Colder than Absolute Zero?

Absolute zero has been considered the lowest temperature possible since the 1800s when Lord Kelvin developed his temperature scale.

Now physicists working with a quantum gas believe they have developed a technique that allows the gas to reach a temperature lower than absolute zero.

Zero degrees Kelvin (negative 459.67 degrees F) occurs when atoms lose nearly all of their kinetic energy. Their state of immobility is called absolute zero. As the temperature is increased, the atoms move with more kinetic energy.

Physicist Ulrich Schneider from the Ludwig Maximilian University in Munich, Germany, and some of his colleagues reached sub-absolute-zero temperatures working in the laboratory with a quantum gas made up of potassium atoms, according to nature.com.

They reached negative Kelvin temperatures by arranging individual atoms in a lattice arrangement using magnets and lasers. In this arrangement, the atoms repel each other at temperatures above absolute zero. This keeps the arrangement stable.

Next, they adjusted the magnetic field to cause the atoms to attract each other. If the temperature was still positive, the atoms would become unstable. To account for this, the physicists also adjusted the trapping laser field to be more energetically favorable for the atoms to remain still.

The result of the experiment is a transition of the gas from just above absolute zero to a few billionths of a Kelvin below absolute zero.

Sub-zero quantum gas mimics dark energy found in the universe and Schneider suggests his experiment with absolute zero may be of interest to cosmologists.

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