The coolest thing in the Universe is now a cloud of sodium atoms in a laboratory in Cambridge, Massachusetts.

Physicists from the MIT-Harvard Centre for Ultra-Cold atoms have chilled 2500 sodium atoms to within half a billionth of a degree of absolute zero, the temperature at which atomic oscillation slows to a standstill.

“Nothing in the Universe that we know of is naturally this cold” says Aaron Leanhardt, who led the research. Even deep space is six billion times hotter.

“The old record for ‘lowest manmade temperature’ was published in the journal Nature, so hopefully publishing our result in Science will be considered good enough for acceptance as a Guinness world record” he says.

Spreading out

To cool the atoms, the team trapped them by balancing gravitational and magnetic fields then allowed the gas to expand. In a gas, temperature is a measure of the average speed of the atoms. When the gas expands the atoms spread out and slow down – lowering the temperature.

In this experiment, the atoms had an average speed of only one millimetre per second by the time the temperature had fallen to 450 picokelvin.

Atomic clocks measure time against the frequency of nuclear transitions inside atoms. When atoms are hot, their motion causes the frequency to fluctuate. Colder atoms could therefore lead to more accurate time-keepers.

Also, when atoms are this cold they all settle into the same quantum state – forming a peculiar type of matter known as a Bose Einstein Condensate. These are used to study quantum effects.

The team’s next set of experiments, however, will look at what happens when the ultra-cold atoms crash into a wall kept a room temperature. Will they stick, or bounce?

More here.