What exactly is Entropy? | | THE WIRE

Entropy is one one of the worst and most misunderstood ideas in science. You’ve probably heard it described as “a lot of chaos” in the system. And the second law of thermodynamics states that the entropy of a closed system always increases with time. So you might be thinking, why do you need to clean your office if it just gets messy?

This may be true, but you can’t blame it on entropy. The image of a messy room is often used to introduce a concept (it’s usually a youth room – can you describe it?), but it’s misleading. See, confusion it does not mean confusion or disorder; refers to the number of ways in which parts of a system can be selected without changing the overall structure of the system.

For example, say your “system” is a box filled with air. Inside, at the most visible level, the gas molecules are moving around like giant cars. Now, imagine that you could map the position and velocity of any object in time. This may be one possible system, or microstate, but there are limits to others, and they are changing billions of times a second.

Yes, you cannot see these things. In fact, what you see is much, much like air pressure; if you print the box at sea level, then it can be 14.7 pounds per inch. And unless you add energy to the system, say by heating it, it will not change. Therefore both microstates correspond to the macrostate of 14.7 psi. Get it?

In other words, entropy is all about the relationship between the invisible atomic state and the visible, measured state of matter, the world in which we live. You could say that it is a conceptual and mathematical bridge between the two realms of reality. I mean, come on, it’s great.

Now, of all the results, which ones actually happen? This is random, so it’s a matter of possibility. In fact, probability is essential to the concept of entropy, and this is what the mess room picture fails to capture. So I’ll use a different metaphor: rolling the dice. Einstein once said: “God doesn’t play dice with the universe. Let’s just see about it, right?”

Rolling the Bones

Imagine that you have rolled a six-sided game. You get a number from 1 to 6, right? There are six outcomes, or states. If you put a 20-sided die in Dungeons & Dragons, there are 20 possible states. If you want to impress your D&D friends, you can casually say that this die has high entropy – because it has many outcomes.

Now say you recognize someone’s skill in D&D, and you roll three six sided dice. The three levels can include anything between 3 and 18, but the range is not the same. To have a high skill, say, you need 18. Well, there is only one way to achieve this: Every die must have 6.

Photo: Rhett Allain