The bubonic epidemic known as the Great Plague broke out in London in 1665 and lasted for two years. During that time, citizens who could escape to the countryside did. Some fled to Cambridge, sixty miles to the north, where the university was shut down. This drove some of its residents to flee even farther from the epicenter.
Among those who did was twenty-three-year-old Isaac Newton. He had just finished his undergraduate studies and was teaching at his alma mater when the plague drove him to spend much of the next couple of years in and around his native hamlet of Woolsthorpe by Colsterworth, located about fifty miles northwest of Cambridge. He was in the prime of his intellectual life, and according to his own recollection, those years proved to be his most fruitful and creative. Indeed, according to the historian of science Robert Palter, it was during his sojourn in Lincolnshire that Newton “developed the integral calculus, experimentally verified the composite nature of light, and refined his gravitational theory to the point that he was able to satisfy himself through calculation that the earth’s gravity holds the moon in orbit.” Since most of this outburst of genius occurred in the single year 1666, scholars refer to it as Newton’s annus mirabilis, his “miraculous year.” Although there may be some hyperbole involved, Palter believes that the year “may surely be taken as symbolic of a decisive turning point in the history of human thought.”
Similarly, the folksy anecdote about Newton being inspired to come up with his theory of gravity by an apple falling on his head may well be apocryphal, but that does not invalidate it as being universally evocative of an Aha! moment. It has been speculated that Newton did not actually get hit by an apple but merely observed one falling from a tree. Still, the idea that he did get physically bonked provides for an enticing vernacular alternative to technical explanations involving calculus, optics, and calculation— all terms appropriated effectively by politicians, by the way—of how he was inspired to formulate his theory of gravitation. Who cannot imagine a falling apple hitting them on the head? Who cannot imagine picking up the apple in anger and throwing it far from the tree? Who cannot see that all the while the apple is flying toward a compost heap it is falling back toward the Earth? Who cannot grant that this might inspire a vision of the Moon orbiting the Earth?
Many a person living long before Newton must have observed fruit falling from trees or rocks thrown at foes. They may also have experienced the physical consequences of being under a tree or on the wrong side in a feud at the wrong time. But observing and feeling do not necessarily lead to internalizing those sensations to the point of inspiration. Galileo came close to a broad understanding of gravity by connecting the phenomenon of a ball shot horizontally out of a cannon with that of one falling from a tower. Newton carried the image further by placing the cannon atop a high mountain and imagining the ball shot with such a speed that instead of eventually arcing back to strike the Earth it encircled it. Newton epitomized the value of imagery and metaphor to express universal concepts when in 1675 he wrote to Robert Hooke, “If I have seen further it is by standing on the shoulders of Giants,” the statement often used to symbolize scientific progress. There is, however, an alternate interpretation of the oft-quoted words. Newton and Hooke were locked in debate over claims of priority when it came to gravitation. According to one view, when Newton referenced the shoulders of giants he was deliberately slighting Hooke, whose body was deformed and far from giantlike.
Especially in the area of mechanical force, progress does not demand abandonment of the past. We can empathize with Newton precisely be cause when we feel a force associated with everyday life today, we cannot imagine that it is different from what Newton and his colleagues felt it to be in the seventeenth century. And, by extension, they experienced force the same way their ancestors did. Thirteen centuries earlier, when Saint Augustine and his friends shook a pear tree to steal its fruit, they must have felt the resistance of the tree’s trunk to being bent in the same way that we can feel the stubbornness of a sapling when we might try to coax it to give up its last leaves in the fall.
The forces described in this book have always been part of the world. It may have taken some time for philosophers to articulate them and their role in effecting change, but the deepest thinkers were not necessarily the ones who first experienced or discovered these tangibles of the universe. That was done by cultures of individuals feeling in the course of everyday life how this thing we now call force in its myriad manifestations shaped our world and was somehow behind its sometimes puzzling behavior.
Artisans, craftspeople, inventors, and engineers never have had an absolute need for a theoretical basis to exploit the forces of nature. They have used them as they found them to be effective in context. Sentient beings learned to use a harder rock to knap a softer one: Anonymous workers in ancient Egypt did this literally to form everything from a cutting edge to an obelisk. Renaissance sculptors hit a harder chisel with a softer mallet to reshape chunks of stone into things of beauty: Michelangelo did so in sixteenth-century Florence to free his David from a block of marble. Modern problem solvers continue to use a hard pencil on soft paper (perhaps in the form of a computer and its output) to reshape the world: Engineers have done so in designing everything from bridges that span a mile to interplanetary probes that reach the outer planets and someday, maybe, spacecraft that carry astronauts there. It is human to learn by feeling and doing and thinking how to apply forces to achieve ends, no matter how intractable at first the problem may have seemed. Successive generations simply do on a grander scale what their ancestors had been doing for millennia and what children do today: they work and play with force. Perhaps it is because of their universality in time and space that such fundamental activities eventually become so unremarkable.
In the three and a half centuries since Newton’s annus mirabilis, our everyday concept of force has served us well, and it can be expected to continue to do so. In spite of Einstein’s theory of relativity explaining the gravitational force as a warping of a spacetime continuum, and the ongoing quest of quantum mechanics for a theory of everything, the forces of Newton remain the mainstay of everyday life and terrestrial engineering, as well as of the flights of fancy that will reach their destination in some not yet fully shaped world.
The fact that Newton’s annus mirabilis occurred during a period of plague should reassure us that in the long run the legacy of the Covid19 pandemic need not include long-term adverse effects on artistic, scientific, and technological progress. The world’s anni miserabiles are likely to be analyzed and reanalyzed intellectually for decades, if not centuries, even if many of our contemporary experiences are forgotten or become unimaginable to some of our descendants. But reflective twenty-second-century citizens should be able to replicate what it was like to wear a crudely designed mask, maintain an unsocial distance, and abstain from touching their hand to their face. And by feeling the past they should be better prepared to touch the future.
 Palter, Robert, ed. The Annus Mirabilis of Sir Isaac Newton. Cambridge, Mass.: MIT Press, 1971.
 Guicciardini, Niccolò. “Reconsidering the Hooke-Newton Debate on Gravitation: Recent Results.” Early Science and Medicine 10, no. 4 (2005): 511–17.
From Force: What It Means to Push and Pull, Slip and Grip, Start and Stop by Henry Petroski. Published by Yale University Press in 2023. Reproduced with permission.
Henry Petroski is a distinguished professor emeritus at Duke University. He is the author of nineteen previous nonfiction trade books, including The Pencil and The Evolution of Useful Things, which consider the invention, design, and cultural significance of common objects.