Life and the Second Law of Thermodynamics

Original Post: 14 May 2012
Posted Here: 4 December 2017

Almost anything that we want to talk about can be said in a variety of ways. That’s great, because it helps us avoid excessive repetition of certain words and phrases in our writing. Perhaps this is not so great when it comes to scientific laws, especially the Second Law of Thermodynamics.

One way of stating the Second Law is “The spontaneous flow of energy is from a place of higher potential to a place of lower potential.” Hot tea is at a higher potential (as expressed by temperature) than the air in the room surrounding it. So heat energy flows from the tea into the room as it cools enough for you to sip. Iced tea is at a lower potential than the air around it, so energy flows from the air into the tea, warming it. Our iced tea never warms up so much that it boils; hot tea never cools off enough to freeze. Once the temperature in the tea and in the air are the same—they  have the same potential—energy does not flow.

Another, radically different, way to state the Second Law is “Spontaneous changes in the universe are in a direction which results in more disorder or randomness.” An example of this is the fact that, no matter how neat your house is, it doesn’t stay that way.

This alternate way of stating the Second Law that is often invoked by folks who insist that evolution can’t happen, that life can’t have come into existence by chance. Living things are highly ordered systems. To say that they evolved to this state from randomly distributed carbon dioxide, water, and minerals in the environment must certainly be a violation of the Second Law, since it states quite clearly that changes in the universe are in a direction which results in more disorder, not less. Draw your own conclusion.

Strangely, the people who come to this conclusion don’t also insist that refrigerators and air conditioners violate the Second Law: heat must flow from a place of higher temperature to a place of lower. But you know that an air conditioner has heat flowing from a room at 70o to the outside where it’s over 90o. Your refrigerator has heat flowing  from inside where its 40o into your 70o kitchen. Obviously a contradiction to the Second Law.

The secret is that the Second Law doesn’t say that energy flows from a place of higher to lower potential, or that changes in the universe are in a direction which results in more disorder or randomness. But didn’t l just say that it did a few paragraphs ago? No, I did not.

Both forms of the Second Law, but not the misstated forms, include the term “spontaneous”—“spontaneous flow” or “spontaneous changes.” Your neat house spontaneously changes to messy. Hot tea spontaneously cools. That is not to say that your house can never change from messy to neat, or that tea at room temperature can’t get too hot to sip. But not spontaneously. You’ve got to expend some energy in both cases.

The same is true of that air conditioner or refrigerator. What happens—spontaneously—when you experience a power failure? Pretty unpleasant. Refrigerators, air conditioners, tidying up your house, or reheating that cup of tea in the microwave are all examples of the Second Law working just as it should. The difference is that instead of talking about spontaneous processes, we talk about the opposite—non-spontaneous processes. Nonspontaneous processes require an input of energy to make heat flow from lower to higher temperature environments, to make changes produce order from disorder. Nothing mysterious, just the natural consequences of the Second Law.

Evolution and living things, as the results of nonspontaneous changes that produce order from disorder, are also just what you should expect from the Second Law of Thermodynamics.

In any environment in which there is an energy source—be it a star with a suitable planet or satellite in its vicinity, or a hydrothermal vent under an ocean—we should not be surprised to find life existing and evolving. If life on Earth is alone in our solar system and in the universe, it won’t be for thermodynamics reasons.

Keep reading/Keep Writing - Jack