Quantum physics governs the universe on the tiniest of scales. At this scale, objects pop in and out of existence, and things over here can affect others over there instantaneously—without anything crossing the space between them. How can the rules of the quantum world, which work so well to describe the behavior of individual atoms and their components, conflict so dramatically with the everyday rules that govern people, planets, and galaxies? Quantum mechanics may be counterintuitive, but it’s one of the most successful theories in the history of science, making predictions that have been repeatedly confirmed. It has also launched the technological advances at the heart of modern life, like computers and cell phones. But today, even with such profound successes, the debate still rages over what quantum mechanics implies for the true nature of reality.