There’s nothing colder than absolute zero. In various scales that’s (in degrees): 0 Kelvin, -273.15 Celsius, -459.57 Fahrenheit. It’s so cold that the rest of the universe would have to reach that temperature to attain it, which is called absolute entropy, or the death of everything. So it’s not even theoretically possible to reach absolute zero. But science can get close. How about a few billionths of a degree above absolute zero? That’s what’s achievable with current technology. But how can temperatures that low be measured? Good question.

It takes one hell of…wrong metaphor…one cool thermometer. Such a thermometer is not like you might imagine – like a mercury tube on a stick. Like so much very subtle science, the temperature is derived indirectly from other measurements, in this case from magnetic readings.

Now a team of physicists has devised a thermometer that can potentially measure temperatures as low as tens of trillionths of a degree above absolute zero. Their experiment is reported in the current issue of Physical Review Letters and highlighted with a Viewpoint in the December 7 issue of Physics.

A team at the MIT-Harvard Center for Ultra-Cold Atoms has developed a thermometer that can work in this unprecedentedly cold regime. The trick is to place the system in a magnetic field, and then measure the atoms’ average magnetization. By determining a handful of easily-measured properties, the physicists extracted the temperature of the system from the magnetization. While they demonstrated the method on atoms cooled to one billionth of a degree, they also showed that it should work for atoms hundreds of times cooler, meaning the thermometer will be an invaluable tool for physicists pushing the cold frontier.

[Source: EurekAlert]

As materials – and their atoms – approach absolute zero, they begin to act differently. At some point, quantum forces come to the fore, and with them come behaviors that are unusual (from the normal scientific perspective) and incredibly interesting. Count superconductivity, superfluidity, and Bose-Einstein condensation among those interesting things.