Even though we know better, many physicists still picture the atom as a mini solar-system type of affair, with tiny electrons orbiting a heavy nucleus. This is the picture that emerged from Rutherford’s scattering experiments (ruling out a stodgy pudding of an atom with electrons embedded like raisins throughout, for instance).
One problem with this ‘orbiting electrons’ idea is that classical electromagnetism predicts that the electrons should lose energy and spiral into the middle very quickly. This would mean all atoms would be catastrophically unstable, in serious violation of observational evidence.
Bohr’s model of the atom forbade such spiralling, by only allowing electrons to have certain specific orbits. Abitrary though that might seem, it made a stable model for atoms, and it provided a model to underpin spectroscopy - the technique in which the characteristic jumps between allowed orbits allow us to determine the atomic composition of everything from stars to drug samples.
Also, the attempts of physicists to build a real theory behind Bohr’s atom, in which the seeming arbitrariness would be explained, led them to treat electrons a bit like waves, and forced them eventually into quantum mechanics.
So it should be interesting to hear more about Niels Bohr, the man, from his grandson. Life and Physics brings you Life behind the Physics...
More on the Perimeter Institute Public Lecture series here, including their archive.
Jon Butterworth’s book Smashing Physics is available as “Most Wanted Particle” in Canada & the US. He is also on Twitter.
