I first heard the track “Fireflies,” by Owl Metropolis, shortly after my junior yr of faculty. In the course of the chorus, singer Adam Younger virtually whispers, “I’d wish to make myself imagine / that planet Earth turns slowly.” Goosebumps prickled alongside my neck. Sure, I believed, I’ve studied Foucault’s pendulum.

Léon Foucault practiced physics in France through the mid-1800s. Throughout one in all his best-known experiments, he hung a pendulum from excessive up in a constructing. Think about drawing a large circle on the ground, across the pendulum’s bob.¹

Think about pulling the bob out to a degree above the circle, then releasing the pendulum. The bob will swing forwards and backwards, tracing out a straight line throughout the circle.

You may anticipate the bob to maintain swinging forwards and backwards alongside that line, and to do nothing extra, ceaselessly (or till the pendulum has spent all its power on pushing air molecules out of its method). In any case, the one forces performing on the bob appear to be gravity and the stress within the pendulum’s wire. However the line rotates; its two suggestions hint out the circle.

How lengthy the guidelines take to hint the circle depends upon your latitude. On the North and South Poles, the guidelines take in the future.

Why does the road rotate? As a result of the pendulum dangles from a constructing on the Earth’s floor. Because the Earth rotates, so does the constructing, which pushes the pendulum. You’ve skilled such a pushing for those who’ve ridden in a automobile. Suppose that the automobile is zipping alongside at a relentless pace, in an unchanging path, on a easy highway. Together with your eyes closed, you received’t really feel such as you’re transferring. The one forces you possibly can sense are gravity and the automobile seat’s stopping you from sinking into the bottom (analogous to the wire stress that forestalls the pendulum bob from crashing into the ground). If the automobile turns a bend, it pushes you sidewise in your seat. This push is named a centrifugal power. The pendulum feels a centrifugal power as a result of the Earth’s rotation is an acceleration just like the automobile’s. The pendulum additionally feels one other power—a Coriolis power—as a result of it’s not merely sitting, however transferring on the rotating Earth.

We will predict the rotation of Foucault’s pendulum by assuming that the Earth rotates, then calculating the centrifugal and Coriolis forces induced, after which calculating how these forces will affect the pendulum’s movement. The pendulum evidences the Earth’s rotation as nothing else had earlier than debuting in 1851. You may think about the stir created by the pendulum when Foucault demonstrated it on the Observatoire de Paris and on the Panthéon monument. Copycat pendulums popped up internationally. One ended up subsequent to my faculty’s physics constructing, as proven on this video. I reveled in understanding that pendulum’s movement, junior yr.

My professor alluded to a grander Foucault pendulum in Paris. It hangs in what gave the impression of a temple to the Enlightenment—stunning in type, steeped in historical past, and wealthy in scientific significance. I’m a romantic in regards to the Enlightenment; I am keen on the thought of making the primary large-scale organizational system for data. So I hungered to make a pilgrimage to Paris.

I made the pilgrimage this spring. I used to be attending a quantum-chaos workshop on the Institut Pascal, an interdisciplinary institute in a suburb of Paris. One quiet Saturday morning, I rode a prepare into the town middle. Town homes a former priory—a beautiful, Eleventh-century, white-stone affair of the kind for which I envy European cities. For over 200 years, the previous priory has housed the Musée des Arts et Métiers, a museum of trade and know-how. Within the priory’s chapel hangs Foucault’s pendulum.²

A pendulum of Foucault’s personal—the one he exhibited on the Panthéon—used to hold within the chapel. That pendulum broke in 2010; however nonetheless, the pendulum swinging at the moment is all however a holy relic of scientific historical past. Foucault’s pendulum! Demonstrating that the Earth rotates! And in a jewel of a setting—flooded with gentle from stained-glass home windows and surrounded by Gothic arches beneath a painted ceiling. I flitted across the little chapel like a pollen-happy bee for possibly quarter-hour, watching the pendulum swing, different artifacts of Foucault’s, wending my method across the carved columns.

Virtually alone. A handful of holiday makers trickled out and in. They contrasted with my go to, the earlier weekend, to the Louvre. There, I’d witnessed a Disney World–esque line of vacationers ready for a glimpse of the Mona Lisa, digicam telephones held excessive. No one was queueing up within the musée’s chapel. However this was Foucault’s pendulum! Demonstrating that the Earth rotates!

I confess to capitalizing on the shortage of holiday makers to take a photograph with Foucault’s pendulum and Foucault’s Pendulum, although.

The remainder of the museum may mannequin in an commercial for steampunk. I discovered automata, fashions of the steam engines that triggered the Industrial Revolution, and a phonograph of Thomas Edison’s. The devices, many shaped from brass and darkish wooden, distinction with the priory’s light-toned majesty. But the priory shares its magnificence with the innovations, a lot of which gleam and curve in ornamental flutes. 

I tore myself away from the Musée des Arts et Métiers after a number of hours. I returned house per week later and heard the track “Fireflies” once more not lengthy afterward. The goosebumps returned worse. Because of Foucault, I could make myself imagine that planet Earth turns.

With because of Kristina Lynch for tolerating my many, many, many questions all through her classical-mechanics course.

This story’s title refers to a translation of Goethe’s Faust. Within the translation, the demon Mephistopheles tells the title character, “You let the good world spin and riot; / we’ll nest contented in our quiet” (to inside punctuational and different minor errors, as I now not have the textual content with me). A prize-winning 2009 novel is named Let the Nice World Spin; I’ve lengthy questioned whether or not Faust impressed its title.

¹Why isn’t the underside of the pendulum referred to as the alice?

²After visiting the musée, I realized that my classical-mechanics professor had been referring to the Foucault pendulum that hangs within the Panthéon, slightly than to the pendulum within the musée. The musée nonetheless accommodates the pendulum utilized by Foucault in 1851, whereas the Panthéon has solely a replica, so I’m content material. Nonetheless, I wouldn’t thoughts making a pilgrimage to the Panthéon. Let me know if extra thermodynamic workshops happen in Paris!