1. The problem statement, all variables and given/known data Currently im doing a question where its asked me to show that the probability per unit length of finding a particle is independent of space and time, and is just a constant. 2. Relevant equations 3. The attempt at a solution The plane wave state ive been given to solve is: [tex]\psi(x) = exp(ikx)[/tex] I separated the variables of the SE and got a formula for [tex]\Psi(x,t) = \psi(x)exp(-iEt/hbar)[/tex] Assume lowercase psi here is constant, i cant be bothered to write it out :P Obviously the probability per unit length is the square of the modulus of this function. For some reason it shows in my notes that when you do this, the exponential part of the wavefunction dissapears when you do the square of the modulus, so you are just left with the square of the modulus of psi. Now that would leave me with the answer, as ive already worked out psi is a constant independent of x, but I cant figure out why the exponential part dissapears. Is it just some basic maths that im not getting here?