Posts Tagged ‘1940s’

Meditations

A bomb without Einstein?

Friday, June 27th, 2014

If Albert Einstein had never been born, would it have changed when nuclear weapons were first produced? For whatever reason, I’ve seen this question being asked repeatedly on Internet forums, as odd as it is. It’s kind of a silly question. You can’t go in and tweak one variable in the past and then think you could know what the outcome would be. History is a chaotic system; start removing variables, who knows what would happen. Much less a variable named Albert Einstein, one of the most influential physicists of the 20th century, and whose importance extended well past the equations he wrote… and those were pretty important equations, at that!

1946 - Einstein Time magazine - detail

Einstein’s 1946 cover of Time magazine. The mushroom cloud is a beautifully executed combination of the Trinity and Nagasaki mushroom clouds.

On the other hand, this kind of science-fiction counterfactual can have its usefulness as a thought experiment. It isn’t history, but it can be used to illustrate some important aspects about the early history of the atomic bomb that a lot of people don’t know, and to undo a little bit of the “great man” obsession with bomb history. Albert Einstein has been associated with the bomb both through his famous mass-energy equivalence calculation (E=mc²) and because of the famous Einstein-Szilard letter to Roosevelt in 1939. On the face of it, this gives him quite a primary role, and indeed, he usually shows up pretty quickly at the beginning of most histories of the Manhattan Project. But neither E=mc² nor the Einstein-Szilard letter were as central to the Manhattan Project’s success as people realize — either scientifically or historically.

In terms of the science, E=mc² gets a lion’s share of attention, most perfectly expressed by Einstein’s portrait on the cover of Time magazine in 1946 (above) with his equation emblazoned on a mushroom cloud. A lot of people seem to think that E=mc² played a key role in the development of the bomb, that the weapon just falls out of the physics. This is wrong. The equation can help one understand why atomic bombs work, but it doesn’t really tell you how they work, or whether you would expect them to even be possible.

The way I like to put it is this: E=mc² tells you about as much about an atomic bomb as Newton’s laws do about ballistic missiles. At some very “low level” the physics is crucial to making sense of the technology, but the technology does not just “fall out” of the physics in any straightforward way, and neither of those equations tell you whether the technology is possible. E=mc² tells you that on some very deep level, energy and mass are equivalent, and the amount of energy that mass is equivalent is gigantic. But it says nothing about the mechanism of converting mass into energy, either whether one exists in the first place, or whether it can be scaled up to industrial or military scales. It gives no hints as to even where to look for such energy releases. After the fact, once you know about nuclear fission and can measure mass defects and things like that, it helps you explain very concisely where the tremendous amounts of energy come from, but it gives you no starting indications.

Eddington's famous plate of the 1919 solar eclipse, which helped confirm Einstein's theory of General Relativity. Very cool looking, and interesting science. But not relevant to atomic bombs. Source.

Eddington’s famous plate of the 1919 solar eclipse, which helped confirm Einstein’s theory of General Relativity. Very cool looking, and interesting science. But not relevant to atomic bombs. Source.

What about the rest of Einstein’s main theoretical work, both Special and General Relativity Theory? They are pretty irrelevant to bomb-making. The physical processes that take place inside atomic bombs are what physicists call “non-relativistic.” Relativity theory generally only shows its hand when you are talking about great speeds (e.g. large fractions of the speed of light) or great masses (e.g. gravitational fields), and neither of those come into play with fission bombs. You can neglect relativity when doing the math to make a bomb.1

An intelligent follow-up question might be: “well, just because relativity theory didn’t play a role in the bomb process itself doesn’t answer the question of whether it started physics on a path that led to the bomb, does it?” Without getting into a long timeline of the “science that led to the bomb,” here, I think we could reasonably summarize the situation like this: Einstein’s 1905 papers (of which E=mc² was one) did indeed play a role in the subsequent developments that followed, but perhaps not as direct a one as people think. E=mc² didn’t inspire physicists to start looking into processes that converted mass to energy — they were already looking into those through an entirely separate (and earlier) line of development, namely the science of radioactivity and particle physics. The fact that huge amounts of energy were released through nuclear reactions, for example, had already been studied closely by the Curies, by Ernest Rutherford, and by Frederick Soddy prior (but only just) to 1905.

Arguably, the most important work Einstein did in this respect was his work on the photoelectric effect (for which he was awarded the Nobel Prize in Physics for 1921), which helped establish the physical reality of Max Planck’s idea of a quantum of energy, which helped kick off investigations into quantum theory in earnest. This had a big influence on the later direction of physics, even if Einstein himself was never quite comfortable with the quantum mechanics that developed in subsequent decades.

The Hahn-Meitner-Strassman experiment apparatus, at the Deutsches Museum in Munich. My own photo.

The Hahn-Meitner-Strassman experiment apparatus, at the Deutsches Museum in Munich. My own photo.

Did any of the relativity work lead, though, down the path that eventually arrived at the discovery of fission in 1939? I don’t think so. The experiments that Hahn, Meitner, and Strassman were doing in Berlin that lead to the discovery of fission in uranium were themselves careful replications of work that Fermi had done around 1934. Fermi’s work came directly out of an experimentalist, nuclear physics context where physicists were bombarding substances with all manner of subatomic particles to see what happened. It was most directly influenced by the discovery of the neutron as a new sub-atomic particle by Chadwick in 1932. This came out of work on atomic theory and atomic modeling that was being done by Rutherford and his students from the early 1910s-1920s. And this early nuclear physics came, most directly, out of the aforementioned context of radioactivity and experimental physics of the late 19th century.

None of which has a strong, direct connection to or from Einstein’s work in my mind. They have some overlaps of interest (e.g. Bohr was a student of Rutherford’s), but the communities working on these sorts of experimental problems are not quite the same as the more theoretical circle that Einstein himself worked in.2 If we somehow, magically, removed Einstein’s early work from the equation here, does the output change much? There would be some reshuffling, probably, but I sort of think that Rutherford would still be doing his thing anyway, and from that much of the other work that led to the bomb would eventually come out, even if it had a somewhat different flavor or slightly different timeline.

