In 1925 Leiden physicists George Uhlenbeck and Samuel Goudsmit discovered a thus far unsuspected property of electrons. It turns out that these particles can ‘spin’ in two directions. Scientists later called this property the ‘electron spin’.
George Uhlenbeck
Samuel GoudsmitThe world of elementary particles is hard to imagine for most people. This makes it all the more remarkable that physicists continue to reveal new properties of this micro-world. One of the most important discoveries in this field was made by George Uhlenbeck, who taught for a year at the Leiden Stedelijk Gymnasium during his studies, and Samuel Goudsmit in 1925. In that year, the two Leiden researchers discovered the electron spin.
This breakthrough began with the idea that electrons not only rotate around the atomic nucleus, but also around their own axis, as do planets in the solar system. George Uhlenbeck (1900-1988) and Samuel Goudsmit (1902-1978) brought their idea to their teachers Hendrik Antoon Lorentz and Paul Ehrenfest. They also quickly submitted an article on their theory to an international journal.
As it turned out, Lorentz did not believe in the idea of a rotating electron. Uhlenbeck and Goudsmit tried to withdraw their article, but it was too late, the article was already in press. Ehrenfest did not believe them either, but he told them reassuringly: ‘Sie sind beide jung genug um sich eine Dummheit leisten zu können’ (‘You are both young, you can afford to make this kind of blunder.’).
However, the discovery proved to be anything but a blunder. Einstein and Heisenberg were quickly convinced, in particular when it turned out that the electron spin smoothly solved some serious problems facing the still young theory of quantum mechanics.
The discovery of the electron spin was so important that it should have led to a Nobel Prize. However, scientific discoveries often ‘hang in the air’ for a while. Unfortunately for Uhlenbeck and Goudsmit it turned out that a German-American researcher, Ralph Kronig, had already tried to publish the same idea.
In his case, however, publication was effectively blocked by the highly influential Swiss physicist Wolfgang Pauli. The Nobel Committee would therefore have had to award the prize to all three researchers (three scholars for one prize is the maximum), but due to the unusual situation, the Committee decided not to award a Nobel Prize for the discovery of the electron spin.
Although the electron spin sounds like a purely theoretical consideration, its practical consequences proved to be tremendous. Thanks to the electron spin, we now have a much better understanding of the structure of the periodic table of elements, the table that includes all the existing atoms. As a result, the electron spin plays a very important role in chemical and medical analytical methods and it is used to construct atomic clocks, the most accurate clocks in the world.
The breakthrough also proved to play a key role in quantum mechanics. Thanks to this discovery, present-day physicists are working in laboratories on developing a so-called quantum computer – a super-calculator that is expected to be able to produce calculations at much greater speed than the current generation of computers.
In creating these quantum computers, researchers use this spin – the electron’s rotation around its own axis – as a data carrier. In computers, information is stored in the form of binary numbers, ‘zeroes and ones’. Since an electron can spin in two ‘directions’, which physicists refer to as ‘up’ and ‘down’, electrons can be used as data carriers. Spinning in one direction corresponds to ‘zero’ and in the other direction to ‘one’.
Before the outbreak of World War II, Uhlenbeck and Goudsmit left for the US and became American citizens. Goudsmit became Chief Scientist of the ALSOS mission of the Manhattan Project. This project’s goal was to establish how close Nazi Germany was to developing a nuclear bomb. He later worked as a nuclear physicist in American state laboratories. He died in Reno, Nevada, in 1978.
Uhlenbeck followed a more ‘standard’ academic career as professor at a number of US universities. In 1979 he was awarded the prestigious Wolf Prize for Physics. Uhlenbeck died in Boulder, Colorado, in 1988.
