Editorial by C P Snow in Discovery, September 1939
Some physicists think that, within a few months, science will have produced for military use an explosive a million times more violent than dynamite. It is no secret; laboratories in the United States, Germany, France and England have been working on it feverishly since the Spring. It may not come off. The most competent opinion is divided upon whether the idea is practicable. If it is, science for the first time will at one bound have altered the scope of warfare. The power of most scientific weapons has been consistently exaggerated; but it would be difficult to exaggerate this.
So there are two questions. Will it come off? How will the world be affected if it does?
As to the practicability, most of our opinions are worth little. The most eminent physicist with whom I have discussed it thinks it improbable; I have talked to others who think it as good as done. In America, as soon as the possibility came to light, it seemed so urgent that a representative of American physicists telephoned the White House and arranged an interview with the President. That was about three months ago. And it is in America where the thing will in all probability be done, if it is done at all.
The principle is fairly simple, and is discussed by Mr D W F Mayer in more detail on p. 459. Briefly, it is this: a slow neutron knocks a uranium nucleus into two approximately equal pieces, and two or more faster neutrons are discharged at the same time. These faster neutrons go on to disintegrate other uranium nuclei, and the process is self-accelerating. It is the old dream of the release of intra-atomic energy, suddenly made actual at a time when most scientists had long discarded it; energy is gained by the trigger action of the first neutrons.
The idea of the uranium bomb is to disintegrate in this manner an entire lump of uranium. As I have said, many physicists of sound judgement consider that the technical difficulties have already been removed; but their critics ask – if this scheme were really workable, why have not the great uranium mines (the biggest are in Canada and the Congo) blown themselves up long ago? The percentage of uranium in pitchblende is very high: and there are always enough neutrons about to set such a trigger action going.
Well, in such a scientific controversy, with some of the ablest physicists in the world on each side, it would be presumptuous to intrude. But on the result there may depend a good many lives, and perhaps more than that.
For what will happen, if a new means of destruction, far more effective than any now existing, comes into our hands? I think most of us, certainly those working day and night this summer upon the problem in New York, are pessimistic about the result. We have seen too much of human selfishness and frailty to pretend that men can be trusted with a new weapon of gigantic power. Most scientists are by temperament fairly hopeful and simple-minded about political things: but in the last eight years that hope has been drained away. In our time, at least, life has been impoverished, and not enriched, by the invention of flight. We cannot delude ourselves that this new invention will be better used.
Yet it must be made, if it really is a physical possibility. If it is not made in America this year, it may be next year in Germany. There is no ethical problem; if the invention is not prevented by physical laws, it will certainly be carried out somewhere in the world. It is better, at any rate, that America should have six months’ start.
But again, we must not pretend. Such an invention will never be kept secret; the physical principles are too obvious, and within a year every big laboratory on earth would have come to the same result. For a short time, perhaps, the U S Government may have this power entrusted to it; but soon after it will be in less civilized hands.
THE EDITOR