These questions are rather like the one mahela007 just asked, but are perhaps a little more specific. I have never clearly understood how the Planck hypothesis (E=nhf for the oscillators of a black body) fits into the later quantum theory of Schrodinger, Heisenberg, et al. Specifically, 1. Since the year 1900 was before the work of Rutherford and Bohr produced a model of the atom that is similar to the familiar, more modern one (massive positive charges surrounded by light, negative ones), what exactly did Planck think was oscillating at frequency f? 2. Solving the Schrodinger equation for a quantum harmonic oscillator yields descrete energy levels separated by nhf. Is this why the Planck hypothesis works? That is, are the restoring forces between atoms/molecules in a solid body Hooke-like (directly proportional to their displacement from an equilibrium position)? Thanks.