We think of gravity as a simple "discovery," but for Isaac Newton, it was a terrifying realization that shattered the ancient world. Here is how a lonely genius decoded the invisible force that holds reality together—and nearly lost his mind doing it.

The story of the falling apple is famous, but the truth is much darker. Isaac Newton was a recluse, obsessed with alchemy and biblical prophecy, who happened to rewrite the laws of physics during a plague lockdown.

His book, the Principia Mat...