Entropy: Entropy is the measure of disorder in a system. In the world of physics we talk about the entropy in the context of the 2nd Law of Thermodynamics. This law, stated formally, is: In any cyclic process the entropy will increase or remain the same. The great writer Chinua Achebe said it much more succinctly, “Things fall apart.”
As so often happens in physics, we make fancy, complex mathematical constructs to prove something everybody already knows. Any one who has over had the experience of cleaning their house only to have it look a mess a few hours later know what I mean. The physics of this are pretty cool and have to do with the probability theory and quantum mechanics. But basically it’s much more probable for something to be disorganized than organized.
Our bodies are pretty organized. We have built into our system a complex of feedback mechanisms that work to create and maintain a delicate balance. But this delicate balance is in defiance of nature, which want to be in a state of disorder.
Let’s take diabetes as an example. Our blood sugar levels are maintained by a complex system of feedback loops involving the stomach, pancreas, liver and muscles. Greatly simplified, it works as follows. Your stomach processes food into glucose and the glucose is absorbed into your blood stream. Your pancreas reacts to the presence of glucose by releasing insulin. Insulin is needed by your muscles in order for them to absorb the glucose and produce energy (Remember that oxidation process we talked about earlier?) If the muscles do not have access to as much energy as they need they send a signal to the liver. Your liver stores glucose and releases it on demand from your muscles. The pancreas detects the additional glucose released by the liver and produces more insulin.
That balanced state exists in a finite range of glucose and insulin levels. But if something happens to upset that balance. There are an infinite number of unbalanced states. Nature prefers a state of entropy and since there are an infinite number of unbalanced states, nature prefers to be in an unbalanced state. So once you get out of balance it is very difficult to reestablish a state of balance.
It is just like what would happen in your house if you just let things go. The odds of your house returning to a state of order by itself are infinitely small. The reason your house is not (hopefully) a disaster zone is intervention from an external system, you! The same applies to your body. Once its delicate system of feedback loops gets out of whack it usually requires an outside intervention to put it back in balance.