If you’re like me, this is about the time of the semester that schoolwork starts gnawing away at every last second of your free time. Your workload keeps you up through all hours of the night, at the expense of things like your friends, nutritional needs and especially cleanliness. In fact, the gradual transformation of our rooms from comfortable dens to refugee camps toward the end of the semester is a pretty good analogy for one of the most fundamental and comprehensive laws of nature — the second law of thermodynamics.
This law basically states that certain properties of matter — temperature, pressure and distribution of particles — tend to become more even and uniform over time. This is quantified by defining what’s called the entropy of a system. A basic, intuitive definition is that entropy is proportional to the amount of “disorder.” The second law of thermodynamics can be restated as “the entropy of a closed system never decreases.” That is, left alone, things only get more and more disorderly.
So, if you think of the objects in your room, you can imagine that the second law of thermodynamics would say you’re far more likely to find them strewn all over the floor than neatly put away like they should be; and of course, that’s exactly what we observe. Strictly speaking, the piles of clothes all over your floor aren’t an example of thermodynamic equilibrium, but they do tend to operate on the same principle.
Another way of looking at it is, oddly enough, in terms of poker hands. Imagine that the air molecules in a room are playing cards. When you first open a brand new deck, you can deal two consecutive straight flushes right off the top, since the cards are all in order. This is analogous to all of the air in a room being only in one small corner — extremely unlikely to happen under normal conditions. In fact, the second law of thermodynamics is exactly the reason why we don’t have to worry about suffocating every time we walk into a room due to the lack of an even distribution of air.
As you shuffle the deck many times, you start to get a more and more disorderly arrangement of cards, and thus would deal mostly ordinary (or if you’re dealing to me, mostly terrible) poker hands. Similarly, as air molecules are free to move around a room, they tend to arrange themselves to be evenly spread out. The difference is, royal flushes actually happen on occasion. The enormous number of air molecules in an average room — on the order of an octillion (that’s a one followed by twenty-seven zeroes) — makes the probability that you’ll find them all in the same corner basically negligible.
The second law of thermodynamics also applies to the universe as a whole. In fact, one of the ways by which we can define which “direction” we are moving in time is the direction in which the entire universe becomes more and more disorderly. So, if you ever find that your room is gradually cleaning itself, don’t panic, but you’re probably going backwards in time. This fact should be pretty comforting, actually; just remind yourself that cleaning your room would only upset the natural disorder of the universe, and all of a sudden you have a lot more time to study.
Nick Mykins is a senior physics major from Raleigh. Contact him at nmykins@email.unc.edu
