Ultracold gas sets record on the kelvin scale
Coaxing a gas to a negative temperature on the kelvin scale has produced, paradoxically, the hottest temperature ever measured. The study, published in the Jan. 4 Science, will help physicists learn about quantum phenomena and perhaps even the strange form of energy that dominates the universe.
A negative kelvin temperature indicates that particles at high energies outnumber those at low energies.
“We are used to positive temperatures,” says Achim Rosch, a physicist at the University of Cologne in Germany who was not involved in the research. “But there’s nothing forbidden about negative temperatures. It’s always fascinating to do something unusual.”
Temperature is commonly interpreted as a measure of the average energy of the particles in a sample. Each of the molecules buzzing around in a pot of boiling water, for example, has more energy on average than a sluggish water molecule within an ice cube.