![]() ![]() Even though order may be increasing on Earth, the total order of the solar system and universe is still decreasing, and the second law is not violated. At the same time, the sun becomes increasingly disordered as it emits energy to the Earth. Therefore, energy input from the sun could give rise to the increase in order on Earth including complex molecules and organisms. This means that an increase in order can occur on Earth as long as there is an energy input-most notably the light of the sun. With biological evolution however, the system being considered is not the universe, but the Earth. Because the universe is an isolated system, the total disorder of the universe is always increasing. An isolated system is defined as one without any outside energy input. However, this objection is grounded in a misunderstanding of the second law, which states any isolated system will increase its total entropy over time. But because evolution results in an increase in the order and complexity of species-which is a decrease in entropy-some critics claim evolution violates the Second Law of Thermodynamics. Buildings don’t strengthen themselves, and no amount of waiting will cause rotten food to become edible again. In both cases, the amount of disorder increases with time, but the opposite is never true. Buildings break down over time, and food spoils if not eaten soon enough. This law has plenty of everyday examples. Ordering the system requires added energy from elsewhere, such as all that elbow grease we used to clean our room.A common argument against evolution is that the theory contradicts the Second Law of Thermodynamics that claims disorder, or entropy, always increases or stays the same over time. Furthermore, entropy doesn't mean that a system can't become ordered, just that a system can't order itself. Common MistakesĮntropy is a measure of disorder. In an isothermal process, it's defined as. We calculate entropy as the measure of disorder. What? This isn't news? It's not fortune telling either, is it? Well, we never said entropy was fortune telling, just that it was like it. This leads us to a third (and we promise, last), way to state the Second Law of Thermodynamics: The entropy of the universe never decreases. The most efficient engine, the Carnot Engine, holds entropy constant. Or if you're rich, you hire someone else to get rid of your entropy for you. And to keep entropy the same we have to put in work-we have to clean that bedroom, refrigerate the ice, and renovate our homes. The very best we can do is keep the amount of entropy the same. Houses, left to their own devices, fall apart. And then they don't put themselves back together. Or in the words of Chinua Achebe (using the words of Yeats): "Things Fall Apart". ![]() For irreversible processes the disorder, or entropy, always increases over time. The Second Law describes this reality as entropy. There's a natural order to things and an "arrow of time." Sandcastles don't build themselves and ice cream doesn't unmelt itself. The annihilation of an electric current in normal metal with the generation of Joule heat because of a non-zero resistance is a well-known example of an irreversible process. Even preschoolers know that, being the astute observers of the natural world that they are. The law of entropy increase postulates the existence of irreversible processes in physics: the total entropy of an isolated system can increase, but cannot decrease. We think all of us would pick the same order-the ice cream sandwich came before the puddle and the sandcastle before the pile of sand. Or how about Picture 1: a puddle of ice cream. Imagine we show you some pictures and ask you to put them in order. It's all thanks to the Second Law of Thermodynamics. Rather than reveal titillating news about who likes whom, thermodynamic's laws identify what processes will (and won't) happen. It might not have a booth at the county fair, but thermodynamics still has a booming fortune-telling business. ![]()
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