Entropy: chaos in science

By: JOSEPH ELLIOTT


posted on: November 15th, 2019

Scientists aim to provide explanations for how our world works. Concepts like gravity and heat help us to understand what happens around us. Entropy is a similar concept and dictates how everything in the Universe works.

WHAT IS ENTROPY?

There are many different ways to define entropy. The easiest way to understand it is that entropy is a measure of how disordered or chaotic something is.

For example, a pile of bricks that have been randomly thrown together will have more entropy than a pile of bricks that have been organised. Something that is more predictable and more ordered will have less entropy.

Everything has a certain amount of entropy. In most cases, it is impossible to determine how disordered something is just by looking at it. Most of an object’s entropy exists on a microscopic (very small) level. However, entropy can be measured and there are some trends we can observe.

Mixing things together will generate more entropy than keeping them apart. You can visualise this by mixing a bag of blue balls with a bag of red balls. If you pick one out, it is harder to guess what colour it is than if you kept the different colours separated. This is because the balls have become more disordered than if they were separated. You can imagine the entropy will increase even more if you add more balls of different colours.

Solids generally have very low entropy because they are well-structured and fixed. Liquids have more entropy as they can flow and move less predictably than solids. Gases have the most entropy and are the least fixed or ordered.

Hotter objects will have more entropy than colder objects.

WHY IS ENTROPY IMPORTANT?

Scientists have discovered that the Universe obeys certain physical laws. One of these laws is the Second Law of Thermodynamics. This law states that the total entropy of the Universe will always increase.

This may seem strange. After all we can see that it is very possible for things to become more ordered. You can pick up and organise bricks if you find them scattered around. Oil and water will separate even if you mix them. Steam gas can condense into liquid water.

However every process that orders something in one place brings more disorder somewhere else. So the overall entropy increases.

Usually this happens by heating up the surroundings. Hotter objects have more entropy, and the amount of entropy gained from heating the surroundings will always be greater than the entropy lost by organising the system.

Putting in work to move bricks into an order will make you become hotter. Steam condensing into water heats its surroundings just as much as one needs to heat water when you boil it into steam. Oil and water separating also heats up the environment, although not by much.

The Second Law of Thermodynamics applies to everything in our Universe. It allows scientists to make important predictions and even gives time its direction.

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