Entropy increase and the thermodynamic direction of time — why the past is different from the future
The second law says entropy increases. But microscopic laws are time-reversible — there is no built-in "arrow." The resolution: the universe started in an extraordinarily low-entropy state (the Big Bang). This "Past Hypothesis" selects a special initial condition that breaks time symmetry.
Phase space volume occupied by ordered states is exponentially tiny. Almost every trajectory from any state leads toward higher entropy — because there are vastly more disordered states to go to.