My least favorite way of depicting the fission process, where energy (E) is a magic lightning bolt coming out of the splitting atom. In reality, most of the energy comes in the form of the two fission products (F.P. here) repelling from each other with great violence. Source.

This is my least-favorite way of depicting the fission process, where energy (E) is a magic lightning bolt coming out of the splitting atom. In reality, most of the energy comes in the form of the two fission products (F.P. here) repelling from each other with great violence. Source.

Do you even need to know that E=mc² to make an atomic bomb? Perhaps surprisingly, you don’t! There are other, more physically intuitive ways to calculate (or measure) the energy release from a fission reaction. If you treat the fission process as being simply based on the electrostatic repulsion of two fission products, you get essentially the same energy output in the form of kinetic energy. This is how the physics of fission is often taught in actual physics classes, because it gives you a more concrete indication of how that energy is getting released (whereas E=mc² with the mass-defect makes it seem like a magical lightning bolt carries it away). There are other more subtle physical questions involved in making a bomb, some of which have Einstein’s influence on them in one way or another (e.g. Bose–Einstein statistics). But I think it is not totally crazy to say that even if you somehow imagine a world in which Einstein had never existed, that the physics of an atomic bomb would still work out fine — Einstein’s specific technical work wasn’t central to the problem at all. We also have not brought up the question of whether without Einstein, relativity in some form would have been discovered anyway. The answer is probably “yes,” as there were people working on similar problems in the same areas of physics, and once people started paying a close attention to the physics of radioactivity they were bound to stumble upon the mass-energy relationship anyway. This isn’t to denigrate or underestimate Einstein’s influence on physics, of course. What makes Einstein “Einstein” is that he, a single person, pulled off a great number of theoretical coups all at once. But if he hadn’t done that, there’s no reason to think that other people wouldn’t have come up with his theoretical insights individually, if slightly later.

A postwar re-creation of the genesis of the Einstein-Szilard letter.

A postwar re-creation of the genesis of the Einstein-Szilard letter.

What about Einstein’s most direct role, the famous Einstein-Szilard letter of 1939 that influenced President Roosevelt to set up the first Uranium Committee? This is a tricky historical question that could have (and may at some point) an entirely separate blog post relating to it. Its writing, contents, and influence are more complex than the standard “he wrote a letter, FDR created the Manhattan Project” understanding of it that gets boiled down in some popular accounts. My feeling about it, ultimately, is this: if the Einstein-Szilard letter hadn’t been written, it isn’t clear that anything would be terribly different in the outcome in terms of making the bomb. Something like the Uranium Committee might have been started up anyway (contrary to popular understanding, the letter was not the first time Roosevelt had been told about the possibility of nuclear fission), and even if it hadn’t, it isn’t clear that the Uranium Committee was necessary to end up with a Manhattan Project. The road from a fission program whose primary output was reports and a fission program whose primary output was atomic bombs was not a direct one. By early 1941, the Uranium Committee had failed to convince scientist-administrators that atomic bombs were worth trying to build. They had concluded that while atomic bombs were theoretically feasible, they were not likely to be built anytime soon. Had things stayed there, it seems unlikely the United States would have built a bomb ready to use by July/August 1945.

The “push” came from an external source: the British program. Their MAUD Committee (an equivalent of the Uranium Committee) had concluded that a nuclear weapon would be much easier to build than the United States had concluded, and sent an emissary (Mark Oliphant) to the United States to make sure this conclusion was understood. They caught Vannevar Bush’s ear in late 1941, and he (along with Ernest Lawrence, Arthur Compton, and others) wrested control of the uranium work out of the hands of the Uranium Committee, accelerated the work, and morphed it into the S-1 Committee. The name change is significant — it is one of the more vivid demonstrations of the increased degree of seriousness with which the work was taken, and the secrecy that came with it. By late 1942, the wheels for the full Manhattan Project were set into motion, and the work had become a real bomb-making program.

Einstein wasn’t involved with any of the later work that actually led to the bomb. He almost was, though: in late 1941, Bush considered consulting Einstein for help on the diffusion problem, but opted not to push for it — both because Einstein wasn’t regarded as politically reliable (he had a fat FBI file), and his approach to physics just wasn’t very right for practical problems.3 Bush decided that Einstein would stay out of the loop.

Usual, rare anti-Nazi propaganda postcard from 1934, showing Hitler expelling Einstein from Germany, titled "The Ignominy of the 20th Century." It is one of the most blatant visual renderings of Einstein as a "scientific saint." Source.

Unusual, rare anti-Nazi propaganda postcard from 1934, showing Hitler expelling Einstein from Germany, titled “The Ignominy of the 20th Century.” It is one of the most blatant visual renderings of Einstein as a “scientific saint.” Source.

Let’s sum it up. Did Einstein play a role in the creation of the atomic bomb? Of course — his physics isn’t irrelevant, and his letter to Roosevelt did start one phase of the work. But both of these things are less prominent than the Time-magazine-cover-understanding makes them out to be. They weren’t central to what became the Manhattan Project, and if you could somehow, magically, remove Einstein from the equation, it isn’t at all clear that the atomic bomb wouldn’t have been built around the time it actually was built. I don’t think you can really credit, or blame, Einstein for the atomic bomb, in any direct fashion. Einstein did play a role in things, but that role wasn’t as crucial, central, or direct as a lot of people imagine. If you could magically drop him out of history, I think very little in terms of atomic bombs would have been affected.

So why does the Einstein and the bomb myth persist? Why does everybody learn about the Einstein letter, if it wasn’t really was sparked the Manhattan Project? There are two answers here, I think. One is that Einstein was, even before the war, one of the best-known, best-recognized physicists of the 20th century, and was synonymous with revolutionary science and genius. Having him “predict” the atomic bomb with equations in 1905 — 40 years before one was set off — is the kind of “genius-story” that people love, even if it obscures more than it enlightens. It also has a high irony quotient, since Einstein was forced to flee from Germany when the Nazis took power.

But there’s another, perhaps more problematic aspect. In many early copies of the Smyth Report that were distributed by the government, copies of the Einstein letter were mimeographed and loosely inserted. The magnification of Einstein’s role was purposefully encouraged by the government in the immediate period after using the weapon. (And it was even a convenient myth for Einstein, as it magnified his own importance and thus potential influence.) Hanging the atomic bomb on Einstein’s head was an act of self-justification, of sorts. Einstein was the world’s greatest genius in the eyes of the public, and he was a well-known pacifist, practically a scientific saint. After all, if Einstein thought building a bomb was necessary, who could argue with him?

