We all know that water flows downhill, not uphill, because that’s the way gravity works. Gravity is a force, and the gravitational pull of the earth acts as if it were concentrated at the center of the earth, and pulls the water downhill. However, there isn’t a similar explanation for why we see ice cubes melt when placed in a glass of hot water but never see ice cubes form spontaneously in a glass of tepid water. This has to do with the way heat energy is distributed, and the solution to this problem was one of the great quests of 19th-century physics.
The solution to this problem was found by the Austrian physicist Ludwig Boltzmann, who discovered that there were many more ways for energy to be distributed throughout the molecules of a glass of tepid water than in a glass of hot water with ice cubes. Nature is a percentage player. It goes most often with the most likely way to do things, and Boltzmann’s constant quantifies this relationship. Disorder is much more common than order—there are many more ways for a room to be messy than clean (and it’s much easier for an ice cube to melt into disorder than for the ordered structure of an ice cube to simply appear).
Boltzmann’s entropy equation, which incorporates Boltzmann’s constant, also explains Murphy’s law: If anything can go wrong, it will. It isn’t that some malignant force is acting to make things go wrong for you. It’s just that the number of ways that things can go wrong greatly exceeds the number of ways that things can go right.
via Popular Mechanics.