Qubits don’t plan ahead

In the 1999 movie Mystery Men, one character has the superpower of making himself invisible, but only when no one is looking. For most people, this raises the question, “What good is that superpower?” For me, it raises an entirely different question: “Since no one can witness this character disappearing, is there a way to find out if the character actually disappears?” Can you verify or disprove the existence of something that, by its very nature, is unobservable? Of course, the knee-jerk answer to this question is, “No, you can’t.”

But, in 1964, physicist John Bell wrote a paper [4] in which he proposed an experiment that could put an end to hidden-variable theories. Then, in 1982, the team of Alain Aspect, Philippe Grangier, and Gérard Roger performed a convincing version of Bell’s experiment [5].

Disclaimer

This section introduces the theory about the nature of entanglement. If this...