The 70th anniversary of the bombings of Hiroshima and Nagasaki has reminded me of an extraordinary incident that occurred during the Manhattan Project, when Edward Teller and other physicists feared the fission bomb they were building might incinerate the planet. I heard about the incident in 1991 while preparing for an interview with Hans Bethe, who headed the Manhattan Project’s theoretical division. Teller reportedly did calculations suggesting that a fission explosion might generate heat so intense that it would trigger runaway fusion in the atmosphere. (Ironically, Teller later helped create thermonuclear bombs, in which fission catalyzes a vastly more powerful fusion explosion.) Teller brought his concerns to other physicists, including Bethe, an authority on fusion (and pretty much everything else in nuclear physics). After considering Teller’s concerns, Bethe and others concluded… Well, I’ll let Bethe tell the story in his own words. Here is an exact transcript of my interview with him, which took place at his home in Ithaca, New York.
Horgan: I wonder if you could tell me a little bit about the story of Teller's suggestion that the atomic bomb might ignite the atmosphere around the Earth.
Bethe: It is such absolute nonsense [laughter], and the public has been interested in it… And possibly it would be good to kill it once more. So one day at Berkeley -- we were a very small group, maybe eight physicists or so -- one day Teller came to the office and said, "Well, what would happen to the air if an atomic bomb were exploded in the air?" The original idea about the hydrogen bomb was that one would explode an atomic bomb and then simply the heat from the atomic bomb would ignite a large vessel of deuterium… and make it react. So Teller said, "Well, how about the air? There's nitrogen in the air, and you can have a nuclear reaction in which two nitrogen nuclei collide and become oxygen plus carbon, and in this process you set free a lot of energy. Couldn't that happen?" And that caused great excitement.
Horgan: This is in ‘42?
Bethe: '42. Oppenheimer [soon to be appointed head of Los Alamos Laboratory] got quite excited and said, "That's a terrible possibility," and he went to his superior, who was Arthur Compton, the director of the Chicago Laboratory, and told him that. Well, I sat down and looked at the problem, about whether two nitrogen nuclei could penetrate each other and make that nuclear reaction, and I found that it was just incredibly unlikely. And I said so, and I think Teller was very quickly convinced and so was Oppenheimer when he'd returned from seeing Compton. Later on we found out that it is very difficult to ignite deuterium by an atomic bomb, and liquid deuterium, which is much easier to ignite than the gas, but at the time in '42 we thought it might be very easy to ignite liquid deuterium. Well, Teller, I think he has to be much commended for that. Teller at Los Alamos put a very good calculator on this problem, [Emil] Konopinski, who was an expert on weak interactors, and Konopinski together with [inaudible] showed that it was incredibly impossible to set the hydrogen, to set the atmosphere on fire. They wrote one or two very good papers on it, and that put the question really at rest. They showed in great detail why it is impossible. But, of course, it spooked [Compton]. Well, let me first say one other thing: Fermi, of course, didn't believe that this was possible, but just to relieve the tension at the Los Alamos [Trinity] test [on July 16, 1945], he said, "Now, let's make a bet whether the atmosphere will be set on fire by this test." [laughter] And I think maybe a few people took that bet. But, for instance, in Compton's mind it was not set to rest. He didn't see my calculations. He even less saw Konopinski’s much better calculations, so it was still spooking in his mind when he gave an interview at some point, and so it got into the open literature, and people are still excited about it.
Horgan: When did Compton give his interview?
Bethe: After the War. I don’t know precisely when. Maybe, I don't know, '47, '48. Some such time. [The date was 1959. See Addendum.] And that got other people excited, and there was one exchange of letters in the Bulletin of the Atomic Scientists, but by then of course it was absolutely clear, and it was absolutely clear before the Los Alamos test that nothing like that would happen. In this form, I think I have no objection to your writing it.
Horgan: I think what makes it such a fascinating episode… is the idea of doing a calculation on which possibly could rest the fate of the world. [laughter]
Bethe: Right, right.
Horgan: That's obviously an extraordinary kind of calculation to do. Did you have any... Did you even think about that issue when you saw the Trinity test?
Horgan: You were absolutely--
Horgan: -- completely certain.
Bethe: Yes. The one thing in my mind was that maybe the initiator would not work because I had a lot to do with its design, and that the whole thing would be a fizzle because the initiator wasn't working. No, it never occurred to me that it would set the atmosphere on fire.
Horgan: In a way, this is like a great test of one's belief --
Bethe: In science. [laughter]
Addendum: Arthur Compton recalled the doomsday discussion when he was interviewed in 1959 by the writer Pearl Buck for American Weekly. Buck reported Compton saying, “It would be the ultimate catastrophe. Better to accept the slavery of the Nazis than to run the chance of drawing the final curtain on mankind!” According to Buck, Compton said he had approved the atomic test after calculating the odds of the runaway fusion reaction to be “slightly less” than one in three million. The Compton-Buck interview was recalled in “The Ultimate Catastrophe,” by physicist H.C. Dudley, in the November 1975 Bulletin of the Atomic Scientists. Dudley’s article provoked an exchange of letters in Bulletin of the Atomic Scientists and a response from Bethe, who said that Buck had “completely misunderstood” Compton and that there was “no chance whatever” that an atomic blast would “ignite the atmosphere.” Bethe concludes his piece with comments relevant to my recent posts (see below) on whether our fears of nuclear weapons are excessive: “There are many excellent reasons against nuclear war, and these are well known to our statesmen as well as to our scientists. On this one point, I can agree with Dudley; there must not be nuclear war. But it is totally unnecessary to add to the many good reasons against nuclear war one which simply is not true.”