is than to say what an irreversible process is.

Now, I want to tell you something about the importance of this new structure in quantum mechanics. And in doing so I will imitate Einstein by talking about God. I do not want to do anything about religious convictions. I am using the concept of God because that concept and some of its consequences are common knowledge. My statement of the great change is this: physicists in the last century, believing what they believed, had to believe that if God existed, He was unemployed, because ten billion years ago He created the universe, together with cause and effect relations. Whatever He did at that time determines the whole future to any accuracy you please and God cannot change that, except by violating the principles of physics, which we like to call a miracle. So, within the description of physics, old fashioned physics, with the future determined, we’ll- did not allow for any concept like God who can do something. The contest is that in quantum mechanics the future is not determined. From microsecond to microsecond there are changes that cannot be predicted. As physicists, we don’t say anything about good or evil, we don’t want to judge what can happen, but we can say that the future is not determined. This is a very simple statement. And I think it is a statement that everyone should understand, that this is the real structure of the world.

Now, I would like to tell you a few stories about the same period. It was a wonderful period, a period full of new discoveries, full of new, new knowledge. And also full of people who have understood what is going on only in part. I want to tell you one story involving myself. Heisenberg, from time to time, recommended to his students to go up to Berlin, to the Kaiser Wilhelm Institute, and listen to some interesting talks. And so, on his advice, with all of my 21 or 22 years, I went to listen to a lecture by Einstein, of his later theories in which he explains relativity and electromagnetism with the same ideas. I listened carefully and I understood everything for the first 30 seconds. And after that I understood less and less and less. And when in the end he finished and some of us including Eugene Wigner went to talk- went to walk in the zoological garden, beautiful sunshine, there I was completely desperate. And Eugene, an old friend and a very kind person, comes to me- What’s the matter? And I answered him, in Hungarian, in very simple terms. I said- I am so stupid. And now, Wigner basically, very basically, the kindest of all men, should have contradicted me but he didn’t. He said- Yes, stupidity is a general human property. Now, you know, the remarkable thing is that, that, that he made me feel much better. That sounded like the truth- All right, I’m stupid; so is everybody else. The point that I did not know then but I know now, that among the people who did not understand what Einstein was saying was Einstein himself. He did wonderful things until 1920, at which time I don’t know, he was not yet forty years old, I believe. After that he tried to explain everything and did not succeed.

 Now, I want to tell you about an experience, or a few experiences with another of the great men of that age, perhaps greater than Einstein if one should apply any measure in these things, I mean Niels Bohr. He was Heisenberg’s teacher and on the strong recommendation of Heisenberg, I went, in one of the vacation periods, to visit Copenhagen and I was sat down at the, the first tea party right next to Bohr. And with all of my twenty-one or twenty-two years, I was foolish enough to give something of a lecture to Niels Bohr, really not a statement of facts, a statement of hopes. I said- What we are doing here, quantum mechanics, we develop and in the future, classical physics, which is obviously full of contradictions between we- waves and particles, will no longer be taught. People will learn Schrödinger’s equations, probability distributions, all the consistent things that we know. I went on for a little while but I had increasing the feeling that with Bohr I was a little less than a full success. In fact, as I was talking, his eye got closed and I tried to end my statement as soon as I could. I ended it. And there sits Bohr not saying a word, for an eternity, I think it lasted for half a minute. And then he said- Yes, yes. You might just as well say that we are not sitting here and drinking tea but that we are dreaming all of this. A good friend of mine about whom I might tell you a little more later, Weizsäcker, Carl-Friedrich von Weizsäcker, was sitting at that table. We stayed together in the same pension. I asked him- What did Bohr mean? He couldn’t tell me either. I was obviously worried. I- after all, all I did is to say- now we have the truth. The truth announced by Bohr. And Bohr didn’t like it. I can’t quite assert that I understand now what he was thinking but I have something of a guess. Bohr liked paradoxes. I wanted to eliminate contradictions. He liked those contradictions. And what I said so far is true, what I am now going to tell you is probably true. And Bohr liked contradictions with good reason. He thought – he told some of us so later, in a more or less complicated manner, but with a clear theme song – the simple, straightforward way, how we see the world, this is a chair, this is a ring. It is a not a wave function, it is something that I can describe and understand. If I don’t start from such ideas, then I can’t possibly know what I am talking about. You must start from practical theory with all the contradictions that a detailed observation then lead to. Then, as a next step, you resolve these contradictions. But what I tried to tell him then; in the future the children will be raised in the world free of contradictions- No sir, we are not drinking tea, we are just dreaming all of this.

 I want to tell you another story about Bohr, a story that I want to tell you just for the sheer fun of it. For once, it has no meaning except to tell you what Bohr was. I listened to him once when he talked, mistakenly, about the oxygen molecule. One of my professors in Leipzig – Hund, Friedrich Hund – taught me about the simple molecules very accurately. Bohr did not know that and actually made some mistaken statements and I had to contradict. I wanted to be polite and I remember to have said to one of his statements- This is an exaggeration. Thereupon Bohr stares at me, quite mad- Teller says I’m exaggerating. Teller does not want me to exaggerate. Well, if I can’t exaggerate, I can’t speak. We then talked about the objective questions and I think it was cleared up. But Bohr’s statement about contradictions, about the use of words, about exaggeration, has something to do with the spirit of the uncertainty principle and the spirit of the times. And also, the spirit of one of the clear statements of moral significance that Bohr liked to make. Everybody – young people at eighteen years – should know that no statement can be believed unless you understand the statement and its opposite. A contradiction is not only likable, a contradiction is basic to understanding.

 I would like to finish my story about Bohr and, in a way, about Heisenberg, by telling you of a very sad fact. When the Nazis came, when Hitler occupied Denmark, Bohr was in danger of his life. He had a Jewish grandfather, I think, at least. He was to escape. Shortly before that, Heisenberg listened- came to him. Bohr came out to America and told us that Heisenberg is working on the atomic bomb for the Nazis. Heisenberg and Bohr have been good friends. Bohr did enormous damage to Heisenberg’s reputation. I heard him say that, I even heard him say that in a one-to-one conversation. I never quite believed it. I went back to Germany, found out – in more ways than in a short time I can tell you – but found out what actually happened. Heisenberg went to visit Bohr, he had to talk with him. He talked with him in his home, the Carlsberg Castle, the, the beer producing Carlsberg people or- I don’t know whether it was beer, but they gave it to Bohr. And when they were talking indoors and Heisenberg was afraid that there might be- that the Nazis might have put in listening apparatus, he said things- I am working for my government and it’s good to work for my country. That is what Bohr quoted. Then they went out into the garden and Heisenberg was no longer afraid. And then he added- I am with a group working on the atomic bomb. I hope we won’t succeed. I hope the Americans won’t succeed either. I cannot do otherwise than give an ab- abbreviated version of all this but here is one point, one generalization which I would like to make. My years in Germany, about which I want to talk a little more later, have been at a wonderful constructive period of science. Hitler destroyed it. You were not allowed to talk about Einstein. A Jewish lie, relativity. Heisenberg resisted it. I have many detailed indications that Heisenberg, if he did not directly sabotage the work on the atomic bomb, he never seriously worked on it. After war he and maybe ten other people were taken to a place in England and kept there and now the British did listen by secret apparatus to what they were saying to each other. I couldn’t get that record until two years ago when it was published. And Heisenberg said about atomic bombs some of things which clearly prove that he did not think about the subject. They were told in August 1945 that we’d dropped an atomic bomb and the Germans didn’t believe it. And then Heisenberg told them- Perhaps they did, and explained to them how the atomic bomb worked, wrongly so. A point about which I am very proud because the mistake that Heisenberg then made, I made a few years earlier when I was starting to think about it – and found out within a few months that it was wrong. That Heisenberg should make the same mistake gives me pleasure. But it shows, in the case of the excellent intelligence of Heisenberg, that he never seriously tried to work on the subject.

 I did get my Doctor’s degree and stayed in Leipzig. Heisenberg employed me as an assistant to his assistant, Bloch, and Bloch and I sat together evenings and corrected students’ papers. You know, I learned a lot by correcting papers. Because what Bloch and I learned – and I’m very grateful for it – I learned in answering a question: what are all the mistakes that one can make? And I believe to this day that a complete understanding of a subject, or at least an approach to complete understanding, is precisely to understand all the wrong answers that you can give. In the course of time, I got an invitation from Göttingen, from a physical chemist by the name of Eucken. And maybe a little less than a year after my PhD degree, in 1931, I decided to go to Göttingen. My main learning years, not all of them, but the great shock of novelty of quantum mechanics, was over. It was now my job to transfer this knowledge which at that time, in 1931, was not very widely spread. The physical chem- physical chemists hardly knew it. I went around with Eucken when he visited his research students and I helped in the discussions. As an assistant, I really believe at that time I did more teaching than at any time in my life. There was a second man in Göttingen with whom I soon get acquainted- got acquainted and my job as assistant of Eucken got transformed into a job of assistant of Eucken and James Franck, an exceptionally nice man who got the Nobel Prize for something I will tell you in a moment. He took me on, on his newly acquired car, in which he was- took a lot of pride, to show me Göttingen, and told me about Bohr. He said- You know, Bohr’s statement, he was now talking about the early ’20s, or maybe the late 10- Bohr’s statement of excited states of atoms was completely crazy. None of us believed it. But Bohr was such a nice man, we thought we should try it anyway. And that is why I got the Nobel Prize. What he was talking about was the famous experiment of himself and Hertz, to have isolated atoms and shoot on that electrons- on that atom, electrons. And the electrons would be scattered, come off in another direction, with the s- practically with the same energy, no loss of energy. Then we got to higher and higher energies. And at a certain energy, the electron dec- decided, now we can lose energy. You surpass that critical energy by 5%, some of the electrons lost all but 5% of their energy. We had very clear experimental proof that atoms will not accept any energy but starting from a minimum energy, which is the energy of the first excited state, in Bohr, that they could take up. That’s why we got the Nobel Prize. And actually, this is, as I understand it, an important representation of the early part of atomic energy. That transformed Niels Bohr from a very nice man with some absurd ideas into a real genius. Because here the absurd ideas, were proven in an entirely different way.

 Now I spent most of my time in Göttingen, two years, in explaining to others what I, myself, have learned in Leipzig. There was one man to whom I needn’t explain it, he had been in from the beginning, he knew absolutely everything, and that was Max Born. He was not very much interested in me, nor in a way I in, I in him. He did everything in an exceedingly mathematical manner. Franck and Eucken were much more interested in the connection with a variety of experiments and so I had the opportunity to apply what I learned, what I learned in Leipzig. All this, of course, was a natural thing for me to do because I had started from chemistry. I had started from the very fact whose physics explanation has now become possible. This is, in my opinion, what at least the early parts of quantum mechanics really consisted in. They made out of physics and chemistry one simple unified science. Now, this unity, this connection, between two ways of looking at the same thing, of course, goes back to the very beginning of Bohr’s ideas. The name for it is the Correspondence Principle. The law in classical physics and the law in quantum mechanics don’t sound the same, they sound quite different. But there is a correspondence between them, so that the laws of quantum mechanics, when many quanta are there, become the laws of physics, of classical physics. Now, what I was con- concerned with was a certain aspect of all this. I came to begin with from a study of chemistry and in chemistry we are, of course, concerned with molecules. And in the molecules, one is concerned with the position of the nuclei of atoms and the connection between- with the glue between these nuclei, the electrons. And here now is a problem whose most simple, practical solution is not classical physics which can’t explain everything, not quantum mechanics either, which can explain everything but in a complicated, indeed, in an unnecessarily complicated way. Here, the correspondence principle has a different and very practical meaning. You make most progress if you explain half the problem relating to the behavior of a nuclei, the motion of the center of the atoms. Do that in classical physics. But explain the behavior of the glue that holds the atoms together – the behavior of the electrons – explain that in quantum mechanics. You apply the correspondence principle as the practical means to explain each part of your problem as it can be best explained.

Now, all this means nothing if I tell it to you this way. It may begin to mean something if I give you some examples. One of these examples is the Raman Effect. Raman, a Hindu, discovered that when molecules scatter light, the frequency of light is essentially unchanged. But, in addition to that unchanged frequency, there are weaker frequencies in the scattering. In comes a frequency of light, the frequency is connected with the energy; the higher the frequency, the higher the energy. Most frequently, the light will come out with the same frequency. But sometimes, the light will come out with less energy and less frequency, enough frequency and enough energy just to excite one quantum of the vibration of the molecule. In quantum mechanics, that’s very simple. What happens in classical theory? And the simplicity is really changed into something complex. When you do not talk about a simple diatomic molecule like nitrogen having two nuclei that vibrate against each other. Instead, take benzene: six carbons and six hydrogens. Take carbon tetrachloride: one carbon atom and two- and four chlorines around it. There are many vibrations that this molecule can execute. And some of them will appear in the Raman effect, some vibrations can retain a part of the energy that have come in, and some not. This is governed by what are called, obviously, selection rules. How do we explain these selection rules? In quantum mechanics it’s straight forward but a little involved.

Now, the whole Raman effect can be explained and, indeed, has been explained, in classical physics. That has actually been done in the very early days by two excellent Frenchmen, Cabannes and Rocard, and I want to give you their explanation. Because, it turns out, and that was a work in which I participated, the ideas of Cabannes and Rocard are very careful to establish, understand, to see explicitly, why some vibrations are excited and others are not. What Cabannes and Rocard say is this: what is scattering? Light comes in, it’s an electromagnetic vibration, primarily changing, oscillating electric fields. The atom or molecule that scatters that light is polarizable, that is, under the influence of light the electrons move to some extent and give a dipole moment to the atom or molecule that changes with the same frequency as the incoming light. This dipole moment then radiates and that is the normal scattering, not the Raman effect. What is the Raman Effect? Take a molecule, a nitrogen molecule. Two nitrogen atoms with electrons all around them. Now, assume that the nitrogen molecule vibrates. The nitrogen molecule is polarizable. The electrons move along with the incoming vibration of high frequency. But this polarizability is a little different if the nu- if the two nitrogen nuclei are close together and again different if they are a little farther apart. And if the molecule vibrates, then the induced dipole moment will vary with the frequency, the high frequency of the light that is coming in, but the amplitude of this frequency will change as the molecule vibrates relatively slowly. I can show you. Oscillation, low amplitude, high amplitude, low amplitude, high amplitude. In this kind of motion can in classical physics be shown very easily; that to an observer it would look like a sum of the high frequency and the low frequency re-describes the envelope. And that is the Raman effect. Completely classical. To my mind, a beautiful example discovered by Cabannes and Rocard of an application of the correspondence principle. You can explain a phenomenon by quantum states or you can explain it by purely classical processes.

Now, a friend of mine, George Placzek, who drew my attention to the problem, he and I applied all this to the Selection Principle. Which vibration of a molecule will appear in the Raman effect and how will it appear? And again, I can best illustrate what we have done by a concrete example, one of my favorite molecules, carbon dioxide. It’s simple enough so you can readily understand what you talk about. It still has the complexity to be a little less boring than the simplest examples. Here is a carbon dioxide molecule: carbon, two oxygens, on a straight line. Now consider two vibrations. This vibration, the carbon remains in the same position, the oxygens move up and dow- away and toward. And this vibration. The carbon moves up and down, relative to the two oxygens. If it- you give it a moment of thought, you will see that purely classically, what I describe to you as Raman effect, should behave quite differently in the two cases. Here, you might go from an easily polarized state to a less easily polarized state, to an easily polarized state, to a less easily polarized state. The polarizability changes, goes through a complete cycle. When the molecular vibration goes through a complete cycle, that’s a simple thing that you would expect. And that corresponds to the case where, in the Raman effect, the vibration, this one, will be excited with a single quantum. But now, look at this. The carbon vibrates against the two oxygen atoms, oxygen atoms. Let the carbon start at the center, has a polarizability. It gets off the center and now it has a greater polarizability. It gets back to the center, it has the original polarizability. If it gets off the center, a greater polarizability, back to the original center, original polarizability. In a complete vibration, from here to here to here to here, the polarizability had two maxima, here and here, and two minima, when the carbon went through the central position. You will never see one quantum added to the original frequency of light, but only two quanta. Because half a vibration is enough to re-establish the original position- original polarizability. And therefore, the polarizability will change twice as many times per second. Then the complete vibration changes. This thing, this kind of idea, applied to vibrations and incidentally, which is the main thing Placzek and I did, applied to rotations – the rotational frequencies also can be imposed on the original frequency. That is what we did for a few years, few- quite a few months, at any rate. Almost all the two years I have been in Göttingen.

And now I want to forget about physics and talk for a moment about people. Placzek wanted to continue with his work in the holidays while Göttingen was closed. I wanted to go home to Budapest and he said- No. I, Placzek, want to visit with Fermi in Rome and you come along. In a way, I was interested but I had just started to make my own money, needed little help from home. Didn’t quite know how to pay for my stay in Rome. Oh said Placzek- I will take care of that. I’ll ask Fermi. Here I get a copy of a letter from Fermi, that he has written to appropriate authorities in Hungary- I hear that Doctor Teller is considering to visit Rome for a few weeks. He’s a very famous physicist, and I want his cooperation. Could you please help him to get to Rome and to stay there? Fermi and I never met. That he had reason to consider me as a famous physicist was, to say the very least, an impudent exaggeration. But what makes the story particularly enjoyable for me is that together with the copy of the letter to the Hungarian authorities, I got, attached, a little note from Fermi- Dear Doctor Teller, I am sending you this copy. I want you to know that actually I would be really very happy to see you in Rome. So he took back the exaggeration but replaced it with a, a premature offer of friendship which, of course, became a very real friendship in the course of time.

Hungary, you know, at that time was not quite Fascist but on the way to it. Italy was the Fascist state. The rela- relations were good. I was asked to come to Italy by a famous physicist in Italy so I was invited to a wonderful place called the Palazzo Falconieri, a palace right on the Tiber which the Hungarian government has rented to house Hungarians who were working- scientists who were working in Rome. And I remember that in Palazzo Falconieri I got a small room, not very furnished, on the top floor, but there was one property of that room – there was a built-in alarm clock, which I needed, because I like to sleep late. The alarm clock was a loud cannon on the other, other side of the Tiber which was fired every day at noon and if I did not wake up earlier, I was woken up at twelve o’clock by the cannon on the Tiber River. I had a wonderful two or three weeks in Rome, got acquainted with Fermi, played ping-pong with him. Actually, our interaction on physics was not very great. I was working with Placzek on the Raman effect. Fermi did something incomparably more interesting, of which at that time I knew little, but which in the course of time became extremely important in my life. Shortly before my visit there, the neutron has been discovered and I will talk about it a little more in detail. But Fermi and his students started to bombard with neutrons practically every element in the periodic system, produced radio activities and studied them. And in the course of this business, they also studied the results on the bombardment of uranium and that was quite different from the rest. Because if you bombard magnesium, or anything else, you got a radioactivity that decayed with a certain period, possibly you got two radio activities together which decayed with two different periods. And they analyzed all this. But when they bombarded uranium, they got a mess. They got something that could be explained by having produced dozens of radio activities. Fermi interpreted this as having found the elements heavier than uranium, uranium being the heaviest element known at that time. And for that discovery, he got the Nobel Prize. The strangest thing in the history of physics: Fermi, a very great physicist, a Nobel Prize winner, got the Nobel Prize for the one error he made in physics because what he found were by no means transuranic elements, they were the fission products. But about that I want to talk later. I only want to say that had Fermi discovered fission in Italy, had told Mussolini about it, the whole development of atomic bombs may have gone differently and very much less favorably to all of us.