Notes
  1. As Robert Serber puts it: “Somehow the popular notion took hold long ago that Einstein’s theory of relativity, in particular his famous equation E = mc², plays some essential role in the theory of fission. Albert Einstein had a part in alerting the United States government to the possibility of building an atomic bomb, but his theory of relativity is not required in discussing fission. The theory of fission is what physicists call a non-relativistic theory, meaning that relativistic effects are too small to affect the dynamics of the fission process significantly.” Robert Serber, The Los Alamos Primer: The First Lectures on How to Build an Atomic Bomb (University of California Press, 1992), 7. []
  2. For a good, non-teleological, non-bomb-centric approach to the context of 19th- and 20th-century physics, Helge Kragh’s Quantum Generations: A History of Physics in the Twentieth Century (Princeton University Press, 2002), is excellent. []
  3. Einstein wasn’t entirely a head-in-the-clouds physicist, of course. He worked at the patent office, and as Peter Galison has written about, even his famous thought experiments were often motivated by experience with practical problems of time synchronization. And he did help invent a refrigerator with Leo Szilard. But his work on diffusion physics was too abstract, too focused on first-principle analysis, for use in producing a practical outcome. []
Meditations

Feynman and the Bomb

Friday, June 6th, 2014

Richard Feynman is one of the best-known physicists of the 20th century. Most of those who know about him know he was at Los Alamos during the Manhattan Project — some of the best “Feynman stories” were set there. But Feynman’s own stories about his wartime hijinks were, like most of his stories about himself, half just-for-laughs and half lookit-mee! Feynman’s always got to either be a lucky average Joe, or the one brilliant mind in a sea of normals. His Los Alamos antics are mostly just tales of a genius man-child running around a secret laboratory, picking safes and irritating security guards. They aren’t very good gauges of what he actually did towards making the bomb. So what did Feynman actually do with regards to making the bomb? And does it matter, for thinking about his later career, especially the work that won him a Nobel Prize two decades later? 

Los Alamos colloquium from 1946, featuring (foreground, from left-to-right), Norris Bradbury, J. Robert Oppenheimer, John Manley, Richard Feynman, and Enrico Fermi. This version is cropped from the scanned copy at the Emilio Segrè Visual Archives. I will note that unlike the more common copies of this photo that have circulated, you can actually get a sense for how many other people were in the room — it looks like a really packed house.

Los Alamos colloquium from 1946, featuring (foreground, from left-to-right), Norris Bradbury, J. Robert Oppenheimer, John Manley, Richard Feynman, and Enrico Fermi. This version is cropped from the scanned copy at the Emilio Segrè Visual Archives. I will note that unlike the more common copies of this photo that have circulated, you can actually get a sense for how many other people were in the room — it looks like a really packed house.

Feynman’s own stories of his wartime work are centered around things other than the work itself. So he describes doing calculations, but doesn’t really say what they were for. He describes going to Oak Ridge, but only as a pretext for a story about dealing with generals and engineers. He describes the Trinity test, but a lot of that is about his claim to being the only person who saw it without welding glass on. And so on. These give glimpses, but not a very complete picture.

The historian of physics (and my advisor) Peter Galison wrote an article on “Feynman’s War” several years back, looking closely at what it actually was that Feynman was doing at the lab, and how it played into the style that he later became famous for in physics.1 Galison argues that Feynman’s postwar work is uniquely characterized by being “modular, pictorial, and proudly unmathematical.” He contrasts this with the work of several of his contemporaries, including Julian Schwinger, who came up with equivalent solutions to the same physical problems but through a very different (much more mathematical) approach. Feynman’s famous diagrams, which had a huge influence on the teaching and practice of postwar physics, exemplify this approach. What in Schwinger and Tomonaga’s hands (the other people Feynman shared his Nobel Prize with in 1965) was solvable only through massive, lengthy, laborious math could, in Feynman’s hands, be solved through a series of clever diagrams which came up with equivalent results. Feynman’s solutions to quantum electrodynamics weren’t the only way to do it — but they were easier to comprehend, to teach, and to apply to new questions.

The first Feynman diagram, published in R. P. Feynman, "Space—Time Approach to Quantum Electrodynamics,"Physical Review 76 (1949), 769-789, on 772.

The first published Feynman diagram, from Richard P. Feynman, “Space-Time Approach to Quantum Electrodynamics,”Physical Review 76 (1949), 769-789, on 772.

OK, so what does this have to do World War II? Well, Galison’s argument is that you can see the same sort of thinking at work in what Feynman did at Los Alamos, and he argues that it is during the war that he really started applying this mode of physics. He divides Feynman’s work into several “projects.” They were:

  • Neutron measurements for determining critical mass (including the famous “tickling the dragon’s tail” experiment” involving creating brief, barely-subcritical masses)
  • Work on the “Water Boiler” reactor at Los Alamos, which provided further data on nuclear chain reactions
  • Work as a safety supervisor at Oak Ridge, Tennessee, at Oppenheimer’s request (which in his own writings is distilled down to a single humorous anecdote where Feynman is simultaneously clueless and brilliant)
  • Developing formulae relating to criticality and implosion efficiency (including the Bethe-Feynman formula)
  • His work on the hydride bomb, an abortive, Teller-inspired approach to make a “cheaper” fission weapon which involved devilishly difficult calculation (because not all of the neutrons produced in the weapon would be of the same energy)

Galison argues that in each of these instances, you can see the germs of his later approaches. He credits this to both Feynman’s own personal scientific style and inclinations as a theorist (Feynman didn’t seem to like to work with fundamental equations, but with “shortcuts” that lead to quicker, more efficient solutions, for example), but also to the requirements of the wartime goal, where theorists had to come up with tangible, practical results in a very short amount of time.  For example, Galison notes that the formulae relating to how the implosion bomb worked “brought the abstract differential equations to the bottom line: how hot, how fast, how much yield?” The practical needs of the war favored a particular “theoretical style” in general, Galison argues, one that could be most easily meshed with engineering concerns, rapid prototyping, and the lack of time to ruminate on fundamental physics questions.2

The "Water Boiler" reactor at Los Alamos. Source: Los Alamos Archives (12784), via Galison 1998.

