Proof of state "collapse? Maybe I don't even have the terminology correct for this... I'm a quantum physics noob :) My question is this: take the EPR experiment for example. What I've heard is that each electron in the pair is in an indefinite state of spin (either + or - with respect to a certain axis). Supposedly, when one is measured, it "collapses" into a definite state of spin (say + with respect to the Z axis). What proof is there that the electron wasn't always definitely spinning +1/2 with respect to the Z-axis. Why do physicists conclude that it was indefinite until the spin was measured?