Fermi was not the one who discovered the neutrons. He was the one who made the first reasonably large scale nutr- use of them. I want to tell you the occasion when I first heard about neutrons, a little earlier than what I just told you. That was connected with another paper that, to my mind, was very amusing and was connected with a controversy between Heisenberg and an excellent Russian physicist whom I had known in Leipzig and later in Copenhagen, Lev Landau. And I’m anxious to try to tell you, in a qualitative way, what the controversy was and how I got into it. Landau calculated, in a formal way, which I don’t want to explain here, that electrons that move freely, as they do in metals, tend to exclude magnetic fields, weaken the penetration of the magnetic fields into the metal. That is called diamagnetism, incidentally, a phenomenon which in its extreme form in superconductivity is known by now very well – the electric fields being- the magnetic fields being completely excluded from the interior of infinitely conducting materials. But Landau had a theory, mathematical theory, calculating how magnetic fields would be weakened as they tried to penetrate into a metal. Heisenberg wouldn’t believe it, that cannot happen. Electrons, free electrons, or electrons moving freely, will not weaken magnetic fields, cannot have an effect on magnetic fields. The only way they can have an effect- they could have an effect was through currents. But in statistical physics, inside a metal, if there is a magnetic field, the electrons won’t move straight, they will move in circles. But at each place the motion will be due to electrons of two circles, this circle and this circle. And the two circles will give opposite currents at each point. The statistics over all the electrons will not permit the flowing of any circle- or of any current and therefore will not produce, cannot produce, any magnetic effect. I knew Landau, I knew Heisenberg. I told them I will try to understand this and they agreed that it might be a nice thing to look at and I did. And I found Landau was right, Heisenberg was wrong. Yet Heisenberg’s argument was a very simple argument. What could- how could it have been possibly wrong?

And that is what I want to tell you. In the interior of the metal it is right; that at each point that had to be two opposite currents. On the surface, near the surface, it still seems to be right. A circle near the surface cannot get completed. It turns into the wall. And instead of going round that, that way, it will go round that way, all the way around the interior wall, jumping that way. And the old argument still holds without any modification. But here comes the correction. According to quantum mechanics, according to Heisenberg, this circle and this series of circles, have different energies. Energies and frequencies are connected in quantum mechanics and it is easy to see that this has a simple frequency and this has some complicated frequency, which leads to a change and calculable energy. Therefore, this current and this current will belong to electrons of different energy, which at a certain temperature will be represented with different probabilities, the electron being more probably here than here. The cancellation of currents near the surface is incomplete and that incompletion then leads quantitatively to the result of Landau. One of my pleasant memories is the occasion when I reported on all that to Heisenberg who was wrong. He was very much interested. I certainly could not detect in him the least trace of displeasure, he was just plainly interested and agreed. He kept me for dinner and I remember from that dinner to other events. Heisenberg who was a great pianist played before dinner a piece from Bach’s Well-tempered Clavichord. I tried to imitate it and I succeeded, after a lot of attempts, only partly. That was the agreeable part of the evening.

I have to tell you more about Lev Landau. Later we had many discussions, one of them even resulted in a joint publication. But I want to tell you now something of my political problems at that time. In Leipzig, in Göttingen, I met with many people with whom I could discuss politics in a way I never discussed it before. People like Heisenberg and his close friend and mine, von Reisecker, strong anticommunists, and people like Landau, a convinced idealistic communist. Remember the times around 1930, the time of the Great Depression, a time when it seemed apparent that capitalism has disproved itself. I did not participate in those discussions a great deal but I listened very carefully. I knew communism from a rather unpleasant angle, from the early communism in Hungary but that was way in the past and now we were in the midst of something that looked like successful communism in Russia, unsuccessful capitalism in America and the rise of Hitler in Germany. What to think about all this. I did think. I did not come to a result. I came to doubts. Many people say now about me that I have been an early violent anticommunist. That is simply not true. At that time, I was full of questions. I came to decisions much later. And I came to decisions for a great number of reasons, of which I want to mention two that were decisive. I worked with one of my Hungarian friends, Tisza. He was one who competed with me for the Eötvös Prize and shared with me the Eötvös Prize in mathematics. He and I wrote a paper together. I really loved that paper. It seemed to give- belong, to a rotation of a dipole moment, a rotation of the whole molecule. And Tisza I- and I discovered that it was not due to a rotation, it was due to a peculiar modification of a vibration that looked like a rotation. We worked together, respected- we respected each other. And Tisza was a devoted communist. A little later, in the early ’30s, he was arrested for having done some service to the communists in Hungary. I don’t know and don’t care what it was. It became quite clear that Tisza who was arrested aft- for a short time and then let go, would never have a career in physics – in science – in Hungary and where- he studied there; he did not have any prospects. So I decided to help him. I recommended him to Landau who had gone, gone back to the Soviet Union and who was working in Kharkov. Tisza went there and worked with Landau. And at a la- somewhat later time, maybe it was ’34, ’35, I think, I was already in the United States, he came back from Russia, completely disillusioned. He was a convinced communist and that he certainly was no longer.

The decisive point. Landau, a real communist, had been arrested by Stalin as a western spy. I heard some rumors before that. I did not hear a simple fact as impressive as that and as close to me as that and I can tell you, my final decision came even later and I’m now deviating from telling you things in proper time sequence. In the early ’40s, I think actually in ’43, after coming to Los Alamos, I read a book by a very wonderful Hungarian author, in English. The name: Arthur Koestler. The title: “Darkness at Noon”. I don’t remember another occasion where one book influenced me so thoroughly. I now know that Koestler had been a convinced communist, had worked for them for years and then turned against them and wrote this book. “Darkness at Noon”. Noon. The triumph of communism in Russia, but darkness. The book is about a man like Landau, not Landau, arrested by Stalin’s apparatus. And the book is really wonderful, because you could read three-quarters of it and you see the problem, you see the accusations, you hear the defense and if you pay attention to nothing but the book, you have no conclusion. You don’t know who is right and you don’t know who is wrong. And then you read the last quarter and it becomes clear, without any doubt, that Stalin and communism in the Soviet Union is the worst kind of dictatorship. Precisely because the book emphasizes doubts, causes the reader – if he’s at all inclined to do so – causes the reader to think and gives the answers only at the end. In a way, that is an approach, not so very different from the approach in physics where the new science of quantum mechanics did arise, not as a simple, straightforward proof, but connected with a lot of doubts and giving the answer to that doubt. I read that book in the first month, the first few weeks I spent in Los Alamos in the early ’40s – early month of ’43. By the time I started to work very seriously on the atomic bomb, I was an anticommunist. But that followed a period of well over a decade where I was looking and searching for an answer.

Now, to get back to my work in Göttingen, there was one more phase of it that again I want to talk to you about for its own sake and because of its consequences, its later continuation. In Göttingen, I met Hertzberg, a man interested in electronic absorption of light by the electrons, in molecules, where the absorption of light was accompanied by the excitation – by giving energy to – the vibration of the molecule. And this process had been already explained in some general simple cases, by what is called the Franck-Condon Principle. Franck, the same James Franck about whom I already told you, and Condon, an excellent American physicist. And the Franck-Condon principle said, very simply, the excitation of vibrations in a molecule occurs like this; we start from a configuration of the atoms in a molecule, with electrons not excited. The excitation of the electron occurs in first approximation instantaneously. The molecule gets excited without the atoms having time to change their position. But in the excited state, the old equilibrium position is no longer an equil- equilibrium position, therefore in the excited electronic state, the molecule starts to vibrate. This was a well-known situation, known as the Franck-Condon Principle, on which Hertzberg started to work. He and I then discussed in detail what happens if the molecule had the same symmetry in the lower state and in the upper state. And the simple conclusion is that in that case, if the molecule was not vibrating in an asymmetric fashion, there is no reason why it should start to vibrate in the excited state. And in this way you can see very easily which are the vibrations which disturb the symmetry and which are those which don’t disturb the symmetry. We discussed that in all kinds of detail. But I later, in the United States, with some of my friends, two ladies, one, Mrs. Nordheim, and one, Herta Schpona, the assistant of Franck, both of whom had come to the United States.

I want to talk to you about one application of my early work on these electronic excitations, followed by vibration. One work which I believe is quite amusing in connection with one of the classical problems of the structure of molecules. I am talking about benzene. What is benzene? Six carbon atoms in an exact hexagon with six hydrogen atoms hanging out, again same six-fold symmetry, all in a plane. The classically accepted formula for that molecule was something a little peculiar. Not one formula but two. Of the six carbon atoms, the six carbon atoms are alternately connected with single bonds representing a pair of electrons and double bonds representing two pairs of electrons. Now, this you can do, obviously, in two ways. Double bond, single bond, double bond, single bond, double bond, single bond, back to double bond. Or the opposite. Single bond, double bond, single bond, double bond, single bond, double bond, single bond.

The two formulae had been proposed in the last century by Kekulé. One of the amusing points, politically amusing points of it was that this chemical theory had been refuted, forbidden, by the leadership in the for- Soviet Union. They referred to a Russian paper of the last century saying a molecule is a molecule is a molecule, it has one formula. To get two formulae for one molecule is nonsense. The Kekulé idea, on the other hand, in the United States, was taken up by one good chemist who actually is the one person I know of, perhaps there are others, who got two Nobel Prizes, one for chemistry, one for politics. And with one I agree more than with the other. And the work on chemistry includes his explanation of the simultaneous existence of two formulae for the same molecule. Linus Pauling has understood, at an early state, quantum mechanics. And he said- Yes, the configuration of the electron wave functions can correspond to one Kekulé formula or the other Kekulé formula. One then can get a lower energy state by describing the wave function of the molecule as a sum of these two wave functions, corresponding to the two Kekulé formulae. Sounded plausible, was accepted.

Now I want to talk about my paper with Porner and Northeim. We asked the question- If Pauling is right, as you believed he’s obviously right and he indeed is, what happens if you do not add these two wave functions but subtract them? That will give rise to a higher energy of benzene, to an excited state of, of benzene and one should see that state in the spectrum of benzene and we found it. It is a state in the near ultraviolet. Not being in the visual spectrum, it leaves benzene colorless, but has some peculiar properties. And here I want to use this example as another illustration of the correspondence principle applied to molecules. In quantum mechanics, the transition from a state representing the sum of two states to a state representing the difference of the two states, having different energies, corresponds in classical theory to a motion and oscillation of the electrons. The transition between these two states gives rise- corresponds to an oscillation of the electrons between one Kekulé formula and the other Kekulé formula. Now from that a number of interesting points follow connected with the symmetry of the problem. The Kekulé formula with three double bonds in a triangle and three s- single bonds in another triangle gives a center of gravity of directed charges smack in the middle. If I go from one Kekulé formula to the other, the average position of the electrons is not changed. Therefore in a simple form the transition cannot occur. It is not connected with an oscillation of electric charges, it will not emit or absorb light – it’s a forbidden transition. Then why do we see it? The answer is simple: here is the molecule, six sides, one and four here. Now let the molecule vibrate like this. The vibration causes a dipole moment to appear because in the one Kekulé formula there is a double bond here and a single bond here. In the other Kekulé formula there is a single bond on top and a double bond here and there are more electrons in the double bond than in the single bond. And if the molecule vibrates like this, then this change in dipole moment is no longer compensated by the change, by similar changes in dipole moment between this pair and this pair of bonds. The vibration causes the transition to become weakly permitted. A conclusion from this is a different behavior of the molecule; not only is the transition weak, but its vibrational structure is different. In an allowed transition you can see vibrations in which for instance the hexagon gets bigger and smaller but does not change its symmetry – for an allowed transition. For a forbidden transition you will never see the electrons change unless a vibration which causes a dipole moment, unless that too is excited. And that is precisely the structure that we found for that weak transition. That was a quantitative proof of the accepted chemical theory of the structure of benzene, and I want to add one political point.

All of us remember, remember with terrible feelings, what happened in January 1933. Hitler was made Chancellor of Germany. I think some of us suspected what is going to happen. I am remembering vividly a discussion of two of my friends, the physicist, Heitler and the more famous physicist, Pauli. It was in February 1933. Hitler has called for elections and there were fears what would happen. And what I heard in that discussion was- We have been both of us in Communist Russia. Dictatorship in Germany is something that just can’t happen. We know what dictatorship is, it won’t happen here. Those were, of course, critical days for all of us. I want to tell you what the first sign was that I saw of Hitler’s dictatorship. On the advertising columns there had been advertisements about better knives or spoons, and equally advertisements about better and poorer candidates for the election. One day in February, all these advertisements disappeared and from then on, no advertisement was allowed unless it was approved by the government. I don’t want to tell you the sad story of the burning of the Reichstag or the arrest of our communist representatives. Of Hitler taking over a government which had a majority only because the communists had been arrested. These are events which we all know.

 Many of us knew we had to leave Germany now but how? And a man was extremely helpful in that; was James Franck. He had invited two excellent British scientists. One was Lindemann, who became advisor of Churchill. The other was a biochemist, Donnan, who studied the transfer of materials across membranes. For instance, why we, in our intestines, let some foodstuffs pass through and stop others. Called the Donnan Equilibrium, whose main point is that it’s a selection and not an equilibrium. Well, Franck got these two people together with some of us and we thereupon got invitations from some of them, from both of them. I got two invitations and one of them, from Donnan said- Come to England at once for a few days. I can’t offer you anything but I want to talk with you. Visit me. So I did. And we talked for a couple of days, three days, at the end of which Donnan said- You know, I think it would be quite good if you came to England but I can’t invite you, unless you do one thing further. In one respect I find you are uneducated. Here is a book, if you read it, I’ll invite you. The title of the book was “Alice in Wonderland”. I read it and I also read “Alice Through the Looking Glass” and I got the invitation. Donnan was a wonderful man. He had got out of Germany a number of us and one little detail, while working with his people in his laboratory, was that we had a party once a week where the language was German. That, of course, was possibly a little help to those of the Britishers who want to learn German. But in a way, was in- kind of very nice compliment, very nice You’re Welcome to those of us who came from Germany.

 I actually did not stay long in London on that occasion because I had applied for a Rockefeller Fellowship to study for a year with Bohr in Copenhagen. And I got in that connection a questionnaire which looked as though I would get the job. I filled it out, sent it back, got it back, with a letter saying- Here it says in the quest- in your answers, that you intend to get married. Can you tell us when and how are you really going to get married? That sounded a little fishy to me. So I went to Donnan- How shall I answer that? And Donnan said- Now look, that is not a very well put question. It should not say get married or not get married, it also should say you are married, will you get divorced? Will you get divorced by killing your wife? There are a lot of possibilities. Somehow I agree with you, this is a funny question. You get a be- go down to Paris, to the headquarters of the Rockefeller Foundation and not answer them but tell them. So, I took the next train and boat and got to Paris. And that was my first meeting with an American official. A very peculiar meeting. The man whom I met seemed a little embarrassed and he said- I don’t want you to get the wrong impression. We in America are really not against the institution of marriage. But I have to tell you that if you get married in that period you can’t get the fellowship. I don’t know how and in what way – I found out that they had a sad experience with another Hungarian who got married while he was a fellow and gave all his attention to the marriage and none of it to the science. But at any rate, I had to make up my mind to get married or go to Copenhagen. So I called up my prospective wife, Mici, and she said- By all means, we can get married a little later. Go to Copenhagen. And I accepted and went. But that was not the end of the story. On an earlier occasion, James Franck, about whom I have to- told you, he and I were together in Copenhagen and he knew about my plans to get married. And so I wrote him a letter, not complaining, but telling him what happened and I got a letter with return mail- This is a scandal. Will you please write to me all the details and I will arrange it that you can get married. At that point I made a mistake. Instead of answering Franck, I thought- This is something concerning my fellowship, I better tell Bohr about it. So I did. And he took me down to have a cup of coffee and he listened to everything and he said- The Rockefeller people are so nice to us, so helpful to us. You must not talk to anybody else about that. Write back to Franck and tell him, ask him why he’s saying these things. You cannot answer. – But Franck already gave his advice. – No matter, write to Franck.

 By that time I was very impatient. I had postponed my marriage by a few weeks already and I was not terribly happy about the arrangement and I told Bohr that I was a little unhappy. And so Bohr said- Let’s talk again. And for the next few days, whenever I saw Bohr at the end of one corridor, he turned his back and ran away. After a week he came to me and he said- I talked with my brother – the very great mathematician, Harold Bohr – he told me that probably you should accept that letter. You should ac- you should complain to Franck. You know, the real problem was that Franck’s suggestion that I’m so unhappy about not being married that I can’t work. And Bohr said to me- had said to me- You know, that is not quite true, you have been working. And I wanted to lie and Bohr didn’t let me. But then he came back and he said- Perhaps you should lie. And there was Placzek and he told me- Now, go ahead and write immediately, just as Franck suggested. And I did. Dropped the letter. It came with a delay of three weeks. And after I dropped the letter, I remembered that I had not explained to Franck why my re- reply came so late. At any rate, the result was a letter I got from the Rockefeller Fellowship- from the Rockefeller Institute that was perhaps the funniest letter that I ever got. It was quantum mechanical in the sense that it was full of contradictions- It is quite clear that if you are getting married, you should not get a fellowship. But in your case- on the other hand- it went on and on with arguments for and against, justifying their earlier position. I did not know what to do about it, except for the last sentence. The last sentence was- Please inform us of the date of your marriage. Then I thought, I cannot possibly do that without getting married so I promptly went back to Budapest, got married and brought out my new wife to Copenhagen and worked happily ever after with a number of little remarkable incidents. One was that in Copenhagen I met a newly- another newly married couple, Johnny Wheeler and his wife. A very good friend who later, together with Bohr, wrote the essential paper on uranium fission, discovering- giving arguments that not all uranium are equally apt to undergo fission. But the light isotope, that is, cons- makes up less than 1% of natural uranium, that is the real stuff. And then even later, Johnny Wheeler did remarkable, and I think a little doubtful things, about far-out speculations concerning the consequences of Einstein’s general relativity, including id- ideas such as black holes, things that I believe actually exist and have the property that you can get into them but not out of them, that’s why they are black.