The “Water Boiler” reactor at Los Alamos that Feynman worked on. Source: Los Alamos Archives (12784), via Galison 1998, p. 404.

Galison’s article is fairly technical. He goes through Feynman’s work (what of it that is declassified, anyway) and tries to follow his thinking in a very “internal” way, and then match that up with the requirements imposed by the specific wartime context. If you are well-versed in physics you will probably find the details interesting. I’m more of a big-picture person myself, and I like the structure of Galison’s argument even if I don’t feel fully capable of digesting all of the physics involved. One small example of Galison’s work can probably suffice. Feynman was sent to Oak Ridge, as noted, to serve as a safety supervisor. He was taking over for Robert Christy, who got pneumonia in April 1944. The safety question was not a general one, but a very specific one: how many barrels of uranium (in various degrees of enrichment) could be safely stored in a room without running a risk of a criticality accident? Feynman himself relates the problem like this in his famous bit, “Los Alamos from Below” (reproduced in Surely You’re Joking, Mr. Feynman):

It turned out that the army had realized how much stuff we needed to make a bomb — twenty kilograms or whatever it was — and they realized that this much material, purified, would never be in the plant, so there was no danger. But they did not know that the neutrons were enormously more effective when they are slowed down in water. In water it takes less than a tenth — no, a hundredth — as much material to make a reaction that makes radioactivity. It kills people around and so on. It was very dangerous, and they had not paid any attention to the safety at all.

In Feynman’s account, he more or less walks in and figures out what the problems were and how to fix them. The story is about ignorance — in particular systemic ignorance due to secrecy — and Feynman’s attempts to cut through it.

Feynman's diagrammatic sketch of storage of barrels of uranium at Oak Ridge, prepared for his "Safety Report." Source: Galison 1998, p. 408.

Feynman’s diagrammatic sketch of storage of barrels of uranium at Oak Ridge, prepared for his “Safety Report.” Source: Galison 1998, p. 408.

Galison’s account is more technical. Feynman told them that pretty much any amount of unenriched uranium could be stored safely in the facility, but that 5% enriched and 50% enriched had to be handled fairly carefully. 50% enriched uranium in water, for example, would dangerous at a mere 350 grams of material unless there was a neutron absorbing material (cadmium) present. Feynman developed a series of safety recommendations for all grades of enrichments, and had to use reasonable safety margins to make up for potential errors in the calculations. He became the “point man” for safety questions involving fissionable materials, and developed (as Galison puts it) “visualizable” methods for answering basic (but important) questions about hypothetical systems (e.g. for “Gunk storage tanks,” whether they had to be coated with cadmium or not). His methods, Feynman himself emphasizes, were “only approximate, as accuracy has been sacrificed to speed and simplicity in calculation” — the kind of computational “short cut” that was both needed for the practical requirements, but also was common to Feynman’s general approach to physics. Galison concludes the section thus:

The admixture of approximation methods, neutron diffusion, nuclear cross sections, floods, fires and wooden walls marked Feynman’s correspondence with the Oak Ridge engineers. From April of 1944 to September 1945, whatever else Feynman was doing, he was also deeply enmeshed in the barely-existing field of nuclear engineering. Out of this interaction came characteristic rules and modular reasoning: visualizable, approximate, from-the-ground-up calculations applied to neutrons, pans, sheds and sludge. Visionary statements reinterpreting established laws of physics ceded to the exigencies of living in a world he had to reach outside the home culture of theoretical physics as he knew it before the war. Now a billion dollar plant was churning out U-235, and only a calculation stood between thousands of workers and nuclear disaster.

Which is a lot more serious-sounding that Feynman’s own somewhat jokey accounts of the work. In the latter part of the article, Galison connects all of these methods for thinking — and sometimes even the specific problems — with Feynman’s postwar work, showing the influence of his time at Los Alamos.

Diagram of neutron fluctuations from a report by F. de Hoffmann, R.P. Feynman, and R. Serber. Galison notes: "Significantly, Feynman and his collaborators captured the situation in a spacetime diagram drawn with time in the vertical direction and space horizontal. Such an image must be kept in mind when viewing Feynman's early postwar spacetime 'Feynman diagrams,' where again particles are absorbed, emit other particles, and scatter as reckoned by a concatenation of independent algebraic rules." Galison 1998, 405-406.

Diagram of neutron fluctuations from a report by F. de Hoffmann, R.P. Feynman, and R. Serber. Galison notes: “Significantly, Feynman and his collaborators captured the situation in a spacetime diagram drawn with time in the vertical direction and space horizontal. Such an image must be kept in mind when viewing Feynman’s early postwar spacetime ‘Feynman diagrams,’ where again particles are absorbed, emit other particles, and scatter as reckoned by a concatenation of independent algebraic rules.” Galison 1998, 405-406.

Feynman stayed at Los Alamos until the fall of 1946, when he relocated to Cornell University. He never worked on weapons again, but he never took a particularly strong stand on it. What did Feynman think about nuclear weapons, and his role in making them? There is some evidence in his private correspondence, much of which was published not too long ago,3 but it is scant. Most of his responses to inquiries were along the lines of “we feared the Nazis would get one first.”4That’s it. No comment on their use at all, or the end of the war, or any of the other common responses from Los Alamos veterans. When asked in the 1970s about his thoughts on nuclear weapons in general, he demurred: “Problems about the atomic bomb and the future are much more complicated and I cannot make any short  statement to summarize my beliefs here.”5

Feynman gave an interview in 1959 where he was asked directly about the bomb. His response was a little lengthier then, but still said very little:

Now, with regard to our own things as human beings, naturally—I myself, for example—worked on the bomb during the war. Now how do I feel about that? I have a philosophy that it doesn’t do any good to go and make regrets about what you did before but to try to remember how you made the decision at the time. …if the scientists in Germany could have developed this thing, then we would be helpless, and I think it would be the end of the civilization at that time. I don’t know how long the civilization is going to last anyway. So the main reason why I did work on it at the time was because I was afraid that the Germans would do it first, and I felt a responsibility to society to develop this thing to maintain our position in the war.6

This, of course, ignores the question of “so why did you continue when the Germans were known not to have made much progress?” and much more.

