APS News

Letters to the Editor

The First Chain Reaction

I always enjoy reading the APS News column entitled “This Month in Physics History” and I value its pedagogical content. This was the case again for the last issue (December 2014), which was dedicated to the first electricity generated by atomic power. However, this article contains a misleading statement, namely that “Zinn was on hand for the first nuclear chain reaction on December 2, 1942...” I believe that many readers, perhaps most of them, will think that this chain reaction was the first one ever produced. In fact, the first experimental evidence of a nuclear chain reaction was obtained by H. Halban, F. Joliot, L. Kowarski and F. Perrin and was published in Le Journal de Physique et le Radium in 1939. The abstract of this paper reads “The experiments described in this note provide the number of neutrons produced in a 50-cm diameter sphere of wet uranium oxide exposed to a source of primary photo-neutrons. The value of this number allows us to conclude that the neutrons produced are of secondary, tertiary, etc. origin, providing evidence that, in such a system, convergent chain reactions are taking place.” This work and some complementary ones done by the same team were acknowledged by a citation presented to the four authors by the Atomic Energy Commission of the United States on June 11, 1968. To be accurate, the sentence should have read “Zinn was on hand for the first self-sustained nuclear reaction....”

Jacques Haïssinski
Bures-sur-Yvette, France

Dennis Sciama and The Theory of Everything

The Theory of Everything (APS News, December 2014) is a well-acted film, (a Stephen Hawking bio, for those who may have managed not to hear about it) which portrays scientists in a more realistic light than most films do. It is based on a memoir written by his first wife, and highlights her role in the struggle with his disability. It does, however, severely minimize and distort the role of Dennis Sciama, Hawking’s doctoral supervisor. Dennis is portrayed as a cartoon character, at first a kind of authoritarian gatekeeper who gradually develops affection for Stephen as he begins to regard him as a colleague. It is understandable that his role would not be portrayed realistically by people who were not involved in research.

Dennis was much more than that portrayal suggests; he was a superb mentor who brought out the best from his students. He cleverly never directly tried to motivate them, but rather responded masterfully and encouragingly when they moved forward. As was relayed to me, after Stephen’s diagnosis and some time in depression, Sciama said to him something like “Well, you’re not dead yet. So, are you ready to work on that problem I suggested?” The rest is history. I believe the history could not have been the same without constant interaction and feedback typical of Dennis. In the film he merely sits and waits for the equations to appear. In real life, Dennis was all about conversation and encouragement about the ideas. I wish that his legacy would have been strengthened by the film.

Adrian L. Melott
Lawrence, Kansas


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