Kibble’s balance

In a problem written for a recent revision workshop on NMR spectroscopy, a colleague quoted the value for the gyromagnetic ratio of the proton to 10 significant figures. I stared at the number in astonishment. What on earth would possess someone to measure anything with that level of deranged precision? And what kind of person might they be? A quick scan of the literature revealed British physicist Bryan Kibble, one of the key figures in the redefinition of SI units.

Kibble was the youngest son of a police sergeant who lived in Letcombe Regis, south of Oxford. Growing up he fiddled with bicycles, repaired radios and rebuilt clocks and watches, activities that no doubt contributed to his abilities as an experimentalist, and was awarded a scholarship to study physics at the University of Oxford. He would later recall a practical in which he was stunned by the perfection of the reflection of a needle placed at the centre of a soap film distorted by a small pressure difference, spherical to within the wavelength of light. When he remarked on this, his tutor said ‘Ah! You see, nature is exact.’