The wiki page https://en.wikipedia.org/wiki/Bell's theorem states the following which I agree with: Suppose the two particles are perfectly anti-correlated—in the sense that whenever both measured in the same direction, one gets identically opposite outcomes, when both measured in opposite directions they always give the same outcome. My question is whether photons really act in this manner. If you measure a pair of correlated vertical photons along their vertical axis in one location and horizontal axis in another location you will get perfect anti-correlation for each photon pair. But, if you measure vertical photons off the vertical axis (say 45 degrees one way and 45 degrees off the other way), you only get a statistical correlation for groups of photon pairs. Experiments are unable to show the above quote is true for individual photon pairs when measured off their basis vectors. Or do they? Why is this assumption made?