Teaching entails not only imparting knowledge and understanding, but also dispelling misconceptions. Physics teachers around the world twirl evacuated glass tubes to demonstrate that the tube’s contents (usually a feather and a coin) do indeed fall at the same rate once the complication of air resistance is absent.
It’s understandable that students have difficulty with Isaac Newton’s first law of motion. For one thing, they rarely, if ever, witness an object moving without some kind of friction retarding its progress. And it took Newton, a genius, to think beyond everyday experience and devise a simple, rigorous, and useful concept of force.
Some subjects deal with phenomena that no student encounters in or outside school. But that unfamiliarity does not mean those phenomena are free of misconceptions. It’s not unreasonable to expect electrons passing through two closely spaced slits to behave like tiny electrically charged bullets.
Dispelling misconceptions early and effectively is important, especially in physics. If your physics education was like mine, you had to master a sequence of increasingly difficult concepts. Retaining or picking up misconceptions along that path can delay or forestall attaining enlightenment.
The central regions of M51 in a composite of images from the Hubble Space Telescope and Kitt Peak National Observatory.
Last week I stumbled across an interesting preprint by Andrej Favia, Neil Comins, and Geoffrey Thorpe of the University of Maine in Orono. Favia and Comins are in the university’s physics and astronomy department; Thorpe is in the psychology department. Together, they conducted a study of 318 UMO students who had completed an introductory astronomy course. The study’s goal was to determine whether the students still held mistaken beliefs about astronomical facts and concepts.
Most of the paper by Favia, Comins, and Thorpe is devoted to explaining the method they used to analyze their survey data: item response theory (IRT). Formulated in the 1950s and 60s, IRT seeks to account not only for the possibility that testing entails measurement errors but also for the possibility that some test takers know more than others. I’m hardly an expert on testing, but the use of IRT seems appropriate for study of misconceptions.
Although Favia, Comins, and Thorpe surveyed students’ misconceptions across all areas of astronomy, they chose to present their results on galaxies first. As they note in the paper, galaxies, unlike stars and planets, are mostly outside anyone’s direct experience. The central bulge of Andromeda, the nearest spiral galaxy to our own, is visible to the naked eye on moonless nights, but its characteristic shape isn’t. Any misconceptions that students harbor about galaxies are therefore likely to have been acquired through misunderstanding or ignorance.
To avoid prejudicing the students, the researchers presented the survey as a set of statements that were explicitly identified as beliefs rather than misconceptions. Here is the full set:
- • the Milky Way is the only galaxy
- • the solar system is not in the Milky Way (or any other) galaxy
- • all galaxies are spiral
- • the Milky Way is the center of the universe
- • the Sun is at the center of the Milky Way galaxy
- • the Sun is at the center of the universe
- • there are only a few galaxies
- • the galaxies are randomly distributed
- • we see all the stars that are in the Milky Way
- • all galaxies are the same in size and shape
- • the Milky Way is just stars — no gas and dust
- • new planets and stars don’t form today
And because the researchers were interested in learning when the students picked up the misconceptions, the survey also asked students to specify for each belief if they
- • believed it only as a child
- • believed it through high school
- • believe it now
- • believed it, but learned otherwise in Introductory Astronomy
- • never thought about it before, but it sounds plausible or correct
- • never thought about it before, but think it is wrong now
IRT is evidently a powerful and sophisticated method. Analyzing their survey results, Favia, Comins, and Thorpe could determine, for example, that the misconception "we see all the stars that are in the Milky Way" is commonly held with the misconception "the galaxies are randomly distributed." They could also tell that the way galaxies are distributed in space is the hardest concept to learn. (Not surprising, perhaps, given that the galaxy distribution is shaped primarily by the way dark matter collapses in the early universe.)
But for me, the survey’s most fascinating finding has to do with the order in which concepts are taught. Thanks to the second set of questions about timing, the researchers’ analysis yielded the optimum order for teaching the concepts to children and adolescents and a different optimum order for adults.
Both sequences end with the tricky distribution of galaxies, but the younger group starts with concepts that have to do with the visual properties of galaxies, whereas the older group starts with concepts that have to do with the unprivileged positions that the solar system and Milky Way occupy in the cosmos.
In his Lectures on Physics (1964), Richard Feynman was so worried that his students would acquire misconceptions about one of the hardest physics subjects to teach, quantum mechanics, that he introduced the Quantum Behavior chapter with a warning. Here’s an extract:
Because atomic behavior is so unlike ordinary experience, it is very difficult to get used to, and it appears peculiar and mysterious to everyone—both to the novice and to the experienced physicist. Even the experts do not understand it the way they would like to, and it is perfectly reasonable that they should not, because all of direct, human experience and of human intuition applies to large objects. So we have to learn about them in a sort of abstract or imaginative fashion and not by connection with our direct experience.
Feynman began his quantum course with electrons whizzing through closely spaced slits. Paul Dirac began The Principles of Quantum Mechanics (1930) with the superposition principle. David Griffiths began Introduction to Quantum Mechanics (1994) with the Schrödinger equation. Thanks to the methods developed by Favia, Comins, and Thorpe, teachers might discover which of these and other pedagogical entrées to difficult subjects are the most effective.
