No matter how many times you vacuum your carpet, do your bed, and fold your laundry, you end up with a messy room again by the end of the week. You might even feel that some invisible force drives your living space toward more disorder and chaos. That’s right, you’re not to blame.
The same sort of unrelenting drive to disorder occurs even at the molecular level. Physicists like to call it entropy, but really, it’s the messy room concept. From the Greek, εντροπος, entropy means “inner tendency.” All matter in the world, large as galaxies and small as atoms, has an innate preference for a state of chaos. Just like your laundry, if we took a hundred gas particles, and neatly lined them up in a row, we can be sure they will break formation. Each particle will go its own way, in a stochastic or random manner. Similarly, by Saturday, you’ll find one sock behind the headboard, and the other, curiously enough, between your mattresses. Or perhaps I am a little messier than you are.
Messier, not simply messy, is the key. Entropy in the physical sense is a relative tendency toward increasing disarray. It is difficult to quantify how messy one room is, but readily apparent which of two rooms is the more disorderly. Similarly, the gas particles in one balloon may move about more randomly than those in another. It’s all rooted in the flow of energy.
Probably the first rule of the universe is that energy must be conserved at all times. You’ve experienced it yourself. Energy occurs in many forms in the world, as heat, light, nuclear, chemical, or electrical energy. When energy converts from one form to the other, it is neither created nor destroyed. It is simply transformed. Consider a simple lamp in your room. Plugging it in, you are supplying the light bulb with electrical energy. However, the main apparatus, the filament of the light bulb, allows this energy to be converted into light, which is useful, and heat. Energy was conserved.
Even that light and heat, though, do not disappear. The gas particles surrounding the bulb absorbed these energy forms. This causes the gas particles to become more excited, more prone to movement. The gas particles will move about with more disorder than before. But this energy expended, this input of heat, was not useful. It simply got a few particles moving about.
In any such process where there is a transformation of energy, and its entropy increases—for example, still water vaporizing to steam—a portion of that energy will remain unusable, useless heat. For energy to be conserved, every last joule must be accounted for. Some joules don’t provide light or heat; they are simply used to make things messier. Thus, entropy balances the equation.
If molecules, reactions, socks, and even galaxies prefer a more disordered state of being, the big question is how could something like the Earth, with all its physical, chemical and biological beauty come to be? Look around you. You will likely see a high level of order.
A simple example is planting a seed. Placing a dogwood seed a few inches below wet earth, you expect some changes to occur. The latent energy in the seed, the small reserve of starch, provides just enough vigor for the seed to sprout a root. The root delivers water and nutrients to the seed. Eventually a shoot forms, which breaches the surface. Over time, a full grown tree will develop, roots, shoots, leaves and all.
Though energy was changing in this process of photosynthesis, from sunlight to biochemical energy, a high level of order was maintained. The DNA within the cells of the plant was able to exert its command over how the plant should grow and develop. This seems in contrast to the world’s tendency toward disorder.
Entropy doesn’t always have to increase, second by second. Over the long term, entropy will increase or at least stay the same. But in small snippets of time, a decrease in disorder can occur, under the right conditions.
The molecules within the seed and eventual tree are all tending toward disorder, all the time. However, to counter that disorder, to develop an ordered biological system, energy was expended. To overcome entropy, energy must be put in. So, some of the plant’s energy was used up in preventing and reversing disorder. Otherwise the plant wouldn’t get past being a primordial lump of cells and molecules.
You do it all the time when you clean your room. Every week, in a routine, you expend effort to organize your surroundings. Similarly, systems that seem to disobey entropy use energy to achieve their feat.
Entropy is relentless and continues to this day, many times, incognito. The next time your significant other complains about your slovenliness, simply say, “baby, it’s entropy.” Bonus points for knowing a little physics.