Leggett–Garg inequality

The Leggett–Garg inequality is a concept in quantum mechanics that addresses the nature of macroscopic realities and the behavior of quantum systems. It was proposed by Anthony Leggett and Anupam Garg in the 1980s as a criterion for distinguishing between classical and quantum behavior in a system that evolves over time. The inequality is framed in the context of a series of measurements performed on a single quantum system at different times.