<<Mentor note: This post and its answers were moved from this thread.>> How do you reconcile a superposition of flavors, with different masses, with conservation of energy and of momentum? Say the rest masses of three flavors are known, and you want to measure the velocity of the neutrinos, and sometimes you get flavor #1, and sometimes flavor #2, and sometimes you get flavor #3. Conservation of energy will say one velocity, but conservation of momentum will require a different velocity. Regardless of what you are measuring, it would seem that you cannot reconcile conservation of energy with conservation of momentum. I reckon we don't see such mixing in electrons and muons and taus because of the greater difference in rest mass, but that is only a matter of degree, not fundamental.