Entropy

Surface

Entropy is a measure of disorder in a system. The Second Law of Thermodynamics states that in any closed system, entropy always increases over time. Things fall apart. Rooms become messy. Stars burn out. The universe trends inexorably toward maximum disorder, a state physicists call heat death.

Middle

Entropy is why time has a direction. The laws of physics at the microscopic level are time-symmetric, they work equally well forward and backward. But entropy increases only forward, which is why we remember the past and not the future, and why broken eggs do not reassemble themselves.

Deep

Life is a temporary, local reversal of entropy, maintained only by consuming energy from outside the system. Every living thing is a pocket of order fighting the universal trend toward chaos. This makes existence not just rare but, in a thermodynamic sense, heroic. We are improbable structures holding ourselves together against the current of the universe.