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Anthony Aguirre
University of California, Santa Cruz, USA

Observer-dependent entropy and the Second Law



The Second Law of Thermodynamics, stating that entropy is non-decreasing in closed systems, is one of our most fundamental laws and points to a core aspect of the physical world. Yet there is a surprising lack of precision or consensus around exactly what it means. I will argue that a new definition of disorder called “Observational entropy“, defined in terms of observer-dependent coarse-grainings and measurement probabilities, is an elegant and satisfactory way to describe the spontaneous growth of disorder in closed quantum systems.

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