What is Entropy?

Entropy measures how spread out and disordered the energy and particles in a system are. It counts how many ways the parts can be arranged while the whole still looks the same, so more arrangements means higher entropy. Left alone, systems drift toward higher entropy, and that drift is the second law of thermodynamics.

The drift happens because disordered states vastly outnumber ordered ones. Air molecules in a room have only a few ways to bunch in one corner and an enormous number of ways to spread evenly, and since they move randomly, the room is almost certainly in one of the countless spread-out arrangements at any moment. Nothing pushes them apart, because spread out simply wins by numbers. The same counting explains everyday one-way streets: heat flows hot to cold, ice melts, a dropped egg never un-breaks, because each ordered state has few arrangements and each ended state has astronomically many. Order can still be created locally, since a freezer makes ice, but the machine doing it always releases extra heat, creating more disorder around it than the order it built. Entropy always increases.

Shuffle a new deck of cards for ten seconds and the factory order is gone for good. There's one factory order and about 8 followed by 67 zeros of other orders, and every shuffle draws randomly from that pool. Ordered isn't forbidden, it's one ticket in a lottery bigger than the number of atoms in the galaxy, and it just never wins.