1. The problem statement, all variables and given/known data A particle is in the ground state of the harmonic oscillator with classical frequency w, when suddenly the spring constant quadruples, so w'=2w, without initially changing the wave function. What is the probability that a measurement of the energy would still return the value hw/2? What is the probability of getting hw? 2. Relevant equations 3. The attempt at a solution I know that |c_n|^2 tell us the probability that a measurement will give energy E_n. But in this case i kind of don't know where to start. So, if you could give me some direction, i would appreciate it.