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.