An apple falls from a tree and a young man from the English countryside jumps up and shouts: “Eureka!” He immediately sees that the force of gravity, which makes apples fall out of trees, must be the same force that makes the moon orbit the earth, the earth the sun, and so on. It all comes together in his fertile and amazingly creative mind. This is an often-told tale about the young Isaac Newton, who was home visiting from his college at Cambridge University in the 1660s. He himself told something like this neat little story later in his life. If you want, you can go to Cambridge, England, and see, not Newton’s actual apple tree but one that is a relative of his. It takes pride of place in the local botanical garden.

Unfortunately, there’s just one problem. Like many good stories that make up our narratives of the past, this little episode never happened. Manuscripts and letters show us clearly that it took much more than a single moment under the shade of a little apple tree for Newton to figure out gravity. In fact, it would be many years before his complete conception of gravity and its extensive and perplexing role in our universe would crystallize in his mind. It’s a great little story but history is more complicated than little stories often make it seem. So what did happen? How did Isaac Newton, a young man whose family lived on a modest farm, figure out the theory of universal gravity, a scientific development that left the world forever changed? The happy truth of the real history is that Newton’s discovery was even more amazing than the story of the apple falling from the tree implies.

But wait a minute: what could be more amazing than a young man discovering a fundamental force of nature while sitting under a tree? For starters, we have to recognize how foreign Newton’s ultimate idea about gravity was to philosophers, astronomers and mathematicians in the era of the Scientific Revolution. Newton provided an answer to a question that hadn’t even been asked yet. The problem with understanding the distant past is that we take our twenty-first century ideas and attitudes for granted. We think, for example, that the following is obvious: if the planets, like the Earth and Jupiter, regularly orbit the Sun, there must be something that causes them to follow their orbits. After all, if nothing caused them to orbit the Sun, they would fly off into deep space. That seems so obvious to us, it’s hard to imagine that for centuries, the world’s leading thinkers, from Aristotle to Ptolemy and onwards, did not have that idea at all. Instead, for many generations, leading philosophers and mathematicians thought this: the circle is a perfect mathematical form, and the planetary orbits are circular, so they are ever-lasting aspects of the natural world. To them, the orbits were so perfect that nothing caused them to occur. They simply were. The question of what caused the planetary orbits was not even on the table for astronomers in those days. Down on earth, apples fell from trees throughout history just as they do now. But philosophers and mathematicians didn’t have any reason to think that whatever causes apples to fall to the ground might somehow be connected to anything going on in the heavens. After all, the heavens were thought to be the home of everlasting motions, of perfect circles, and were therefore nothing like the constantly changing, messy world down below, where worms eat through apples as they rot on the ground.