Charles Critchfield, Richard Feynman, J. Robert Oppenheimer, and an unidentified scientist, at Los Alamos. Source: Emilio Segrè Visual Archives, via Los Alamos.

Charles Critchfield, Richard Feynman, J. Robert Oppenheimer, and an unidentified scientist, at Los Alamos. Source: Emilio Segrè Visual Archives, via Los Alamos.

During the interview, Feynman was asked, point blank, whether he worked on any secret projects. Feynman said no, and that this was “out of choice.” Pushed further, he elaborated:

I don’t want to [do secret work] because I want to do scientific research—that is, to find out more about how the world works. And that is not secret; that work is not secret. There’s no secrecy associated with it. The things that are secret are engineering developments which I am not so interested in, except when the pressure of war, or something else like that, makes me work on it. … Yes, I am definitely anti-working in secret projects. … I don’t think things should be secret, the people developing this. It seems to me very difficult for citizens to make a decision as to what’s going on when you can’t say what you’re doing. And the whole idea of democracy, it seems to me, was that the public, where the power is supposed to lie, should be informed. And when there’s secrecy, it’s not informed. Now, that’s a naive point of view, because if there weren’t secrecy, there’d be the Russians who would find out about it. On the other hand, there’s some awfully funny things that are secret. It becomes secret that we know what the Russians are keeping secret from us, for instance, or something like that. It seems to me that things go too far in the secrecy.7

After that point in the interview, he steered away from political opinions, explaining that he had strong ones, but he didn’t think they were any more valuable than anyone else’s opinions.

There were those, of course, who did try to recruit Feynman for military work. John Wheeler, his doctoral advisor at Princeton, and the man who had roped him into Los Alamos in the first place, appealed to him strongly to join the Princeton work on the hydrogen bomb (Matterhorn) in late March 1951. Wheeler had heard the Feynman was trying to spend his sabbatical in Brazil, but Wheeler thought the chance of global war was “at least 40%,” and that Feynman’s talents might be better spent helping the country. It was a long, emotional letter, albeit a variation on one that Wheeler sent to many other scientists as well. Wheeler tried to win him (and others) with flattery as well, telling Feynman that “You would make percentage-wise more difference there than anywhere else in the national picture.” In response to Wheeler’s long, many-pointed letter, Feynman simply responded that he didn’t want to make any commitments until he found out whether the Brazil idea would work out. End of story. Nothing specific about the hydrogen bomb one way or the other.

High resolution detail of Feynman's Los Alamos security badge photograph. A this resolution you can see a lot more strain on his face than the one I posted awhile back. Source: Los Alamos National Laboratory Archives.

High-resolution detail of Feynman’s Los Alamos security badge photograph. At this resolution you can see potentially more strain on his face than the one I posted awhile back. Source: Los Alamos National Laboratory Archives.

What should we make of this? Feynman is a complicated man. Much more complicated than the zany stories let on — and I suspect the stories themselves were some kind of defense mechanism. As Feynman’s friend Murray Gell-Mann said at Feynman’s memorial service, Feynman “surrounded himself with a cloud of myth, and he spent a great deal of time and energy generating anecdotes about himself.” They were stories “in which he had to come out, if possible, looking smarter than anyone else.”8 He was not a moralizer, though. His work on the bomb fit into his stories only as a context. He no doubt drew many lessons from his work on nuclear weapons, and he no doubt had many opinions about them in the Cold War, but he kept them, it seems, much to himself.

Oppenheimer famously said that, “In some sort of crude sense, which no vulgarity, no humor, no overstatement can quite extinguish, the physicists have known sin…” Perhaps Feynman agreed — perhaps no more humor could be wrung out of the bomb after Hiroshima and Nagasaki. Maybe it’s harder to write a zany story about the hydrogen bomb. And maybe he was just truly not interested in them from a technical standpoint, or, as he said in 1959, just didn’t think his opinions on these matters, one way or another, were worth a damn, going against the notion held by many of his contemporaries that those who made the bomb had a special knowledge and a special responsibility. To me, he’s still something of an enigma, just one that wrapped himself in jokes, rather than riddles.

Notes
  1. Peter Galison, “Feynman’s War: Modelling Weapons, Modelling Nature,” Stud. Hist. Phil. Mod. Phys. 29, No. 3 (1998), 391-434. []
  2. This is an argument that Galison also makes at length about wartime work in his 1997 book Image and Logic: A Material Culture of Microphysics, both for Los Alamos and for the MIT Rad Lab, which if you’re interested in this kind of thing, is a must-read. []
  3. Michelle Feynman, ed., Perfectly Reasonable Deviations from the Beaten Track: The Letters of Richard P. Feynman (Basic Books, 2005). []
  4. See e.g., Ibid., 268: “I did work on the atomic bomb. My major reason was concern that the Nazi’s would make it first and conquer the world.” []
  5. Ibid., 305. []
  6. Ibid., 421. []
  7. Ibid., 422-423. []
  8. James Gleick, Genius: The Life and Science of Richard Feynman (Pantheon, 1992), on 11. []
Visions

Oppenheimer and the Gita

Friday, May 23rd, 2014

What was going through J. Robert Oppenheimer’s head when he saw the great fireball of the Trinity test looming above him? According to his brother, Frank, he only said, “it worked.” But most people know a more poetic account, one in which Oppenheimer says (or at least thinks) the following famous lines:

I remembered the line from the Hindu scripture, the Bhagavad-Gita; Vishnu is trying to persuade the Prince that he should do his duty and, to impress him, takes on his multi-armed form and says, “Now I am become Death, the destroyer of worlds.” I suppose we all thought that, one way or another.

This particular version, with a haggard Oppenheimer, was originally filmed for NBC’s 1965 The Decision to Drop the Bomb. I first saw it in Jon Else’s The Day After Trinity (1980), and thanks to YouTube it is now available pretty much anywhere at any time. There are other versions of the quote around — “shatter of worlds” is a common variant — though it did not begin to circulate as part of Los Alamos lore until the late 1940s and especially the 1950s.

