Now before we get into the second law of thermodynamics, it's first important to understand the idea behind this term called entropy. Entropy is defined as a measure of disorder, or in other words, a measure of randomness. The greater the disorder is, the higher the entropy will be. Let's take a look at this image down below right here to get a better understanding of entropy. Notice over here on the left-hand side, we have this pool table, and the billiard balls here that you see are very, very highly organized and very, very ordered.

However, notice over here on the right-hand side, this pool table has the same billiard balls here that are scattered throughout the entire table, and so they're not very highly ordered. They're not very highly organized. Instead, they're pretty greatly disordered over here. And so because they are more disordered over here, the greater the disorder, the higher the entropy. And so this system over here is going to have higher entropy.

And, of course, this system over here that is highly ordered and not very disordered, it's going to have low entropy. And so the lower the entropy, the more organized and the more ordered it is, whereas the higher the entropy, the more disordered it is and the more unorganized it is. Now, the natural tendency of reactions is to move the universe towards a state of maximum entropy or maximum disorder. And so the natural tendency of the universe is for things to go from a state of order, towards a state of disorder, a state of higher entropy. This represents the natural tendency of reactions.

However, reactions can decrease the entropy of a system, essentially going backwards in this direction, with an energy input. As you can see down below, with an energy input, reactions can become more ordered. And so this is really what life is capable of doing. Living organisms are capable of inputting energy so that they can create order in their systems. But the natural tendency of the universe is to go from a state of low entropy towards a state of higher entropy.

And so the reactions are going to have this tendency to move towards the state of maximum entropy or maximum disorder. And so this is an idea that you would get to learn a lot more about in a chemistry course. But here in our biology course, this concludes our introduction to entropy and we'll be able to apply entropy in the second law of thermodynamics which we'll cover in our next video. So I'll see you all there.