Six Impossible Things: The Mystery of the Quantum World

by John Gribbin

“Reality” is the idea that there is a real world that exists whether or not anyone is looking at it, or measuring it. Because of the probabilistic nature of the quantum world, Bell’s proposed experiment would need to involve measurements of large numbers of pairs of particles (such as electrons or photons) passing through the apparatus. The hypothetical experiment was designed in such a way that after a large number of runs, two sets of measurements would be produced. If one set of numbers was greater than the other, it would prove that the assumption of local reality is valid. This ratio became known as Bell’s Inequality, and the package of ideas as Bell’s Theorem. But if the other set of numbers was greater, Bell’s Inequality would be violated, which would mean that the assumption of local reality was incorrect. If quantum mechanics is correct, Bell’s Inequality must be violated. You can have a real world with spooky action at a distance. Or you can have locality, at the cost of saying that nothing is real unless it is observed.