Thought experiments are a natural part of human cognition. We engage in a thought experiment when we watch the Super Bowl and try to imagine what the winning players will do during the locker room celebration or when we try to imagine how we'll go about telling our spouse that we spent more money than the budget allows on a new computer. A thought experiment occurs anytime we create a mental projection of some event that we can't actually observe at that point in time. These projections aren't static; rather, they involve the conscious manipulation of images.
Thought experiments have a rich history in the development of knowledge. For example, Einstein used a thought experiment when he imagined himself running to catch up with a beam of light. He imagined that running at the front of the beam might be like running from the end of a pier toward the shore alongside an incoming wave. He figured that if he ran at the same speed as the wave, the wave wouldn't appear to be moving. This thought experiment led to the development of his theory of relativity.
Why Thought Experiments?
The most straightforward use of thought experiments in the classroom is to examine causal and correlational relationships in academic content. In causal relationships, one event causes another. For example, the moon's relationship to the tides on earth is causal. To be considered a causal relationship, the cause must precede the effect, and there must be no other plausible explanations for the effect.
Correlational relationships involve two (or more) events that vary in predictable patterns but don't have a direct causal relationship. The relationship between the number of lemmings and the number of caribou in the arctic habitat is correlational. One event doesn't cause the other, but they vary in a coordinated manner.
Guiding Students Through the Process
- The moon's gravity pulls the water in the earth's ocean, causing a bulge (high tide) on the side of the earth facing the moon.
- The moon's gravity also pulls on the earth's core, which creates a counterforce pushing away from the earth on the opposite side. Although it may seem counterintuitive, this counterforce creates another bulge (high tide) on the opposite side of the earth.
- The moon rotates very slowly around the earth about once every 27 days, but the earth's daily rotation on its axis makes it appear as though the moon moves around the earth once a day.
Phase 1: Imagine
When sufficient background knowledge is in place, the teacher begins by guiding students through the creation of mental images—the "imagine" phase of the experiment. The teacher might say, "Form a picture of the earth rotating, with the moon next to it. Focus on the ocean on the side of the earth that's closest to the moon. Feel the pull of the moon on the waters of the ocean and see the bulge in the ocean start to rise, creating a high tide on that side. Now imagine the opposite side of the earth," and so on.
Phase 2: Explore
In this phase of the experiment, the teacher introduces a new element to the students' images. The teacher might ask students to broaden their mental image to include the sun. The teacher might say, "During the 27-day rotation of the moon around the sun, the relative positions of the sun, earth, and moon continually change. Sometimes the sun and moon line up on opposite sides of the earth to form a perfect straight line. Other times, the sun and the earth form a right angle with the earth and the moon."
The teacher would ask students to keep manipulating this mental image, trying to imagine how the tidal cycle would change on the basis of the relative positions of the moon, earth, and sun. During this phase, students might wish to sketch or create graphs to aid in their exploration.
Phase 3: Describe
In the "describe" phase, the teacher asks students to explain their conclusions to one another and to the class. Ideally, in this case, students would come to the realization that when the sun, earth, and moon are perfectly aligned, tides are extremely high (that is, spring tides) because the sun's gravity is also acting on the ocean on the side of the earth opposite the moon. However, when the moon is at a right angle to the sun and the earth, tides don't vary as much (that is, neap tides) because the gravitational pull of the moon and the sun tend to cancel each other out to some degree.
Phase 4: Confirm
In this last phase of the thought experiment, the teacher and students seek out information from textbooks and the Internet to determine whether their conclusions are accurate, and they discuss what they've learned. One of the many useful websites that simulate the generation of spring tides and neap tides is www.valdosta.edu/~cbarnbau/astro_demos/tides/neap_sp.html.
Across the Board
A teacher can use thought experiments in many content areas: with characters in literature (one character's actions are causally or correlationally related to another character's actions); in history (one historical event is causally or correlationally related to other events); or in the execution of physical skills (one part of a physical skill is causally or correlationally related to another part of that skill), to name just a few. Using this four-phase approach, teachers can guide students through this challenging but fruitful process.
