The fundamental asymmetry of heating and cooling is discovered

The physicists exposed colloidal microparticles to different temperatures, carefully controlling the ambient temperature. This allowed them to track the particle’s motion with extreme precision and to gather statistics on the distance it travelled and its speed.

It turned out that for any two values of temperature, not only was heating faster than cooling, but it also followed a fundamentally different path, explained within a new theoretical framework called thermal kinematics. In general, cooling was a more complex process. Heat engines, microscopic machines designed to do useful work by means of temperature differences, obeyed this asymmetry.