What does your bedroom, the polar ice caps, and a black hole have in common? All of these objects are consistently and spontaneously increasing in disorder; they are moving towards maximum entropy. Entropy, in its simplest definition, represents the amount of disorder present in a particular system. The disorder of a system tends to increase unless energy is expended to order it again. The easiest way to imagine this is in your bedroom. Even after you’ve cleaned and organized your bedroom, over time, it becomes disorganized and messy again. The only way to return your room to its original organized state is by expending your own personal energy. It may seem like there must be some particular force or deliberate action that is causing your room to become disorganized (maybe you really are a slob after all). But, in reality, there’s no force that makes the entropy of a system increase. It increases spontaneously because of thermodynamic statistics (coincidentally, mentioning thermodynamic statistics will definitely make people stop asking about the disorganized state of your bedroom).
Entropy is sometimes referred to as “time’s arrow,” because, universally speaking, it is always increasing. The universal increase of entropy is irreversible—i.e., you cannot go backward in time. In the same vein, the increase of entropy is what makes time meaningful. For example, if you made a cup of coffee this morning and forgot it on the counter for an hour, you would expect the coffee to be cold once you returned. Time has moved forward, so without any outside input of energy, the entropy of your coffee system has increased. This may seem both obvious and counterintuitive. Of course, your coffee got cold; that’s what happens when hot things are left in cool environments. But why does that happen if “disorder” is supposed to increase? Isn’t hot coffee (where the molecules of coffee are moving very fast) more disordered than cold coffee (where they are moving very slow)?
The problem with that logic is that you’re looking at the coffee as an isolated system. We already know that the coffee is in a mug that is sitting on a counter, which is surrounded by air (unless you happen to keep your kitchen in a complete vacuum). Heat from the coffee doesn’t spontaneously disappear, it disperses into the surrounding medium (counter, air). This is the more useful definition of entropy—the dispersal of energy. In the beginning, more energy was centralized in the coffee than in the surrounding medium. But as time moves forward, the energy disperses until the mug of coffee, the counter, and the air all contain the same amount of energy. The coffee loses energy to the surrounding environment until the entire system reaches thermal equilibrium.
The universe has a set amount of energy that cannot be created or destroyed, only transformed (this is the first law of thermodynamics). You can, of course, reheat your coffee if you want. But to do so your microwave must expend energy in the form of electromagnetic radiation, which it generates from the power supply in your house. The energy supply in your house is transferred from a power plant (also known as a powerhouse . . .), which derives energy by burning fuel. Burning fuel involves breaking high energy chemical bonds and dispersing that energy. Once energy is dispersed, there is no way to put it back into order without dispersing other energy. This is why coal, oil, and other chemical forms of energy are considered “non-renewable.” There is a finite amount of those high-energy chemicals on earth, and once their energy is dispersed, it cannot be recovered.
At the beginning of the post, I mentioned that the entropy of a system, in this case your bedroom, is related to thermodynamic statistics. But what do thermodynamic statistics have to do with the messiness of your room? Well, take a look around your room. How many configurations of “messy” could it be in? It could be messy in that all your clothes and books are on the floor, but your bed is made and there is no dust. It could be messy in that nothing is out of place but a single pair of pants are on the ground, and every surface has a thin layer of dust or crumbs. You could imagine billions of slightly different configurations that would make a “messy” room. On the other side of that coin, there is only one true configuration for a “clean” room (assuming you aren’t a liar like me who claims their room is “clean” when they haven’t vacuumed for years). At any given point, which scenario is more likely? That your room is in one of the billions of “messy” states? Or that your room is in the one “clean” state? Becoming ordered isn’t impossible. It’s just very unlikely.
This explanation also fits with the definition of entropy as a dispersal of energy. In our coffee mug system, there are very few ways for the system to exist with all of the energy isolated in the coffee. But there are billions of ways for the energy to exist dispersed throughout the coffee, mug, counter, and air. In a casino, if someone wins a bet with one in a billion odds, then you know the game has been rigged in their favor. Similarly, if a system goes from disordered to ordered, from cold to hot, or from dispersed to isolated, then you know energy is being spent to make it that way. The game is being rigged.
Luckily for us, there is enough energy in the universe for the game to be occasionally rigged. The Sun provides the Earth with a seemingly endless amount of electromagnetic energy that makes all life possible. Life is, in terms of entropy, an impossible gamble. You exist as an improbable conglomeration of energy waiting to be dispersed. Much of your life is spent taking in and breaking down energy-storing molecules, in order to keep your energy isolated within your body. But even with the additional energy, eventually, your cells, tissues, and organs begin to break down. Not because anything is necessarily damaging them, but because the cost of keeping them together becomes too high. Time moves forward. Entropy increases. The game can be rigged, but no matter what, the house always wins.
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