[Physics] The second law of thermodynamics and life on Earth


The second law of thermodynamics says that order always decreases in a system. The appearance of life seems to contradict that law, but if we invoke the Sun, everything falls into place again. But what if humans create order (which is obvious as we take a look around), what does that mean for the Natural order (biodiversity)? If we consider only the closed system of the Earth, this means that the increase of human-made order must be compensated by a decrease of order in Nature, which means a decrease of biodiversity. Does what I write makes sense?

Best Answer

As mentioned in a comment, entropy cannot decrease in a closed system. When you are considered life on Earth, it is not a closed system. Energy comes into the earth from the sun and radiates away from the earth as heat.

In thermodynamics, we normally consider mostly engines because they are really simple in comparison to other systems. If we ignore the fact that we had to put in energy Q_h and exhaust head Q_c then yes it seems like we not only violate the second law, but also the first law. This approach to engines is analogous to trying to understand the Earth as a closed system.