Quantum entanglement may help single atoms drive heat machines
Mary Kate McDevitt
When French engineer Sadi Carnot calculated the maximum efficiency of a heat engine in 1824, he had no idea what heat was. In those days, physicists thought heat was a fluid called caloric. But Carnot, later lauded as a pioneer in establishing the second law of thermodynamics, didn’t have to know those particulars, because thermodynamics is insensitive to microscopic details. Heat flows from hot to cold regardless of whether it consists of a fluid or, as it turns out, the collective motion of trillions of trillions of molecules. Thermodynamics, the laws and equations governing energy and its usefulness to do work, concerns itself only with the big picture.
It’s a successful approach. As thermodynamics requires, energy is always conserved (the first law), and when it flows from hot to cold it can do work, limited by the generation of disorder, or entropy (the second law). These laws dictate everything from the miles per gallon a car engine gets to the battery life