It’s a chilling delivery and an evocative quote. The problem is that most of the time when it is invoked, it is done purely for its evocativeness and without any understanding as to what it actually supposed to mean. That’s what I want to talk about: what was Oppenheimer trying to say, presuming he was not just trying to be gnomic? What was he actually alluding to in the Gita?

An Indian greeting card for Diwali from 1998, celebrating India's nuclear tests. Source.

An Indian greeting card for Diwali from 1998, celebrating India’s nuclear tests. Source.

I should say first that I’m no scholar of Hindu theology. Fortunately, many years back, James A. Hijiya of the University of Massachusetts Dartmouth wrote a wonderful article on “The Gita of J. Robert Oppenheimer” that covers all of this topic as well as one might ever want it to be covered.1 Everything I know about the Gita comes from Hijiya’s article — so read it if you want much more discussion of this than I have here. I am particularly fond of Hijiya’s opening line, that Oppenheimer’s paraphrase of the Gita is “one of the most-cited and least-interpreted quotations” of the atomic age.

Oppenheimer was not a Hindu. He was not much of anything, religiously — he was born into a fairly secular Jewish family, embraced the Ethical Culture of Felix Adler, and saw philosophy as more of a boon to his soul than any particular creed. He enjoyed the ideas of the Gita, but he was not religious about it. Hijiya thinks, however, that much can be understood about Oppenheimer’s life through the lens of the Gita as a philosophical and moral code, something necessary in part because Oppenheimer rarely discussed his own internal motivations and feelings about making the bomb. It helps explain, Hijiya argues, that a man who could utter so many public statements about the “sin” and “terror” and “inhumanity” of Hiroshima and Nagasaki could also have been the one who pushed for their use against Japan and who never, ever said that he actually regretted having built the bomb or recommending its use. It helps resolve one of the crucial contradictions, in other words, at the heart of the story of J. Robert Oppenheimer.

J. Robert Oppenheimer, from the Emilio Segrè Visual Archives.

J. Robert Oppenheimer, from the Emilio Segrè Visual Archives.

It’s not clear when Oppenheimer was first exposed to the Gita. I have seen accounts, in oral histories, that suggested that he was spouting Gita lines even while he was a young graduate student studying in Europe. What is definitely known is that he didn’t start studying Sanskrit seriously until 1933, when he started studying with the renown Sanskrit scholar Arthur W. Ryder while he was a professor at Berkeley. In letters, he wrote gushingly about the book to his brother, and much later he quoted from it at the service held at Los Alamos in April 1945 upon the death of President Roosevelt.

The story of the Gita is that of Arjuna, a human prince who has been summoned to a war between princely cousins. Arjuna doesn’t want to fight — not because he lacks courage, or skill, but because it is a war of succession, so his enemies are his own cousins, his friends, his teachers. Arjuna does not want to kill them. He confides in his charioteer, who turns out to be the god Krishna2 in a human form. The text of the Gita is mostly Krishna telling Arjuna why Arjuna must go to war, even if Arjuna does not want to do it.

Krishna’s argument hinges on three points: 1. Arjuna is a soldier, and so it is his job — his duty — to wage war; 2. It is Krishna’s job, not Arjuna’s, to determine Arjuna’s fate; 3. Arjuna must ultimately have faith in Krishna if he is going to preserve his soul.

Arjuna eventually starts to become convinced. He asks Krishna if he will show him his godlike, multi-armed form. Krishna obliges, showing Arjuna an incredible sight:

Krishna revealing himself to Arjuna. Source.

Krishna revealing himself to Arjuna. Source.

A thousand simultaneous suns
     Arising in the sky
Might equal that great radiance,
     With that great glory vie.

Arjuna is awestruck and spellbound:

Amazement entered him; his hair
     Rose up; he bowed his head;
He humbly lifted folded hands,
     And worshipped God. . . .

And then, in his most amazing and terrible form, Krishna tells Arjuna what he, Krishna, is there to do:

Death am I, and my present task
     Destruction.

Arjuna, suitably impressed and humbled, then agrees to join in the battle.

The above quotes are from Ryder’s translation of the Gita. You can see that Oppenheimer’s is not especially different from that, even if it is somewhat changed. Personally I find Ryder’s version of the last part more impressive — it is more poetic, more stark. Ryder’s translation, Hijiya explains, is a somewhat idiosyncratic but defensible one. What Ryder (and Oppenheimer) translate as “Death,” others have translated as “Time,” but Hijiya says that Ryder is not alone for calling attention to the fact that in this context the expanse of time was meant to be a deadly one.

If you would like to see the famous “death” verse in the original, it is chapter 11, verse 32 of the Gita, and looks like this:

Gita verse 11:32

This website (from which I got the above) translates it as:

Lord Krsna said: I am terrible time the destroyer of all beings in all worlds, engaged to destroy all beings in this world; of those heroic soldiers presently situated in the opposing army, even without you none will be spared.

While I find Ryder’s more poignant, the longer translation makes it extremely clear what Krishna has in mind. All will perish, eventually. In war, many will perish whether you participate or not. For Oppenheimer and the bomb, this may have seemed especially true. The cities of Hiroshima and Nagasaki (and others on the target list) were on it not because they were necessarily the most important, but because they had so far been spared from firebombing. They were being actively preserved as atomic bomb targets. Had the bomb not been used or made, they probably would have been firebombed anyway. Even if the physicists had refused to make nuclear weapons, the death toll of World War II would hardly have been altered.

Trinity long exposure

“A thousand simultaneous suns”: a long-exposure shot of the Trinity test.

So let’s step back and ask who Oppenheimer is meant to be in this situation. Oppenheimer is not Krishna/Vishnu, not the terrible god, not the “destroyer of worlds” — he is Arjuna, the human prince! He is the one who didn’t really want to kill his brothers, his fellow people. But he has been enjoined to battle by something bigger than himself — physics, fission, the atomic bomb, World War II, what have you — and only at the moment when it truly reveals its nature, the Trinity test, does he fully see why he, a man who hates war, is compelled to battle. It is the bomb that is here for destruction. Oppenheimer is merely the man who is witnessing it. 

