What is Entropy?
The simplest definition of Entropy is that it is a measure of the disorder of a system. Entropy is often called the arrow of time because the matter in undisturbed systems tends to move towards higher degrees of entropy.
Imagine, a tyre being punctured. It is common knowledge that the air in the tyre will escape into the surroundings instead of the other way around. Although this can be explained in terms of the difference in air pressure, it can also be explained in terms of entropy. The air in the tyre wants to achieve equilibrium with the environment. Therefore, when the tyre is punctured, the air in the tyre rushes out into the surroundings and achieves a greater degree of entropy. Entropy generally increases till equilibrium with the surroundings is achieved.
One of the leading theories for the ultimate fate of the universe is that the entropy in the universe will increase to a point where the randomness creates a system incapable of work. Some critics of this theory argue that our universe is part of a larger system and hence entropy can stay the same or even decrease under certain circumstances.