As of 1 July 2017, the worldwide effort to redefine the International System of measurement units in terms of fundamental constants has entered a new phase. Michael de Podesta, temperature scientist at the National Physical Laboratory (NPL), explains all on his Protons for Breakfast blog
At midnight on 30 June 2017, the world stepped over the threshold into a new domain of metrology. It is now too late to ever measure the Boltzmann constant or the Planck constant.
What do you mean?
Measuring is the process of comparing one thing – the thing you are trying to measure – with a standard, or combination of standards. So when we measure a speed, we are comparing the speed of an object with the speed of 'one metre per one second'.
- The Boltzmann constant tells us (amongst other things) the amount of energy that a gas molecule possesses at a particular temperature
- The Planck constant tells us (amongst other things) the quantum mechanical wavelength of a particle travelling with a steady speed
To measure these constants we need to make comparisons against our measurement standards of metres, seconds, kilograms and kelvins.