On the morning of August 6, 1945, five months after vandals painted anti-Japanese slogans on Pauling’s home, the United States dropped the first atomic bomb on Hiroshima, Japan. Pauling, like many scientists, was stunned by the news. He had been asked by Robert Oppenheimer to join the Manhattan Project when it was first started, but Pauling had refused -- not because he was against the idea of working on weapons, but because he did not want to relocate his family to the project’s secret site in New Mexico. After Hiroshima and then, a few days later, the atomic devastation of Nagasaki, Pauling began reading everything he could find about how this extraordinarily powerful new weapon worked. His interest was widely shared. It seemed everyone wanted to know about the A-Bomb. When a local Rotary group asked Pauling to explain it all a few weeks after the war ended, Pauling obliged. He used his first talks as technical primers, explaining in clear terms how the bombs worked, and why nuclear fission released so much energy. Pauling was comfortable in front of audiences and had the ability to make science understandable to the public. He was soon was invited to give more speeches to more groups.

Even before Hiroshima, researchers working at the A-Bomb-related laboratories in Chicago, Oak Ridge, and Los Alamos had started meeting informally to share their concerns about the new weapons they were creating. The discussion groups, convened in cafeterias, conference rooms, and private homes, became the seeds of a political movement. After the first bombs were dropped on Japan, when it became clear that their research had incinerated tens of thousands of men, women, and children -- and made it possible to kill millions more -- many of the atomic scientists became ardent opponents of further development.

The A-Bomb, it seemed, vaporized more than cities. It also broke down some of the restraint and political apathy that had typified scientific researchers, making it clear that "objective" scientific research could have horrifying real-world effects, and spurred a mix of revulsion and moral outrage in many scientists. The discussion groups spread to scores of universities and government laboratories, where professors, laboratory workers, and theoreticians gathered to talk about how this new power should be channeled and used for good.

The more Pauling read about their concerns, the more convinced he became that the new atomic age presented scientists with unprecedented moral and political responsibilities. "The problem presented to the world by the destructive power of atomic energy overshadows, of course, any other problem," he wrote a few weeks after Hiroshima. "I feel that, in addition to our professional activities in the nuclear field, we should make our voices known with respect to the political significance of science."