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Leo Szilárd, a traffic light and a slice of nuclear history

The views expressed are those of the author and are not necessarily those of Scientific American.

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A reenactment of Einstein signing the famous letter to FDR warning of nuclear weapons in Hitler's hands. Szilard drafted the letter (Image:

Yesterday marked Leo Szilárd’s one hundred and fifteenth birthday. Leo Szilárd: peripatetic Hungarian genius, imperious habitue of hotel lobbies, soothsayer without peer among scientists. Among twentieth century scientists Szilárd stands out as the great prophet who anticipated both the advent of Nazism and the coming of the nuclear arms race. Part of the group of brilliant Hungarian “Martians” – scientists whose intellects and achievements were considered off-the-charts – Szilard was the most perspicacious in anticipating world events, and the most politically savvy. Even as a student in Berlin, where he hobnobbed with the likes of Einstein, Planck and von Laue, Szilárd was convinced that world government was the only solution to our collective problems; this conviction was only strengthened after the atomic bombings of Hiroshima and Nagasaki.

Partly by accident and partly by design, Szilárd played a key role in some of the most important scientific events of the twentieth century. In Berlin he befriended Einstein and later filed a patent for a safe refrigerator with the technically savvy former patent clerk. He also made important contributions to what we know call information theory. Perhaps he is most famous for the twin achievements of convincing his friend Einstein to pen the famous letter to FDR in 1939 and for working on the world’s first nuclear reactor with Enrico Fermi.

During the war Szilárd was characteristically known as a troublemaker, an irksome iconoclast who, more so than even the notoriously free-spirited scientists around him, liked to flout authority. His upstart dismissal of security rules and emphasis on open debate infuriated security personnel and almost led General Groves, the head of the Manhattan Project, to consider incarcerating him for the duration of the war. When the time came to use the bomb, Szilárd was in the forefront of efforts to convince politicians that a demonstration of the weapon would be much more in the United States’ long-term interests if it wanted to prevent a dangerous global arms race, another prophetic prediction that went unheeded. After the war, partly disillusioned with the cruel use to which his beloved physics had been put, Szilárd turned toward biology and was an important influence on the pioneering young scientists who were then inaugurating the fledgling field of molecular biology.

But Szilárd’s real significance goes back much further in ways that had personal resonance for me. In 2007 I made a research-related trip to London. One of my key goals was to go and stand at a particular traffic light near the British Museum and take a photo of myself standing there. This ordinary traffic light was so important for me that I had made up my mind to visit London at least once in my lifetime for the sole purpose of standing at the intersection. What was so special about this traffic light?

It was 1933. Adolf Hitler had come to power in January, The Depression was raging and the future looked bleak to many. On the morning of September 12, 1933, on a miserable, wet, quintessentially English autumn day, at the intersection where Russell Square meets Southampton Row, Leó Szilárd waited irritably at a traffic light waiting for it to change from red to green. He had just attended a lecture by the great English physicist Ernest Rutherford. Rutherford, known to many as the father of nuclear physics, was discussing the newly prophesied release of energy from atoms, most notably by science-fiction pioneer H G Wells in his book The World Set Free. In his baritone voice, Rutherford, acknowledged master of the atomic domain, dismissed this fanciful idea as nonsense. Any thought of releasing the energy locked in atoms, he said, was “moonshine”.

Szilárd was irritated by this flippant repudiation. Accomplished as he was, how could even the great Lord Rutherford know what the future held in store? Szilárd had himself thought deeply about nuclear matters before, most often during his extended morning bathtub ablutions in expensive hotels. Now waiting for the light to change, Szilárd pondered Rutherford’s words…

From here on I will let the acclaimed historian Richard Rhodes do the talking. It was the riveting description of this event in Rhodes’s magnificent book that engraved it in my mind like nothing else:

“In London, where Southampton Row passes Russell Square, across from the British Museum in Bloomsbury, Leo Szilard waited irritably one gray Depression morning for the stoplight to change. A trace of rain had fallen during the night; Tuesday, September 12, 1933, dawned cool, humid and dull. Drizzling rain would begin again in early afternoon. When Szilard told the story later he never mentioned his destination that morning. He may have had none; he often walked to think. In any case another destination intervened. The stoplight changed to green. Szilard stepped off the curb. As he crossed the street time cracked open before him and he saw a way to the future, death into the world and all our woes, the shape of things to come”…

Time cracked open indeed. What Szilard realised as he stepped off that curb was that if we found an element that when bombarded by one neutron would release two neutrons, it could lead to a chain reaction that could possibly release vast amounts of energy. Leo Szilárd had discovered the nuclear chain reaction long before anyone else, six years before the discovery of nuclear fission and any inkling that anyone could have had about the release of atomic energy, let alone the woeful apocalyptic future that would await the world because of its release.

I first read Rhodes’s book in college; it was one of the books that sealed my resolve to become a scientist. The book begins with this story. Since then the event has been etched in my mind like words in red hot steel. The description is so riveting, the tale so profound and evocative, the person so singular and the implications so prophetic, that I resolved to visit Szilárd’s traffic light even if I had to once make a trip to London for just that. Several years later I got a chance.

