On January 2, 1939, Enrico Fermi landed in New York. He has just won the Nobel, but work difficulties and the racial laws threatening his wife Laura convinced him to leave. In the United States, there are already Albert Einstein and other European physicists of Jewish origin who managed to escape the Nazis. Among them also Leó Szilárd.

Niels Bohr also arrives in mid-January to attend a conference in Washington. He brings incredible news.

While Enrico Fermi was travelling, German physicists Otto Hahn and Fritz Strassman repeated his experiments, bombarding the uranium nucleus with neutrons and obtaining something they could not explain: the reaction product is barium, an element that has an atomic number corresponding to half that of uranium. Hahn then wrote to Lise Meitner, his longtime collaborator who had fled to Sweden, to ask for help. And on Christmas Eve, she could interpret the data and provide the physical explanation for fission.

Amid a World War, scientists are demonstrating that not only is it possible to split the atom’s nucleus, but this “fission” could develop a chain reaction capable of releasing massive energy. Could it be used as a weapon far more potent than anything else? Who will be able to manufacture it before the others?

It is at that moment that, as Pietro Greco writes, “European physicists in America, due to Nazism, find themselves having to act as politicians”. (Science and Europe. The early twentieth century, The Golden Donkey)

For the 2024 Open Lessons cycle, we decided to try to tell what those crucial years were from both a scientific and historical point of view. To do this, we have chosen to rely on the voices of exceptional witnesses, with a perspective on the events that is all the more interesting as it is less official and celebrated.

Go to the conference program “Manhattan Project. A tale of many voices.”