The second law of thermodynamics, formulated by Sadi Carnot, Rudolf Clausius, and William Thomson (Lord Kelvin), states that the total entropy of an isolated system always increases over time. Entropy, a measure of disorder or randomness, is a fundamental concept in thermodynamics that characterizes the direction of spontaneous processes. Atkins explains that the second law is a consequence of the asymmetry of time, which implies that the future is different from the past.
Clausius, R. (1850). On a mechanical theory of heat. Four Laws That Drive The Universe By Peter Atkins -.PDF-
Nernst, W. (1906). The theorem of heat.
Atkins, P. W. (2007). The four laws that drive the universe. Oxford University Press. The second law of thermodynamics, formulated by Sadi