Second Law of Thermodynamics and Evolution

Earth and Sun
Earth and Sun. AdStock/Universal Images Group/Getty

The "Second Law of Thermodynamics" plays a common role in debates over evolution and creationism, but mostly because supporters of creationism don't understand what it means, even though they really think they do. If they understood it, they'd realize that far from conflicting with evolution, the Second Law of Thermodynamics is completely consistent with evolution.

According to the Second Law of Thermodynamics, every isolated system will eventually reach "thermal equilibrium," in which energy is not transferred from one part of the system to another. This is a state of maximum entropy where there is no order, no life, and nothing happening. According to creationists, this means that everything is gradually running down and, hence, science proves that evolution cannot happen. How? Because evolution represents an increase in order, and that contradicts thermodynamics.

What these creationists fail to understand, however, is that there are two key words in the above definition: "isolated" and "eventually." The Second Law of Thermodynamics only applies to isolated systems - to be isolated, a system cannot exchange energy or matter with any other system. Such a system will eventually reach thermal equilibrium.

Now, is the earth an isolated system? No, there is a constant influx of energy from the sun. Will the earth, as part of the universe, eventually reach thermal equilibrium? Apparently - but in the meantime, portions of the universe do not have to constantly "wind down." The Second Law of Thermodynamics is not violated when non-isolated systems decrease in entropy. The Second Law of Thermodynamics is also not violated when portions of an isolated system (as our planet is a portion of the universe) temporarily decrease in entropy.

Abiogenesis and Thermodynamics

Aside from evolution generally, creationists also like to argue that life itself couldn't have arisen naturally (abiogenesis) because that would contradict the second law of thermodynamics law well; therefore must have created life. Put simply, they argue that the development of order and complexity, which is the same as a reduction of entropy, cannot occur naturally.

First, as was already pointed out above, the Second Law of Thermodynamics, which limits the ability of a natural system to have a decrease of entropy, only applies to closed systems, not to open systems. The planet Earth is an open system and this allows life to both start and to develop.

Ironically, one of the best examples of an open system decreasing in entropy is a living organism. All organisms run the risk of approaching maximum entropy, or death., but they avoid this for as long as possible by drawing in energy from the world: eating, drinking, and assimilating.

The second problem in the creationists' argument is that whenever a system experiences a drop in entropy, a price must be paid. For example, when a biological organism absorbs energy and grows - thus increasing in complexity - work is done. Whenever work is done, it is not done with 100% efficiency. There is always wasted energy, some of which is given off as heat. In this larger context, overall entropy increases even though entropy decreases locally within an organism.

Organization and Entropy

The fundamental problem which creationists seem to have is the idea that organization and complexity can arise naturally, without any guiding or intelligent hand and without violating the Second Law of Thermodynamics. We can easily see exactly that happening, though, if we look at how gas clouds behave. A small amount of gas in an enclosed space and at uniform temperature does absolutely nothing. Such a system is at its state of maximum entropy and we shouldn't expect anything to happen.

However, if the mass of the gas cloud is large enough, then gravity will start to affect it. Pockets will gradually start to contract, exerting greater gravitational forces on the rest of the mass. These clumping centers will contract more, beginning to heat up and giving off radiation. This causes gradients to form and heat convection to take place.

Thus we have a system which was supposed to be in thermodynamic equilibrium and maximum entropy, but which moved on its own to a system with less entropy, and therefore more organization and activity. Clearly, gravity changed the rules, allowing for events which might seem to be excluded by thermodynamics.

The key is that appearances can deceive, and the system must not have been in true thermodynamic equilibrium. Although a uniform gas cloud should stay as it is, it is capable of "going the wrong way" in terms of organization and complexity. Life works the same way, appearing to "go the wrong way" with complexity increasing and entropy decreasing.

The truth is that it's all part of a very long and complicated process in which entropy is eventually increased, even if it appears to decrease locally for (relatively) brief periods.