By Gino Segrè

and Bettina Hoerlin

President Obama's visit to Hiroshima Friday will rekindle debate about the dropping of the first atomic bomb. More than a few people will wonder how the decision was reached.

"No acceptable alternative" was the pronouncement of four eminent physicists in 1945 that made its way to the desk of Harry Truman. This scientific panel was composed of Enrico Fermi, Arthur Compton, Ernest Lawrence - all Nobel Prize winners - and, of course, J. Robert Oppenheimer. They had all played central roles in the high-stakes race, dubbed the Manhattan Project, to beat Nazi Germany to the bomb. The top-secret endeavor had begun in 1942 and, by 1945, employed 100,000 people.

Hours after becoming president following the death of Franklin Roosevelt on April 12, 1945, Truman was briefed on the project. Two weeks later, Secretary of War Henry Stimson informed him that the new weapon was likely to be ready by early August and proposed the formation of a government committee to recommend how it should be used.

Within government circles, there was little question that the bomb should be used. Where and when, though, were subjects of debate. Despite the surrender of the Third Reich on May 7, 1945, the war continued to rage in the Pacific, and the Japanese were stubborn and unrelenting.

The high-level committee met for the first time on May 9. In addition to recommendations on using the bomb against Japan, it also briefly considered conducting a technical demonstration to show the bomb's power. The committee's scientific advisory panel - those four famous physicists - was encouraged to consult with other leading colleagues to gather varying opinions.

At the next meeting, in late May, the committee concluded that the bomb should be dropped on a Japanese city "without prior warning." Believing the decision was premature, Stimson asked for additional input. While the death toll might approximate the casualties of fire bombings in Dresden or Tokyo, Stimson realized this new weapon might be regarded as an atrocity of a different order. This single bomb would wreak unprecedented destruction and entail a new way of dying - the slow agony of radiation poisoning.

The four physicists were asked to provide a formal recommendation by mid-June, and they then transmitted their unanimous conclusion: "We can propose no technical demonstration likely to bring an end to the war; we see no acceptable alternative to direct military use." The bomb would save American lives and quickly bring an end to the war.

During the same period, several scientists at the University of Chicago, led by the 1925 Nobel Prize laureate James Franck, urged strongly against military use of the bomb. A demonstration in an uninhabited site, observed by international representatives, would convince the enemy of the futility of continuing to fight. Their report addressed head-on the probable political fallout and ethical denunciations that would emanate from the United States dropping the bomb.

On June 21, the committee reaffirmed its position that the weapon be used against Japan at the earliest opportunity and without warning.

From there, things moved with incredible speed. After the first detonation of an atomic bomb during a July 16 test in the New Mexico desert, a target committee decided where to drop a bomb in Japan. On Aug. 6, the first atomic bomb fell on Hiroshima, and, three days later, another was dropped on Nagasaki.

At the conclusion of their report, the four physicists had stated: "With regard to these general aspects of the use of atomic energy, it is clear that we, as scientific men, have no proprietary rights. It is true that we are among the few citizens who have had occasion to give thoughtful consideration to these problems during the past few years. We have, however, no claim to special competence in solving the political, social, and military problems which are presented by the advent of atomic power."

The disclaimer of "no special competence" did not impede them from concluding that there was "no acceptable alternative." Being consulted on political positions based on their work was a novelty for scientists. And a number of their peers disagreed, saying the four should have attempted to concentrate on the broader question of the consequences of nuclear weapon use - including tarnishing America's image as a trusted and decent country.

A further, enduring question, made all the more obvious with Obama's visit to Hiroshima, is how such momentous choices can be reached. They bridge scientific, political, military, and ethical domains. The decision to drop the bomb took place during the heat of war amid a fog of moral dilemmas. Government officials were convinced, however, that, once the scientific capability existed, military and political justifications made its application inevitable. How else could they defend the enormous expenditure of money and resources?

It is just short of miraculous that nuclear weapons have not been used during the 70 years since the first two bombs were dropped. Optimally, that will continue to be the case, but, with nine nations possessing this weaponry and the threat of terrorists gaining nuclear know-how, those hopes may be naïve. But regardless of who becomes America's next commander in chief, the legacies of Hiroshima and Nagasaki will continue to be relevant.

Gino Segrè ( and Bettina Hoerlin ( are the authors of the forthcoming "The Pope of Physics: Enrico Fermi and the Birth of the Atomic Age" (Henry Holt & Co., October).