Hijiya argues that Oppenheimer’s sense of Gita-inspired “duty” pervades his life and his government service. I’m not sure I am 100% convinced of that. It seems like a heavyweight philosophical solution to the relatively lightweight problem of a life of inconsistency. But it’s an interesting idea. It is perhaps a useful way to think about why Oppenheimer got involved with so many projects that he, at times, seemed ambivalent about. Though ambivalence seemed readily available in those days — nobody seems to be searching for deep scriptural/philosophical justifications for Kenneth Bainbridge’s less eloquent, but equally ambivalent post-Trinity quote: “Now we’re all sons-of-bitches.”

A rare color photograph of Oppenheimer from October 1945, with General Groves and University of California President Robert Sproul, at the Army-Navy "E" Award ceremony. Source.

A rare color photograph of Oppenheimer from October 1945, with General Groves and University of California President Robert Sproul, at the Army-Navy “E” Award ceremony. Source.

One last issue that I find nagging me. We have no recording of Oppenheimer saying this except the 1965 one above. By this time, Oppenheimer is old, stripped of his security clearance, and dying of throat cancer. It is easy to see the clip as especially chilling in this light, given that is being spoken by a fading man. How would it sound, though, if it was coming from a younger, more chipper Oppenheimer, the one we see in photographs from the immediate postwar period? Would it be able to preserve its gravity?

Either way, I think the actual context of the quote within the Gita is far deeper, far more interesting, than the popular understanding of it. It isn’t a case of the “father” of the bomb declaring himself “death, the destroyer of worlds” in a fit of grandiosity or hubris. Rather, it is him being awed by what is being displayed in front of him, confronted with the spectacle of death itself unveiled in front of him, in the world’s most impressive memento mori, and realizing how little and inconsequential he is as a result. Compelled by something cosmic and terrifying, Oppenheimer then reconciles himself to his duty as a prince of physics, and that duty is war.

Notes
  1. James A. Hijiya, “The Gita of J. Robert Oppenheimer,” Proceedings of the American Philosophical Society 144, no. 2 (June 2000), 123-167. []
  2. Oppenheimer, in his 1965 interview, identifies the god as Vishnu, perhaps in error. Krishna is an avatar of Vishnu, however, so maybe it is technically correct along some line of thinking. []
Visions

The plutonium box

Friday, March 28th, 2014

I’ve found myself in a work crunch (somehow I’ve obligated myself to give three lectures in the next week and a half, on top of my current teaching schedule!), but I’m working on some interesting things in the near term. I have a review of Eric Schlosser’s Command and Control coming out in Physics Today pretty soon, and I’ll post some more thoughts on his book once that is available. And I have something exciting coming up for the 60th anniversary of Oppenheimer’s security hearing.

In the meantime, I wanted to share the results of one little investigation. I’ve posted a few times now (Posing with the plutoniumLittle boxes of doom, The Third Core’s Revenge) on the magnesium boxes that were used to transport the plutonium cores used for the Trinity test and the Fat Man bomb:

The magnesium cases for the world's first three plutonium cores. Left: Herb Lehr at Trinity base camp with the Gadget core. Center: Luis Alvarez at Tinian with the Fat Man core. Right: The third core's case at Los Alamos, 1946.

The magnesium cases for the world’s first three plutonium cores. Left: Herb Lehr at Trinity base camp with the Gadget core. Center: Luis Alvarez at Tinian with the Fat Man core. Right: The third core’s case at Los Alamos, 1946.

Just to recap, they were a design invented by Philip Morrison (the Powers of Ten guy, among other things), made out of magnesium with rubber bumpers made of test tube stoppers. They could hold the plutonium core pieces (two in the case of the Trinity Gadget, three in the case of Fat Man), as well as neutron initiators. Magnesium was used because it was light, dissipated heat, and did not reflect neutrons (and so wouldn’t create criticality issues). All of this information is taken from John Coster-Mullen’s Atom Bombs, an essential book if you care about these kinds of details.

But all of the photographs of the box I had seen, like those above, were in black and white. Not a big deal, right? But I find the relative lack of color photography from the 1940s one of those things that makes it hard to relate to the past. When all of Oppenheimer’s contemporaries talked about his icy blue eyes, it makes you want to see them as they saw them, doesn’t it? Maybe it’s just me.

The only place where I almost saw a color photo of the box is in a photo that the late Harold Agnew had taken of himself on Tinian. It’s one of a large series of posing-with-plutonium photos that were taken on the island of Tinian sometime before the Nagasaki raid. Only this one is in color! Except… well, I’ll let the photo speak for itself:

Harold Agnew with plutonium core redacted

Yeah. Not super helpful. This was scanned from Rachel Fermi and Esther Samra’s wonderful Picturing the Bomb book. They asked Agnew what had happened, and he told them that:

I was in Chicago after the war in 1946. The FBI came and said they believed I had some secret pictures. They went through my pictures and found nothing. Then like a fool I said, “Maybe this one is secret.” They wanted to know what that thing was. I told them and they said that it must be secret and wanted the picture. I wanted the picture so they agreed if I scratched out the “thing” I could keep the slide.

Thwarted by nuclear secrecy, once again! You can try to look extra close at the scratches and maybe just make out the color of the “thing” but it’s a tough thing to manage.

Ah, but there is a resolution to this question. Scott Carson, a retired engineer who posts interesting nuclear things onto his Twitter account, recently posted another  photo of the box — in color and unredacted! His source was a Los Alamos newsletter from a few years back. It is of Luis Alvarez, another member of the Tinian team, in the same exact pose and location as the redacted Agnew photograph… but this time, un-redacted! And the color of the box was…

Luis Alvarez with the Fat Man core, Tinian, 1945.

…yellowNot what I was expecting.

Why yellow? My guess: it might be the same yellow paint used on the Fat Man bomb. Fat Man was painted “a mustard yellow rust-preventing zinc-chromate primer” (to quote from Coster-Mullen’s book) that made them easier to spot while doing drop tests of the casings.

The box for the Trinity core doesn’t look painted yellow to me — it looks more like raw magnesium. Maybe they decided that the tropical atmosphere of Tinian, with its high humidity, required painting the box to keep it from oxidizing. Maybe they just thought a little color would spruce up the place a little bit. I don’t know.

