The New SI: Units of measurement based on fundamental constants
A Discussion Meeting organized by Dr Terry Quinn CBE FRS, Professor Ian Mills FRS and Professor Patrick Gill
At the origin of the metric system was the idea of units of measurement based on invariant quantities of nature. After more than 200 years we are now within reach of achieving this. Plans now exist to redefine the kilogram, still defined as the mass of a Pt-Ir cylinder kept in a vault at the BIPM, by fixing the numerical value of the Planck constant h; and the ampere, kelvin and mole by fixing numerical values for e, k and NA. With the metre already being defined by the speed of light and the second by an atomic microwave transition, we shall have at last achieved what the savants of the 18th century had sought.
The Discussion Meeting held at the Royal Society on 24 and 25 January 2011 reviewed the relation of the International System of Units to the fundamental constants of physics and progress towards the redefinitions. The proceedings have been published as an issue of Philosophical Transactions A, 2011, 369 (1953), 3903–4142. Copies of the presentations can be downloaded here.