Niels Bohr was born in 1885. The late nineteenth century was an exciting time for physicists. Bohr entered just late enough that some of the foundations were beginning to be laid, but early enough that he could take on a pivotal role in the revolution. On the one hand, his work built largely on the quantum theories of Albert Einstein and Max Planck. His own atomic model was a basic extension of that of his mentor, Ernest Rutherford. On the other hand, the questions were far from answered, and Bohr's work merely led to more difficulties to be resolved.
Following his atomic model came rapid developments from other young scientists. For this new generation of physicists, Bohr would serve as a mentor. He was the founder and head of the Copenhagen institute, which would soon become the international center for modern physics. Young minds came to Copenhagen for cultivation; established geniuses came to lecture and to take part in colloquia that often provided the backdrop for conversations that changed the course of history. Those who visited Copenhagen included Pauli, Heisenberg, and Schrödinger, all of whom made discoveries that shattered conventional physics and shocked even those who had tried to keep up with its rapidly developing pace. Many of these young scientists came to Bohr for guidance, evaluation, and criticism. Bohr served not only as an individual mentor, but a symbolic leader of the physics community at large.
Bohr lived in Denmark, and it was not long before Nazi Germany influenced his life. Denmark was officially neutral, but Bohr recognized the necessity of offering refuge to people fleeing Nazi terror. Copenhagen became a haven for scientists who could not work in their home countries. Bohr also spoke out more against the Nazis (though cautiously, since Denmark was officially a neutral country), proposing a scientific argument for cultural acceptance. Despite the urging of American colleagues, Bohr refused to leave Denmark until the last possible moment. After Denmark had been captured by the Nazis, Bohr stayed because he knew that his departure could damage the spirit of his country. It was only when he had been informed that the Nazis were coming for his arrest that Bohr made a last-minute escape to Sweden by fishing boat. Even then, he continued to support the Danish resistance and aided in the rescue of thousands of Jews when it was announced that the Nazis would begin to round them up in Denmark.
At this time also came the dilemma of atomic energy, which had become possible largely through the work of Bohr and his close colleagues. On the one hand, there was enormous potential for beneficial use, but Bohr from the beginning recognized that its destructive potential could also lead to diplomatic problems. Even while the war was still going on, Bohr tried to persuade leaders to consider ways to avoid an arms race. He urged international cooperation, knowing that the edge held by Britain and the United States could not last long. But his warnings were ignored, and the arms race unfolded exactly as he had feared.
After the war, Bohr returned to Denmark. He continued for the rest of his life to encourage the appropriate use of atomic energy and attempted to lead the scientific community in taking the first steps where political action failed.