Entropy is for the most part really badly explained in layman's terms. I think the "disorder" description fails to adequately describe it.
Entropy is better described imo as the tendency of useful energy to spread out. When you have a bunch of gas atoms with different velocities, all smashing into each other, they are exchanging energy in such a way that the velocity of each individual atom is approaching the average. The energy of each atom with different velocities is useful energy... the faster atom has done work on the slower atom, causing it to gain kinetic energy. In turn, the faster atom loses kinetic energy. As the atoms approach average velocity, the acceleration from collisions is lower, until the system reaches thermal equilibrium and each atom collides with equal velocity, meaning they just bounce without an exchange of energy. The amount of work each higher-velocity atom does when it collides is always getting lower, on average. That's basically the same as saying entropy is always increasing. It happens because useful energy is spreading out over the system. The total energy of the system of course remains constant.
How this relates to gravity is not something I even remotely understand.
Originally Posted by wufwugy
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