The 2nd law of thermodynamics is a crazy thing to fathom. It can be stated about a thousand different ways, like “No process is possible whose sole result is the transfer of heat from a body of lower temperature to a body of higher temperature” or “No process is possible in which the sole result is the absorption of heat from a reservoir and its complete conversion into work”; but my favorite is:
The entropy of the universe never decreases.
Entropy is an expression of disorder, or “randomness”, or the relative absence of information or patterns. It’s easy to see different levels of entropy in the different phases of water. Ice is made up of water molecules in a very ordered state, whereas water vapor is made up of water molecules in a very disordered state. Molecules in a snowflake form an ordered crystal lattice, while the molecules in a cloud bounce around without much of a pattern. So if the entropy of the universe never decreases, why are there snowflakes? How can you get patterns in a universe where entropy always increases? Shouldn’t the universe be a sea of disordered matter?
The answer is feedback. Feedback occurs when the output from some process influences future inputs. It’s a loop or cycle that allows a system to exhibit some means of control upon itself. Feedback is how we get complexity in a universe where entropy always increases. Even in a universe constantly moving from a more-ordered to less-ordered state, there can be a chain of events that happens by chance to increase its own chance of happening again. Some events, some processes, some phenomenon, act like replicators. They output the ingredients for themselves. We can see it in the snowflake: once water molecules are moving slow enough, they don’t have the momentum to escape the electromagnetic forces of their neighbors, and they form stable hydrogen bonds. Being tetrahedral, water molecules tend to tesselate when they stick together. Their forces are spread out into a shape that tends to form hexagons, over and over.
So once you get an ice crystal going, it acts like flypaper for slow moving water molecules still in the cloud. The fast moving water vapor molecules can bounce right off the crystal, but the slow movers get assimilated. They fall into position on the surface, and become the new front-line of glue. So at low enough temperatures, this self-replicating event occurs and water is added in the same pattern, over and over again, building up the snowflake. And from this feedback loop, complexity emerges.
But why does everything look ordered? Complexity isn’t exactly rare, it surrounds us. Just about everything we’ve got a word for is a complex pattern, from atoms to galaxies. Why should that be the case if the entropy of the universe is always increasing? The answer is once again feedback. Processes that tend to replicate themselves tend to stick around longer than usual. By their very nature of making themselves happen again, they keep making themselves happen again and again. They can form stable patterns in the universe, little whirlpools in the sea of disorder that loop back on themselves, continuing their own existence. These things survive long enough to deserve names.
And since these patterns continue their own existence, over time, there gets to be a lot of them. Stable patterns can form in the stable patterns of other stable patterns. A hexagonal crystal lattice can form in the hydrogen bonds of water molecules. The feedback between subatomic particles can form a pattern we call an atom, which stick together in molecules within the planets of a star system in a galaxy. These feedback loops can build upon each other to astronomical proportions, creating us, and the complex cosmos we inhabit.
What’s true in the physical realm is also true of our abstract human interactions. Most of our encounters are random, and they are quickly forgotten. But occasionally, we form feedback loops. Much like water in a snowflake, we can fall into a pattern of behavior and stick to it. These actions can form complex systems that perpetuate their own existence long enough to deserve names. Families, businesses, cities, governments; these patterns of interaction tend to make themselves more likely to happen again in the future. And because of that property, they tend to stick around. Groups can form from simple interactions between members and grow into colossal complex systems, all because of feedback. And none of this breaks the second law of thermodynamics.