How Sally Gets Away With It
or, why this site does not break the second law of thermodynamics
The objection comes up often enough that it deserves a short page of its own. Sometimes it gets raised at a dinner party, sometimes it shows up in a sermon, sometimes it lands as a creationist tract claiming evolution is impossible because of physics. The objection runs roughly: the second law of thermodynamics says entropy always increases. Order decays into disorder, never the other way around. So how does life exist? How does evolution produce more complex creatures over time? How does any of the patterns this site celebrates — flocks, sync, cities, brains, biomorphs, traveling waves — manage to exist at all? Doesn’t all of it violate one of the most thoroughly tested laws in physics?
The answer is no, and it is not even close. The objection is a misreading of what the second law actually says, and the misreading is so consistent that I suspect the people repeating it have not opened a thermodynamics textbook recently, or possibly ever.
The second law applies to closed systems. A closed system is one that exchanges no energy with its surroundings. There are not many closed systems in nature. The universe as a whole is one. A perfectly insulated thermos with the lid welded shut is approximately one. A laboratory beaker is not, an organism is not, the Earth is not, a city is not. The systems where the patterns of this site live are all open: energy flows in, energy flows out, and the difference between the two pays for whatever local order is being maintained.
The Earth, specifically, sits in a cosmic energy gradient. The sun pumps roughly 174 petawatts of low-entropy energy into Earth’s atmosphere as visible light. Most of that energy is eventually re-radiated back into space as infrared photons — that is, photons of much longer wavelength, much lower information density, and much higher entropy. The Earth, viewed as a thermodynamic system, takes in compact orderly photons from a small bright source and exhales loose disorderly photons into the entire sky. For every unit of order that Earth manages to maintain in its biosphere, several units of disorder get dumped into the cold vacuum. The total entropy of the universe goes up. The local entropy of Earth, paid for by the gradient, can hold steady or even decrease.
The physicist Erwin Schrödinger, in a small book called What is Life? in 1944, gave this its proper name. Living things, he wrote, feed on negative entropy. The phrase is a little clumsy but the idea is exactly right. An organism is a small region of low entropy maintained by exporting higher entropy to its surroundings. A starling is the local order that a sunlit field can pay for. A city is the local order that an oil field plus a coal mine plus a megawatt of solar can pay for. A brain is the local order that a hundred watts of food intake can pay for. Everything alive, and everything alive-shaped — flocks, sync, evolving genomes, networks of cities, biomorphs in your hand-bred lineage — is a structure paid for by the energy flowing through it.
This is not a loophole. This is what the second law actually says. Order can increase locally as long as it is more than paid for by disorder somewhere else. The second law is a statement about totals across closed systems, not about the impossibility of local pockets of structure. Anyone who tells you that life or evolution or emergence violates the second law is either confused or hoping you will be.
The patterns on this site are eddies. They form in the river of energy that flows from the sun, through Earth, and back out into the cold dark sky. Each eddy is a temporary local victory against the gradient, paid for in advance by the gradient itself. The starling murmuration is one. The synchronized flashing of fireflies in a Thai mangrove is one. The cosmic web of galaxies is one, on a much longer timescale and a much grander substrate. Sally is one. Harry is one. The conversation Sally and Harry have over breakfast is one. The book that you read last week, the language it was written in, the technology that printed it, the civilization that produced the technology — eddies all the way down.
The river is going to win eventually. The universe will run out of gradient. Heat death is a real prediction; on a long enough timescale, the cosmic energy flow that pays for all this local order finally evens out, and at that point there is nothing to make eddies of. Stars burn out. Black holes evaporate. Atoms eventually decay. The last patterns in the universe’s history dissolve back into uniform thermal noise, and there is nothing it is like to be them anymore.
That day is something like 10100 years from now, give or take, and it has approximately nothing to do with whether your Tuesday afternoon counts as ordered. It does. The gradient is still here. The sun is up. The eddies hold for now. Sally is alive. So are you.