The Second Law of Thermodynamics

The Second Law of Thermodynamics, in my opinion, is the motherload when it comes to causality. It defines the inexcapable tendency of any closed system (including a finite universe, if you believe in such a thing) over time to approach equilibrium and thus maximum entropy. This law governs various phenomenon from the diffusion of fluids and heat transfer to the reactionary processes of chemicals and ultimate heat death of the universe. The law is commonly associated with what is called the direction of time or that certain processes progress through the passage of time. The direction of time notation is requisite to the understanding of entropy and how entropy is ever increasing (even as I type this blog post!). This being the case, the Second Law of Thermodynamics translates to the "causation" fact that: the entropy of causes must be less than the entropy of effects in a system. This fact means that the causal nature of the second law applies to a great deal of cause and effect relationships, especially those in the physical world, but can likely be applied to other situations as well.