Lab trickery achieves negative temperature
Ulrich Schneider must be a hit at cocktail parties. The physicist at Ludwig Maximilians University of Munich can tell awed guests that he is responsible for creating both the world’s hottest substance and lowest temperature — at the same time.
Schneider’s substance — a gas consisting of about 100,000 potassium atoms — reached a temperature below absolute zero, about –0.000000001 kelvins.
Unlike Fahrenheit and Celsius temperatures, where the zero point is arbitrary, absolute temperature (measured in kelvins) supposedly can go no lower than zero. And in fact, nothing can get colder than absolute zero. But a negative absolute temperature, though technically below zero, is actually infinitely hot.
That’s because a positive or negative