Science and Ethics – On physics losing its innocence 70 years ago

It is rare forphysiciststo pay a great deal of attention to an historical discussion or anniversary. In these early days of August 2015, this is different. They and many other people commemorate the 200,000 people killed in one of the most controversial military operations in history – and many more in the following years. On 6 August 1945 the American fighter plane „Enola Gay“ dropped a uranium atomic bomb on the Japanese city of Hiroshima. Just three days later, a plutonium bomb (with about twice the detonation energy) on the port city of Nagasaki put it equally into ruins. The atomic bombs ended World War II after a total of more than 50 million deaths. The discussion about the motivation, legitimacy and consequences of the decision to use the atomic bomb against the remaining opponents Japan, which the American President Harry Truman took only two months after he came into the Oval Office, however has so far found no end.

Let us take a look only a few years back: In 1938 the German scientists Otto Hahn and Lise Meitner performed experiments with uranium, during which the latter had to flee headlong from Berlin becauseas a Jew she was no longer safe in Nazi Germany. In December 1938 Meitner received a letter from Hahn, in which he told her that afterbombarding the uranium atom with neutrons he had been able to detect barium atoms, askingher to reflect on this. Meitner came to the conclusion that due to the high number of repulsive protons the uranium nucleus must be relatively fragile and could be brought to burst by the bombardment with neutrons. Because of the electrical repulsive forces, the fragments of the fission greatly accelerated and thus take up a lot of energy, far more than any that had emerged in previously known nuclear processes. Meitner calculated that the two nuclei resulting from the fissionare in their sum slightly lighter than the original uranium nucleus. The energy of the nuclear fragments had thus come directly from the mass of the uranium nucleus. Thus for the first time the physicists had been able to detect a process, in which the equivalence of energy and mass formulated by Einstein 33 years earlier revealed itself.

But more had become clear: Unimaginable energies rest inside the atom, millions and billions of times more mighty than in conventional chemical reactions. These could be released in a very short time by a chain reaction of nuclear fissions bringing up the possibility of military application of this „nuclear power“. This finally caught the attention of non-physicists. As a leading nation in science and technology Nazi Germany was predestined to first use nuclear energy for military purposes. A bomb with such tremendous explosive power in the hands of Hitler would have catastrophic consequences for the world, not only Meitner and her nephew Otto Frischthought. The Hungarian physicist Leo Szilard thus persuaded the hitherto strict pacifist Albert Einstein to write a letter to the American President Franklin D. Roosevelt suggesting to initiate the construction of an American „nuclear bomb“. Roosevelt agreed and had the US government under the utmost secrecyput together a team of high-level scientists and engineers, most of them from Europe and motivated not to give Hitler the sole access to nuclear weapons. The so called „Manhattan Project”was to become the hitherto most complex and difficult engineering project in history.

The first step was to demonstrate that to trigger and maintain a chain reaction of nuclear fission with neutron releases was possible. This was achieved in December 1942 by Enrico Fermi, who had also emigrated from his fascist home country Italy. This cleared the way for the atomic bomb. The research was centered at a place called „Los Alamos“ in the desert of New Mexico. The scientific director of the Manhattan Project and thus „father of the atomic bomb“ was nominated to be Robert Oppenheimer, who had received his scientific training under Max Born in Germany. Early on, two viable ways to build a nuclear bomb loomed: a first one by means of fission of uranium nuclei and a second one using with plutonium nuclei. Oppenheimer and his colleagues decided to pursue both simultaneously. After four years of intensive and strictly classified work the physicists had developed both types of bombs. By July 1945 they had completed four in total. On 16th of the month, the physicists brought the first atomic (plutomium)bomb to explosion at the test site in New Mexico. Many of them felt a sense of deep unease, as the first mushroom cloud of history loomed on the horizon. Upon the sight of it Oppenheimer himself recounts remembering the line from the Hindu scripture, the Bhagavad-Gita.

If the radiance of a thousand suns

wereto burst at once into the sky

that would be like

the splendor of the Mighty One and I am become Death, the shatterer of worlds.

With the atomic bomb physics had lost its innocence (with the development of poison gas weaponsthe same applied to chemistry already during World War I). Many of the scientists who had been involved in the Manhattan project for the rest of their lives felt confronted with the agonizing question whether they bore a direct responsibility for the death of so many people. Oppenheimer was so badly plagued by his conscience that he was even persecuted by the American secret service, who believed that his remorse could hurt the US in the Cold War against the USSR. Andrei Sakharov, the father of the later Soviet hydrogen bomb, became a peace activist in his home country and was even awarded the Nobel Peace Prize in 1975.

With Los Alamos, Hiroshima and Nagasaki at latest the activity of physicists has won a dimension that they have not been able to get rid of since: the dimension of social responsibility. 70 years ago, scientists came to realize: their discipline itself does not provide them with the relevant ethics for their work. This necessitates a much more extensive discourse with the society in which science lives. With the nuclear bomhthey had put into the hands of the military, the physicists had to realize: The use and abuse of the technologies lies outside their influence.Considering the meanwhile even bigger and in the future foreseeably yet again much more extended technological possibilities based on scientific progress, we should never lose sight of this today.