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.