What is the theory of a tendency to chaos of the universe called?

The theory of the tendency to chaos of the universe is called entropy. Entropy is a measure of disorder or randomness, and it is bound up with thermodynamics, the branch of physics that deals with heat and mechanical work. The second law of thermodynamics states that all closed systems tend to maximize entropy, which means that the entropy of the universe tends to a maximum. As entropy increases, disorder increases, and energy disperses, causing systems to dissolve into chaos1. Successful relationships, houses, and teams require effort to create stability, structure, and simplicity because the universe naturally slides towards disorder

what is the second law of thermodynamics and how does it relate to entropy?