Bolztmann's H-theorem
In his 'H-theorem' Boltzmann tried to formally prove that inter-molecular collisions drive gases toward equilibrium, confirming the Second Law (for gases at least). In this approach, he aimed show that it is not just overwhelmingly probable but an exceptionless law like conservation of energy.
The H-theorem was the first of two approaches to demonstrating the Second Law associated with Boltzmann. The second approach utilized a probabilistic argument and has proven much more durable (it is cross-linked to this map element).