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# The second law of thermodynamics and the increased complexity of the world

September 12, 2011

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The second law of thermodynamics tells us entropy in the universe is always increasing. Assuming that is true, how can we understand the beginning of life and the increased complexity of the world?

The second law of thermodynamics says randomness, or entropy, in the universe tends to increase. But that applies to the universe as a whole, not necessarily to every individual part of it.

For example, as the inside of a refrigerator gets cooler, the random motion of molecules that we call heat lessens, which means the entropy decreases.

But the refrigerator isn’t isolated. Energy comes into it through an electrical cord and leaves it through a radiator at the back that eliminates waste heat, which is disorganized motion of molecules. While entropy decreases inside the refrigerator, it increases outside the refrigerator as waste heat is eliminated.

More interesting, systems placed in a flow of energy from hot to cold will often spontaneously generate structure.

You can demonstrate this by heating a pan of still water with a thin coating of oil on a stove. You will soon see a mostly hexagonal pattern form on the oil due to structured patterns of warm water rising from the bottom, cooling, and falling. An ordered structure appears in the pan, which means less entropy, but resulting in greater entropy for the whole universe.

Think of the water taking in and reradiating heat and becoming ordered in the process as a model of what happens on our planet: Objects absorb energy from the sun and radiate it back into the darker sky.

The science behind this is a new and active field, but it’s by no means incompatible with the laws of physics that say organization can increase in a specific spot without violating the second law of thermodynamics.

We don’t really know how life arose, but the increase in order and complexity that came with it is not in conflict with any laws of physics we know about.

Ask Dr. Knowledge is written by Northeastern University physicist John Swain. E-mail questions to drknowledge@globe.com or write to Dr. Knowledge, c/o The Boston Globe, PO Box 55819, Boston, MA 02205-5819.

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