Physics: A Man of the Century

He was a gentleman who helped create the world’s most deadly weapon; a humble man who collected as many honors as almost any man of his time. Before he died of a heart attack last week at 77, Danish Physicist Niels Bohr left an unmistakable imprint on the 20th century.

For a boy who always wanted to be a physicist, Niels Henrik David Bohr could have chosen no better age in which to live. By the time he was in college, physics was in fascinating chaos. Blow after blow had shattered its foundations: Albert Einstein proved that matter is energy, Max Planck proved that energy comes in indivisible packets he called quanta. Lord Rutherford proved that though the very name atom means “indivisible” in Greek, atoms are not indivisible. Nothing seemed certain. One physicist declared that all students should be warned: “Caution! Dangerous structure! Closed for reconstruction!”

Chewing on Stubs. In this chaos Bohr found his own future. In 1912, he went to Rutherford’s laboratory at Manchester, England, just after Rutherford had advanced the theory that atoms are miniature solar systems with electrons revolving like planets around a sunlike nucleus. The idea had serious faults, which Bohr, then 27, spotted promptly; he corrected them by applying the unfamiliar principles of Planck’s new quantum theory.

Bohr’s atomic model answered dozens of questions that had the physicists of the time chewing their pencil stubs. It won him a Nobel Prize, but it, too, had faults which were gradually corrected by mathematical abstractions that seemed to grow more and more bizarre. Bohr himself did much of the correcting, and even the most recent concepts of atomic structure reflect his genius for inventive analysis.

Golden Age. In 1920, Bohr organized the University of Copenhagen Institute for Theoretical Physics, which quickly became a kind of scientific shrine, attracting students from all over the world. “The unique and exciting feature of Copenhagen,” wrote Professor John A. Wheeler of Princeton, “lies in the stimulus that Bohr gives. I know of nothing with which to compare it except the school of Plato.” J. Robert Oppenheimer, who was later to head the atom-bomb-making Los Alamos Scientific Laboratory, said about physics in the 19205: “It was a heroic time. It was not the doing of any one man; it involved the collaboration of scores of scientists from many different lands. But from first to last, the deeply creative, subtle and critical spirit of Niels Bohr guided, restrained, deepened, and finally transmuted the enterprise.” He never dogmatized. “Every sentence I utter,” Bohr liked to tell his students, “must be understood not as an affirmation but as a question.” Once he defined truth as “something that we can attempt to doubt, and then perhaps, after much exertion, discover that part of the doubt is unjustified.”

Niels Bohr deeply resented any restrictions that hindered the search for scientific truth. When the Nazis began to harass the great German universities, he wrote to physicists who he thought might be in danger of persecution and invited them to Copenhagen. Many came, and whenever any of them arrived, Bohr always made certain that he or one of his colleagues was at the railroad station to welcome them to his pleasant refuge.

Terrible Secret. The Nazis were not the only terror loose in the world. There was something else that only the physicists suspected. With their new mathematical tools they had been delving deep into atomic secrets, and they had come to realize that atomic nuclei hold enormous stores of potentially destructive energy.

Early in 1939, before the start of World War II, Bohr made a trip to the U.S. Just as his ship was about to leave Copenhagen, two German refugee physicists, Lise Meitner and O. R. Frisch, rushed aboard with a dismaying report. They had just heard that German Chemists Otto Hahn and Fritz Strassmann in Berlin had split the uranium atom. This was atomic fission, and with it the Nazis might soon be able to build an atomic bomb.

Bohr took the terrible news with him to New York and passed it along to U.S. physicists whom he trusted. By then the U.S. was well supplied with first-rank physicists, many of them Bohr’s former students; they understood only too well the implications of his message. Soon confirming experiments were in full swing. Bohr himself worked for a while at Princeton. And there, one snowy night as he walked from his club to a laboratory, a problem that he had been puzzling over was unexpectedly resolved and the facts fell into place. Bohr realized that it was the rare uranium isotope U-235 that fissions. That knowledge was a signal contribution to further U.S. research.

He returned to Copenhagen before the Nazis overran Denmark in April 1940. At first they did not bother Bohr, despite his part-Jewish ancestry. Then, in 1943, he learned that he was slated for arrest. That same night Bohr, his wife and his son Aage sneaked aboard the fishing boat Sea Star and escaped to Sweden. (He was the kind of man about whom absent-minded professor stories are told, and legend has it that he had kept a bottle of heavy water, then important for atomic research, hidden in his refrigerator; in his hasty departure he left the heavy water behind and rescued an ordinary bottle of beer.)

Soon after Bohr reached Sweden, a British bomber arrived to pick him up. During the dangerous flight, while the bomber dodged German fighters, he almost died of asphyxiation from a faulty oxygen mask. From England he went on to the U.S., where the news that he had brought in 1939 had already mushroomed into the enormous Manhattan Project for constructing the first atom bomb.

First Bomb. At Los Alamos, Bohr, whose face was familiar to just about every physicist alive, was introduced with transparent secrecy as Mr. Nicholas Baker.

Though he probably did as much as any other man to ensure the success of the Manhattan Project, once the first bomb was built, he would not wait to see the first test explosion at Alamogordo. For the rest of his life, all nuclear weapons were objects of horror to him. His fondest hope was to find a way to abolish them.

After the Nazi defeat, Niels Bohr returned home to Copenhagen; soon his own institute was open for business once more. Bohr was recognized as the leading citizen of Denmark, but to the end of his life he never quite believed that he was really a famous man. Once he went into the office of Scandinavian Airlines and asked diffidently whether he might cash a small check. When the manager offered to cash any amount he wanted, he was amazed that his name had been recognized. Though creative theoretical physics is for younger men, Bohr did extraordinary work in getting European science on the track again after the war. He pleaded tirelessly for the peaceful uses of atomic energy, was one of the leading backers of CERN, Europe’s cooperative research center at Geneva. Honors came so thickly that he could not have worn all his medals at the same time.

Last summer Bohr suffered a slight cerebral hemorrhage. After an autumn vacation in Italy, he seemed to recover, and he began writing his eagerly awaited history of quantum physics. But he spoke of a growing concern: Who would carry on his work when he was gone? One afternoon last week, while talking with a colleague, he felt dizzy. He went to bed with a slight headache, lost consciousness and died.