“Instead, let’s consider an equal superposition of two basis states, one with both spins up, and the other with both spins down: If Alice measures her spin along the vertical axis, she has a fifty-fifty chance of getting spin-up or spin-down, and likewise for Bob. The difference now is that if we learn Alice’s outcome before Bob does his measurement, we know what Bob will see with 100 percent confidence—he’s going to see the same thing that Alice did. In the language of textbook quantum mechanics, Alice’s measurement collapses the wave function onto one of the two basis states, leaving Bob with a deterministic outcome. (In Many-Worlds language, Alice’s measurement branches the wave function, creating two different Bobs, each of whom will get a certain outcome.) That’s entanglement in action.”