I myself did a bit of work with a nice young Danish physicist by the name of Kalchar. The work concerned the rotational states of hydrogen and I have no great reason to tell you about its detail, only to tell you the story how we reported about it to Bohr. No- Bohr wanted to hear what we are doing- Let’s talk about it in a seminar. We were there, Bohr wasn’t. Postponed it. Postponed it again. Well, I already told you that sometimes I slept late and in one of those occasions I came to Bohr’s institute early in the afternoon and there was my collaborator, Kalchar, reporting on our article. That was all right with me. But Bohr, for whatever reason, wanted me to talk. Kalchar was talking in bro- in broken German, he was a Dane. And Bohr said- Ah, here is Teller. It would be very much better if we would hear about that in English. Will Teller continue now? Well, the joke of the point is that while I did talk English, I have never before that given any talk in English. So my first talk in English was delivered on a paper with Kalchar, about orto- and para-hydrogen, in English. I survived it; so did the rest of the audience.

 I would like to hurry on now. After a very nice year in Copenhagen, very wonderful, because I did do my job in physics and I did everything else that the Rockefeller people were afraid I would do exclusively. We got back to England. Very soon after that we went off for a Christmas holiday to Hungary and coming back from there I had two letters waiting for me. One of those letters were- was from my friends Johnny von Neumann and Eugene Wigner who invited me to come to America for a job in Princeton. The other was from a Russian, George Gamow, who went to America, became professor in Washington at the George Washington University and invited me to join him there. Well I must tell you, I had gotten acquainted with George Gamow in Copenhagen and a very solid part of our connection was due to an expedition we made to there in my Rockefeller year, when he was also there and invited me to come on his motorbike all the way across Denmark. That excursion was wonderful. It started with a total eclipse of the moon. It was the only time in my life I sat on a motorbike. But, I want to tell you this about Gamow: he had good ideas. Most of them wrong, all of them adventurous and some of them excellent. But this is the important thing about Gamow. His physics and his riding a motorbike were completely different. His physics was ingenious. He’s the one who explained the connection between the energy of an alpha decay and the lifetime of the alpha particles, that the alpha decay was really due to a particle’s wave function leaking into a region where the particle should not be, according to classical mechanics. Gamow’s physics was ingenious and very often wrong. Fortunately, his driving a motor- motorbike was very much less ingenious and absolutely safe. We had a good time. And when he came to America, he invited me to join him.

 My being invited as a professor, I thought gave me the right to apply for a non quota visa. They accepted my request as a request and in a few weeks wrote back- Sorry, you cannot be admitted. I was very happy in England and I was just as happy not to come. But Mici, who had visited in the United States was absolutely adamant we have to go. And both of us and particularly she, had a Hungarian friend by the name of Thomas Balogh. He was in the same high school as I and for whatever reason, not clear to me, we used to call him, in his student days, Lord Balogh. That is what he became eventually. He went to England, was an excellent economist and was knighted and made a Lord. At that time he wasn’t yet. But Mici complained to him and he said- I’d go and straighten it out. And he did go to the American embassy and found out why I wouldn’t be invit- admitted. I asked for a non quota visa and got a professorship but a non quota visa cannot be granted for an occupation that you did not exercise for the last year before you applied for the visa. I was a professor at the time I applied but a few months earlier I was a Rockefeller Fellow rather than a professor, so I could not get a non quota visa. However, they also told Balogh, which they did not tell me, that the Hungarian quota was not filled and all I had to do was to apply for a quota visa, then I could be admitted. So that is how, for the second time, I got into a little trouble with American administration, which, however, with appropriate effort and good luck, was surmounted. I accepted Gamow’s invitation.

I liked Johnny von Neumann and Wigner better, but I somehow liked the idea of a professorship, liked the idea to work with a man who needed me, because my mathematics was stronger than his. That I certainly could not have said in connection with Wigner and most certainly I could not have said it in connection with Johnny von Neumann, whose mathematics was clearly better than anybody’s mathematics, at least at his time. That is how I got to the United States, in 1935. And how I started to teach quantum mechanics, to continue the same kind of work I did in Göttingen, I did in Copenhagen, I did in London. Quantum mechanics- mechanics, correspondence principle, what is new in physics, which at that time in the United States was less well understood than it was in Europe. And those physics exercises, those agreeable afternoon lectures that I gave for a few years at the George Washington University are probably the best time of my life.

In Washington, of course, I continued what I like to do. Many particular papers; I might mention only one because it became rather practical – the BET paper, Brunauer, Emmet, Teller – discussing the very simple problem of absorption of whatever, molecules, on a plain surface. That was well understood in the case of a single layer absorption. But my friends in Washington had worked on absorptions where obviously many layers were absorbed and had fantasies about molecular forces that reached out over many layers. And I knew that such a thing was nonsense. And I’ve told my friends, Brunauer and Emmet, that it is nonsense. And my- their answer was- Well, here are our facts and we will consider that as a proof of distant forces, unless you can offer us something better. So under compulsion I said- Very simple, we have a monolayer absorption and that layer then acts as the new surface to absorb the next layer and that absorbs the next layer. And therefore, once you have ten layers you are almost as good as having a liquid on which you condense one more layer. And your polylayer absorption must therefore have a lot in common with the formation of liquids. That was the origin of the BET Theory which has one very particular property. Because it connects the absorption with other known quantities, like the vapor pressure, the equilibrium between gas and liquid, it was possible from that theory to get the best way how to determine the area of the absorbing layers.

 There was another activity in Washington, initiated by Gamow, which was very interesting and very useful. He introduced an annual conference, essentially for theorists, with an entirely different subject each year. In organizing those conferences, getting the invitations, getting people amused, and getting the work done I, and also my wife, participated thoroughly and with enthusiasm. I might perhaps mention only one of those conferences, where we decided to discuss the energy production in stars, on which Gamow and I did some preliminary work and so did one of my students by the name of Critchfield. Now, my great contribution at that time was that invited my friend, Hans Bethe to this conference, who would not come, not interested in the subject. Well, I called him, I think, at least three times and told him- It’s very interesting and you must come. He did. He did not regret it, but rather he got the Nobel Prize for having found some of the most effective ways how energy production in the stars will occur. That is the se- famous Carbon Cycle; the carbon absorbing a proton, absorbing a proton, and so on, making beta decays and in the end, after the fourth proton got absorbed, you split up a helium nucleus and start the cycle from the beginning.

 That was perhaps the most interesting conference, except for one event, and that happened in January 1939. I have mentioned several times that I was not an enthusiastic early riser. Well, during… at the time of one of these conferences, Gamow had invited Niels Bohr, and he came at me at one early morning, the day before the conference, with the statement: Bohr has gone crazy. He claims that the uranium nucleus splits. I was sleepy and did not respond.

Next morning, Bohr gave his paper. By that time, I had figured out what he probably would say. And the details I could not know, the general idea I could. I told you that Fermi had absorbed neutrons in almost everything. And when he got the neutrons absorbed in uranium, then he got a great number of radioactivities, I knew about that. I knew that this was supposed to lead to transuranics and I also heard, by that time, about some objections to the point that quite so many radioactivities might be found. The actual possibility of a neutron getting absorbed in a uranium, the absorption energy being sufficient to split the uranium and thereby to give new radioactivities of known elements, that was the solution. And by the time I heard it, it was hardly a surprise.

 Let me perhaps explain, lest the point be lost, why you get so many radioactivities. The heavier an element is, the more the repulsion between the positive charges, the protons betters. The nucleus is actually composed of protons and neutrons approximately equal in number for the light elements, but as elements get heavier and heavier, the fraction of neutrons gets greater and greater. And the charge on a nucleus makes the nucleus less and less stable, so a little additional energy can cause the splitting. But the parts into which uranium splits, which now is a lighter nucleus, with fewer neutrons and protons, have a neutron to proton ratio which is high as is the fashion for very heavy nuclei. And radioactivity consists in the transformation of neutrons into protons or vice versa. And the fission of uranium leads to individual particles which for size are over rich in neutrons and therefore will give a lot of decays. In addition to the point that the splitting can be into unequal parts or into equal parts and hence the great amount of various radioactivity. Now, this point has been considered carefully in Germany, in the Kaiser Wilhelm Institute. And it was considered, to a very great extent, of looking at the radioactivities which are created, chemically separating out some of these radioactivities and finding that, for instance, one of them was indubitably iodine, clearly less heavy than uranium. That was discovered by Hahn and Strassman in Germany and they wrote to their friends, their Jewish friend, Lise Meitner, who had to leave Germany and was in Copenhagen, and Lise Meitner, together with her nephew, Frisch, actually planned an experiment in which these fragments, the higher the ionizing particles, could be seen. In the usual experiments of Fermi, a neutron was attached to a nucleus and then sent out one lowly beta decay. In this case, the neutron absorption led to two highly charged, fast moving particles which could cause strong ionization in Geiger counters, which I think I have already told you about in connection with the experiment on the unfortunate cat. Meitner and Frisch made the experiment and actually have seen these fragments. They did that after Bohr has sailed for the United States and by the time of his arrival in the United States he heard of the successful experiment. It was a real succe- sensation. And characteristically, and in a way, surprisingly, it was repeated in a short time in several American laboratories.

 I tell you what happened at our conference. Bohr gave this talk and somebody came to me toward the end of the talk- Better not discuss that in detail. It may have all kinds of funny consequences. And for some reason or other, we did not discuss it. But instead, one laboratory in Washington reproduced the fission experiment on that very same evening. And we saw the thing actually in action, a very remarkable discovery. I already talked to you about it. Fermi saw it. For years it was not understood. Eve the suggestion of this fission came up and Fermi disproved it. The point is that this fission cannot occur except in a way in which radioactivities emitting heavy particles occur according to Gamow. Heavy particles, relatively heavy particles have to go into regions where they are not supposed to be, according to classical mechanics; not enough energy. But in wave mechanics, they can do it. Well known to all of us. The suggestion was made to Fermi long before this conference and he calculated whether this could happen and found conclusively and clearly that it can not happen. The reason: the energy released in fission depends on measurements of energy. And energy is connected with mass, according to Einstein’s E=mc?. The masses and therefore the energies have been measured. And it turned out not measured quite rightly. Measured years earlier by Aston. Fermi used slightly wrong energy figures and the little diss- difference in mass or energy makes a lot of difference in the possibility of fission. Here fission – that was suggested, discarded – had suddenly become a fact. And that fact was, of course, at the basis of everything that we now know about atomic energy, about atomic bombs.

 There was one of my acquaintances who later became a very good friend. I had met him in Hungary when I was a high school student. His name was Leó Szilárd, perhaps – even including Johnny von Neumann – the most ingenious person whom I ever met. Some also thought the most disagreeable person. He paid no attention to people’s feelings, he was ready to violate everybody’s taste, except there was one thing, one bad thing he never did. Never, never did he bore anyone. Whatever he said may be objectionable, less often wrong, but boring or obvious, never. He was not invited to our conference, ever, but we knew each other. When the conference was over and Mici and I relaxed, we got a phone call. We’d got- had plenty of reasons to relax because most of the social entertainment for the conference was our job. And as I say, we’d said to each other- This was a nice conference, and thanks God it’s over. And there goes the phone. Leó Szilárd- I heard about your conference, I am on my way to Washington. Meet me at the railroad station at such-and-such a time. OK. I told Mici and Mici said- Now, one thing, I am dead tired. Fine, but for God’s sakes, not invite Szilárd to stay with us. So we went out, Mici was waiting in the car. I brought Szilárd and the first thing Mici says- Will you stay with us? Fine. Szilárd said- Of course. And this part of the story has a rapid and happy ending. We took Szilárd home, showed him to his room. He sat on the bed, he said- I slept here before and this bed is too hard. Is there a good hotel in the neighborhood? Well, Mici was exceedingly happy. The Wardman Park Hotel was visible from our place and there is where we put up Szilárd. But of course, the other part of the story was that Szilárd gave me a very detailed statement- Now is the time to make atomic bombs. That is what we did not discuss in the conference; that is what we avoided discussing. And I knew that this question in Szilárd’s mind was not a novel one. Years before, just when I returned to England from Copenhagen, at that time I did not know Szilárd very well, but he came to me and he said- We now know that in nuclei there is a lot of energy. We now know that with the help of neutrons, this energy can be released. If we find a good way of doing it, that would lead to nuclear explosives.

 I cannot tell you which happened earlier, whether this conversation with Szilárd or my attendance to an American Association of Physicists, where the great nuclear physicist, Lord Rutherford, was talking. It was a remarkable talk. In a way it was boring. Lord Rutherford said- There are some people who think that nuclear energy can be released. They are complete fools. It is so hard to get nuclei close to each other, this will never happen. Now, I’m sorry, I cannot repeat to you what Rutherford said, because Rutherford, using different words, repeated that long enough to take twenty or twenty-five minutes. He talked of practically nothing else. And then I saw Szilárd and I knew – I got up from him – that the fool who thought that this could be done was none other than Leó Szilárd and this rejection by Rutherford annoyed him to a point that he took out a patent on it. The special way he wanted to do it happened to be wrong. I already told you that at that time atomic weights and atomic energies were not known very accurately. One of the light atoms, beryllium – the fourth in the periodic table, hydrogen, helium, lithium, beryllium – had – normal beryllium, beryllium 9 – had four protons and five neutrons and the last neutron was bound so lightly that Szilárd thought it was not bound at all energetically; just stayed there for some unknown reason. And beryllium was the obvious donor of neutrons. He made experiments on it and found it didn’t work. Then he heard about uranium fission. He came down to Washington and told me what now is obvious. Here, we have fission in uranium. If, in the process where uranium splits into two, if there is not only a neutron absorbed, but at the end more than one neutron emitted, then we could have the chain reaction. One neutron in, maybe two out, then those being absorbed giving four and then eight and then sixteen and after ten steps a thousand, and after twenty steps, a million. And after fifty steps, enough to turn most of the nuclei- most of the energy, in a chunk of material into actual explosion, explosive. And that is what should be done. But nobody knows whether actually these neutrons, these additional neutrons, are emitted. That was the very end of January 1939. The discovery in Germany happened a few weeks earlier.

 A few weeks later, I was engaged in one of my favorite occupations. I already told you that my mother almost made a pianist of me. I was interested in music. In high school, during my high school years, I went to the opera again and again. And then I took up not just piano playing but chamber music. And I remember an evening where with a friend we played Mozart violin piano sonatas. The phone goes. New York, Szilárd- I found the neutrons. He did not need to tell me any secrets. That meant that nuclear energy could be released; that meant that the possibility of nuclear explosions had- was no longer an possibility but a probability. And you know, the next thing that has happened was nothing. It was discussed. Two important people – Fermi, who had gotten out of Fascist Italy and come to the United States; and Tuve, the head of an important laboratory in Washington – have gone to the Navy and suggested that they look into uranium fission. And they were told that the Navy is not interested in any fantastic scheme of that kind. And Fermi, who was real one to understand these things, in a new country, and due to his conservative nature, was not willing to push along any more. So, by the summer, all these possibilities were on the best way to go back to sleep.

 The one man who really wouldn’t give up was, of course, Leó Szilárd. He, together with Eugene Wigner, went to Einstein, whom they knew way back from Berlin and they put the case before Einstein and asked him to use his authority. I don’t know to what extent Einstein then agreed, but I know of first hand- first hand about it – was concerning Szilárd and concerning the point that Szilárd, with all his ingenuity, still did not know how to do one thing. He did not know how to drive a car. And so he asked, where I was teaching then summer school at Columbia, summer of ’39, the 2nd of August, I think, to be precise, to drive me out, to drive- drive him out to the end of Long Island where Einstein spent his summer weeks. And I did drive, we didn’t get into any trouble. We couldn’t find Einstein, for the simple reason that Szilárd did not know where he lived, he only knew the name of the place. So we asked and finally we came down to a nice little girl, I don’t think she was ten years old yet. She hadn’t heard ever about Einstein either but then Szilárd said- This nice old man with the long white hair. – Oh yes, right there, next door. So we arrived. And Einstein invited Szilárd for tea and since he was very democratic he invited Szilárd’s chauffeur as well. So I was there on the historic occasion when Szilárd took out the letter of Einstein to Roosevelt, from Szilárd’s pocket – I think Szilárd’s writing – informing the President of the possibility of an atomic bomb, of the real danger that the Nazis might do something about it. Szilárd gave the letter to Einstein and Einstein read it carefully. And my impression is that he read it- that he never had seen it before. At any rate, when he was through reading it, he said- Yes, yes. This would be the first time that nuclear energy would be re- would be released closer to us than in the sun. And he signed.

 The letter went back to Szilárd’s pocket and I have secondhand information what then happened. Szilárd did not send the letter to Roosevelt and indeed, had he done so, probably the letter would have been stuck on the desk of one of the secretaries. Instead, Szilárd gave the letter to a friend, a banker, who knew the President well. His name was Sachs. And how this happened, I don’t know, it happened and it’s important. Sachs at the time did not give the letter to Roosevelt, probably he could not get to him, until a few weeks between the beginning of August and the second half of October. And that was a fortunate time, because at that time Poland had been occupied by the joint effort of the Nazis and the Soviets. And by that time, Roosevelt was really and completely aware of the worldwide danger. So he promptly called Briggs – Doctor Briggs – the Head of the Bureau of Standards- Call a conference and make a decision, recommend a decision. Szilárd was invited, Wigner was invited, I also was invited but my main function was something else. I was to get Fermi to come to a conference and I did.

 I want to say something about Fermi here, even if it puts a little delay here. In between the long gone days of Europe and Rome, Fermi and I became much better acquainted. He received the Nobel Prize, he came to the United States and then we met at a conference in Stanford. I believe in the summer of ’38. And Fermi, my wife and I drove back in the car from Stanford to East Coast. And I remember that conference- that drive because Fermi was not interested in many things, he did want to see Hollywood. And I did not know how to get to Hollywood except again, through a Hungarian who knew everybody and everything, the great aerodynamicist, Theodore von Karman. We drove down to Los Angeles. Fermi and von Karman. Von Karman just came back from China. He rode some Chinese plane there to a strange place on the Yangtse Chiang. And Fermi asked him- Were you not afraid to fly the Chinese plane? And Uncle Theodore said- Well, I decided- I designed it myself. But when I was carried up by four Chinese, in a chair, on top of the mountain where I had an appointment with the President of China, you know, that was bad. Because two of the Chinese, once in a while would stand on one end of the precipice and the other two at the other end, the road curving in between, and I was sitting right on the top of nothing and then I was afraid. Well, Fermi and I discussed that. Fermi and I discussed many other things. In the fall of ’39, I went to him- Come and help us plan the atomic bomb. – I went to the Navy, I don’t want to have anything more to do with it but listen, said Fermi- you may go as my representative. I tell you what I would say if I went there. So he told something to me.

