What is entropy, really? | Wired

Entropy is one One of the most misunderstood and misunderstood concepts in science. You may have heard it defined as the “amount of chaos” in a system. The second law of thermodynamics says that the entropy of a closed system always increases with time. So you might be wondering, why should you clean your desk if it’s just going to get messier?

This may be true, but you can’t blame entropy. The metaphor of a messy room is often used to introduce the idea (usually a teenager’s bedroom – can you understand that?), but it is misleading. see, disorder It does not mean chaos or chaos; It refers to the number of ways in which the parts of a system can be arranged without changing the overall state of the system.

For example, let’s say your “system” is just a box filled with air. Inside, at the microscopic level, gas molecules bounce around like bumper cars. Now, imagine that you could plot the position and velocity of each particle at a given instant. This may be one possible arrangement, or exact state, but there are infinitely many others, and they change trillions of times per second.

Of course, you can’t really see these things. Instead, what you observe are general macro-level properties such as air pressure; If you closed the box at sea level, that would be 14.7 pounds per square inch. Unless you add energy to the system, for example by heating it, this will not change. So all those micro cases correspond to the macro case of 14.7 psi. get it?

In other words, entropy is about the relationship between the invisible atomic world and the visible, measurable world of things, the world in which we live. You can say that it is a conceptual and mathematical bridge between two levels of reality. I mean, come on, that’s pretty cool.

Now, of all the possible outcomes, which ones actually happen? This is basically random, so it’s a matter of probability. In fact, probability is fundamental to the idea of ​​entropy, and this is what the photo of the messy room fails to capture. So I’ll use a different analogy: rolling the dice. Einstein once said: “God does not play dice with the universe.” Let’s just see it, shall we?

Rolling bones

Imagine that you are rolling a six-sided dice. You get a number from 1 to 6, right? There are six possible outcomes or situations. If you roll a twenty-sided die in Dungeons & Dragons, there are 20 possible situations. If you want to impress your D&D friends, you might casually notice that these dice have higher entropy, because they have more possible outcomes.

Now let’s say you select a character’s abilities in D&D, and you roll three Six-sided dice. The three values ​​can add up to between 3 and 18, but the different amounts are not equally likely. To get maximum dexterity, for example, you need an 18. Well, there’s only one way to achieve that: each dice must roll a 6.

Photo: Rhett Allen