Every now and again, I read that Oppenheimer and the boys weren’t quite sure if the first A-bomb would accidentally ignite the atmosphere, thus rendering the Earth a burning cinder and making “who will win WWII?” a moot point. Nevertheless, they went ahead with the first test at Los Alamos.
Three questions:
a) is this true, or just a legend? :rolleyes:
b) why would they have thought there was a chance it would ignite the atmosphere - what did they think the bomb would have done?
and, perhaps most important:
c) if they really weren’t sure the atmosphere would survive, WTF were they doing, setting it off? :eek:
b) They were heating up a chunk of atmosphere to millions of degrees for the very first time. Teller had done some calculations that showed there to be a slight chance of setting off a fusion reaction in atmospheric nitrogen. Others were concerned about the possibility of igniting heavy hydrogen fusion in the oceans. Basically they were doing something new, so they thought up and disproved as many paranoid fantasies as they could think of before actually setting of the bomb.
c) It is never possible to be absolutely sure that any new process is 100% safe. You have to make educated guesses at what the hazards are going to be and do your best to minimize them.
From the results of a search at http://www.google.com for
Edward Teller “atmospheric ignition”
The search gives a couple of good links that don’t translate well to the SDMB forum.
Really? From what I understand, nitrogen is so unreactive it’s gonna take much more than a mere A-bomb to cause a fusion reaction. Or maybe I’m deluded.
Ok, I think I’m deluded.
In The Making of the Atomic Bomb, Rhodes quotes Hawkins official history Project Y on the subject as follows:
“It was assumed that only the most energetic of several possible reactions would occur, and that the reaction cross sections were at the maximum values theoretically possible. Calculations led to the result that no matter how high the temperature, energy loss would exceed energy production by a reasonable factor. At an assumed temperature of three million electron volts the reaction failed to be self-propagating by a factor of 60. This temperature exceeded the calculated initial temperature of the deuterium reaction by a factor of 100, and that of the fission bomb by a larger factor … The impossibility of igniting the atmosphere was thus assured by science and common sense.”
The American government told the Manhattan project physicists that Hitler was close to deploying an A-bomb. They understood that it was going to be tested soon, whether it was Americans doing it or not.
The people afraid of igniting this disastrous reaction were very uncertain and in any case in the minority. There were some excellent arguments against the idea - including the fact that cosmic rays with much greater energy were already raining down on the atmosphere all the time.
They were trying to save the wold from a madman. The magnitude of this project is pretty hard to appreciate in recent decades, as there have not been any comparable threats since.
The very first explosion was in June 1945, more than one month after Hitler’s suicide and Germany’s surrender. The last remaining enemy was Japan, and Japan was far away from the bomb.
Well, sure, when you’re talking about putting the Pinto on the road, I guess that’s okay, but somehow that kind of analysis doesn’t sit well when it’s potentially the end of the earth. However, I take it from the postings that they concluded it wasn’t really a possibility.
The ‘unreactive’ property of nitrogen you’re thinking of is its resistance to chemical reactions-i.e. interactions between the electron clouds of the nitrogen atoms which form the nitrogen gas molecule. A fusion reaction would be between the nuclei of these atoms, which is a whole 'nother ball game. And a ball game about which little or nothing was known in the 1940’s … The only thing that they could have known for sure was that a self-sustaining fusion chain reaction of the nitrogen nuclei would release one hell of a lot of energy, based on the measured packing-fraction of the mass of the nucleus compared to that of heavier nuclei. What circumstances could cause this to happen, they could really only guess at.
Given that Sam Allison was an experimental physicist by trade, I’m quite sure he wasn’t going to take any prediction by a bunch of theorists entirely on trust. At least, not until they’d actually done the experiment to see whether a fission bomb could ignite the atmosphere.
Yup, the “suck it and see” approach is more powerful than a million mathematicians !
It’s nice that the theorists considered the possibility of the bomb starting a chain reaction in the atmosphere, and even nicer that they modelled the process as best they could in order to see how serious the problem was. But even after they calculated the odds of a runaway reaction to be less than 1 in 6,000,000 it still took a lot of faith in the theoretical model, the theoreticians, and physics in general to push the button.
One Nit. The Manhattan Project started officially in December 1941, the Sixth, to be exact. The feasability was known to Roosevelt in October of that year. So Hitler and his plans could very well have been on their minds.
Certainly, but after VE-Day the we-had-to-test-the-bomb-since-Hitler-will-do-it-anyway-argument became pointless; in July 1945 there was no need to blow up the bomb any more.
AFAIK was Hitler’s nuclear research program much less advanced than estimated; Hitler did not trust nuclear physics too much since many of the high-rank scientists were Jews (Einstein, Oppenheimer,…) and had emigrated long before the war. The few physicists who remained in Germany (Hahn, Heisenberg) had no chance to get the bomb.
