Quantum theory is very strange. No act is wholly sure. Everything works by probabilities, described by a wave function. But what is a wavefunction? One theory is that every possibility is in fact a real world of sorts. This is the Many Worlds interpretation of Hugh Everett—and what it claims boggles the brain. You can’t…

Quantum theory may be weird—superposition and entanglement of particles that in our normal world would make no sense—but quantum theory is truly how the microworld works. What does all this weirdness mean? How to go from microworld weirdness to macroworld normalcy? Will we ever make sense out of quantum mechanics?