The philoshophy is confusing me. If i understand correctly, it comes down to the following: when a pion decays (which decays to an electron and positron), we can make a measurement of the spin of both resulting particles. If I measure the spin in the z-direction of the electron, I instantly know the spin in the z-direction of the positron. According to EPR, there are two possibilities: * measuring the spin on the electron the result instantly travels to the positron : ***spooky action at a distance -> impossible ***or the spin in this direction is an element of 'physical reality' However, the spin in 2 directions of a particle can't be simultaneously known (this would violate the heisenberg uncertainty principle), therefore quantum theory is incomplete. Is the line of thought correct? If we first measure the spin in the z-direction on 1 particle, then we can't say anything about the spin in the x-direction: it can still be two values. So in other words, the value the spin in the x-direction can have, depends on what we measure on the other particle. If we measure the x-direction of the electron, we KNOW what the spin in the x-direction of the positron will be. But if we measure the spin in the x-direction of the electron, we don't know what the spin in the z-direction will be. This is the paradox, right?