Connecting Concrete and Abstract (page 2)

We mentioned in the introduction to the chapter that our definition of mathematics is changing. It is important for us to take just a few moments to consider the vital and foundational question, "What is mathematics?" Before reading any further, take a few moments and write down some of your thoughts in answer to this question. If possible, perhaps through the use of electronic communications,² try to share your ideas with some of your colleagues and take a look at their answers to the question before reading further.

It would be helpful if you would think of the water cycle as an analogy to the way mathematics operates. (In the water cycle, liquid water evaporates into a vapor, or gaseous form; then the gaseous water condenses onto bits of dust in the atmosphere, and these drops of water become large enough to fall from the sky in the form of precipitation.) The stage of the water cycle at which water is in its vapor form is the closest to mathematics itself. Water vapor is invisible, and it is in the air around us. The closest thing to visible water vapor is a cloud, which is normally high above our heads and out of our reach. To many people, this is a perfect description of mathematics. (We hope to change that perception!) Mathematics is an abstraction. In a sense, mathematics itself is invisible. But where does it come from? In our analogy, where does water vapor in the air come from? It comes from the process of evaporation, which operates on liquid water on the face of the earth. Mathematics, in a similar way, is abstracted from real-world situations. For example, we look around us and we see many objects in nature that have an identical shape: the sun, the moon, the shape of ripples on the water when a pebble is dropped, and so on. From those observations we construct a mental picture of a shape that we name as a circle. The idea of a circle is just that: an idea that a person must construct in his or her mind. An idea is an abstraction, and this particular abstraction has its roots in things we have observed in the physical world. Now we have something mathematical: our mental representation of a circle. We can study characteristics of a circle. We can measure parts of it; we can compute relationships between various parts of it; we can describe it in such detail that someone could follow our description and draw exactly what we have in mind. We can even use the idea of a circle as a model to make things that help us accomplish goals. For instance, we can make a wheel in the shape of a circle and use it for transportation. When we take a mathematical idea and bring it back down to earth in the form of something we have made, this is like the part of the water cycle where water returns to the earth in the form of precipitation. This is the application of mathematics from the abstract to the concrete.