Agendanken experiment is proposed for distinguishing between two models accounting for the macroscopic arrow of time. The experiment involves the veloeity revesal of components of an isolated system, and the two models give contrasting predictions as to its behavior.
Everyday experience tells us that it is impossible to travel backwards in time, no matter what science-fiction writers and movie directors tell us. However, this seemingly natural impossibility is actually one of the greatest mysteries in physics. Currently most physicists associate the irreversibility of time with the production of entropy in the warm macroscopic world. One consequence of this irreversibility – often called the “arrow of time” in thermodynamics is the ageing process. In plain terms, one grows old because of the irreversible physical processes that occur during one's life. However, the fundamental classical laws of physics discovered by Galileo, Newton and Einstein do not distinguish between the future and the past. In other words, they appear to be symmetric in time.
Irreversibility is one of the most intriguing concepts in physics. While microscopic physical laws are perfectly reversible, macroscopic average behavior has a preferred direction of time. According to the second law of thermodynamics, this arrow of time is associated with a positive mean entropy production. Using a nuclear magnetic resonance setup, we measure the nonequilibrium entropy produced in an isolated spin-1/2 system following fast quenches of an external magnetic field. We experimentally demonstrate that it is equal to the entropic distance, expressed by the Kullback-Leibler divergence, between a microscopic process and its time reversal. Our result addresses the concept of irreversibility from a microscopic quantum standpoint.
Irreversibility is one of the most intriguing concepts in physics.While microscopic physical laws are perfectly reversible, macroscopic average behavior has a preferred direction of time.According to the second law of thermodynamics, this arrow of time is associated with a positive mean entropy production.Using a nuclear magnetic resonance setup, we measure the nonequilibrium entropy produced in an isolated spin-1=2 system following fast quenches of an external magnetic field.We experimentally demonstrate that it is equal to the entropic distance, expressed by the Kullback-Leibler divergence, between a microscopic process and its time reversal.Our result addresses the concept of irreversibility from a microscopic quantum standpoint.