Hey. Trying to wrap my head around this maths. And given that the wave function is a superposition of a bunch of stationary states, each with a different coefficient. The coefficients squared added add to one. And the probability of finding the particle in a given state is cn^2. I know all of this and I know that if you observe the particle you will find it in one of the stationary states. But is there anything in the maths which ensures you cannot measure the En to be say the E=E1+E2, why can't you measure energies in between, is there any mathematical rule which prohibits this. This still just rattles my brain. Thanks.