Column: This year, the answers are different

In one of my stories for the May issue of Physics Today, I wrote about craters on Pluto and its largest moon, Charon . Analyzing their sizes tells us about the collisional dynamics of the Kuiper belt, the vast toroidal region beyond the orbit of Neptune that’s home to countless small icy bodies. While I was working on the story, I came to a startling realization: My mental picture of our solar system was a couple of decades out of date.

It wasn’t that I was ignorant of the basic facts. Like most scientifically interested people, I’d heard about Pluto’s reclassification as a dwarf planet in 2006, just two months before I joined the staff of Physics Today. And like many, I was initially hesitant to accept the change. In the first draft of one of my early Search and Discovery stories , about radar observations of Mercury, I waffled over whether Mercury was really the smallest planet in the solar system. When I sent the draft to the researchers for their feedback, they gently scolded me: The new definition of planet was perfectly serviceable, and Mercury was the smallest, without qualification. The published version of the story incorporated their correction.

Miller’s Diary

Physics Today editor Johanna Miller reflects on the latest Search & Discovery section of the magazine, the editorial process, and life in general.

I’ve also known about the Kuiper belt since at least 2008, when I edited a feature article by Don Brownlee on comets. Many of the comets we see from Earth were once Kuiper belt objects, so the article includes a few paragraphs about the Kuiper belt and its history.

But I hadn’t fully processed what those facts meant for the picture of the solar system I’d been taught as a child. I still had the idea that Pluto, even as a dwarf planet, held a position at the edge of the solar system that was somehow special. In fact, as Kuiper belt objects go, Pluto is pretty ordinary. It’s still the largest known Kuiper belt object, but it makes up a far smaller fraction of the total mass of the Kuiper belt (on the order of 2–5%) than Ceres, the largest asteroid, does of the asteroid belt (30%). We hadn’t learned any of that in school in the 1980s—for the obvious reason that no Kuiper belt objects other than Pluto and Charon would be discovered until 1992.

That realization got me thinking about other changes in the world that have failed to make their way into the public consciousness. I’ve long been fascinated by the Gapminder Foundation ‘s research on our understanding of global development. When presented with multiple-choice questions about the state of the world—what fraction of people have access to electricity, for example, or what fraction of girls go to school—residents of rich countries systematically do worse than they would if they’d guessed randomly. (You can take the test for yourself here .)

Gapminder calls this the Ignorance Project but notes that the problem is more than simple ignorance: The fact that respondents do worse than random means that they must actively believe things that are wrong. Where do those beliefs come from? Part of the problem may simply be outdated information: Many of the favored wrong answers are ones that would have been correct 30 to 50 years ago. Gapminder also emphasizes the role of sensationalist news coverage, which tends to focus on disasters and crises around the world at the expense of the bigger picture.

But big-picture information isn’t wholly absent from the news. I suspect that at least some of the subjects who took the Ignorance Project test had heard at least something about the recent decades of rapid economic growth in India and China, two countries that together make up more than a third of the world’s population. But they might not have fully realized what that growth means for the standard of living of ordinary people or the need to update what they think they know about global wealth and poverty.

There’s an old joke about a professor (in some versions of the joke it’s Albert Einstein; in some it’s an economist) who gives his class an exam with all the same questions as he’d asked the previous year. When challenged by a student, he replies, “Oh, but this year the answers are different.” Next year they’ll be different still.