Free Radicals - Michael Brooks [26]
The aetherian explanations of electrical disturbance held no appeal for Einstein: he believed in Thomson’s electron. Furthermore, he suspected that magnetism resulted from the circulatory motion of electrons within atoms of iron. As a diversion, he decided to put the matter to the test.
With the help of a colleague, he suspended an unmagnetised iron rod from a glass fibre, then used a magnet to change the magnetism of the iron. If his suspicions were correct, changing the magnetism would change the amount of circulatory motion within the rod. By the law of conservation of angular momentum, it is impossible to do that without causing some opposing, compensating motion. The iron rod would be forced to rotate in the opposite direction to the electrons in order to preserve the angular momentum. And that is exactly what Einstein found.
His theory predicted that a particular amount of magnetism would induce a particular amount of motion. The exact ratio of magnetism to motion, called the gyromagnetic ratio, would be 1. His experiment put the value at 1.02, close enough ‘to silence any doubt about the correctness of the theory’, as he told the German Physical Society in his report. ‘A wonderful experiment!’ he wrote to Michele Besso, a friend and former colleague at the patent office in Bern. ‘A pity you didn’t see it.’
When others tried to replicate the experiment, however, things weren’t so wonderful. After six years of testing, the gyromagnetic ratio was found to be 2. Einstein, guided by his own (erroneous) theory, continued to refuse to believe that it was anything other than 1. Many years later, Einstein’s collaborator in the experiment, the Dutch physicist Johannes de Haas, admitted that they had done the experiment twice, obtaining values of 1.02 and 1.45. Einstein had picked and published the value that matched his theory.
It is hardly a major crime. But Einstein’s little misdemeanour does tell us two things. First, cherry-picking is rarely punished. It is just what you do to get science done. Sometimes, as with Millikan, it works, and history paints you a hero. Sometimes, as with Einstein and the gyromagnetic ratio, it doesn’t, and history shrugs – either because it doesn’t matter much, or because you are found out only when others get the right answer. The catcalls that might be aimed at you are drowned out by the applause directed at those who have succeeded.
The second insight from that episode is perhaps the more interesting. Einstein was entirely cavalier about the ‘sacred’ processes of science. And so, to some degree, are all scientists. Einstein once advised that if you want to know how theoretical physics gets done, the last person you should ask is a theorist. ‘I advise you to stick closely to one principle: don’t listen to their words, fix your attention on their deeds,’ he said.
He was aware that such an attitude was not how science should be presented, and was fond of making public statements such as the famous ‘no amount of experimentation could ever prove me right, while a single experiment could prove me wrong’. Such fine words are all very well, but the fact remains that Einstein refused to accept the gyromagnetic ratio as anything other than the value offered by his theory. He had a similar mindset when it came to the theory of relativity. It would always be correct in his eyes, even if experiments proved it not to be so. ‘I would feel sorry for the Dear Lord,’ he once told a student. ‘The theory is right anyway.’
For theorists, this is an entirely defensible stance. Paul Dirac’s take on the problem of theory vs experiment is similar: ‘If there is not complete agreement between the results of one’s work and experiment, one should not allow oneself to be too discouraged,’ he said. The one exception to the acceptability of such