How do you take the temperature of the coldest thing in the universe? With a quantum thermometer, of course. And this new ability could provide fresh insights into black holes. The coldest matter known is a Bose-Einstein condensate (BEC) -millions of atoms that act as a single quantum object when cooled inside a magnetic trap. Lab experiments have formed BECs at half a billionth of a degree above absolute zero. "It's the coldest thing we can produce in the lab; the closest thing to absolute zero," says Ivette Fuentes at the University of Nottingham, UK. Even deep space is warmer.
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