 Now, in the discussion around the table with Doctor Briggs presiding, presiding, Szilárd made his case. The representative of the Army, that representative said- Wars are not won by weapons, wars are won by the moral conviction of the people fighting. A statement to which I would have liked to agree except for the fact that the Polish, that the Poles have been defeated by the moral superiority of the Nazis and the Soviets. And after some discussion it was my turn and I said- Well, I am here to give you a message from Enrico Fermi. We believe that the atomic bomb can be made but not out of the materials that we now have. We first need a nuclear reactor and that nuclear reactor can be made with uranium. And there are all the people who are willing to make it. They are working for the university here, no need to hire us but we need money because to make the reactor we need the substance to slow down the neutrons, which will not eat up the neutrons, pure graphite. That will take some money. – How much? I gave the figure- $6000. I never lived it down. I had been advanced from chauffeur to messenger boy but at any rate the low figure of Fermi, which I transmitted, had its effect on the colonel from the Army- Well, listen, if you want $6000, that you can have. So that is how it all started, with the complete benevolence of Columbia University, with the help of the relevant administrator, Dean Pegram. And with six kilobucks. I also was needed and I can tell you my very important contribution. There were two outstanding people who were leading the project. One was Fermi and the other one was Szilárd. The only trouble was that they did not talk to each other. I was perhaps not the quite unique but rare personality who talked to both of them so I was invited as a guest lecturer to Columbia, gave classes and talked to both Szilárd and Fermi, and incidentally, Wigner, who started out by planning a reactor.

 Now, I have to interrupt this progress and tell you that in the meantime we had one more very important participant, a negative one. That was Niels Bohr. We had a meeting with him, I believe even before the time that we had the important meeting of Fermi signing the letter. But I remember quite a few of us, not Fermi, but Szilárd and Wigner and Weisskopf and a few others, met with him at Stanford. He told us- Won’t go, cannot be done. The active element which- which could do it, is the rare isotope of uranium; uranium 235. His friend, Johnny Wheeler and himself, Bohr, had proved that- We cannot get the material to make an atomic bomb, unless you wanted to turn the whole country into a factory. And incidentally, what we were doing then and there was very wrong. We tried to do it in secrecy and secrecy never worked and never will work. And to violate scientific openness would be a dreadful thing. Bohr was very serious about it. He took us one by one and each of us was to be convinced by Bohr. He did not convince us altogether. We wanted to proceed with it in secrecy and even Fermi agreed, if the others won’t publish, we won’t. But it was in vain, because in, in the meantime, the ideas also arose in France, to Joliot. He published everything, the possibilities and, at least in part, the work became open. At any rate, with the conference chaired by Briggs, recommending that we go ahead, we did go ahead, slowly. Heard that the British, under the influence of another German refugee, Peierls: they were doing very similar things but with the war effort going on they were very willing to work with us, to come to the United States and do whatever need be done. All this took time, month, many months and sometime arou- in that period, I believe it was still in ’39, I first heard of the possibility in which later I was, was to per- participate in a rather thorough manner. I mean, the hydrogen bomb.

 I worked at Colombia. A group of us, including Enrico Fermi, went to lunch together quite regularly and on one of those occasions, coming back from lunch, Fermi says to the- to me- Now, if we make an atomic bomb, if we reach high temperatures, we might reproduce things, thermonuclear reactions, reactions between heavy hydrogen nuclei that go on in the sun. What about the hydrogen bomb? I thought about it and next Sunday went on a hike with Fermi and convinced him that it cannot be done. In order to have enough energy for nuclei to approach each other, with a sufficiently high probability, you needed enormously high temperatures. And at those temperatures, practically all the energy would go into radiation and there wouldn’t be enough left for the nuclei to approach each other- Then why does it work in the sun?- Well, it does because in the sun it can take billions of years and we wanted to do it in an instant. It cannot be done. The next development was that to a great extent, under the influence of the British, it was decided that our whole effort should be stepped up. Not the hydrogen bomb, the atomic bomb. Yes, there should be an effort to separate the uranium isotopes. That was to go on at Columbia. Yes, there should be another effort to make a nuclear reactor in which neutrons got slowed down, in which a new element, plutonium, would be produced, that could be separated from the bulk of the uranium relatively easily, and that could be the explosive. And that is what actually Fermi had planned in parallel with the British effort and that was to take place, to be concentrated in Chicago. After some difficulties connected with the fact that I was an American citizen, but only quite recently, I even got my clearance and got to Chicago and found Fermi and Wigner busily at work on the reactor. I felt I was not needed. I got a colla- collaborator, a very nice young man by the name of Emil Konopinski and I told him I had been working on the hydrogen bomb and it can’t be done- Let’s write down the arguments to settle that question once and forever, it cannot be done. Well, that’s what we did, or rather, that’s what we tried to do but the more we discussed it, the more it seemed that perhaps it could be done anyway. In a few weeks, our minds have changed and we now proposed that a hydrogen bomb can be made, because we could reach temperatures where the nuclei could reach enough- reach each enough fast enough, soon enough, so that before all this radiation was emitted, you had the reaction going. By that time, it was decided that the theoretical effort should be headed by one of the really outstanding American physicists who had not been previously involved in all that, Oppenheimer.

 By that time, it was the summer of 1942 and Oppenheimer invited a number of people, Felix Bloch, Hans Bethe, a few of his students, Serber, Frinkel, myself, and on my recommendation, Konopinski, to discuss matters. And there, in our conference in Berkeley, I had an opportunity to propose a hydrogen bomb, the design that we had at that time. We had a thorough and long discussion. It was obviously of general interest. In the middle of it, Oppenheimer left for a conference with the head of the Chicago group, with Compton. He reported on what we were doing and what he has said, that is in the record- There are novel possibilities. Even when we have the nuclear explosive, it will not be a simple matter. A major theoretical effort and a major practical effort will be needed. We need a new and separate laboratory to do all this. And this was to be set up at the very secret, remote place at Los Alamos. There was a boys school there that was bought. It was taken over by the Army. And, beginning of ’43, we were to start an effort there to make whatever, an atomic bomb, or more. I had some difficulties.

 Los Alamos. It was a new undertaking. It was something rather different from going to a university and changing one research from one topic to enough- to a somewhat different topic. What was the motivation of all of us? I don’t know. I know something about myself. Even what brought me to Chicago and what drove me from Chicago to Los Alamos. Because, in fact, I was not happy about any of this. What I had been doing in pure physics was wonderful. What we are now setting up, up to do was something very, very different. And I want to tell you about one of my thorough motivations and also how one of my friends, Eugene Wigner, felt about all of this. As far as I am concerned, I took an increasing ins- interest, not really, I’m sorry to say, not from the time of Hitler invading Poland, but a little bit later, when he invaded the West, Belgium. I was still, at that time, in Washington and there was a conference, an international conference, no, an inter-American conference to be exact, that Roosevelt was to address. And against my usual habit, I did not miss an op- opportunity to hear a politician, because of the invasion of Hitler of the Netherlands, Belgium, by Hitler. That was a few months after Einstein has written to Roosevelt and Roosevelt asked our opinion. Roosevelt talked about the dangers, not to Western Europe; the dangers to the whole world. He made a point of how much- how smaller, how much smaller the world had become, that from century to century, from decade to decade, politics here and there were coupled more closely. And then he concluded, in a remarkable fashion. He said- I know that you will be told that without the new weapons of science, the danger would hardly exist. I am telling you that this is in a great measure true, but at the same time, it is true that if you scientists don’t work on weapons, the National Socialists will conquer the world. I listened. I had a strange feeling that Roosevelt was talking to me. We never met. But I may have, been among the couple of thousand people in the audience, I may have been the only one who knew of the letter that Roosevelt got, who knew that among the new weapons Roosevelt had the atomic bomb in mind. So that was a part of my motivation.

 Now, let me tell you the opposite of this. While we were working in Chicago, my good friend Eugene Wigner and I, we did not work on the same thing. Eugene told me- It’s enough, if we prepare the materials to put together the atomic bomb will be an easy thing, don’t go to Los Alamos. I thought I knew otherwise. But I also was influenced by Wigner in other ways. The war was going on, as the Nazis moved forward in the Soviet Union. I saw Wigner once a week or once in two weeks- How does it go? And Eugene will say- It’s terrible. A counter offensive was beginning to go and Eugene said- Well, we take back a village here, a town there, it does not make much difference, it’s terrible. Then came the day that the Nazi armies in Stalingrad were surrounded and I now was expecting to see something new; an optimistic Wigner- How does it go? So Eugene shakes his head and he says, in the old voice- It is terrible. What kind of a peace will we make? We knew at that time, and I say it for this reason, we knew at that time that we are working on terrible problems in connection with the war and in connection with everything that would follow the war. When it came time, early in 1943, to go to Los Alamos, I had some difficulties. By that time, Mici and I had been married for a few years. We did not have any children. We ha- did not have enough confidence in the future. But when America entered the war, then I began to be a little optimistic about defeating Hitler. Then we started to work seriously on a family and early in 1943, our first- first child was to arrive and did – Paul was born beginning of February. But I had to leave for Los Alamos and Mici and the little boy could not follow immediately, so I went alone. There was- there was the boy high school in Los Alamos, with a few houses for the administrative leaders. The rest of us were given small rooms in what was- in what was called The Big House. I remember my discomfort there due to the fact that I had a room next to Dick Feynman. And Dick Feynman preferred to make very loud and not very melodious music late into the night. I had plenty of opportunity to find out later that his physics was incomparably better than his music.

 We started in Los Alamos. Mici and my son, Paul, arrived a few weeks later. We got a little house, or rather, a little apartment in a house and were comfortable. And Wigner’s prediction that we would be not facing any important points, any important problems, turned out to be very, very wrong. At first we thought we knew what to do. We had to bring together an amount of active material, the material to be produced in Chicago so that each half of it would be harmless, because more neutrons could diffuse out of it than where produced in the same time by the fission process. But if the two pieces were brought together, then they would explode and the whole point was to bring them together fast enough so that they should not explode prematurely when the neutrons were barely able to multiply. Now that did not seem so difficult because to start the whole process needed a neutron and there were a few- few enough neutrons around naturally so that the two pieces could be brought together fast enough, if one piece was shot into the other by a gun. And that’s what we were working on. And then came the discovery. Yes, if you used uranium 235 as the active multiplication material, it could be done but if you tried to use the material that came out of the reactors, plutonium, then it would be a very, very difficult problem, why? The material we tried to make was plutonium, one unit more heavy than the ample uranium, uranium 238, from which we started. We fed uranium into a reactor, the uranium would ab- would absorb a neutron, become uranium, of the weight 239; that made two disintegrations, turned into plutonium and that is a very good bomb material. Nothing wrong with that so far, except that when you leave the material for a long enough time in the reactor, you also made another kind of plutonium, plutonium 240 and that was a material which spontaneously emitted neutrons, spontaneously split into two much too frequently and following that it would emit a neutron. And so, our pieces of plutonium that we were to bring together were swamped with neutrons to a sufficient extent where- where at the time when they became just slightly critical, when the neutrons just began to multiply, they multiplied fast enough to throw the whole thing apart and get a small explosion instead of a big one. What to do about that?

 One of the very ingenious people in Los Alamos, Seth Neddermeyer, had idea that instead of starting with two pieces, we should start with a shell and surround it with high explosive and have the whole thing converge and that might work fast enough. It was a proposal that looked good but was not yet accepted. In the meantime, I had a personal proposal. I found in many other instances that when I had a problem it always could be solved by getting the advice of somebody who was, in my opinion, better than anybody else, a fellow Hungarian, Johnny von Neumann. Oppenheimer was under orders to keep Los Alamos closed, or almost closed, not letting- let many people in but when he got convinced that somebody would be really needed, he was very good at getting him so we got permission for Johnny von Neumann to come in and help us. We told the problem, he made some suggestions, I won’t reme- I won’t mention them, they did not turn out to be very good. But that first evening, I invited Johnny for dinner and that dinner I remember, for reasons more than one. I remember sitting with him near the heating equipment which did not function perfectly and which would send off a loud report of some  unstable condition once every half hour. I don’t know that Johnny was really alarmed but he told me- I would feel that it is a real shame to be killed in Los Alamos by a mere sub-critical explosion. That was a part of it. Another part was that I told Johnny about the proposal of Seth Neddermeyer and Johnny did something extremely simple, I don’t know why all of us did not do it earlier. He assumed, as was the sort of obvious thing to assume, that uranium or plutonium would be incompressible and then let it be sent in by the velocity that an explosive could produce. As the material got into smaller and smaller radii, in order to make room for the incoming material, the shock formed had to go faster and faster. The material had to accelerate. And in order to do so, had to have a big pressure. And Johnny came to the conclusion you could do that; in the process you would produce more than 100 million atmospheres. And I have told you that at the George Washington University we had conferences. One of them was about the interior of the Earth, where I learned that a pressure- at a pressure of barely a few million atmospheres, not 100 million, iron in the center of the Earth would be compressed. If Johnny was right about these big pressures, then the material, plutonium or uranium, would surely be compressed and compressed material can lead to neutron multiplication in smaller amounts. You could get nuclear explosions by the method of an initial implosion, we could get the job done, with less materials, at a much earlier time, possibly before the end of the war. That point we put next morning before Oppenheimer. He caught on very fast. The whole program of the laboratory was changed. The implosion was put down as number one priority.

 I had, in that connection myself, something of a difficulty. The whole work seemed to be planned by Johnny von Neumann. Well, he told us about methods to produce in high explosives a spherical convergent motion. But the question, the hydrodynamics of an imploding shell, required a solution of differential equations that looked to me anything but simple. The Head of the Physics Department, of the theoretical work, Hans Bethe, wanted me to do this calculation. I begged off. It looked to me impossible to form- perform in an accurate manner. And there was a way out, because by that time, computers had made a lot of progress and instead of accurate analytic solutions, we could work with computer solutions, with numerical solutions. That would not have been, in itself, so hard. The difficulty was that the whole situation was a kind of motion which we call unstable. If we have a little inaccuracy in it, that the sphere was not quite a sphere, a shell was not a uniform shell but at some place it was a little thinner than at other places, then this lack of symmetry will grow. And to avoid that and to produce something really reliable, seemed to me a very difficult problem. I begged off. I don’t think Bethe ever forgave me. Oppenheimer apparently, I think, in fact, understood. He let me do things that I felt I could accomplish better.

 In the meantime, the British contingent appeared, among them the very excellent, effective workman, Peierls. It was his job in the end to do this calculation and I can tell you something peculiar about the results. What he did was good and sufficient. It was not sufficiently good and sufficient for us, in the end, to trust it and the actual shot was made on a simplified, not optimized model, in which we could have greater confidence. Instead, I did a number of other things that I felt I was more qualified to do in the sense that with the help of a few others, like Konopinski, a little group all together or not much more than half a dozen people, we could do- accomplish things that others would not do so easily. One of these was something that came up way back in Berkeley, in our original discussions on the hydrogen bomb. Something that Oppenheimer transmitted to Compton and Compton took it seriously enough to consider it as one of the main arguments for us to have a separate place and it was thi- If something like a thermonuclear reaction was possible, was not there some possibility that a nuclear explosion could set off a much bigger explosion engulfing the whole world? How could that happen? Would it? There are two obvious ways to consider and one of them, frequently mentioned, is quite wrong- An explosion in the water, in the ocean, would be surely not terribly harmful. There are nuclei in the ocean, for instance, a few heavy hydrogen nuclei, that could react, but they are so few and far between that before a reaction that feeds upon its own energy – a thermonuclear reaction – could get going, the energy would be long since dissipated by the initial shock. No. Our worry was the air. The main component in the air is nitrogen and the collision of two nitrogen nuclei could produce neutrons that then could propagate the reaction in the nitrogen. We made very thorough estimates about it and proved, I think sufficiently, that this could not happen either. But I must say – I’m glad to say – that this same point was pursued with the measurements, in Oak Ridge and with excellent calculations, by Lowell Wood after the war, so that to increase our assurance of one in a million, to where it belonged, to none at all, call it one in many trillions. It could not happen. That was a part of the job. I was interested in another part that I started to take very seriously and that I can easily explain.

 Some of the other things I was doing I did with great enthusiasm and with the full approval and support of Oppenheimer for which I’m really grateful. Early in the game I brought up a possibility that might make a nuclear explosion work much more effectively than had been predicted. It wouldn’t work, we know that, except at a very high temperature. At a high temperature a lot of the energy, and I already said that too, is in radiation and this radiation, as it happens in the stars, can leak out. If it leaks out rapidly enough then the nuclear explosive stays together for a longer time and multiplies better and it would be a great improvement in the yield. This is a point I already brought up in the conference in California in the summer of 1942. In the course of discussion we convinced ourselves, not completely, but we came to the conclusion that that is probably quantitatively not important. But I kept worrying. I wanted to continue to work on it and Oppenheimer said no, but he agreed if I can find a group outside Los Alamos that would do it, let’s do it. I found such a group. An excellent theoretical physicist whom I knew well, who later got the Nobel prize, Doctor Maria Mayer, working at Columbia University, seemed to me a very good candidate. With Oppenheimer’s permission I went to talk to her. She got her students together, got going. I was not allowed to tell her why I am interested and I did not violate security at all. She did not know why I was doing it but there was one little detail that I could not be silent about. Maria asked me- And please, at what temperature shall we calculate this opacity? I told her. I had to tell her. And at that point her eyebrows went up one tenth of an inch, but she did not ask any further question. Incidentally all this, this remarkable business – how security, so-called security, how secrecy works – it had a little sequel. All this came to the knowledge of the administrative people who called me in and who called in Maria, that we do not let too much information out.

 One of the few physicists who were there was a very well known man, Tolman, and we came under serious attack: Did we give away too much? One of the points was, did not- did we not have to- did we have to tell on what element we were working? Wouldn’t it be sufficient if we would say that Z=92? Well it did not take very long for me to explain that if I said the one thing I have said the other thing. But the amusing point about all of this was that in our being questioned a lot had been disclosed about the reactors that worked in Hanford and after the meeting when I took Maria to the railroad station she said- Well I really learned a great deal, very interesting what was said about reactors. Secrecy on occasion seemed to work against itself.

 I am apt to confuse this occasion with another one, when General Groves, a very effective man, an intelligent man, but an uninformed man, who knew much more about administration than about technical things. One of- on one of my trips he called me early in the morning in New York- Come down to Washington at once. I went down. Another method of separating isotopes – due to some peculiar effect called thermal diffusion, which did work- did not work too effectively – it blew up. Be- I did not know how and why. I was sent to talk to people and found that a chemical mistake was made. In the afternoon here was General Groves, the leader of our effort and all his colonels and people and they asked questions about it and they asked and they asked, and General Groves tried to pay attention, but once in a while his chin dropped and I’m not quite sure for what fraction of a time he was napping, but once in a while he would become conscious and say- Well, Doctor Teller, all this is only theory. Finally, in discussing generally the methods of separating isotopes, one of the colonels spoke up and said- But wouldn’t it be possible that by chance, just by chance, in one of these processes in Oak Ridge, all the uranium 235 would go to one end and all, all the 238s to the other end and you would have an explosion? So I said- Yes, that’s possible. But it is just as probable as that all the oxygen in this, oxygen molecules in this room should meet under the table and let us up here to suffocate. At which point General Groves raised his chin and said- But Doctor Teller, you said it’s possible. At which point Tolman spoke up and he said- General, Doctor Teller really means that it is not possible. The remarkable thing is Groves respected Tolman and having Tolman’s approval in that one case he never again doubted anything I said.

