But French and US scientists have succeeded in reversing this dictum. It sounds unearthly, and it is. This states that the flow of heat from one region to another that is hotter is vastly too improbable ever to be observed. The results of the space experiment do not contradict this law, because they rely on something other than simple diffusion of heat, which is the usual mechanism for shifting it from one place to another.
Heat diffusion is what causes a metal bar to heat up at one end when warmed at the other.
I in France and co-workers found that the influence of diffusion and convection is outweighed by an opposing effect. Convection, in fact, did not take place at all, because a less-dense fluid gains no buoyancy amidst a denser one if there is no gravitational field to create differences in weight. It was to eliminate convection that the team staged the experiment in space, as part of the French-Russian Perseus mission on Mir from February to August 1999. The diffusion of heat through a fluid becomes slower as it gets closer to its critical point. In other words, the gas 'overshot' the warming, seeming to draw heat out of the cooler walls.