Rutherford, Bohr, and the atom
Curie’s 1897 discovery of radiation was a revolution! Over the next few years there was a surge in Atomic Physics. The field was further enhanced by Einstein’s estimation of the size of atoms in 1905. By 1913, Manchester was the world’s center of Atomic Physics. The two people most responsible for this uprising were Ernest Rutherford and Niels Bohr; two of the most extraordinary men in the history of science, who found themselves working at the Physics Department of Manchester University. They couldn’t have been more different from each other. Rutherford was a simple man, born in a remote part of New Zealand, who famously said “that's the last potato I'll ever dig” when he received a scholarship to study in the UK. Bohr, on the other hand, was practically a Danish aristocrat who loved philosophy as much as he did science, and who was raised around deep thinkers who loved to speak in paradoxes and allegories. Rutherford and Bohr became the ultimate experimentalist and the ultimate theoretician, respectively—and were destined to change science and the way we view the world forever.
Rutherford: After winning a Nobel Prize in chemistry for his studies on radioactivity in 1908, Rutherford's most important contribution to Particle Physics happened in 1909 when he set up his assistants Hans Geiger and Ernest Marsden to expose a piece of gold leaf to the alpha particles coming from a piece of radon. After weeks of observation and uninteresting results, his assistants' frustrations were met by an off-the-cuff remark when Rutherford asked them to see if anything was bouncing back. Years later he claimed he had no basis for this suggestion, but the results would astound the world by revealing that atoms are nearly all empty space—with a nucleus so dense that the powerful alpha particles (which had given Rutherford the Nobel Prize) would ricochet off it. It was “as if you had fired a 15-inch [artillery] shell at a piece of tissue paper and it came back and hit you”. Seeing the rate of alpha ricochet events, Rutherford calculated that the nucleus was 10,000 times smaller than the atom itself. He imagined it as a little solar system—coincidentally just as empty—with the sun in the center (the nucleus) and the planets (electrons) orbiting around it.
Bohr: But there was a problem: why aren’t these positive nuclei attracting the negative electrons and collapsing into solid, neutral matter. This is where Neils Bohr comes in. He sailed to the UK in 1911; tried to work for JJ Thompson, but not getting along, the trail led him to Manchester University and Rutherford. Here, he made it his mission to find out why the atom didn’t collapse, and he was ready to abandon common sense and human intuition to find an answer. Bohr’s brilliant contribution to the atomic model placed a series of counterintuitive arguments—such as the existence of “stationary states” in which the electrons would exist (and were forbidden to exist in between), and that light would be emitted when an electron jumped instantaneously between these states. The result was one of the most complex and ludicrous ideas in the history of science: quantum Physics. Strange as they were, Bohr pointed out that these ideas were showing “conformity with experiments on a number of different phenomena” and therefore they must be regarded as real. This flew in the face of centuries of careful observation, analogies, calculations, and deductions that had been the basis of science since the days of Newton. And sent Bohr in a direct collision path with some of the most important names in Physics.
Source: Rhodes, Richard. The Making of the Atomic Bomb. New York: Simon & Schuster, 1986
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Full disclosure, I may occasionally borrow a sentence from Will Durant's Story of Civilization. I absolutely love that collection!