 A little bit about the administrative side. In the meantime progress was done. The calculations that I did not undertake led to results which later proved to be good enough, but we did not trust them sufficiently so that at the end a greatly simplified model was actually used. In the meantime also, the various separation methods, the methods of making material, made progress, improved. There were three different ways to get the material. One was separating the really useful active low abundance uranium 235 for the bulk of U238 by using a gaseous molecule containing uranium, uranium hexafluoride, and using the fact that the lighter isotope diffused faster. It worked. It worked much too slowly. Urey at Columbia University worked- was working on it. He worked out the method that proved very useful in separating other isotopes used in other parts of physical chemistry, but for the war effort; no.

 In the meantime, in California, Lawrence worked a more effective way of separating isotopes that depended simply on a deflection of ions that have been given a certain energy by accelerating them and then deflecting them by a magnetic field. The same energy at different masses will give different deflections. That method worked, but it worked only to make enough explosive material for one or two bombs. The mass production looked too expensive, too difficult. There remained a third method, the main method pursued in the Metlab, Metallurgical laboratory in Chicago; make a reactor, construct a reactor, produce a new element, plutonium. In the meantime we, at Los Alamos, found a method to compress the plutonium and make little of it enough to make an explosion, but at the same time the work at Chicago in the Metallurgical Laboratory really took on impressive dimensions.

 The first reactor was produced at a remarkably early time, end of 1942, by Fermi and his collaborators. But in the meantime others, including particularly Wigner, and people working with him, scaled up that reactor into much more powerful reactors that were set up in Hanford, Washington. Remarkably enough, and in a way contrary to usual practice, set up at the minimum of experimental experience and a maximum of theoretical calculation. And the reactors worked. They almost worked. It turned out that they worked and then the reactor got shut down and they started to s- get it going again and it would not get going. That was unexpected and unexplained.

 On one occasion two of the most important people, Fermi and Wigner, went to visit the site and these people were not known to the guards. For security reasons, Wigner was called Wagner and Fermi was called Farmer and when they came in the guards knew Wigner, or Wagner, but they were a little worried about this strange man with an accent who was called Farmer. And so they objected and what did my friend Wigner say?- His name is Farmer, as truly as my name is Wagner. And I don’t know whether it was Wagner or Farmer who gave the explanation.

 One of the fission products decayed into an element, I think it was xenon 135, a violent neutron absorber. But that saved the day because due to its strong neutron absorption it was destroyed rapidly. But if you close down the reactor, let xenon 135 accumulate, then you could not start it up again, a difficulty that took care of itself by waiting a while, but you have to understand it. At any rate, enough of the plutonium was made that together with our work on implosion there would not be a really bad shortage of it at the end- well when it became the end- at the end of the Second World War. All this work in Chicago was concluded by the end of 1944 and at that time, much to my pleasure, Fermi transferred to Los Alamos. He was put in charge of various things, among other things of the group with which I worked. And at that time I had a privilege which I share with very few people. I became the teacher of Fermi. I had to tell him what everybody in Los Alamos was doing and even excellent people- excellent student as Fermi was, and I claim not to have been a poor teacher, it took, it took almost a week before Fermi understood everything he wanted to know and that was just a little mot- bit more than everything that we knew. These were the conditions under which we were working. I, to some extent outside Los Alamos and a part of it of course was, what I already mentioned, the safety from nuclear explosions in other places like Oak Ridge. And one detail about that that I think is worth, worth mentioning, that I had a slightly ticklish job because I was not allowed to answer any questions, but people working on the other projects were instructed to answer all my questions. It says a lot about the character of the effective people who worked at that time, like Manson Benedict, that under these very unfavorable conditions, we worked well together and in fact established all the necessary mutual information.

 In the meantime the war proceeded and the war ended in Europe. Remember, in the spring of 1945, the Nazis were finally defeated, Hitler committed suicide and there was peace. But not in the Pacific. There the fighting was continuing. Around that time, end of June 1945, I got a very interesting letter from my good friend, Szilárd, the very man who got the enterprise started in the United States. Now he said- The dangers of Nazi atomic bombs are gone. We are approaching the ability to make atomic bombs. What shall we do? Is it necessary to use them? Shall we use them? Would it be better perhaps first to demonstrate? A number of us in Chicago are submitting a request that a bomb should not be used against the Japanese without prior demonstration. Would you collect signatures for that proposal in Los Alamos?

 Well, I must confess that I did not give very serious thought to the problem before that, but I liked it. It was impossible to do anything about that without asking Oppenheimer. So I did, and Oppenheimer was very determined on that point- What does Szilárd, and for that matter what does James Franck, who was in that with Szilárd- what do they know about the Japanese? About how possibilities of peace work? We should do nothing about that. Here is something that in retrospect I regret. The whole question of using the atomic bomb actually was something that bothered me and it either bothered me too much or not enough. I did not think about it in a sufficiently serious manner. I did not say to Oppenheimer what I should have said- It may not be our business to determine how to use the atomic bomb. It is our business to discuss and present the alternatives: if it is not used, how can it be demonstrated and how effectively it can be demonstrated. Perhaps I should have said that. I didn’t. Oppenheimer persuaded me not to sign and I wrote a letter in that sense to Szilárd. Later I found out that Washington did ask the leading physicists for advice. In the chair: Oppenheimer.

 Oppenheimer said we must use the bomb, we could not demonstrate. He knew much more about it than Compton or Lawrence and Fermi wouldn’t talk. So the unanimous recommendation of the four people was to go ahead and use the bomb. Quite possibly that was the right thing to do. It cost the lives of many people, but the war going on for even another month would have cost more lives. I have no definite opinion on that, but there is one circumstance which in retrospect continues to bother me: these discussions, exchanges, occurred throughout June 1945. Early morning July 15th we were to try out one of the plutonium bombs. Those could be produced one every few weeks, maybe three months – we already had two of them – we could try out one. And so we planned to do it.

 We decided – it was a very obvious decision – we were not quite certain whether our somewhat difficult design would be… would work, we better test it. And the test was scheduled for the middle of July. I was invited to look at the test, not with the group that was closest and was operating the actual atomic bomb on the top of a tower. I was with another group of sort of senior people. I say senior – I was of course not yet 40 years of age – and there we were on the early morning of the 16th July 1945, looking at a spot where something was going to happen. We were instructed to lie down with our backs to the bomb, not look at it. I did not obey. I did lie down, but looked straight at the point, but we were also given welding glasses to shut out too much light. I used those and had an extra pair of dark glasses and I was among those who… who expected a big yield – I put suntan lotion on my face. And the shot was canceled. It rained out. Then we waited and a little time before the sun went up, it was still quite dark, the rain had stopped, we go ahead. Countdown worked fine up to minus 30 seconds, then whatever went wrong, our group no longer got the countdown. There was half a minute to go. It was an infinity. It was clear that the shot did not work – and then it did, just on time. Thirty seconds was too long to wait and I very distinctly remember my first impression. I looked straight at it. It was a weak point of light that spread and started to rise and my first feeling was of disappointment- is that all? Then I remembered all the nice absorbers I had in front of my eye. I did not take them off, I tipped the welding glasses and looked down on the sand next to me and you know, if in a dark room, you lift the curtain and the full daylight is streaming in, that was what I saw and then I was impressed. By and by, in a matter of quite a few seconds the light faded and we saw the fire ball rising, dissipating. We didn’t talk much. I am sure that all of us, the two dozen of us on that spot were thinking: soon this will be used and at that time it will not be an experiment.

 One remarkable reaction to that, that is well known, generally known, but I better quote it, came from Oppenheimer. He was with a group much closer to the explosion and when people from the media got to him, he made that- a very memorable statement. One of his remarkable properties was that he was familiar with world literature including the Hindu Bhagavad-Gita and in his response to the press he quoted the God Shiva- I have become Death – the destructor, the destruction of worlds. I would like to remind of that because that was the same Oppenheimer who weeks earlier, couple of weeks earlier, convinced me that we should not make an effort merely to demonstrate before using. All this happened in southern Me- New Mexico, a good couple of hours drive home. When I arrived at home, Mici, who was not supposed to know about any of this, received me with the news- I read in the newspaper that there was an explosion in one of the ammunition centers in Mexico, but nobody was hurt. I’m quite sure Mici knew something but I was not supposed to tell her more. I tried to go to sleep. I couldn’t. By eleven o’clock I was at my desk and here comes a very wonderful young woman who worked with me in the small group, I brought her along from Washington, Maria Jacob- Mr Teller, Mr Teller – we were not allowed to use any titles, I was not Doctor – Mr Teller, have you ever seen such a thing in your life? What do I do, what do I tell her? I laughed and she did too. Did I see anything like that in my life? She was with a group of uninvited junior people who went to the top of the San- Sandia mountain, quite a few miles from the place where the bomb was to be detonated. They knew when it was to come. It didn’t. They decided it was a failure and were coming down the mountain and then unexpectedly, there it went. All this you know, July 16. Three weeks later, the first actual bomb was used on Hiroshima. There was quite a stir, a lot of discussion, but not much after that. The 15th of August the Japanese surrendered and that was the time of people really getting excited, going from place to place, from party to party, very great happiness. The job is done.

 There had been plan that when we finish with the atomic bomb, the next thing would be the hydrogen bomb. It was even decided that at that time the two very excellent people, Fermi and Bethe, should take over the work on that. But the next day, I think it was the 16th of August, Oppenheimer came to see me and he said- The war is over. We stop working on everything, including the hydrogen bomb. He was very friendly, he was very definite. There was no point in arguing. People decided to go home. Oppenheimer’s proposal about Los Alamos was- Give it back to the Indians. It was decided however in Washington to continue. Oppenheimer wouldn’t continue and picked a professor from Stanford, Bradbury, who joined Los Alamos in the middle of his wartime work, he should take over the directorship. People prepared to go home, to go back to their usual work. Some of my friends from England, the Peierls, decided first to go down to Mexico, do a bit a sightseeing, I was going with them, my wife and I, and then I couldn’t. I was called to testify in Washington. I tell you this for two very different reasons. One was my testimony which was open, which is available, was available then and now, and the main point I went to Washington for was- We have the atomic bomb. Now we better to look for a way to defend against it. And that will not be easy. It will be necessary to control the skies, but that is the main job ahead of us. That was February 1946. The other reason was I couldn’t go, my wife wanted to go, there was an open place to fill. One of our friends was asked to go. His name is familiar to all of you. He was a very nice man, an excellent physicist, a little peculiar because he did not talk much. His name was Klaus Fuchs. One of the ladies called him Penny-in-the-slot Fuchs, because if you asked him a question, he gave an answer and if it was a very interesting question, it might be longer than just yes or no. One clearly had the impression that he had a lot to say and did not say it. Mici, the Peierls had a good time. We all went wherever we were going and I very happily accepted a new, a new job, Professor of Physics at the University of Chicago – not back in Washington – Chicago, and I was very happy about that because Chicago made a special effort to invite people who played a role in the recent developments. These people included Enrico Fermi, included Maria Mayer with whom I worked on peripheral projects at Columbia. There followed four years of wonderful, effective scientific work in Chicago.

 I like to think about it, in the way what I did was not terribly relevant. Maria Mayer and I tried to explain the abundance of elements and out of these discussions Maria Mayer’s ideas of the magic numbers took its origin. She noticed that certain numbers of neutrons, or certain numbers of protons in nuclei were quite abundant and from that she deduced that these particles, contrary to what, what most people, including Bohr believed, these particles moved in a relatively smooth potential, making up closed shells. It was development I wouldn’t believe for some time. I was too much of a disciple of Bohr. She almost got mad with me, for not believing me and it turned out, she was 100% right and got the Nobel Prize, which was a very nice thing to happen.

 I also worked with Fermi on particles occurring in cosmic rays, origin of cosmic rays, of very particular kinds of cosmic rays that we discussed. All of this was a part of the main work at that time and I want to tell you one personal experience. I had a nice paper published with Fermi and I remember how it came about. We discussed the substance of it and came to an agreement, but then it had to be written, and it was written actually in a way in which perhaps few if any other papers were ever written. We had a very nice secretary who made me acquainted with travel plans to put in my pocket if I wished to be led when I was away from home, Mrs Macmillan. Fermi hardly ever used a secretary. When we had to use- write the paper, Fermi didn’t write it, I didn’t write, Mrs Macmillan wrote it. We brought her in and alternate parts were dictated to her by Fermi and by me. Needless to say what I talked was an American modality of Hungarian and what Fermi was talking was practically Italian but Mrs Macmillan managed to put down, all down in English, so that it was publishable.

 In the meantime I had left Los Alamos, but I did not forget about it. I went back to a conference which closed off, supposed to close off, and said it closed off research on the hydrogen bomb. That kind of research, which was supposed to get thermonuclear reactions very fast before too much radiation could be emitted. The conference thought that this would work, but I kept to think of modifications. One of them looked particularly simple, in which there was equilibrium between the thermonuclear reaction and fission and in which some light elements, like lithium, was also involved. Some thermonuclear reactions originating from the light elements which did not give much energy, but which gave rapidly a great number of- of added neutrons. This kind of thing, either with the light elements or otherwise, we called a Booster and was generally accepted and tried out. Another one was, a big and clumsy subject- substance, where again with the help of light elements you could get a lot of yield. We called it the Alarm Clock, because we said that would wake up people to the fact that new things can be done. It was a great secret at that time. We never tried it out. It turned out that the Soviets thought of very similar things and their first attempts were in that direction.

 In the end, after four years, I decided I go back to Los Alamos for a year. They had planned a number of added important tests a year later and I wanted to work on it. So, in the late spring of 1949 I went and joined Los Alamos on leave of absence from Chicago. In the meantime I got involved in all kinds of other activities, including working on a committee, chairing a committee on the safety of nuclear reactors. And just at the time we were going to- I was going back to Los Alamos, we had planned a joint meeting with the British on the safety questions. So in the summer of ’49, I went back to England for a number of discussions, mostly at Oxford. I remember that visit in England mostly because something not connected with reactors. The leader of the British delegation, the leader of the delegation of the British people who worked with us during the war years, Chadwick, had become one of the important people at Cambridge and invited me to lunch. Now Chadwick was very British. He hardly ever said a word, very reserved, very nice. I was invited to dinner and he sat there, but the conversation was between his wife and me. And we continued to talk about Los Alamos days, about this person, about that man. Chadwick sat there and said nothing.

 And then, Lady Chadwick – he was knighted by that time – Lady Chadwick asked me about General Groves. Now you know General Groves was not very popular. My few meetings with him, which I had mentioned, did not give me a terribly high opinion about him and so I made some not terribly complimentary remarks. At that point something happened to James Chadwick. In physical chemistry we would call it a phase transition. He suddenly became a talkative person and he spoke and he spoke and he praised General Groves; I was wrong in not giving him more credit, without General Groves we never would have finished the atomic bomb, all the scientists just played with the ideas; that there were- was really work on it was due to that one man. I got in a word edg- edgewise at that point and I said- But you know, General Groves was opposed to our collaboration with the British. – Oh yes, said Chadwick- I know that. Whatever- whatever General Groves said I could believe. What for instance, Oppenheimer said, I could not. He went on and on. In the end I said- Good night, walked back to my hotel and Chadwick walked me home and as- at the entrance of my hotel I said- Good-bye, he said something that I obviously cannot ever forget. He said- Remember what I told you today. You will use it. Would have been a remarkable statement coming from anybody, but coming from the reserved Chadwick, what was he talking about? I came back from this trip, stopped in Washington where in the Pentagon we discussed something of no interest that I forgot, but the man who talked to us, after he finished, at the very end, he said- Incidentally, I wanted to tell you that what Truman said today is true. I did not know what he meant. I stayed, asked him- Oh. Truman had said that the Soviets have exploded an atomic bomb.

 Well, it was a great surprise. I probably did not believe as firmly as most of my colleagues that it would take the Soviets many years to do what we had done. I was probably a little less surprised than most that they had succeeded four years after we did. But still, I was surprised and I felt something ought to be done. The first thing was then and there, in Washington, to call up Oppenheimer and I got a very brief reply from him- Keep on your- keep your shirt on. I felt that I didn’t quite know what else to do, but what you would call my shirt did not feel quite comfortable. I went back to Los Alamos, discussed the question with some people, no real proposal, no real action. A few weeks later I get a phone call from my good friend Luis Alvarez in Berkeley, a close collaborator with of Ernest Lawrence and during the war we had worked together- Ernest and I want to come down and talk to you in Los Alamos. Most welcome. Very soon afterwards, a phone call from Bradbury- I hear you have visitors from California. Would you mind if Manley sat in on your discussion. Manley was his deputy, good man- Of course, Doctor. So there was Ernest and Luis Alvarez and Manley and I, and Ernest wanted to know about the hydrogen bomb. I told him. I told him in detail how we planned to make a very big explosion, not allowing est- equilibrium to be established, but having discussed it very thoroughly, having some preliminary calculations on it, and having decided not to do anything more about it. Ernest says to me- You must do this. You must go ahead. And then, he was going down to Albuquerque, taking a plane- Come with me. I came with him to the hotel and there Ernest used a method of persuasion on me which was very peculiar and exceedingly effective. He was prepared to go to bed, took off his shirt and washed it. The washable shirts around ’49 were something of a novelty and Ernest told me- Listen, if you want to go ahead with the hydrogen bomb, you will have to have a lot of discussions, you have to do a lot of traveling, and I find traveling much more easier since I don’t need to carry half a dozen shirts along, but can wash them every night as I did just now. You cannot tell me that this was among physicists a standard argument, but Ernest managed to convey to me- This is important. You are the one who have to do it and I will support you, but you have to go ahead. Had he used these words they may not have been completely effective. Having gone into the irrelevant detail of washing his shirt, made me decide indeed to go ahead.

 A lot of discussions which I don’t need to mention – visits to Los Alamos from people in Washington inquiring what could be done, what should be done. One thing I did was, if we were going to go ahead with anything like the hydrogen bomb, we needed more people, more organization in Wash- in, in Los Alamos. I got permission from Bradbury to go and talk to people and do some recruiting. Obviously the first man I went to see was Fermi. He knew what we were trying to do, he knew the technical details; he had just been coming back from a trip abroad. He listened and then he came out with a statement, quite unusually strong for him- I hope the hydrogen bomb will not work. You might try it. I believe that everybody, ourselves, the Soviets, would be much happier if it did not work and I will not work on it. So I went to the next man, Hans Bethe, a man of really unusual powers of concentration who was very much in the habit of succeeding in whatever he tried. He had an appetite for anything important and new and he said- Yes, I will come. And while we were talking he got a phone call from Oppenheimer inviting him to come to Washington and then, perhaps because I was there, I was to come along. And shortly afterwards there were the three of us, in Oppenheimer’s Washington office, discussing the question. Oppenheimer did not take a strong stand, at least not on the face of it. He told us that one man on the- among the important advisers, Conant, had written him a strong letter in which I remember the phrase- The hydr- the hydrogen bomb would be built over my dead body. And then Oppenheimer said something with which I happened to be in very full agreement. He said- Maybe we should work on it, but if we worked on it, we can no longer do it in the kind of extreme secrecy that we have used in the past. Now that was a point on which I agreed and Bethe did not.

