Week 6: How do organised structures persist at all?
The second law says disorder tends to grow. A whirlpool, a flame, and a living body all keep their shape anyway. None of them are cheating. All of them are open.
31 August 2026
Watch water drain out of a bathtub and a whirlpool forms. It has a shape, a structure, a recognisable spiral that persists for as long as you watch it. Watch a candle and the flame keeps a shape too, a steady teardrop sitting in the same place above the wick, hour after hour if the candle is long enough. Watch almost any living thing and you find something far more elaborate: cells organised into tissues, tissues into organs, a shape held together and actively repaired for years or decades.
None of that looks like what last week described. Entropy was supposed to rise. Left alone, systems drift toward whichever arrangement has the overwhelming statistical majority, and the result usually looks less structured, not more. A whirlpool, a flame, a body — these are all pockets of order that should, on the face of it, be exactly what the second law is working against.
They are not exceptions to it. And they are not loopholes in it either.
Look again at each one, and each is doing the same thing: matter or energy is flowing through it, continuously, and the shape is a feature of that flow, not a thing floating free of it. Cut off the water and the whirlpool disappears. Cut off the wax and wick and the flame goes out. Cut off food, air, and the constant expulsion of waste heat, and a living body stops being able to hold its shape at all.
None of these things are closed systems sitting quietly and somehow dodging the tendency toward disorder. They are open systems, with energy and matter passing through them, and that changes what the second law actually applies to. The second law makes a statement about a closed system’s overall entropy, or about a system and everything it exchanges energy with, taken together. It never promised that every local patch inside that larger system has to become progressively featureless. A local pocket of order can persist, and even grow more elaborate, provided maintaining that local organisation is accompanied by enough entropy increase elsewhere — usually as waste heat, radiated out into surroundings that are only too glad to accept it.
A living organism fits this description exactly. It draws on useful energy gradients — food, sunlight, chemical differences — to maintain and rebuild its structure, uses part of that energy to build and maintain intricate structure, and constantly discards degraded energy and material back into its environment. It is not resisting the tendency toward disorder. It is riding a flow of energy that lets it maintain low entropy locally while the total entropy of organism plus environment keeps rising, same as it always does.
That reframes what life is, at least from this angle. It is not a rebellion against thermodynamics and it is not a special case the second law happens to overlook. It is a particular kind of structure — a dissipative one — that thermodynamics permits, given the right conditions: order sustained by a sufficiently large and steady flow of energy passing through.
On Earth, trace that flow back far enough and it converges almost everywhere on a single source. Plants capture it directly. Animals eat plants, or eat things that ate plants. Even the wind and the rain, and the fossil fuels that formed from ancient life, are downstream of the same input.
The Sun.
It has been supplying that energy, apparently without interruption, for the entire multi-billion-year history of life on this planet. That is a very long time for anything to keep burning.
What we explained#
Persistent structures like whirlpools, flames, and living organisms are not exceptions to the second law and not loopholes in it. They are open systems: energy and matter flow through them continuously, and their order is sustained by that flow while the total entropy of the system and its surroundings still increases. Life, in particular, is a non-equilibrium structure kept going by a steady input of energy, not a special case thermodynamics forgot to cover.
What became stranger#
Why hasn’t the Sun burned out?