Three Papers That Tamed the Atom
Niels Bohr was born in Copenhagen in 1885 into a household of ideas, son of a physiology professor, brother of a mathematician, and a good enough goalkeeper that Danish papers noted the family's lesser footballer had won a Nobel. Working under Rutherford in Manchester after a prickly stint with J. J. Thomson, he confronted the scandal of Rutherford's atom: orbiting electrons should radiate, spiral inward, and end matter in a flash. In 1913 Bohr simply forbade it, postulating stationary orbits and light emitted only in quantum jumps between them.
The trilogy of 1913 papers explained the hydrogen spectrum's mysterious lines with startling precision and won him the 1922 Nobel Prize. It was a scaffold, half classical and half quantum, and Bohr knew it; his gift was living productively with contradiction. In 1921 he opened his Institute for Theoretical Physics in Copenhagen, funded partly by a brewery foundation, and made it the world capital of the new physics: Heisenberg, Pauli, Dirac, and Gamow cycled through, arguing at colloquia, over ping-pong, and on walks Bohr prolonged until his interlocutors surrendered from exhaustion.
Arguing with Einstein
When Heisenberg's mechanics and Schrodinger's waves collided in the mid-1920s, Bohr forged the uneasy synthesis: complementarity, the doctrine that wave and particle pictures are both required and never simultaneously applicable, with measurement itself setting the terms. Its Copenhagen interpretation became textbook orthodoxy, though critics from Einstein to Bell and beyond have kept the argument alive; Bohr's notoriously fog-bound prose, drafted and redrafted aloud to weary assistants, did not help. His running debate with Einstein, at the Solvay conferences of 1927 and 1930, remains science's most celebrated duel of thought experiments, conducted in perfect mutual affection.
In 1939 Bohr carried the news of fission to America and, with John Wheeler, explained why uranium-235 was the fissile culprit. In September 1941 his former protege Heisenberg, then leading Germany's nuclear research, visited occupied Copenhagen; what was said between them is history's most famous unfinished conversation, dramatized on stage, disputed in dueling letters Bohr drafted and never sent. In 1943, warned of imminent arrest, the half-Jewish Bohr fled by fishing boat to Sweden, where he helped press the king to shelter Denmark's rescued Jews, then flew to Britain in a Mosquito's bomb bay, nearly suffocating.
The Open World
At Los Alamos, where he consulted under the name Nicholas Baker, the physics needed him less than the young physicists did; Oppenheimer recalled him asking whether the bomb was big enough to end war itself. Bohr's real campaign was political: convinced that the weapon would otherwise ignite a ruinous arms race, he lobbied Roosevelt and Churchill in 1944 to tell the Soviets and pursue international control. Churchill, enraged, wanted him watched as a security risk. The arms race arrived on schedule, and Bohr's 1950 Open Letter to the United Nations restated the plea for transparency between states.
He spent his last decades building institutions instead: CERN's theory group began in Copenhagen, and he helped found Denmark's Riso laboratory and presided over the first Atoms for Peace award. He died in Copenhagen in 1962, the blackboard in his study still bearing a sketch from the previous evening of Einstein's light box, the old argument literally unfinished. Element 107, bohrium, carries the family name; so does a style of doing physics, collective, conversational, and comfortable with paradox, that his institute taught the century.
