What does the concept of entropy mean?
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Let’s start with an easy-to-conceptualize model and work out from there.
Picture one of those plastic link clicky chain toys, like [this](https://i5.walmartimages.com/asr/b1066da1-a213-4153-9d9e-1e74aed4ac43.d6f545ff4d1793551235411f6a4cbe4f.jpeg). There’s 23 joints in the chain, and each can be clicked into one of five positions. There’s exactly one configuration that makes a completely straight line – all 23 joints are clicked into the “straight” position. By contrast, there are 46 different configurations where exactly one joint is bent into a 90-degree corner in either direction, 2 for each joint. Then, for each of those 45 configurations, there’s another 44 configurations where exactly two joints are bent at a 90-degree angle, which is over 2000 possibilities. Once you start getting into 3, 4, 10 links bent, the number quickly grows into the millions, billions, and beyond. So if someone were to walk up and click each joint into a random position, there’s only one possible outcome where the result is completely straight, while there are huge numbers of outcomes where the chain is bent somehow. This means that functionally, you’re basically never going to end up with a completely straight chain from just random bends. Entropy represents how likely a certain state is within the available space of all states. The rule goes “Within a given system, entropy always increases unless it’s acted on by an outside force.” Because of likelihoods, your chain is going to end up more bent over time until it reaches a point of maximum entropy. You can come in and manually straighten every link in the chain, decreasing entropy, but that requires you as an outside force to act on the system.
Let’s try a more complex example. Let’s say you have a glass jar. You pour in colored sand, from 8 different colors, one layer at a time, making a rainbow. Each layer contains millions of grains of sand. Your jar is going to start out neatly layered, but as it gets jostled, shaken, moved around, the grains will move around and blur the neat lines, until eventually you have a jar of indeterminate rainbow mush. In theory, there’s a tiny possibility that you could shake this mixed jar and the layers would separate out – but the possibility is so small that the chances of this happening randomly are effectively zero. You could use a microscope and an extreme precision tweezers to separate out the grains of sand again by hand, but it’s easy to see how the energy required to do this is extraordinarily high compared to the effort it took to jumble them together. The sorted, separated state has a much lower entropy than the jumbled state.
The fundamental particles that make up everything are an infinitely more complex version of grains of sand and chains of links. Without any outside interference, solid structures will break down, energy leaks out into the void of space, and you are eventually left with an indiscriminate mass of inert, diffuse particles, the highest entropy state.
So how is it that anything actually works? The key is in forces outside the system. The sun is a powerful force that puts out absolutely insane levels of energy out into the solar system. Our planet absorbs this energy through various means, and uses it to decrease entropy on a much smaller scale. The solar energy of our sun gets converted into energy in plants, which is used to build cellular structures. These plants are consumed by animals that break down those cells and use the energy to build their own cellular structures. Animals burn the energy stored in their cells to power their brains and muscles, exerting effort on the environment around them to craft tools, build buildings, create art, etc. Each one of these acts is a small fight against entropy. But on the loooong scale of things, the sun will eventually run out of fusion-able matter and burn out, Earth will stop absorbing this energy, whatever is left on the planet will decay and disperse into the universe, and the entropy of everything will increase. The end state of this is a theoretical state known as “the heat death” of the universe, wherein there are no systems that have localized decreases in entropy.
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