Free The Canon by Natalie Angier Page B

toluene concentrations in different workplace settings, including nail salons. Elsewhere on the Internet, you can gather results from inhalation surveys to see how much air the average person breathes in over the course of an hour, which is about how long you'll spend on a task that is literally as thrilling as watching paint dry. After analyzing these and other statistics, you may conclude, as the young student did, that her weekly manicures are reasonably harmless, but that she wouldn't want to work ten-hour shifts in a nail salon and that maybe she should give really big tips to the women who do.

    Another surprising barrier to thinking scientifically is that we often believe we already understand how many things work, especially simple things we were supposed to have learned in one of our formative, single-digit grades. Even absent specific exposure to this or that kiddie science problem via a parent, a camp counselor, or the Professor on
Gilligan's Island,
we develop an intuitive grasp of physical reality, a set of down-to-earth, seemingly sensible explanations for everyday phenomena: why it's hot in the summer and cold in the winter, or what's going on when we throw a ball into the air. Sometimes these intuitive concepts are so comfortably lodged in our brains that if that tossed ball were to become a cartoon piano and fall on our heads, we'd pick ourselves up like a dazed Wile E. Coyote, shake the twinkling phosphenes from our eyes, and go back to our same misguided schemes for catching the bleep-bleep Road Runner.
    Susan Carey, a professor of cognitive neuroscience at Harvard, has explored the ways that our lovingly cultivated and often erroneous models of physical reality can subvert understanding and impede our capacity to learn. She uses as an example a ball that has been tossed into the air and then falls back to the ground. Say you draw a picture of this trajectory, she said, with a series of balls in a steep arc to represent the ball rising upward, at midpoint in the air, and coming down again. You then ask people to draw arrows showing what sort of forces they think are acting on the ball during its trajectory—their strength and direction. The vast majority of people look at the picture and draw big force arrows pointing up while the ball is headed skyward, and big arrows pointing downward while the ball is descending. A sizable fraction of respondents, recognizing that gravity is acting on the ball during its entire voyage, will add little arrows pointing down next to the big arrows pointing up for the ascent portion of the curve. For the ball at its zenith, many will draw a little up arrow and a little down arrow that effectively cancel each other out.
    It makes sense, doesn't it? Ball going up, force arrows pointing up; ball going down, force arrows plunging earthward. In fact, it makes so much sense that people believed exactly this model of motion for hundreds of years. There's even a name for it—the impetus theory, the idea that when something is in motion, a force, an impetus, must be keeping it in motion. As reasonable and as obvious as this theory seems, however, it is wrong. True, there was an upward force exerted on the ball when it first was thrust into the air, compliments of the pitcher. But once the ball has been launched, once it is in midexcursion, there is no more upward force acting on it. Once the ball is in the air, the only force acting on it is gravity. All those arrows on the diagram should be pointing down. If there were no gravity to worry about, a ball tossed upward would keep sailing upward, no further encouragement necessary. This is one of Isaac Newton's many brilliant productions, the famed law of inertia: an object at rest tends to stay at rest, unless induced by the nudge of a police officer's stick to get up off the park bench, this isn't the Plaza Hotel, you know; while an object in motion tends to stay in motion unless a force is applied to stop it. Yet even though