One day in the early 1660s, Isaac Newton spent a rare few hours outside, at the annual market near his college in Cambridge, England. He bought a toy—a prism, a piece of glass cut at precise angles. Though he had next to no money, the prism was so cool he bought another one.

He was not yet Isaac Newton the greatest scientist ever. He was merely an unpopular, solitary, brilliant college student.

Then an epidemic of bubonic plague broke out in England, as happened every so often. The only way to avoid catching it was to avoid other people—not a problem for the unsociable Newton. In 1666, at age 24, Newton left college to wait out the plague in his mother’s farmhouse,