Imagine pouring cold milk into a cup of hot coffee and finding that the milk stays cold while the coffee stays hot. Physicists have now achieved a similarly strange result by restricting atoms of an ultracold gas to motion in just one dimension.
In the new system, atoms of different energies collide but don't share energy in the usual way that, for example, equal amounts of hot and cold liquids make a lukewarm mix, notes David S. Weiss of Pennsylvania State University in University Park. He says that his team has devised an experimental means to investigate what causes and controls the energy-distribution process, called thermalization.
To do so the researchers