I thought I understood it. The two particles have opposite spin and when you observe one the wave function collapses and both are known. But not sure how this is really "action at a distance" as you cannot do anything with the knowledge of the spin of the remote particle. In fact it seems no different than this macro situation: I put a black ball and white ball in separate boxes without looking. The wave function of each is 50/50. One box is taken to the other side of the world. Now I open the first box. I see it is white, so the wave function of the other box collapses to black. I cannot be the only person to have thought of this, but cannot find an expanation anywhere?