Say we have two electrons in a spin entangled state about the z-axis |01> + |10>. One electron travels off to our left, the other to our right. The right electron passes through an inhomogeneous magnetic field with gradient solely in the z direction (Stern-Gerlach type), and subsequently passes through an appropriately placed plate with 2 slits, and then to a screen where its position can be measured. Basically a Stern-Gerlach magnet followed by an appropriately placed double slit experiment. If we do NOT measure the spin of either electron then isn't it true that, after repeating this experiment several times, the right electron will show an interference pattern on the screen? If we DO measure the spin of the left electron then isn't it true that we will not see the interference pattern (since we know the spin and therefore deflection and which-slit info for the right electron)? Evidentially there is something wrong with the argument above because, if it were true, then it would be a conceptually trivial way to communicate information faster than c -- someone at a (theoretically) arbitrary distance away can decide to measure the spin of the left electron or not, and another person at the screen after the double slit can see what the other person did (essentially a binary signal). Question: What is wrong with the conclusions I'm making about the above experiment? PS: I asked this question on this or another form a long time ago, but I'm asking again because the only answers I received were things like "it's impossible to transfer info faster than c." What I am wanting to know is exactly where/why the above experiment breaks down.