 What developed then I do not know. I know the results, but how they could have come about I do not know. As Bethe and I left Oppenheimer’s office, Bethe said to me- I am still planning to come to Los Alamos. You should be satisfied. And I was. Within a week I heard that he changed his mind: he was not coming. I believe that the situation implied, and I accepted the implication, that the work had to be done, and I better not run around and ask others to do it. I should take care of it as best I could myself. One of my not so close friends reacted differently – Johnny Wheeler, He and I had met as Rockefeller Fellows in Copenhagen. He worked with Bohr, showing some of the difficulties, the need to separate isotopes in order to get anywhere with the atomic bomb. He was in France on leave of absence, doing some special physics there that he enjoyed. I wrote to him, he wrote back- You seem to be alone doing that. I’d be delighted to come back. And did. Showed up in Los Alamos after we had started on the President’s recommendation to do a little more and indeed, Bradbury’s contribution was that he said- We have to work our own people harder. We shall work on Saturdays and I will raise everybody’s salary by 20% for working six days a week rather than five. Johnny Wheeler arrived. We talked about it – well, I tried to talk about it – about the whole situation and Johnny was not talking, he was very, very sleepy. Next morning I saw him and then he said- Well, you know, Edward, when I went to sleep last night, there was a Bible next to my bed and I opened it and you know what I found? Six days shall thou labor. Well he did. He brought others who did and he was a very, very great help. In the meantime things were going on in Washington. I got an invitation from an important senator, Brian McBain. He was chairman of a committee that kept watch on the atomic developments.

 As I went I was told that I will be met at the Washington train station by Manley, whom I have already mentioned, who worked in Los Alamos and who was also the Secretary of the General Advisory Committee that gave scientific advice to the administrators in charge of atomic energy. And John had one purpose- You are on your way to the senator, Senator McBain. Don’t go. There is a unanimous opinion among those of us who know about the hydrogen bomb – we must not work on it. Don’t break the unanimity. I did not know what to say. I remember I said to him- All right. I won’t go. I will call up the senator’s office and tell him precisely what you told me. At that point Manley said- Then you better go. Let me say one thing: I did work on the hydrogen bomb, I did work on the original proposal of preventing equilibrium, I did work on boosters, I did work on alarm clocks. I was going to work on other things. None of these ideas were particularly difficult to produce. Practically all of them were independently developed in the Soviet Union. I claim that I made one contribution that really counted and that was not in science. I made contributions there, but had I not made them, others would have. It did not make a great deal of difference. But, the hydrogen bomb was very strictly secret, top secret. The number of people who were allowed to know about it were few. Most of those did not know the details. And those who had the other information, again the majority had no access in Washington. Among the people who had the full knowledge and had access, I was the only one who really made strong and clear arguments for the hydrogen bomb. In this sense, what Manley told me, has to be understood. I did break the unanimity of the scientists and, had I not done so, it may well have happened that our work would never has started again. It well may have developed in such a way that the Soviet Union would have gotten far ahead of us in developing nuclear explosives. I don’t want to say more about it. I have been attacked for the very point of advocating strongly the hydrogen bomb. Even recently I have been asked- Aren’t you sorry that you did so? And to that question I have a simple answer: I am not sorry. To the extent that one can say the opposite, I do say so. I had to work on it and I am glad I did.

 When I arrived at McBain’s office he told me- Here is the recent report of the advisors to the Atomic Energy Commission. I am not misquoting. McBain said- Here is the report. It makes me sick. Can the hydrogen bomb be made? I did not have to convince him. He was convinced, but he did not know what the subject was. I told him, I told him in detail and within a few weeks President Truman’s decision was made public early in 1950, January 1950- Go ahead with all forms of nuclear explosives, including the so-called super-bomb. I think even today it is very interesting to see the record of the reaction among scientists and that record is explicitly available. A periodical had been started, “The Bulletin of Atomic Scientists”, in which at that time I collaborated. It was from Chicago, but it really tried to get all opinions on nuclear energy. I believe I am talking about the issue of April 1 of The Bulletin. There may have been something in there a month earlier. The most important article there was by Einstein- This is a terrible thing. If the military will work on the hydrogen bomb, that is the decisive step that will lead to Fascism in the United States. Oppenheimer wrote, in very soft terms, essentially not giving an opinion. Harold Urey wrote- Regrettable as it is, we ought to go ahead. I wrote, I don’t think very convincingly. I believe however that that contemporary document is worth reading today and there is no question that among scientists Einstein’s very explicit and very strong opinion had the greatest influence. In Los Alamos itself there was a very clear difference between the way people in general thought and in the way how Bradbury’s leadership acted. The main point, it appears, in Bradbury’s mind was- We must not get out of step with the best of scientists. We should not go ahead too fast. We should not undertake anything that will not succeed. There was not a very explicit, not very strong statement against the hydrogen bomb. In the rank and file it was I believe difficult and I can best describe that feeling by saying; to the average worker in Los Alamos the opposition of hydrogen- to the hydrogen bomb appeared in this way; if we make a little progress toward more, more effective nuclear explosives, that is what we should do. If we take- make a lot of progress, that is wrong. And that to the average worker at Los Alamos did not make sense.

 What happened was that then, in early 1950, we had been planning a number of tests for the next year, for the spring of 1951. Everybody agreed that for that test series we should gather as much information as ever possible, and I, having planned to go back to Chicago in the summer of 1950, I now made up my mind. There was a possibility of the hydrogen bomb. I was at least going to stay another year. We planned, we calculated, and among the calculations a job done by one of my colleagues, Stan Ulam, was particularly important. There had been calculations about the planned hydrogen bomb which were, I have to admit, superficial. Ulam and his collaborators did not have a good a computing machine available, they did things by hand, and Ulam’s collaborators did a very good job and found difficulties. In fact in their formulation which I don’t think was really quite as definite as it should have been. But in their formulation our plans just wouldn’t work.

 The calculations of Ulam and the excellent people he- who worked with him, was worrisome, but to my mind were not conclusive. At the same time however, Johnny von Neumann, with recently improved and greatly improved computers, repeated the calculation and his results were similarly negative. And that now, toward the end of 1950, looked really like evidence that the most radical versions of the hydrogen bomb would not work. The worries of that led me some time, a few weeks before Christmas, to a very definite new approach. You see, in the original discussions of the hydrogen bomb the problem was, you may remember, that too much energy went into radiation and not enough energy remained for making nuclei collide in a sufficiently close fashion to make them react. All this had happened before – was really planned and discussed – before we came to Los Alamos.

 In Los Alamos a new development was occurring, a development due in part, in very important part to Neddermeyer and to a contribution of Johnny von Neumann and myself: with a strong implosion one could make materials at more than the usual density. Several people have raised the question- Wouldn’t the hydrogen bomb work better if you compressed it? And I said- No, no, no. Why? Because I got it in my mind that the hydrogen bomb will not work unless you could cut off the time, make the time short enough so that a mixture of radiation could not occur. Compression would speed up the desirable reactions, but equally speed up the emission of radiation, so in the end it would not count. When it began to look as though the original plans would not work, I was forced to review everything and at that point I got, late in 1950, an exceedingly simple idea: you try to compress. In the thermonuclear reaction what you would compress would be to a great extent hydrogen. That is easy to compress many-fold and when it is compressed, in the compressed state radiation would be present to a lesser extent proportional to the volume. I no longer need to worry about how fast radiation gets emitted, because in the dense state it would be absorbed again. That was the idea of the Equilibrium Super.

 A few weeks later – I believe it was my 43rd, 43rd birthday, the 15th of January of 1951 – we had a session with all the senior people present that made the final decisions on what the tests that were to be made within a few months in the Pacific, what they would consist in. Bradbury said- Prior to those tests we should not think of any new approaches. It was a peculiar statement. I had discussed my novel ideas with a few people around me, but not in general. I wanted to present it at that meeting and Bradbury said- No. Tests first. No new proposals in the meantime. And there it stood, with one little exception; that within a few weeks Stan Ulam came to me with suggestions to use the nuclear explosion in order to compress some materials. That was not the first time that such a suggestion was made, but it was the first time that in a discussion with Ulam I took it very seriously. I told Stan- Indeed, you could compress and there are other methods to compress, which I will promptly- which I will very soon describe and that can then lead to the actual working of the hydrogen bomb. I’ll write a paper and we’ll publish together. And that is what happened.

 Now in actual fact, for the moment all that was not taken too seriously. We went to the Pacific. We tried and we did not test the real hydrogen bomb. We did test the booster, where thermonuclear reactions enhanced to a considerable extent the fission reactions; and we tested what seemed to me very important, the calculations of Johnny Wheeler, where we did not try to get thermonuclear reactions between the usual heavy hydrogen, deuterium and deuterium, but between heavy hydrogen deuterium and ultra heavy hydrogen tritium. That was sort of a model, not very practical in the end, because it would have required a lot of the ultra heavy hydrogen which was difficult to make. But the essential point is that this relatively easy case was calculated in detail and precisely by Johnny Wheeler and his people and we were testing whether our calculations were the right thing. And for the first time in these tests in 1951, we did not just try a model and find out did it work, yes or no, we tried something more scientific: was our procedure of calculation right?

 There it was, one fine morning in the spring of 1951, I was looking at the explosion. So was Ernest Lawrence who kept the interest in the whole business. We saw the explosion go off and we had no idea whether it was a success or not, because what we looked at was the fission energy which was to be used to set into motion a chain of events which Johnny Wheeler and his people calculated – rightly or wrongly? That was the question. There were a number of sensors, of sensitive equipment placed around the explosion from which we received input that was to be evaluated and found, did it work or did it not work and did it work the way that Johnny Wheeler calculated it? That afternoon Ernest took me out to swim in the lagoon and I told Ernest, you know, for the perhaps not right but usual reasons, I said- I’m afraid it didn’t work. And Ernest said- I bet you five bucks it did. Next morning, not yet dressed, brushing my teeth, one of the experiment- excellent experimentalists was doing the same thing next to me and he told me- We found a fast proton. That was telling me that it worked- But, my friend said- it’s only one. We are not certain. Don’t tell anybody yet. That morning Ernest was taking off to a visit for Japan, I didn’t tell anybody, but as Ernest’s car was about to leave, I ran out and gave Ernest five bucks. I think that was the most serious security violation I ever committed. The fact is that the predictions of Johnny Wheeler turned out to be very quantitatively and completely correct.

 By that time I was quite confident of real success. On the one hand the calculations were confirmed, on the other hand I had a new method where the difficult question of working the reaction out of equilibrium could be sidestepped. I now have reason to believe that the original plans would also have worked. They would have worked marginally, not in the sense that they would not have given very big yields, but in the sense that the prediction of their working was at that time quite obviously not possibly a very firm prediction. What we were now proposing; to compress and make the emission of radiation essentially less harmful, that was something we could count on. A conference was announced, in Princeton, for the advisers of the, of the Atomic Energy Commission. I was invited. I would have liked to bring along Ulam, but he really did not think that the consequence of our work would be a real success. He was not prepared to argue, so I had to go alone. I did. The day before, I talked with Oppenheimer, told him about our new approach, did not get a clear answer whether he was impressed or not. We went into the meeting. The recommendations of Los Alamos were made by the Head of the Theoretical Department, Carson Mark, and what he said was- The experiments were a success. By working on it in this way we have satisfied the request, the instruction from the White House. We have now done our job. We don’t need to do anything more. The remarkable thing was that even at that time the leadership at Los Alamos, for reasons I do not quite understand, ignored the suggestion that was described in first approximation in the paper by myself and Ulam and then in an immediate more detailed follow-up paper produced by my office. I asked a word, I wanted to propose the new approach to get the hydrogen bomb going in equilibrium. Bradbury would not permit it. One man on the General Advisory Committee, he has a famous name, Smyth, the author of the Smyth Report which in ’45 disclosed quite a bit about the working of the atomic bomb. Smyth said- Why don’t we listen to Teller? I described the new approach. I don’t think I took quite twenty minutes. The first remark came from Oppenheimer, who had heard about it the day before. His remark was, and it’s on the record- This is such a good idea that we cannot afford to do anything but to follow it up. That was what had to be done and now with Oppenheimer’s approval it was on the program in a manner that could not be changed.

 Coming back to Los Alamos, the developments were not all that favorable. The new approach was to be studied, but the man put- was put under the leadership of one of the strongest opponents of the hydrogen bomb. And at that time I began to feel quite uneasy. The right decisions had been reached but it seemed to depend on something that was almost an accident, that one man from the General Advisory Committee was willing to listen to the new approach. Without the intervention of Smyth, the decision of Princeton might have been different.

 In a scientific development, the judgement what should be tried and what should not is not easy. In that instance the right decision was arrived at, but under conditions where the development might have very easily gone in an opposite way. I made up my mind that we very badly needed not one laboratory, but two. In general, scientific progress depends on widespread careful discussion by many scientists. In the case of the hydrogen bomb the discussion was strictly limited to a few people and the interactions as I described them almost led to stopping the process. It was not hopeful to open up the subject so that everybody could participate in it. The only alternative to me to- seemed to me to have two competing groups, to make the wrong decision much less likely. While staying at Los Alamos, I could not argue for a second laboratory therefore I went back in the summer of ’51, in the early fall of ’51, to Chicago, did not resume to a very great extent my scientific work, and put a lot of effort into just that, what Ernest Lawrence has recommended- Try to establish work on the hydrogen bomb. And that to my mind, not for the hydrogen bomb itself, but for the continuous uninterrupted development of all real possibilities, it needed a second laboratory. I would have loved to see that second laboratory right in Chicago where my close friends were, but the closest of them, Enrico Fermi, did not like the idea and I did not feel at all like disagreeing with Fermi. Ernest Lawrence still loved the idea, invited me to California, did not tell me that he would argue for a new laboratory, but encouraged me to do so and told me that if I got permission to go ahead with the second laboratory, I can count on every support of himself and his people. And that is what actually happened. With the help of Ernest Lawrence it was decided that work, future work on nuclear explosives should go on not at one place, Los Alamos, but at two places, Los Alamos and Livermore, a newly started group some thirty or forty miles east of Berkeley. It was not an easy decision for me to leave Chicago for good. That’s where my friends were, but my friends did tell me- You want to do that, it’s fine if you do it as well. I had to get it done where the conditions were right.

 There is one event, early in the history of Livermore. You know, the arguments that led to the establishment of Livermore took a little longer than what I, I seem to have described here. We did not get going until the summer of 1952 and not much later the first plans on a real hydrogen bomb were to be tested. The details had been actually worked out by Johnny Wheeler’s group, not in Los Alamos, but back in a small temporary group in Princeton, an excellent piece of work. The test was to occur in the Pacific. I was kindly invited to attend, but Livermore was just getting going, I did not feel I could leave for even a couple of weeks. It is one of my memories that I like to tell about. I could not be at the test, but one of my very excellent friends, Dave Giggs, a man who knew everything about earthquakes, made calculations. The planned big explosion above ground would push the surface down, would generate a relatively mild earthquake wave. However, with any decent apparatus, this mild wave could be sensed around the world. So I, not being able to go to the Pacific, went to a seismograph in Berkeley. At the right time I sat before it and watched a little green spot. If there was an earthquake wave, that spot would dance, would move. But somehow things did not work.

 The spot moved all the time. It moved all the time as I very promptly found out, because my eye was not sufficiently steady, my eye was moving. But there was an obvious remedy: hold a pencil against the spot. My finger was not moving. The relative position of the spot and the pencil could be clearly seen and now I saw the spot was at rest and I waited for the time announced for the explosion and nothing happened. Of course, nothing could happen because at that time the shock was generated thousands of miles away. It would take, and I knew it well, some fifteen or twenty minutes for the earthquake wave, the mild earthquake wave to travel under the Pacific and reach Berkeley and just at the time when it should happen, the green spot moved. It looked to me right. I did not quite completely dare to believe it. I waited. Will more follow? Five minutes, ten minutes, nothing more came. I went up to the place where all this would be recorded and evaluated and it turned out not only did the earthquake wave arrived, it had with good accuracy the amount of motion that we anticipated. Ernest Lawrence came over, congratulated me. I had a strong desire to tell my friends in Los Alamos that it worked, but of course that was out of the question, anything of that kind was a secret. I had an idea. The man in charge, Graves, had a very nice and scientific wife, Elisabeth Graves. So I sent a message by wire, open wire, in a code that I have invented on the spot. The full message was- It’s a boy. The message, I’m very happy to report, was received in Los Alamos, was understood in Los Alamos and we beat their official notification by hours.

 Los Alamos did not hear from the Pacific for several hours. They had to get everything clear, everything reclassified, look up the right kind of language in which it can be transmitted. I think it is the one case where I can claim to have beaten the official procedure, if not by years, at least by hours. Of course some of my friends now say that what I said was sexist and quite improper. There is a question, had it not worked, would I then have wired- It’s a girl? Well, I better skip any further discussion of this delicate question and remain with the success not only of the explosion, but of my positive notification of my friends. We could now go ahead with work at Livermore, a part of it, the big part of it, was nuclear explosives; a part of it was the non-explosive use. The controlled use of the same reactions produce energy, not by fission of heavy nuclei, but by fusion of hydrogen-like nuclei. We worked on that, but our main point was nuclear explosives.

 Unfortunately, early in this development there was a political action that I think managed to make relations within the scientific community much more difficult. A series of events which hurt me personally more than anything else in my life, by separating me from many, maybe from most of my scientific colleagues, and that was the question of the clearance of Oppenheimer. I want to tell you how I first heard about it. Livermore had started and the Atomic Energy Commission had a new chairman, a man with whom I got acquainted, who turned out to be a great supporter, Admiral Louis Strauss. He became an admiral in the Second World War. He was a friend of President Eisenhower and he was given the job of chairing the Atomic Energy Commission and Livermore had its very welcome full support. I had appointment with him in Washington.

 Louis Strauss was uncharacteristically late for his appointment and when he came he was deeply disturbed. We did not discuss what I wanted to discuss. He told me something in great confidence, I must not mention it to anybody and of course I didn’t for many years but of course by now all this is clearly in the public domain. Louis Strauss was told – he came from a discussion with the President, Eisenhower – he was told that Oppenheimer’s security clearance, his access to classified material must be investigated. And Louis was very disturbed about it, told me he wants to prevent that; told me that actually there have been reasons not to seek Oppenheimer’s advice any more, and nothing need to be- needs to be done about it, if Oppenheimer would simply say that he is not particularly interested in continuing to give advice. -I hope, said Louis- we can avoid anything worse. Oppenheimer was abroad. When he came back the suggestion was made to him- Return all classified material, don’t worry any longer about atomic explosives, otherwise we have an order from the President to investigate your clearance. Oppenheimer decided he wanted the investigation. The reason of all this was a letter by a man called Bill Borden. He was an assistant of Senator McBain and on the occasion a few years earlier when I saw McBain, he called in Bill Borden- This is my assistant, an excellent man. If you have any further questions, be in touch with him. He’ll do the right thing. Bill Borden did not like the opposition to the hydrogen bomb, did not like the record of Oppenheimer, wanted Oppenheimer investigated. But his boss McBain and his colleagues told him- Don’t do anything. Nonsense. A few years later, with a change in the personnel of this committee, Bill Borden stopped working in Washington, got a job with the industry and was now free to do what he wanted. And he did – and to my mind did unfortunately – write a letter.

