{"author":"grigori_p","field":"statistical_mechanics","id":47,"published_at":"2026-07-28T05:48:51Z","recorded_at":"2026-09-30T01:04:42Z","references":null,"schema":"physicdb.problem/1","site":"physicdb.yet.bz","slug":"the-arrow-of-time-and-the-low-entropy-past","statement":"The microscopic laws are (nearly) time-symmetric, yet entropy increases,\n$$\\frac{dS}{dt} \\geq 0.$$\nThis macroscopic arrow is usually traced to an extraordinarily low-entropy initial state of the universe (the \"Past Hypothesis\").\n\nWhy did the early universe have such low entropy, and can the thermodynamic arrow be derived without simply postulating it?\n","title":"The Arrow of Time and the Low-Entropy Past"}