First: Hello all. Theres a very important equation in non-relativistic quantum mechanic called schrödinger equation. I'm sure you know it. I searched for it in this forum but couldn't find what i want to find. I attached a file with this equation. And now my questions: I know the wave function psi(x,t) but psi(x,y,z,t)? Someone know an internet site that explains how it comes to this psi(x,y,z,t)? Or can someone explain me that? Whats the meaning of this driangle? I guess it's called nabla. Rest is clear if i am right. I know the basics of physics (compton effect, photoelectric effect, ...) but what do I need indeed to derive the schrödinger equation? Thanks for your answers.