Physicists Find Way to Make Cold Heat the Hot: Had to Mix Up Cause and Effect

At the heart of classical thermodynamics lies a principle that determines the direction of physical processes in the universe: thermal energy always spontaneously flows from a hotter body to a cooler one. The reverse flow of heat is impossible without an expenditure of external mechanical or electrical energy. This law relies on a fundamental assumption about the nature of time. In the classical description of the world, all interactions unfold in a strict cause-and-effect sequence: if an object interacts with two environmental factors, contact with the first either strictly precedes contact with the second or follows it. Space and time serve as an unchanging coordinate system in which events are distributed along a rigid chronological scale. Conceptual quantum…