RNA, DNA in the Breathing Universe

This is a record of life on Earth told as a single journey along the arc of cosmic expansion, watched from the outside by an observer who takes no side; its organising principle throughout is the second law of thermodynamics. The universe began in an extraordinarily low-entropy state and has run down ever since — the one-way slide of order into disorder that is the arrow of time and, equally, the engine of life. A living thing is a structure held far from equilibrium by a continuous throughput of free energy: it does not defy the second law but serves it, keeping its own order only by degrading a larger gradient and exporting the entropy elsewhere. Evolution is what follows once such structures can copy themselves — selection sharpens whatever best captures free energy and turns it into descendants — so the drive for survival that shapes every organism is the second law expressed in replicating matter. The record follows the molecules that carry heredity — RNA, and later DNA — from the raw ingredients delivered in the young universe, through the first cell, a long age of microbes, a brief flowering that includes a creature able to model the arc it lives on, to the end of life on Earth, which arrives long before the universe stops expanding. The physical reason a molecule can copy itself at all is derived rather than assumed: a faithful copy is a low-entropy state that cannot be made or held without dissipation, so heredity itself runs on the second law, and the forces of all later change — reproduction, food, and the dangers of heat, cold, and predation — are each a face of the same thermodynamic imperative. The cosmic figures are computed from the model: the universe is 13.73 billion years old today; its expansion stops 17.08 billion years from now at 1.69 times its present size, then collapses to an end 47.89 billion years from now, a total lifespan near 61.6 billion years. The record closes on the one fact none of its physics explains — the extraordinary order of the beginning, the low-entropy reserve that every later increase has been spending — and sets three readings of it side by side, ending on the third: that the beginning may have been set, deliberately, before anything else happened.