SI Units Redefined - ScienceNerds

The SI - the fashionable system of weights and measures - has seven base units from which all other measurement units are often derived
           

These redefinitions are going to be applied from 20th May 2019
                                                                                 
there are two units for temperature the first is the Kelvin that's used by scientists and engineers and the second is the degree Celsius that's used more commonly we currently define the Kelvin in terms of the temperature of the triple point of water so to create that we start with a glass cell and we put pure water inhere up here we've taken out all the air so this is just water vapour and in operation we chill the middle of it so that we have ice around the center then we have at this point here we have ice liquid water and water vapor altogether and that temperature stabilizes naturally and we call that temperature the triple point of water temperature 273 point one six Kelvin and every temperature measurement on earth is a measure of how much hotter or colder something is than this temperature in a triple point of water cell the new definition will be in terms of the Boltzmann constant the Boltzmann constant says how much energy of molecular motion corresponds to one Kelvin or one degree Celsius so when were define the Kelvin what we will do is instead of using the temperature of the triple point of water as a standard we'll throw this away and we'll use the Boltzmann constant itself so we can use any piece of physics to measure the temperature by measuring the energy of molecular motion using many different types of physical principles

~sciencefreak