The traffic light itself is completely nondescript, standing among dozens of other nondescript lights. My friend and I almost missed it; as I mused aloud about my great disappointment in a cafe and wished I had a map, a Spanish tourist sitting at the next table saved my life and procured one. The intersection was there. We had missed it by a block. Back we went and indeed there it was, with not an indication that a famous and prophetic physicist had seen into the future at that light some 75 years ago.

As it turned out at the time, Szilárd’s choice for the element he was thinking about turned out to be wrong. Nuclear fission would be discovered only six years later in Germany after a series of close misses in Italy and France. But Leo Szilárd went down in history as the man who saw death before anyone else, a glimpse into mankind’s Faustian pact with fate, the shape of things to come.

Ironically, when the first atomic bomb test was conducted in the New Mexico desert in the deathly stillness of the morning, in the midst of war and hope, the flash was so bright that it would have been seen reflected off the moon. It was, literally, “moonshine”. The rest was history.

But I lived one of my dreams that day at that traffic light in London. Szilárd’s traffic light. My traffic light.


1. Rhodes, Richard: The Making of the Atomic Bomb (1986), Simon and Schuster.

2. Lanouette, William, Szilard, Bela: Genius in the Shadows: A Biography of Leo Szilard, the Man Behind the Bomb (1994), University of Chicago Press.

Ashutosh Jogalekar About the Author: Ashutosh (Ash) Jogalekar is a chemist interested in the history and philosophy of science. He considers science to be a seamless and all-encompassing part of the human experience. Follow on Twitter @curiouswavefn.

The views expressed are those of the author and are not necessarily those of Scientific American.

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  1. 1. M Tucker 2:13 pm 02/12/2013

    I think Szilard was the “most perspicacious in anticipating” the atomic bomb but you have not convinced me he was more adept than others in anticipating the rise of Nazism. Arms races had become commonplace by the middle 20th century and anticipating one for nuclear weapons is a trivial matter. Suggesting that a demonstration of the bomb to the Japanese leadership would have prevented “a dangerous global arms race” with the Soviet Union is, I think, a bit silly. Soviet spies had penetrated the Manhattan Project and the arms race could not have been prevented. Using the bomb on an actual target or on a demonstration target would not have prevented the Soviets from desiring to acquire the technology.

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  2. 2. curiouswavefunction 3:16 pm 02/12/2013

    The main purpose of the proposed demonstration was to possibly persuade the Japanese to surrender. You are right that it would have probably not stopped the Soviet Union from developing their own bombs, but it would have given the US the higher moral ground and put them in a better position to negotiate treaties and test bans. As it turned out, the secrecy under which the US built the bomb gave the Soviets the perfect excuse to build their own.

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  3. 3. M Tucker 5:21 pm 02/12/2013

    The US could have been completely open about the development of the weapon and the Soviets would have wanted their own. Secrecy had nothing to do with Soviet desire to obtain the best and latest weapons technology. The Soviets distrusted every nation on every issue. They felt they needed the biggest army with the best weapons, just like the West. The Soviets had never been a true ally. This can be seen by Soviet support for and a hopeful treaty with Hitler early in the war and how they treated downed US and British pilots during the war. US support of the Soviet Union during the war was nothing more than enlightened self interest to combat a foe that presented a much more immediate threat. Churchill had seen the Nazi threat and the Soviet threat before most others. Not only did the Soviets want to acquire the technology to develop nuclear weapons but so did the Brits and the French.

    As for the demonstration question…If you had said in your post, “The main purpose of the proposed demonstration was to possibly persuade the Japanese to surrender.” I would not have brought it up.

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  4. 4. xingbot 6:26 am 02/13/2013

    What a great article. Thanks, Ashutosh!

    Have you by chance read Bernstein’s “Review: An Analysis of “Two Cultures”: Writing about the Making and the Using of the Atomic Bombs”? Bernstein is pretty critical of Rhodes’ work, especially his treatment of Szilard. But he talks a fair bit about the decision to use the bombs and is pretty plentiful with his sources—it is a great work. Like everything, those decisions were pretty complicated affairs, but it simply isn’t clear that even if the Soviet bomb was a forgone conclusion, that an arms race had to result.

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  5. 5. curiouswavefunction 11:25 am 02/13/2013

    Thanks for the reference, will take a look. I do know that Bernstein and Gennady Gorelik had a remarkable exchange with Rhodes in Physics Today where they basically said a lot of condescending things Rhodes’s books and even about Rhodes himself. Some of their complaints seemed rather petty and uncalled for. Rhodes who usually does not directly answer to criticism thought the letters nasty enough to step in with a rejoinder.

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  6. 6. xingbot 5:18 am 02/14/2013

    Bernstein is an old school historian for the most part, and unfortunately is unnecessarily scathing when he feels the standards of his field aren’t being lived up to. He’s pretty brutal in his view of Rhodes, but his grasp of the history and historiography of the period is also highly impressive. If you haven’t seen it, I recommend tracking down his work on Oppenheimer’s trial (or if you want to DM me at @neva9257 I’ll send them to you), it is a real treat.

    It shouldn’t come as a surprise that Szilard’s history is contested—he lived a colourful life that was sometimes stranger than fiction. His work endures because of his remarkable personality, and people should definitely pay a lot more attention to him. :-)

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  7. 7. Gene Dannen 12:29 am 10/19/2013

    What a cool dream to have, and to fulfill. But I must correct you. Szilard didn’t attend Rutherford’s talk. He read about it the next day in the London Times.

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