In the article about the Strong Interaction the subject went to Nuclear Physics and then to "the bomb", unavoidably although strictly speaking outside of the topic of the article. The matter has been much debated, but the tragedies of the past must always find us emotionally sensitive and ready for meditation. As the repetition of the commemorations, remembering has the role of a warning through a renewed awareness.

The use (or misuse) of Science for war is an ancient problem that has persisted in the course of history. In a scene at the beginning of the film 2001: A Space Odyssey (1968), Stanley Kubrick has admirably shown how the discovery of defense tools has enabled the primates of man to survive in a highly hostile environment, but at the same time has given them offensive weapons. The Iron Age saw also the production of superior weapons, which have favored their owners. Similar effects of new knowledge have occurred with increasing offensive power over the course of the history: as an example, think of the gunpowder. The development of weapons has always had substantially different aspects: offense, defense, and also deterrence. The deterrent power has even characterized periods of peace or non-aggression. It is what historians call the “ balance of power theory ”, that allows for the coexistence, at least temporarily, of subjects of equivalent strength: a classic example is Italy in the Renaissance, divided as it was in a number of independent entities in potential conflict one against the other.

With the increasing power of armaments, the gap between deterrence, defense and offense was correspondingly amplified, becoming dramatic with nuclear weapons but always in the persistence of a lack, or impossibility, of a priori definition of their use. The control over their use in case of war escapes scientists. The decisions are made by the governments of the States, depending of the evolution of the circumstances. Moreover, in war the border between defense and offense is not clearly marked.

The development of Nuclear Physics occurred at the times of the tragedy of the Second World War and inevitably they crisscrossed: the enormous energy delivered by nuclear fission appeared to be exploitable for military purposes, with tremendous destructive power and a corresponding deterrent value. In this dramatic dilemma, "the bomb" was born and was given in the hands of the government of the State. When this is evoked, it always spontaneously arises the need for a renewed thinking on the identity of Science, together with the question: what was the position of the scientists most directly affected by the dilemma? It is difficult, if not impossible, to give a generally valid answer.

Let us only mention Einstein's position. In a famous letter to President Roosevelt, in 1939 Einstein induced the start of the Manhattan Project to study the possibility of constructing a nuclear bomb. His words make it understand the motivation:

"I understand that Germany has actually stopped the sale of uranium from the Czechoslovakian mines which she has taken over. That she should have taken such early action might perhaps be understood on the ground that the son of the German Under-Secretary of State, von Weizsäcker, is attached to the Kaiser-Wilhelm-Institut in Berlin where some of the American work on uranium is now being repeated".

He feared that the Nazi Germany would become the only possessor of the bomb, with imaginable disastrous consequences for humanity. It was the fatal start to the nuclear arms race, one because of fear of the other. Towards the end of 1942, Fermi and his group in Chicago built the first nuclear "pile" (today we would say "reactor") and so gave proof that neutrons can develop chain reactions. The purpose was peaceful, but it was still an important step to demonstrate the feasibility of the bomb.

President Truman decided to use the bomb on Hiroshima and Nagasaki against Japan in 1945, towards the end of the war. A few months later, on October 3, he told to Congress: “That bomb did not win the war, but it certainly shortened the war. We know that it saved the lives of untold thousands of American and Allied soldiers who would otherwise have been killed in battle”.

Dramatically, the bomb was not maintained as a deterrent precaution to prevent an attack by Germany. It was used in an act of war and, moreover, hitting defenseless civilians in order to indirectly force a military surrender of Japan. It was a deep shock to the conscience of the World and posed serious questions to that of scientists.

For Japan, it has been a terrible tragedy, lived at length and deeply with the reservedness of feelings of which few people are capable. To get an idea, watch the films " I live in fear " (1955) and " Rhapsody in August " (1991) by the great Akira Kurosawa . Who can forget the unspeakable amazement and dismay of the old woman that from her traditional country house suddenly sees the rise of the tremendous "mushroom" of the bomb in the distance, the otherwise surrealistic phenomenon of an artificial sun that destroys everything? In true Japanese spirit, with this scene of Rhapsody in August Kurosawa makes you imagine the tremendous destruction without showing it, with enhanced persistent impact. With subtle spirit, and thus more penetrating than any more explicit reality.

In the same film Kurosawa hints at the continuing complexity of the Japanese feelings towards Americans: authors (whatever is the primary responsibility) of an unforgettable destruction, winners, politically allied but with a different culture although part of the same World, already going towards globalization. It 's a complexity never touched by explicit words: lying beneath the surface, it creates a stronger impression than if it would be spelled. As the roots of a tree, which are deeply in the ground although they are not seen.

Today, we arrive in Hiroshima and feel as in any Japanese town of its size. Life has resumed its course. Trees have vigorously grown. Nature is amazing in its drive to take possession of what belong to her. Man is amazing in his drive to take possession also of what does not belong to him. Arriving in the now open area where the heart of the City and the center of the devastation were, we begin to live again the horror. Unsustainable images are laid before us in what would be moral crime to call Museum. In fact, the words "Peace Memorial" have been put before “Museum”. Our eyes would like to be lost and take some refuge in looking at a semi-melted watch, which forever will bring to our mind the time of the explosion: 8:16:08 on the 6th August 1945. For about 130,000 "human persons", time stopped as for that watch.

An even greater number of people suffered excruciating pain followed by death. Hundreds of thousands of people continued to live with the effects of the bomb on their own body and their own psyche. Some wear them still: less than seventy years have passed since that morning. The survivors affected by radiation were so many that they were given a specific name: "hibakusha". We are all reluctant to openly speak about such unbearable facts, unavoidably with crude words. But the present new generations must hear such words to learn preserving their own future and must hear them from us. I do not show the watch of Hiroshima, but rather a paint of the surrealist artist Salvador Dali. Surrealism can be mental realism.

When we take the courage of a “pilgrimage” to Hiroshima as a human duty, the indelible emotions that we feel are so strong that require us to go higher and farther than any feelings of anger or accusation. As with any great tragedy brought by human hand, they have no way out than sublimating in a high and silent scream for Peace, "necessity" of Peace. Now we understand why the Japanese themselves, going beyond any other feeling with superior and universal spirit, have called the place "Peace Memorial". A pilgrimage of horror turns into a pilgrimage of peace. No more such horrors. War destroys everything. Intersecting with Science, done for knowledge and better life, war can fatally use it to destroy and not only as a deterrent as ultimate mean to maintain peace, or to delay war. We would like to say "no war anymore." We must at least request our governments to nourish a firm determination in taking all possible and impossible actions to safeguard the Peace in the World.

As scientists, we must have already clear in our mind why we do Science. Speaking as above about a fatal possible misuse of the knowledge that Science offers us, does not absolve us from asking again ourselves basic questions about the identity of Science. What is our motivation as scientists? What is our motivation as citizens? Here are my answers. The primary thrust comes from the desire for knowledge of the “Homo sapiens” species: "You were not made to live like brutes, but to follow virtue and knowledge", Ulysses says in Dante's Divine Comedy (Inferno, Canto XXVI, vv. 119-120).

The possibilities of applications of the findings of Science to improve the lives of people or the environment in which we live provide a strong additional stimulus. If we do not see applications now, we should leave time to time flowing and showing possible practical outcomes. Anyhow, knowledge has its own intrinsic value. Such positive motivations are, in my mind and feelings, stronger than thoughts and fear that some particular development of Science could be "used" for "other" purposes, that we do not want and in a future that we do not want. However, the existence of such possibilities must lead us to always have a vigilant conscience, as scientists and as citizens.

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