by Jonathan Kujawa
One hundred and fifty years ago atoms were mysterious things. They could only be studied indirectly. We knew about their interactions with each other as a gas, the frequencies of light they prefer to absorb and emit, and various other properties. Nowadays we can capture the image of a single hydrogen atom, but back then atoms could only be understood through the shadows they cast in the macro world.
At the time two explanations were in vogue. The atomists went with the ancient Greeks and viewed atoms as small billiard balls clacking against each other as they moved through empty space. This point of view worked great for explaining the behavior of gases, but didn't help much in explaining the intrinsic properties observed by chemists. On the other hand, the followers of the theory of Boscovich, an eighteenth century Jesuit, thought that atoms were points of force which alternately repelled and attracted each other depending on how close they were. This theory held promise for explaining the electromagnetic properties of atoms, but it also had its drawbacks.
On February 18, 1867 William Thomson (aka Lord Kelvin) read out his paper “Vortex Atoms” to the assembled members of the Royal Society of Edinburgh. In it he suggested a novel alternative to these two theories.
As everyone knew at the time, the universe was permeated by the luminiferous ether. Light traveled as a wave even through “empty” space and, well, waves travel through something, so what was that something? Luminiferous ether! It was a beautiful idea, but eventually the evidence piled up against the ether. The Michaelson-Morley experiment put a stake through its heart in 1887.
But in 1867 the luminiferous ether was widely considered a standard feature of the physical world. Taking his inspiration from recent work in hydrodynamics and, presumably, a fine pipe of tobacco, Lord Kelvin realized that instead of viewing atoms and the ether as two separate things, we could instead think of atoms as vortices in the ether itself. Specifically, he thought of each atom as a knotted tubular shape:
His theory neatly explained a wide variety of atomic phenomena. The rich variety of possible knots justified the wide variety of atoms, the fact that the type of knot is unchanged under small perturbations (after all, you can't turn the knots in Lord Kelvin's table from one into another without applying real violence) explains the robust stability of atoms, and knots will clearly vibrate at different frequencies from one another and so will naturally prefer to absorb and emit light energy at differing levels. For example, Thomson thought the two linked circles in the lower left might be the sodium atom because of sodium's two spectral lines.