I have a few questions: What’s that formula called? The correlation formula? Is cos^2 the formula for only particles with spin=1 like photons? If so, what’s used for electrons (1/2 spin). Also, cos^2 seams funny to me since it returns 1 for 0 and 180 degrees. Zero I can understand since you should expect complete correlation if you measure from the same angle each time. But I would expect something like a -1 correlation from the opposite side. In that case, if one measurement is spin up the other is spin down.