1848 – Scotland
‘Molecular motion (or heat) approaches zero at temperatures approaching -273.15 degrees C’
This temperature is known as absolute zero. It is the theoretical lowest limit of temperature. Like the speed of light, absolute zero can be approached closely but cannot be reached; as to actually reach it an infinite amount of energy is required.
The temperature scale based on absolute zero is the kelvin scale (kelvin, symbol K without the degree sign). One kelvin degree equals one celsius degree.
The energy of a body at absolute zero is called ‘zero-point energy’. The twentieth century model states that atomic particles can exist only at certain energy levels; the lowest energy level is called the ground state and all higher levels are called excited states. At absolute zero all particles are in the ground state.
Thomson, together with JOULE, discovered the effect whereby most gases fall in temperature on expansion due to work taking place to pull apart the molecules. He independently enunciated and publicised the second law of thermodynamics describing the one-way spontaneous flow of heat – from a hotter body to a colder one. The German RUDOLPH CLAUSIUS also arrived at the same conclusion during the same period.