The question
Why does milk mix into coffee but never unmix?
The short answer
Entropy counts how many ways a system can be arranged without looking different. Disordered states vastly outnumber ordered ones, so systems drift towards them, and that drift gives time its direction.
What science knows
Established ScienceRudolf Clausius coined “entropy” in 1865. The second law of thermodynamics says the entropy of an isolated system tends not to decrease.
Ludwig Boltzmann explained why: S = k log W, where W is the number of microscopic arrangements consistent with what we observe. The formula is engraved on his tombstone in Vienna.
The pattern
Established MathematicsIn 1948 Claude Shannon defined information entropy, the average surprise of a message, in bits. A fair coin flip carries 1 bit; a fair six-sided die about 2.58 bits (log₂ 6).
What is still uncertain
Active ResearchWhy the universe began in such a low-entropy state, which is what lets entropy keep rising, is an open question in cosmology, sometimes called the “past hypothesis”.
Why humans find it interesting
Cultural TraditionEntropy has become a metaphor for decay and disorder in literature and everyday speech, often more loosely than physicists use it.
CUE perspective
CUE PerspectiveEntropy is a reminder that order takes energy to keep, whether in a room, a schedule or a relationship.
CUE borrows no physics from it; the metaphor is simply useful: small, regular attention holds things together better than rare effort.