Observations vs. Explanations

Students should learn the difference between observations and explanations.

Process of Science Goals

Students should learn to separate the observations upon which scientists base their explanations from those explanations. Scientific observations tend to be relatively durable, but more than one explanation for any set of observations is always possible. If students are to learn to rationally evaluate scientific claims, they need to be able to pick out which parts of these claims are the most durable (observations), and which are creations of the scientific imagination (explanations).

This type of activity could be adapted for any type of introductory science class, from secondary to college levels.

No special materials are needed for this activity. Don't be put off by the fact that I haven't included a bunch of information about the origin of the Solar System, because the activity can be adapted for any topic.

It is very common for students to think that the work of a scientist is to go out and "make discoveries," (which students then have to memorize). Furthermore, they usually have not had any formal training in logic. The result is that they often think of most scientific claims simply as observations that have been "discovered," and don't tend to think much about the process of scientific thought. This isn't necessarily their fault, because this point of view meshes very well with the way science is generally taught. They are given a list of scientific "facts" or "theories" to memorize, but usually do not receive much about what that means. They may also be given some equations to manipulate so they can solve some basic problems.

Many student responses during this activity reflect this kind of misconception. Here are a couple of examples.

1. Usually one of the groups will say that if they wanted to explain the origin of the Solar System, they would determine where the Sun is in "the life-cycle of a star." I point out that we can't observe the life-cycle of a star, which may span billions of years. All we can do is make various observations about whatever stars, nebulae, etc., we can see during a relatively short period of time. The "life-cycle of a star" is essentially a story constructed to explain those observations.
2. Another group always says that they would observe what the Sun and other objects in the Solar System are made of. I consider this a good answer, given the stage of the course at which we do this activity. But when we discuss this answer I point out that, depending on what the students mean, it might reflect a somewhat more subtle version of the misconception. We can collect and analyze meteorites and materials in the Earth's crust, hydrosphere, and atmosphere, for example, but cannot go collect samples on the Sun or most of the planets. However, we can compare the absorption spectra of stars and planets with the spectra generated when light passes through the different elements here on Earth.

Here are some examples from other topics that come up in my class.

1. Plate Tectonics: If you were in Alfred Wegener's place, what observations could you make to gather evidence for/against the idea that the continents were formerly in different places? Some students might answer that they would measure the movement of the continents, but at that time this wasn't feasible. Rather, it was an inference based on other observations like the distribution of Paleozoic glaciation, fossil organisms, mountain ranges, and so on.
2. Geologic Time: What kinds of evidence do you think might have led the original geologists to conclude that the Earth is many millions of years old? Students should come away realizing that you have to combine observations of how long various processes take with the principle (assumption) of Uniformitarianism.

Throughout the semester, I use the same type of activity in different contexts to give the students practice at this type of thinking. Also, when I explain some concept I may stop and ask, "Which parts of what I just said are the observations, and which parts are the story?" I have noticed that many students demonstrate greater facility at separating the two as the semester goes on.

I also create multiple-answer questions for quizzes and tests in which I ask, "Which of the following are observations that are explained by [X theory]?" Some of the possible answers are always elements of the theory that are not observations.