Abstract
In this paper we will briefly discuss several examples of results, from the Big Bang to galactic sources, obtained in different frequency regions by many space-- and ground--based experiments. We will remark the fundamental problems born from a comparison of experimental multifrequency results and theories. We will discuss also the importance of having a network of robotic telescopes that can provide long term optical monitoring of different classes of cosmic sources for providing fundamental data for a progress in understanding many problems still open. The results selected are biased by our knowledge and feelings and extend over several decades, starting from the 1970's, when the space experiments opened practically all the windows for investigating the Universe, up to-date. We discussed about this topic many times (e.g. on the review paper "The impact of the space experiments on our knowledge of the physics of the Universe" (Giovannelli & Sabau-Graziati, 2004) and subsequent revisions (e.g. Giovannelli & Sabau-Graziati, 2012a).
