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.