We have a lot of confidence that we measure temperature accurately. But how do thermometers in the kitchen or doctor’s office work? Thanks to the laws of thermodynamics, thermometers respond to heat moving from hot to cold as a means of measuring temperature. Clever physical chemists and engineers have taken temperature tools from the simple, but still useful, lined glass thermometers to digital readouts. And you might be surprised to find out how Einstein took thermometers the distance.