The fight between Einstein and Bohr is a delightful story in history. Einstein, good at using his thought experiment crafted below method go violate uncertainty rule in QM

So here is Bohr’s comeback, but it’s more or so philosophical, hence later Bell finally came up with an idea/equation that can be experimentally verified.

Here is what Bell’s idea

Now use photon to experiment and theoretical reasoning/computation:

when theta is greater than 45 degree, Bell’s inequality is violated.