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Description
(From the Physics series...entire series can be browsed here: [link] )

Entropy is one of the most important concepts in science. It's why everything happens in the universe the way it does. It’s been called "the arrow of time."

What exactly is entropy? Some people describe it as a measure of disorder. Actually, it's better described as a measure of energy dispersement. When scientists say that "entropy increases," what they mean is that the potential energy of something—or a concentrated amount energy—changes into dispersed energy. Once this energy is dispersed, it’s no longer usable to do work. To achieve a highly ordered state of matter, energy must be concentrated. Once this energy becomes dispersed, that’s usually associated with matter becoming disorganized.

The Second Law of Thermodynamics says that in any closed system, the entropy must either increase or stay the same. Why is this important? Because the universe as a whole is a closed system. And, because entropy can only stay the same in an ideal (read: unattainable) process, that means every process that occurs increases the entropy of the universe. Other localized systems can (and do) evolve into highly organized states of matter with lower entropy, but these are temporary. In the process of decreasing local entropy, the entropy of the entire system increases. For example, a living creature is a highly organized state of matter, and could be considered to have low entropy. But to achieve that state, a creature has to consume food, expend energy, etc., and these activities increase the entropy of its surroundings.

Now consider the First Law of Thermodynamics, which says that energy can neither be created or destroyed, it can only change form. So the amount of energy in the universe is constant. And all processes in the universe increase its entropy, dispersing this energy. Eventually, the entropy of the universe will reach a maximum value, and there will be no usable energy left for anything to happen.

Description
(From the Physics series...entire series can be browsed here: [link] )

Entropy is one of the most important concepts in science. It's why everything happens in the universe the way it does. It’s been called "the arrow of time."

What exactly is entropy? Some people describe it as a measure of disorder. Actually, it's better described as a measure of energy dispersement. When scientists say that "entropy increases," what they mean is that the potential energy of something—or a concentrated amount energy—changes into dispersed energy. Once this energy is dispersed, it’s no longer usable to do work. To achieve a highly ordered state of matter, energy must be concentrated. Once this energy becomes dispersed, that’s usually associated with matter becoming disorganized.

The Second Law of Thermodynamics says that in any closed system, the entropy must either increase or stay the same. Why is this important? Because the universe as a whole is a closed system. And, because entropy can only stay the same in an ideal (read: unattainable) process, that means every process that occurs increases the entropy of the universe. Other localized systems can (and do) evolve into highly organized states of matter with lower entropy, but these are temporary. In the process of decreasing local entropy, the entropy of the entire system increases. For example, a living creature is a highly organized state of matter, and could be considered to have low entropy. But to achieve that state, a creature has to consume food, expend energy, etc., and these activities increase the entropy of its surroundings.

Now consider the First Law of Thermodynamics, which says that energy can neither be created or destroyed, it can only change form. So the amount of energy in the universe is constant. And all processes in the universe increase its entropy, dispersing this energy. Eventually, the entropy of the universe will reach a maximum value, and there will be no usable energy left for anything to happen.