UK scientists' plan to base temperature on the Boltzmann constant could make measurements much more accurate

UK scientists want to redefine temperature using the Boltzmann constant, changing the way in which it has been calculated for over 50 years. The group, working at the UK’s National Physical Laboratory, published a study today that could make it possible to measure temperature much more accurately in the future.

The current definition of temperature relies upon the triple point of water – the state at which water can be ice, liquid and vapour in equilibrium – but this makes accurate measurements of extreme temperatures difficult. The team say that the solution is to link the standard unit of temperature, the kelvin, to the Boltzmann constant, a measure of the relationship between kinetic energy and temperature. By making precise measurements of the speed of sound in argon gas the team could gauge the average speed of the gas molecules and therefore their kinetic energy. From this they were then able to calculate the Boltzmann constant

‘It is fascinating that we worked out how to measure temperature long before we knew what temperature actually was. Now we understand that the temperature of an object is related to the energy of motion of its constituent atoms and molecules,’ says lead author Michael de Podesta. ‘The new definition directly links the unit of temperature to this basic physical reality.’