 He wrote his letter to Hoover, the head of FBI and stated in the letter, with all kinds of arguments, that – I believe I quote correctly- More probably than not Oppenheimer is a Communist agent. This indeed was something that Hoover could not and probably did not want to stop. It was taken to the President and the President gave instructions to Louis Strauss to stop Oppenheimer’s clearance. Oppenheimer’s term as Chairman of the Advisory Committee was terminating in any case. Everything could have been done quietly, but Oppenheimer returning from a trip in Europe, said- I want this case to be investigated. I want to make my case and be cleared of any accusations of this kind. That was the beginning of the hearings in the spring of 1954 of Oppenheimer. Many of the scientists were asked to testify. My connection with it in a way started when I saw Oppenheimer at a meeting, I believe it was in Pittsburgh, and Oppenheimer said- This investigation is going on. You will be asked to testify. Will you please see my lawyer. – All right. I went to see Oppenheimer’s lawyer and I got for him- from him a half an hour speech, or longer, telling me what I knew, what was entirely unnecessary for me to hear, that Oppenheimer indeed did good and most valuable work as head of Los Alamos during the war. – Thank you. I heard it. Fine. I was called to testify. I could not very well say I won’t come and I intended to testify for Oppenheimer. I was then of course already in Livermore, in close touch not only with Ernest Lawrence, but also with Luis Alvarez and they kept talking with me about the subject, giving me all kinds of details that I did not know before of Oppenheimer’s connections with- well, let us say simply people who were on the left wing. Whether they did anything illegal was not clear to me. Eventually I went to Washington with the clear intention to testify that Oppenheimer should be cleared. I was not comfortable about that. There was quite obviously a lot of evidence on the other side, but that’s what I thought I ought to say. I arrived and just before going in for the hearing the attorney who carried the case against Oppenheimer, a Mr Robb, said- I want to talk with you. I had an impulse not to talk with him, but after all I have talked on Oppenheimer’s request to his lawyer; was it fair for me to listen to one side and not to the other? Robb asked me- How will you testify? I said- Clear Oppenheimer. Robb thereupon showed me a part of a secret document that was the testimony, the sworn testimony, a part of the sworn testimony of Oppenheimer himself – it was at that time secret – a few weeks after the hearing it was published and it is now available, of a lengthy document that does not take nice reading, almost a thousand pages on the Oppenheimer hearing.

 This is the testimony of Oppenheimer and in particular he is being asked about one of his friends, I think originally from Norway and then teaching at Berkeley, by the name of Haakon Chevalier. According to what I read, and it was new to me then, Oppenheimer while director at Los Alamos, being investigated and being asked about his associates, said- Chevalier is connected with the Soviets. Information may get to the Soviets through him. Watch him. Actually I am simplifying this a little unduly. Oppenheimer said all this and not mentioned Chevalier’s name. He was then for weeks, perhaps even months, pressed to name someone who should be particularly watched and, under pressure, as Director of Los Alamos, he gave the name of Chevalier. He was asked about this in his sworn testimony and he said- Chevalier was not really suspicious. I was wrong, says Oppe- Oppenheimer- to give his name. – Then why did you do so? Here is Oppenheimer’s literal and complete answer, under oath- Because I was a fool. That’s all he said. But Chevalier lost his job. I did not know it then, I found out later that Chevalier wrote two books about all of this, the second quite explicit, has the title “Oppenheimer: The Story of a Friendship”. I read all this and Robb asked me- Now, will you say that Oppenheimer should be cleared? And my answer said, was- I don’t know.

 I testified and in my testimony I still talked, I believe, positively about Oppenheimer. I said- I feel very confident that he never did anything that was intended to harm the United States. That is as far as I went. Then I was cross-examined by Oppenheimer’s lawyer, and he asked me more explicitly- You have to tell us, should Oppenheimer be cleared or not? And then I did something which I regret. I said- As far as intentions are concerned he should be cleared. But many of his actions are complicated, I don’t understand them, and I would like to see the security of the United States in hands which I understand better and therefore can trust. I said that under oath and, being under oath, I don’t think I could have said less. But I tell you what I regret. I should have then and there told the story, Robb showed me the testimony, and that is the kind of thing which makes me sufficiently doubtful so that I cannot support Oppenheimer’s clearance. What I said did not anywhere mention the hydrogen bomb and that was not in my mind. What was primarily on my mind is what I have heard about Oppenheimer’s connections and specifically Oppenheimer’s own testimony. But what I said has been misunderstood and could be easily misinterpreted as to saying that I didn’t like Oppenheimer’s actions on the hydrogen bomb and that is why I don’t recommend his continued clearance. All of this had really hard consequences on me. My life from beginning to end was closely connected with science and not only with science, but with scientists. I don’t like to think alone. I like to debate. I like to collaborate. That’s what I did all my life. The way how I testified and the way how my testimony was interpreted separated me from most of the American physicists and this over the years, over the decades hurt me more and more. From my point of view in all of this, there is a bright spot. There were some whose friendship I did not lose and they included all of my Hungarian friends. People like Eugene Wigner, like Johnny von Neumann, understood, perhaps even in- approved of what I had said.

 Szilárd was another case. While Wigner and von Neumann agreed with me in being worried about the Soviet Union, Szilárd was part of- became part of the movement wanting to work with the Soviets as much as ever possible. This attitude of Szilárd even separated him quite strongly from his one-time friend, Wigner. But Szilárd and I had lots of opp- of opportunities to talk to each other. We disagreed, but Szilárd, who was a man differing all his life from the majority, did certainly not criticize me from having a different opinion. He and I appeared together on television and had as pointed yet a friendly debate. And here I would like to insert a little point of personal history that makes me particularly- makes my feelings towards Szilárd particularly strong and warm. A few years later, maybe three or four years later, I ran into Szilárd in Washington, invited him for lunch, and Szilárd told me- You are all wrong about the Soviets. You don’t understand what they are up to. You go to Moscow for two weeks and you will have changed your mind completely. I said- I won’t go. – Why not? Szilárd was quite willing to acknowledge that I ac- that I did not accept his advice, but I had a reason for that. I said to Szilárd- Look, for instance, my mother and sister live in Budapest. If I am in Moscow their position maybe used to blackmail me. Szilárd said- Nonsense. That never will happen. But I will do something about it.

 The remarkable thing is that he did, very effectively. I had tried through official connections to get permission for my mother and sister and my nephew to leave Hungary. My nephew actually had escaped by that time, but my mother and sister were still there. No success. Szilárd went to the next conference that carried the name of Pugwash, a conference of people all over the world, but particularly Americans and Russians, to collaborate for peace. The next Pugwash conference occurred in Austria and Szilárd went to the leader of the Soviet delegation- Why don’t you let Teller’s mother and sister leave Hungary?- Hungary’s an independent country. We have nothing to do with that in Moscow. But in a few hours the Hungarian delegate came to Szilárd and asked him the same question, same kind of exchange, almost. The result was that the Hungarian delegate saw my mother and sister within weeks and in a short time they were allowed to come out and join me in the United States. What does that mean? What I was doing, they, my mother and sister had no idea about. My sister was once detained and she was very disagreeably interrogated about what I was doing. She correctly said- I don’t know. I was cautious enough not even to correspond with them but do all my correspondence through an aunt. They knew nothing. They could get out- the Soviets could get out of them nothing. But by letting them go they retained a good opinion of Szilárd and I gained the company of my mother in her last years of life and my sister who is still around. Many friends I lost. A few I retained and that of course was particularly valuable. In the meantime our work in Livermore went ahead.

 Back at Livermore we continued to look at a variety of problems: how nuclear explosives can be made more effective by making more kinds of them. And at first our only real success was to get people like Harold Brown, Johnny Foster, John Nuckolls more and more interested in the various things that we could do and at the beginning we produced  remarkable record of lack of success. Our first attempt was to go ahead with one of my favorite ideas, still not realized, but I believe of considerable importance: making very small nuclear explosions, essentially by using slower neutrons and much less material. Well in a way we succeeded only too well. The first test we made, a shot in Nevada, I remember our watching it. The shot went off all right but it was immediately clear that there was something a little unexpected. The shot was fired on top of a tower and after we fired it, the bottom of the tower was still standing. We found out that the properties of the material with which we were working were well known at high neutron energies, at low neutron energies, but not at in- intermediate nuclear energies, which was the source of our trouble.

 We also made changes in the design of the hydrogen bomb and that too worked not at all well. There we fired a shot in the Pacific which effectively misfired. That was an introduction to a second and more expensive shot. The analysis of what we failed to do was very rapidly and effectively carried out by one of my great physicist friends, Montgomery Johnson, and we found out not only – or he found out not only – that we did not succeed, which we knew, but the next shot could not possibly succeed. We were sitting there in the Pacific, spending money at an appreciable rate. That had to be stopped. Well, nobody could stop it, except possibly Ernest Lawrence. He came up to the laboratory, listened to our worries and when I rode back with him to Berkeley, he asked me- Well, are these people any good? I said- Yes, they are good, but there are mistakes and we understand them and one of the things that has to be done is that this particular line that has been proposed will not work; we should cancel the next shot. Ernest did something very remarkable. He refused to cancel it. He said- The people who have planned the shot – the laboratory director at that time, Herb York and the man more or less second in command who wound up later as Secretary of Defense, Harold Brown, were out in the Pacific – Ernest said- I will not tell them what to do. If the right thing is not to fire the next shot and save the money for preparing it, you go out to the Pacific and you convince them. I won’t interfere. So, that’s what I did. And I first talked with Harold Brown who loved the ideas, wanted to go ahead but was fast in catching on. After half an hour he agreed but he could not stop the shot. It had to be Herb York. So Harold and I marched up to him and Herb was more so- stubborn; it took, I forget, not half an hour but an hour and a half. At any rate, quite a few million dollars were saved and incidentally that was the introduction of a new system at Livermore. In Livermore we had a committee called the Post-mortem Committee, put together after each shot to evaluate how it worked and if it did not, why it did not work. We instituted, and I had a lot to do with that, at least with the naming of it, we instituted a Pre-mortem Committee. Whenever a shot was going to be fired we put together a group of people who were not connected with planning of the shot and let them make all the possible objections that they could think of. Those committees went to work and our failure at that time in the Pacific was the last failure. From then on our shots worked. That very occasion when we tried to fire the shots in the Pa- in the Pacific I believe in 1952, Los Alamos got into trouble for the opposite reason as ourselves.

 That was 1954 and Los Alamos after its first success with the hydrogen bomb, they now attempted and succeeded in constructing a hydrogen bomb that was really relatively easily deliverable. Their trouble was that it gave about twice as much yield, or a little more, quite a few megatons, more than they counted on. What was much worse was when they decided to fire the shot they had a wind pattern that looked all right. At the time of the shot in an unpredicted way, the wind pattern changed and there was radioactive fallout on an island quite a few miles, almost 100 miles I believe, to the east of the shot. Actually, the people on that island got too much radiation, none of them got permanently hurt, but temporarily, a temporary radiation sickness did occur. There was one thing that was even worse. The shot was announced and ships were said not to go into certain parts of the Pacific next to the island. A Japanese fishing boat whose translated name was “The Fortunate Dragon”, got some fallout and the people on the fishing boat did not know what was happening, did not wash down the material and they did get radiation sickness and as a consequence one of the people on that fishing boat died in a few weeks. Now here is this very remarkable fact: the end of the war was accomplished by two nuclear explosions, more than hundred thousand people killed, now in peace time, by an accident one person died. The reaction in the United States was extremely strong. There was a twofold consequence of all this which I would like clearly to state right here. One is that all – or one was – that all our experiments, both those of Los Alamos and Livermore, were from that- then onward, carried out with much greater caution and that was the last serious accident that ever occurred. On the other hand, there also originated a fear, a fear of radioactivity that in the course of years kept growing, growing out of all proportion, all- of all proportion of reality.

 There is an excellent Japanese book by the name of a man called Kondo, – K-O-N-D-O – “The Health Effects of Low Level Radiation”. That was published just a few years ago. Here is actual situation and I want to talk about it, because I think it is something that people in general should understand and from year to year, so far, the fears and misunderstandings have become greater. These are the simple facts. All of us are exposed to radiation from natural sources. Practically all of us are exposed to radiation from various medical procedures and that added radiation is comparable to a natural background. Now we know that if somebody gets radiation in a short time, which is a couple of thousand times bigger than what we naturally get in a year, that is fatal. It has been generally assumed that radiation is damaging, the more radiation the greater the damage. The simple assumption on which many regulations have been based was an assumption of proportionality between cause and effect. The Japanese Kondo wrote a thick book and 20% of it are tables – so much radiation so great an effect. Hiroshima, Nagasaki, the accident in the Soviet Union at the place called Chernobyl, and many others – and what Kondo finds is that a little radiation is not proved to be harmful- That a little radiation hurts you, he explicitly says- is a myth. On the contrary, there appears to be evidence, not conclusive, but an indication that an increase of the natural amount of radiation that we all are getting, by a factor of five or ten, is helpful rather than harmful. That is a statement that cannot be proved or disproved without an enormous amount of experimentation, of research and that has not yet been carried out. But here’s the question: how can it possibly be that radiation which causes disorder in an otherwise orderly sequence of molecules that in our genes determines the nature of our very body, how can something that disrupts the simple structure, how can that be helpful? Whether it is helpful is not proven, merely indicated. But that it might be helpful is not absurd. We know that we have in our bodies chemicals which counteract the irregularities that might lead to cancer. These natural anti-cancer substances are absent in a few people and it is clear, no doubt about it, that their probability of having cancer is much higher. This is the suspicion, unproven, but should be investigated, that a little radiation stimulates these cancer preventing activities. A little radiation may in a way act like an inoculation and maybe helpful rather than harmful. At any rate, nuclear energy is a possible source of really practical energy production, electricity production, throughout the world, and the facts – is it dangerous, how dangerous is it even if it is only slightly dangerous – certainly needs more investigation.

 Now having told you about the first difficulties we had in Livermore, I would like to mention to you the first real success. It was connected with the activities of a remarkable man in the Navy, a man who incidentally was not appreciated by the Navy, at least not originally. The name is Rickover, I met him first in Los Alamos. He came to me and introduced himself- I am Captain Rickover. I am a dope. So, my eyebrows went up slightly and he says- Yes. I’m a dope. Here are the papers to prove it. I took a course in nuclear engineering and I am a Doctor Of Pile Engineering, DOPE for short, and I am planning submarine reactors, reactors for submarines which will allow the submarines to run practically without refueling, practically for ever. He died many years later as a famous Admiral Rickover and the submarines that he introduced have become extremely important. What had Livermore to do with it? A very few years later in the late ’50s, the Navy called a conference in Massachusetts somewhere, the name of the place, I don’t know why, or the name of the conference was Nobska. – Can you put rockets carrying nuclear explosives on these submarines? I headed a little group from Livermore and the head of the physics department; another little group from Los Alamos and we found ourselves with very complete lack of unanimity because we Livermorians said it could be done, Los Alamos said it could not. Having argued in this vague and inconclusive fashion for a while, the man chairing the meeting, I forget his name, asked me- You said it can be done. How much time? How much money? What weight? What yield? Of course I did not know. I did not talk about something that was done, I talked about something that I guessed could be done. So I gave him my guesses.

 ‘And you Dr Mark, what do you think?’ Here Mark, from the point of view of a debate, made I believe a mistake. He did not say that my statements was… were complete nonsense. He merely mentioned a little longer time, a little higher expense, a little lower yield, maybe by a factor or 2.  The consequence was unavoidable – Livermore got the contract.  And then on the way home Harold Brown, whose technical job it was to turn my promises into reality, looked at me without any amount of approval that could be even approximately proper.  ‘I can’t possibly do what you have said’. 

Well there was a problem, and the problem was solved by the same Harold Brown. He managed in a shorter time, at a lesser amount of money, and with a higher yield.  That was our first success and the nature of it depended on the hydrogen bomb.  The hydrogen bomb in a new context.  The original discussions on the hydrogen bomb were concerned with the point that with the hydrogen bomb very, very large explosions had become possible.  We were looking into using the same methods to produce yields, maybe 10 times a much as Hiroshima.  Still limited.  And using it in an inexpensive, light, effective, easily carried fashion.  It turned out that what started as a super weapon, turned out to be relatively useless as a super weapon and extremely useful in a practical scaled-down version.

 All this had become clear gradually and I might tell you one of the important considerations; yes, we can construct weapons, explosions of sizes as big as you ever please, but if they are to be delivered, if they are to be used in a conflict, what is the useful size? I would like to tell you something that is exaggerated and unrealistic and too big but illustrates the point I want to make. – Make something hundred thousand times bigger than what happened at Hiroshima. Can be done, we know how to do it, it will be very expensive, hard to deliver, not hard to make, and will really destroy, really everything in a radius of about ten miles. It also will take a chunk of air, ten miles across, and throw it out into interplanetary space. – Not satisfied, make it a thousand times bigger still, what will be the effect? It turns out that the destruction on the surface of the earth will have hardly increased. Why? Because the pressure is propagated by the presence of the atmosphere. If you make something a thousand times bigger, the main effect will be that the same amount of air, very little more, will be thrown out into interplanetary space but with thirty times the velocity. When it came down in the course of time to the actual construction of these objects, the important advantage in the hydrogen bomb was not its size, it was its adaptability to a variety of purposes. For military purposes there is a limit what is useful, and actually the smaller and the more deliverable something is the more effective it can be.

 Of course one of the results of the accident which I had described before, and the general fear connected with nuclear explosives, led to negotiations to limit testing. I had doubts about that. I felt – I still feel – that knowledge obtained by testing, if done carefully enough, should not be eliminated. But the situation in the late ’50s, in the early ’60s, was a strong movement toward elimination of testing and there was actual ban on testing for a two or three year period around 1960. The story about that is that this ban was eventually and rapidly broken by the Soviets who started to test again using a very big explosion – I think the biggest ever actually fired, 100 megatons, approximately five thousand times that of Hiroshima. It became quite evident that while we were not testing we were under instructions essentially to slow down or stop all progress in that direction whereas the Soviets had prepared for a test series. The result in the early 1960s was many more and more effective tests by the Soviets than by ourselves and the result was that at that time the Soviets effectively managed to catch up with American nuclear technology, explosive technology, to the extent that that was possible, or that is verifiable. In the meantime however Livermore had made a very important specific change. A new type of explosion, not in the atmosphere, but underground.

