Hi there, I'm having a bit of trouble with this problem. The book tells me that I have a particle in the gorund state of a box of length L. Then suddenly the box expands to twice it's size (symmetrically), leaving the wave function undisturbed. I supposed to show that the probability of finding the particle inm the ground state in the new box is (8/3pi)^2. I'm not quite shure what to do. I know that the wave function is S(x)= (2/L)^2 sin(n*pi*x/L) for n=even =(2/L)^2 cos(n*pi*x/L) for n=odd The first thing I thought was that the probabilty is just(sorry I'm new to the forum and don't know how to write integral sign here) P=int from 0-2L of S*(x)S(x) dx and I was just getting 1 but then realized, of course I'm just going to get on, I'm just finding the probability that the particle will be somewhere in the box which sure as hell should be 1 right? So I'm not quite sure how to find the probabilty of finding something in the ground state (or any state for that matter). Perhaps you could just steer me in the right direction without actually giving me the answer? Any help would be greatly appreciated.