Orbital stability and the quantum atomic spectrum from Stochastic Electrodynamics
High order terms in the electromagnetic multipole development expose a stabilizing mechanism for the atomic orbitals in the presence of the ZPF-background. Boyer and Puthoff set forward the idea that for the Bohr orbits in the hydrogen atom, radiation losses could be compensated by absorption from a background of zero point vacuum fluctuations. This balance is, on average over the orbit, a necessary condition for stationarity of the movement, and imposes a relation on the pair $R_{0}$ (orbital radius), $ω_{0}$ (orbital angular velocity). That relation is simply what we have for long known as angular momentum quantization. Taking into account the stochastic nature of the ZPF, we have to realize that nothing, however, has been said yet on how could this balance be attained on a quasi instantaneous basis, in other words, how could the orbit accommodate the instantaneous excess or defect of energy so as to keep constant the (at least average) values of its parameters ($R_{0}$, $ω_{0}$). Using classical electromagnetism, we explore some high order interactions between realistic particles, exposing a mechanism (a feedback loop between variables) that makes that stability possible. Puthoff's work led necessarily to the quantization of angular momentum: "if stable orbits exist... then their angular momentum must be quantized"; now, too, we are able to do a much stronger statement: "the equations of the system, in the presence of ZPF background, lead necessarily to a discrete set of stable orbits".