 My friend Dave Giggs, the seismologist who helped me to understand the earthquake wave by which I noticed the first nuclear explosion, he pushed the idea and I liked it: perform nuclear experimentation underground. Of- offhand one would imagine that such underground tests would limit the ability to observe detailed effects. It turns out that this limitation is not very serious and a lot can be done by underground experiments. The first shot of that kind was fired before the moratorium, before the Soviets and Americans stopped testing in ’58. The eventual result was that when the Russians resumed testing and we resumed testing, shots were fired on both sides in an accelerated fashion, but negotiations also went on toward a permanent elimination of tests. I felt at that time that the demand to stop atmospheric testing was so strong that in fact it was irresistible and also that what we needed to do could be done by testing underground. The great advantage being that to the extent that you are worried about radioactivity, it will be contained, it would not spread at all, and it also turned out that with appropriate instrumentation you could find out practically everything that you wanted to find out about nuclear explosions by such underground tests. There was a last component. It was and is more difficult to eliminate underground testing in such a way that the actual elimination can be checked. Underground explosions do cause, do bring about earthquake waves that can be noticed, but a result of a group of excellent people, of the work of excellent people in southern California, this earthquake wave could become practically innoticeable- unnoticeable if the explosion is not too big and is fired in a cavity of a sufficient size. In the end we wound up with a treaty limiting testing to underground tests and this was in the end done in a realistic manner so that the treaty actually said most of the things that in a practical way could indeed be stopped, could be checked. In the meantime these same underground explosions, together with a lot of added ideas and added work, has led to a completely new concept: the peaceful uses of nuclear explosives.

 The underground shot that we fired, the first of its type in the end of the ’50s, was the beginning of a discussion of using explosives for the purpose of displacing big masses of earth, digging harbors, digging canals – the idea was taken up in a very effective way, quite probably independent of Los Alamos, independent of Livermore, by the Russians. I want to tell you of the name of the thing. It was established in connection with the Nobska Conference that I have mentioned where a group of us, of our people from Livermore got together with a group of people of Los Alamos. We told them about our intention of turning weapons into peaceful uses, turning swords into plowshare. It was an expression used by our friends in Los Alamos in derision, as an objection, but we liked it and we called our effort to use nuclear explosives in a peaceful way Plowshare. We happened to know that the Russians did a great deal in the same line. One remarkable thing they did, of a kind that we never duplicated, was connected with natural gas. In their working with natural gas they got into trouble in fires, by accident, where the streaming gas from underground gave rise to a flame so powerful that they did not quite know how to extinguish it. What they actually did was to drill down next to this gas well, make quite a sizable nuclear explosion, not at the place where the gas was coming out, but near by, which shoved a mass of earth over the source of gas and actually put out the flame.

 I believe that this whole idea of using nuclear explosions for peaceful purposes have been stopped in a premature way. For me personally they gave occasion to some very interesting expeditions, plans to engage in geographic engineering, making harbors, making canals. One of the very interesting possibilities was a harbor in northern Alaska. Another one, to get a sea level Panama Canal, which turned out in the end not to be practical at the location of the Panama Canal because at that time- at that place the consistency of the earth did not allow to dig a canal with sufficiently steep walls and the amount of earth that had to be moved in order to make a sea level canal would have been too big. But a possibility of a sea level canal somewhere between South and North America is not quite excluded. Here we have one big field that because of fears of nuclear explosives has been eliminated, at least temporarily stopped. And I believe in the future we will find the methods where, to everybody’s benefit, appropriate changes of this kind will be performed. To my mind the best counter to the fear of the atomic bomb is not the elimination but the use of these means in a manner that benefits several nations and that helps to make nat- international cooperation much more of a reality.

 We had made progress in Livermore in many different fields, not all of them connected with nuclear explosions. One active field which remains very active to this day is connected with the development and the use of lasers. Perhaps the idea of lasers is not yet quite generally known, so let me explain the concept in a few words. The usual behavior of light as it goes through material is absorption and absorption proceeds in an exponential fashion, such that in a certain thickness half of the light will be absorbed and only half is left over. You add that distance once again and only one quarter will be left over, and once again and only one eighth, and ten times the distance and one tenth of 1% of the light remains. Now this process of absorption is due to a transition of atomic structures from a lower state to a higher state where in the natural presence of a material, practically all the particles are in the lower state, and their systematic absorption of light gives rise to this exponential decrease of the radiation that can get through. The idea and the practice of the lasers is, by a number of various often not simple means, to create a temporary situation where, for instance in a gas, more molecules will be in the upper state than in the lower state. Then the opposite of absorption will happen. It turns out that the idea goes back to Einstein, that in addition to a possibility absorption, where an atomic system goes from a lower state to an upper state, and the relevant energy is then subtracted from the energy of radiation that caused the transition, Einstein proposed that the opposite process should also exist and was indeed found to exist. If you manage to produce a great number of atoms with the majority in the upper state, then when light goes through, after a certain distance enough of the atoms which ha- will have delivered their energy to the light so that the intensity of the light is doubled. And you repeated that ten times and you have increased the intensity of light tenfold. This is a development that had been foreseen for a number of years but became a reality a third of a century ago and the result is that we can now produce very energetic, very precisely directed beams of light, and these are the lasers.

 All work at Livermore is connected with the lasers, very particularly in the use of these exceedingly intense and well directed beams for the purpose of heating up a small amount of material in a manner that can be very precisely governed. In particular we expect to produce and have made progress toward producing or delivering energy to a spherical hollow structure and make it implode in a similar way as this implosion process was used in the hydrogen bomb; except that in the hydrogen bomb the original source of energy was already a fission bomb. Whereas in this particular case that I am now discussing the original energy source is a laser and that delivers energy, quite a bit of energy for an implosion that then multiplies that energy further, or rather multiplies the energy density and the temperature to an extent where thermonuclear reactions can take place. And this can be done in a repetitive way and the result will be – and I have little doubt that it can be done – but the result will be to produce an amount of thermonuclear energy which is proportional to the laser energy that has been put into the system, but can be a rather high multiple of that energy. This is something we are trying to do and we are doing, and I want to say two things about it. I feel sure that it will succeed. I do not feel sure that it will succeed in a manner that will in the end deliver energy at a sufficiently low cost. I believe that it must be tried, it is beginning to work and I hope that it might give a lot of energy – and incidentally, and this is what counts a great deal in reality and even more in pubic opinion – the energy can be produced connected with practically no radioactivity. We use an original energy source that is radioactively clean and we can manage to keep it not completely clean, but almost completely clean even when the nuclear energy is delivered.

 The remarkable thing about the work at Livermore is precisely the fact that it has so many aspects: big explosions, small fission explosions as has been developed very highly by John Foster who was for a while our director. So was Harold Brown, so was John Nuckolls who had a lot to do with the peculiar development of light, the exponential increase in the laser light intensity and its uses. Now all of this has led to a further and I believe extremely important development; not weapons of attack, but for once the possibility of very real defense. It might be a good idea to talk about that in connection with an important event in Livermore. In the late 1960s, when Ronald Reagan became Governor of California, I invited him to come and visit the remarkable weapons laboratory in California. He came and we talked for a few hours about one of our, at that time, novel approaches to stop incoming missiles. Now Governor Reagan as he was at that time, listened very attentively, asked – I don’t know – in two or three hours maybe a dozen questions clearly showing that the subject was new to him and equally clearly showing that he was making a successful attempt to understand it. Here was a topic on which I testified to Congress in February 1946: we must be able to stop incoming objects, planes, projectiles. How to do it? It was not something that was discovered in one special way; it was an accumulation of a great variety of approaches. To begin with, we relied quite heavily on the possibility to use nuclear explosives on the incoming objects but as time went on we got more and more interested in a defense that was not based so much on the size of the defensive explosion, but on the great accuracy of its delivery.

 The role of Reagan when he became President is vit- quite remarkable in that regard. As I told you, the late 1960s were the first time that apparently he has heard about it and given thought to it in a serious manner. As a man well known from shooting from his hip, he did react to that early. It took him only about fifteen years before he made the really essential statement about it.

 As President of the United States he said- It is very important to find a defense against missiles and, he said- I am convinced it can be done. Many of us, including me, were invited on the occasion when he gave this speech. I had a few opportunities to reinforce details about that possibility before he gave that talk. Eventually he did something that I believe is important and exceptional. He accepted our emphasis on defense, he accepted our optimism on the feasibility, he did not quite accept our way of trying to do it. Originally we put emphasis on the energy of the defensive explosion. He said- Maybe, but let- let’s try to do it without nuclear explosives. And particularly under the leadership of one of the younger member of our community, Doctor Lowell Wood, we developed a method that depends much less on the size of the defensive explosion, and much more on accuracy. Indeed, the plan which Lowell called Brilliant Pebbles, was based on a violent collision of a small defensive object with the much bigger incoming object.

 The proposal is to use accuracy as it was used in Biblical times by David’s brilliant pebble that hit Goliath in the forehead. This is something where we hope and believe in a very effective way to be ahead of the Soviets and to remain ahead of the Soviets, where we rely on high technology, on accuracy, then the basis of that in the United States is probably stronger and better than anywhere in the world. Of course the remarkable modern fact is, the great good news is that at least at the moment the Communists are no longer ruling Russia. That may change. They may come back. If they do, I hope at any rate not as viciously as in the past. But here is a point which I would like to emphasize: at the end of the Second World War the democracies disarmed. They had to disarm, public opinion would not tolerate the great expenditure of arms in peacetime. Stalin did not disarm therefore it was quite clear that Stalin had to win. Of course we know he didn’t and I think we should know, we should realize the obvious; he didn’t win because modern developments shifted emphasis from masses of conventional weapons operated by a great number of people, into new weapons, nuclear weapons, and very particularly weapons of increasing accuracy. It became very clear, for instance in discussions in Reykjavik not so many years ago, between Reagan and the Soviets, that the Soviets were really worried about American defenses. Why? Because they knew that in accurate defenses the United States was apt to win. There can be a difference of opinion to what extent high American technology in nuclear weapons, in accurate defensive weapons, how much all this contributed to the Cold War, to the end of the Cold War, to the United States winning the Cold War. You may find difference of opinion how important it was – there cannot be any difference of opinion that it was very important, and that without advanced technology the world of today would be, today, a very different and more dangerous place. All this is something of unusually great importance.

 There is a situation, there has developed a situation which to my mind is truly alarming. I have already referred to it in part. I want to talk about it now in general. And that is the fear of people, the fear of technology. I came to the United States just about sixty years ago. At that time anything that was new was good. Sometimes it wasn’t quite good. Some times it had to be corrected but the feeling of the people was- Progress and more Progress. All of this fortunately to some extent is still with us, but not quite in the old way. People to a greater and greater extent are afraid of progress. Why? And the connected question: what to do about it? These to my mind are exceptionally important questions. In the last few years development of weapons was de-emphasized. Let me give you a rationale why that should be done, a rationale which is wrong, which is crazy. I want to put it before you as though it were real: Wars are caused by weapons. The best weapons are made by the United States. Therefore, if only the United States would stop making weapons the world would be a safe place. This is as wrong a statement as it possibly can be. Perhaps even a little more, more wrong. Yet, we behave as though that would be a reality.

 I believe that peace depends on a different set of statements. Peace depends in the first place on strength in the hands of those who want peace more than anything else. But this is only half the story and I believe it may be even the smaller half of the story. Peace depends on co-operation between nations. Peace depends on the increasing realization of a situation, of the establishment of that situation and its realization, where nations co-operate for the benefit of everyone who is co-operating. We are talking about international treaties which forbid this or forbid that. I don’t believe in treaties that start with the word- Don’t. I believe in treaties and they are very important, treaties which start with the word Do. The Don’ts can be circumvented, the co-operation is a reality which proves, which makes evident itself. And here I would take very specific reference to the Strategic Defense Initiative, to the planning of defense against missiles. I claim that this is the most obvious, the most immediate measure that needs to be done. Even today there are something like twenty nations and the number is increasing, that can deliver missiles to increasing distances. Missiles carrying what? Missiles carrying conventional explosives or chemical weapons or biological weapons or nuclear weapons. But any one of these, even conventional weapons, are already extremely dangerous.

 Actually, the Strategic Defense Initiative, for instance in the form developed by Lowell Wood and others with him, is extremely important. Not only, appears it to- appears it to- appears to be- I’m sorry. Not only did it frighten the Soviets in a way that may have contributed to the end of the Communist regime in Russia, it also answers the obvious problems that arise in connection with space developments. If space can be only used to attack anybody on earth at any distance, that of course is a source of extreme instability. I believe to get rid of it we should not forbid space development. We should introduce space development for positive purposes.

 I would like to add, I would like to end by mentioning three developments of very different kinds, very different dimensions, and quite possibly a fourth or a twenty-fifth may be more important. One space development that I would like to see is greatly improved weather information from space, measuring at all times, at all places, at all altitudes wind velocities and other data that could greatly improve weather prediction in detail – let us say one week – ahead of time. It will be expensive but the amount of money it saves, for instance in agriculture, in defining the right time for the various agricultural activities, it would be one thing that would benefit everybody. And that cannot be carried out except over the whole world, should not be carried out except by the co-operation of all people. As a second let me mention what I have already been talking about. Let us use space to make aggression in space practically impossible. How to do it? Let’s have an international agreement which will allow the firing of any missiles provided that the firing, the purpose, the orbit are all disclosed a week ahead of time. If anything is fired without announcement, or anything is fired in a way not in conformity with the announcement, then such a missile should be shot down by the methods of the Brilliant Pebble, with the help of orbiting objects. One may object that this is too difficult, too expensive. Actually what our people in Livermore are arguing and fi- and finding is, it is difficult if you try to shoot down missiles in orbit and even more difficult if you try to shoot down missiles which approach their target, but it is easy if you fire, shoot down missiles while they are accelerating. In the very early phase the job can be done effectively and simply. That is how it appears at present and I don’t believe that the situation is quite as simple as I am presenting it, but what I am saying may surprise. To convince you that there are real possibilities here to get a job of safety done, for everybody’s benefit, because we won’t try to defend ourselves or this or that country, we defend everybody against anything whose purpose is not clear.

 Now let me finish by telling you of the third use of these technologies which looks probably more fantastic than anything I’ve talked about and which, while being fantastic, is completely real. I talk about meteorites hitting the earth. It happens. Air Force observations have shown that in not very long time intervals, meteorites come and burn up in the atmosphere, whose total energy in their burn-up can easily become as big as the energy developed in Hiroshima. Actually such meteorites hit the earth – the last big event of that kind occurred when I was about five months old. It was called the Tunguska Meteorite; an object more than hundred feet in diameter came in over Tunguska in Siberia not far south of the Arctic circle. It did not hit the Earth, it approached the Earth on a tangential orbit and as it got into more and more dense atmosphere the pressure ahead of it built up. This uneven distribution of pressure caused the object to disintegrate into small parts which in turn vaporized and released an energy very many fold that of Hiroshima. The trees were uprooted, pushed away, over an area of a thousand square miles. Maybe one or two people were hurt, there were not many people around, fortunately. Such an event, which we estimate is likely to come in once in a hundred, once in a few hundred years, if it should occur over a big city could kill millions – not likely.

 Something that is much more likely to happen and is very dangerous, is for such a sizeable meteorite not to hit a populated city, but hit an appropriately deep part of the ocean, hundred or even more miles from shore. That would give rise to a big tidal wave, tens of feet high, that could sweep inland and do a lot of damage, could happen on the long ocean shores of the United States or, let us say, of Japan. Something of that kind might well happen, not just a hit of meteorite, but a hit of meteorite that costs very many lives, might well happen once in a few thousand years. An unlikely event but its unlikely nature, I believe, is really cancelled by the size of the trouble which may occur with a small probability, and it is probably known by everyone that these things are now known to happen in remarkable places. It happened recently on Jupiter where fragments of a comet have hit and disturbed regions of the size of the Earth. Of course Jupiter with its bigger surface and mass is a much better collector of such dangerous objects, but on Earth itself we have definite knowledge of a catastrophic event of this kind.

 It was noted by my very good friend Luis Alvarez and his son who made the original approach. A meteorite of ten miles or more in diameter that hit sixty-five million years ago in the Caribbean. It is practically certain by now that it was the cause of the extermination of the dinosaurs. It is estimated that as a consequence not only of the impact but of the dust it stirred up and the exclusion of the sunlight for a long period of time, at least 90% of the living beings were killed and something like 70% of the genera, of the kinds of living beings, was exterminated. Indeed, that event marks the division between the Mesozoic and the Cenozoic period, the biological middle ages of the Earth and the biological recent ages of the Earth. People analyzing the history of life on Earth used to believe in relatively slow transitions from one period of the ancient Earth into the next. Now there is a spe- suspicion that some, or maybe all, of these changes have been due to impacts by meteorites of great sizes. Now of course it so happens that for us humans that was a fortunate event; the dinosaurs were gone, a period followed that for reasons that we do not understand completely, although do we- we do understand it in part, many mutations, our ancestors very small animals changed in all kinds of forms of which the latest, and I may modestly say, ourselves, are the most recent product.

 Well, I don’t know, I hope you will agree with me, that for this happening in the past, particularly if it leads to such wonderful things as humans was quite all right; but for us to be subject to extermination as the dinosaurs have been, that is a less wonderful prospect. Of course, who cares about it? It will take 100 million years before it happens. It might happen, it’s a small probability, sooner. And here is the very remarkable thing. This rare catastrophe, an immense catastrophe, will practically certainly be predictable by careful observation and probably preventable. We may find ways, I’m sure we will find ways, either to break up or slightly to deflect such big objects and a slight deflection is abs- suffice to cause such an object to change its orbit from one hitting the Earth to one avoiding the Earth, at least by a few Earth radii. I believe that early attempts to accomplish this could be performed by careful observation, careful calculation, and impact of the object- on the object from fast- by fast, relatively small missiles shot up from the Earth. In the end for the bigger object it is apt to be true that the deflection will require the energy carried in a nuclear explosive. That might be the only way to do it for the big objects and it might be in any case the least expensive. But initially we don’t need to talk about it. What is apt to happen in the next few thousand years, that is, that may happen with a probability of one-tenth of a percent or 1% even, in the life time of those who listen to my talk, these smaller objects probably can be dissuaded from hitting the earth, or else broken up and thus not producing any harmful effect. That probably can be done with the expenditure of $100 million worldwide or less; the preparation not much more than a few years.

 And here is now the point that to my mind is even more important than preventing the catastrophe. This is something that is of general interest to all people on Earth. It is a subject where international co-operation is needed and is possible. And I would like to end by saying I believe in two things, in a very practical way: I believe in knowledge and in more knowledge, and I believe in the unifying power of knowledge, as long as we continue to be interested in knowledge and as long as we are willing to take a reasonable and broad view of knowledge. Recent fears of technology, perhaps due to lack of understanding of much of modern science, perhaps due to people’s addiction to dangerous fantasies, all this can be overcome and in fact if it can be overcome, the United States has a better tradition than I believe any other country in the world, a better tradition for being interested in what is new and being interested in real co-operation and peace. I believe that a positive future will not be accomplished by fears and by saying no. I think the right thing to do is the old American tradition which was very evident when I arrived in 1935 in the United States; what is new can be good, what is new can be made into something that is new – if we are willing to take a hopeful, strong, positive approach.