Does it matter? In some sense this is pure trivia. If the box was blue, green, or dull metallic, history wouldn’t be changed much at all. But I find these little excursions a nice place to meditate on the fact that the past is a hard thing to know intimately. We can’t see events exactly as they were seen by those who lived them. Literally and figuratively. The difficulty of finding out even what color something was is one trivial indication of this. And the secrecy doesn’t help with that very much.

Visions

Firebombs, U.S.A.

Wednesday, March 12th, 2014

After the atomic bombs were dropped on Japanese cities, it didn’t take long for the US public, to start drawing what it would look like if atomic bombs went off over their own cities. PM, a New York City newspaper, may have inaugurated the genre with its August 7, 1945, issue, when it took what scant facts were known about Hiroshima and superimposed the data onto the Manhattan skyline:

PM - NYC atomic bomb - August 1945

This impulse — to see what the bomb did to others, and then to apply it to one’s own cities — worked on at least two levels. In once sense it was about making sense of the damage in intuitive terms, because maps of Hiroshima don’t make a lot of intuitive sense unless you know Hiroshima, the city. Which very few Americans would.

But it’s also a recognition that atomic bombs could possibly be dropped on the USA in the future. The atomic bomb was immediately seen as a weapon of the next war as well as the present one. It was a weapon that would, eventually, make the United States very vulnerable.

Considering how many non-atomic bombs the US dropped on Japan during the war, it’s a little interesting that nobody has spent very much time worrying about what would happen if someone firebombed the United States. Why not? Because the U.S. has never imagined that any other nation would have the kind of air superiority to pull off sustained operations like that. No, if someone was going to bomb us, it would be a one-time, brief affair.

When the US did invoke American comparisons for firebombing, it was to give a sense of scale. So the Arnold report in 1945 included this evocative diagram of Japanese cities bombed, with American cities added to give a sense of relative size:

Arnold map - Japan firebombing

So I was kind of interested to find that in the final, late-1945 issue of IMPACT, a US Army Air Forces magazine, contained a really quite remarkable map. They took the same data of the above map — the Japanese cities and their equivalent US cities — and projected them not on Japan, but on the continental United States.

It’s the only attempt I’ve seen to make a visualization that showed the damage of the ruinous American air campaign against Japan in such a vivid way:1

Click to enlarge.

Click to enlarge.

The correspondences between US and Japanese cities were chosen based on the US Census of 1940 and presumably a Japanese census from around the same period. The above map isn’t, the text emphasizes, a realistic attack scenario. Rather, it is meant to show this:

If the 69 U.S. cities on the map at right had been mattered by Jap bombers free to strike any time and anywhere in this country, you can vividly imagine the frightful impact it would have had upon our morale and war potential. Yet this is precisely what the B-29s did to Japan.

What’s remarkable is that this isn’t some kind of anti-bombing screed; it’s pro-bombing propaganda. Both of these images are bragging. The text goes on to emphasize that if someone were really targeting the US, they’d hit industrial centers like Detroit, Philadelphia, and Pittsburgh — to say nothing of Washington, DC, which is conspicuously absent and unmentioned.

IMPACT was classified “confidential” during the war, meaning it had a circulation of about 10,000 airmen. It’s a pretty wonderful read in general — it’s a vociferously pro-Air Forces rag, and is all about the importance of strategic bombing. As one might expect, it de-emphasizes the atomic bombings, in part to push back against the very public perception that we have today, where the last two major bombings are emphasized and the other 67 are forgotten. On the above maps, Hiroshima and Nagasaki are unremarkable, easily in the crowd.

I thought it would be interesting to copy out all of the data (city names, damage percentages, and look up the US Census data) and put it into an interactive visualization using a Javascript toolkit called D3. If you have a reasonably modern browser (one that supports SVG images), then check it out here:

Firebombs, USA, interactive

One thing you notice quickly when putting it this way is how large some of the metropolises were versus the relatively modest of most of the other cities. The idea of someone bombing out 55% of Sacramento, or 64% of Stockton, or 96% of Chattanooga, is kind of mind-melting. Much less to consider that a New York City minus 40% of its land area would look like.2

You can also see how cramped Japan is compared to the USA (they are at the same scale in the above image, though the projections are a bit tweaked for the layout). Even that could be more emphasized, as the text does: because Japan is so mountainous, its inhabited area is only roughly the size of Montana. So it’s even smaller than it looks.

Still, for me it’s just remarkable that this mode of visualization would be used in an official publication. These guys wanted people to understand what they had done. They wanted people to know how bad it had been for Japan. They wanted credit. And I get why — I’m not naive here. They saw it as necessary for the fighting of the war. But it also shouldn’t have been surprising, or unexpected, to those at the time that people in the future might be taken aback by the scale of the burning. Even Robert McNamara, who helped plan the firebombing operations, later came to see them as disproportionate to the US aims in the war:

This sequence, from Errol Morris’s Fog of War, has been one of my favorites for a long time. But it wasn’t until recently that I realized its source was one of these maps used for postwar boasting. It’s an incredible re-appropriation, when looked at in that light. A document meant to impress an audience, now being used to horrify a different one.

Notes
  1. Regarding the image, I scanned it out of a reprint of the IMPACT issue. Because of the crease in the center of the pages I had to do some Photoshop wizardry to make it even — so there is a lot of cleaning up around the center of the image. The data hasn’t been changed, but some of the state outlines were retouched and things like that. Similar Photoshop wizardly was also applied to the Arnold Report image to make it look clean. I suspect that the IMPACT image may have come first and the Arnold report image was derived from it, just because the IMPACT caption goes into details about methodology whereas the Arnold report does not. []
  2. But don’t confuse “destroyed” with casualties — I don’t have those numbers on hand, though if I can find them, I’ll add them to the visualization. The nice thing about D3 is that once you’ve got the basics set up, adding or tweaking the data is easy, since it is just read out of spreadsheet file. The maddening thing about D3 is that getting the basics set up is much harder than you might expect, because the documentation is really not aimed at beginners. If you are interested in a copy of the data, here is the file. []