### Hans Bethe & the Manhattan Project

The Manhattan Project Heritage Preservation Association presents a lengthy tribute to Hans Bethe's contribution to the Manhattan Project--full of fascinating details and a few easily discardable flaws.

"As theory chief, Bethe had to oversee and coordinate the work of the various theory groups, who had plenty to work on. They had to come up with a model for the immensely complicated problem of how neutrons diffuse through a critical mass. They had to figure out how to calculate the effects of different kinds of tampers on neutron reflection and absorption. They had to figure out how to calculate the efficiency of nuclear explosions. They had to determine critical masses and - perhaps more importantly - the limits of sub-critical ones. They had to understand how liquids and gases behaved in fractions of micro-seconds, under pressures and temperatures greater than at the center of the sun. They had to design an initiator. They had to determine the behavior of plutonium when they had hardly any plutonium to work with. And on and on.

"Once, when a friend, physicist Victor Weisskopf, asked him how long a certain calculation would take, Bethe answered cheerfully, 'It would take three days for me and it will take three weeks for you!' This was not boasting, merely clear-sightedness. (Weisskopf reports that the calculation, indeed, took him three weeks.)

"Years after Los Alamos, the physicist Richard Feynman, himself famous for his ability to perform calculations in his head, would say that he learned it from Bethe, who was 'absolutely topnotch. He was nearly always able to get the answer to any problem within a percent.'

" 'No one any longer pays attention to--if I may call it--the spirit of physics, the idea of discovery, the idea of understanding. I think it's difficult to make clear to the non-physicist the beauty of how it fits together, of how you can build a world picture, and the beauty that the laws of physics are immutable.' --Hans Bethe"

-- Shrikant Rangnekar

"As theory chief, Bethe had to oversee and coordinate the work of the various theory groups, who had plenty to work on. They had to come up with a model for the immensely complicated problem of how neutrons diffuse through a critical mass. They had to figure out how to calculate the effects of different kinds of tampers on neutron reflection and absorption. They had to figure out how to calculate the efficiency of nuclear explosions. They had to determine critical masses and - perhaps more importantly - the limits of sub-critical ones. They had to understand how liquids and gases behaved in fractions of micro-seconds, under pressures and temperatures greater than at the center of the sun. They had to design an initiator. They had to determine the behavior of plutonium when they had hardly any plutonium to work with. And on and on.

"Once, when a friend, physicist Victor Weisskopf, asked him how long a certain calculation would take, Bethe answered cheerfully, 'It would take three days for me and it will take three weeks for you!' This was not boasting, merely clear-sightedness. (Weisskopf reports that the calculation, indeed, took him three weeks.)

"Years after Los Alamos, the physicist Richard Feynman, himself famous for his ability to perform calculations in his head, would say that he learned it from Bethe, who was 'absolutely topnotch. He was nearly always able to get the answer to any problem within a percent.'

" 'No one any longer pays attention to--if I may call it--the spirit of physics, the idea of discovery, the idea of understanding. I think it's difficult to make clear to the non-physicist the beauty of how it fits together, of how you can build a world picture, and the beauty that the laws of physics are immutable.' --Hans Bethe"

-- Shrikant Rangnekar

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