Entropy

(2) Any system might transition, at any time, to one of its less probable states, because energy can, in a sense, go anywhere it wants to; it is simply much less likely to go some places than others. In systems containing trillions of atoms or molecules, such as a roomful of air, the probability that the system will transition to a highly organized state analogous to microstate 1 in the Figure—say, that all the energy in the room will concentrate itself in one molecule while all the rest cool to absolute zero—is extremely small; one would have to wait many trillions of years for such an even to happen.