This problem assumes a pa
This problem assumes a pair of protons in close proximity with a total spin angular momentum equal to zero.  If the protons move in opposite directions, their spin angular momentum must remain equal and opposite.  Thus, if you measure one proton's spin angular momentum, you know the other's as well. It concludes that this knowledge of more than one mutually noncommuting observable of either proton is a violation of quantum mechanics.  An attempt to solve it resulted in Bell's Inequality Theorem, which proved unsuccessful.  FTP, name this paradox, devised in 1935 and named for Albert Einstein and two of his colleagues.
This problem assumes a pair of protons in close proximity with a total spin angular momentum equal to zero.  
EPR Paradox or Einstein Podolsky Rosen Paradox