This thesis develops a new theory combining the beam-plasma instability and IGMF in one picture. Recently, it was observed that the expected cascade emission of gamma rays in the TeV range from some distant blazars is not seen in their spectra. The underlying physical processes are well known, and a failure of the model predictions would shake the foundations of modern physics unless a credible explanation for this failure is found. One could argue that a femto-Gauss strong magnetic field in the cosmic voids would disperse the cascade emission, although the question remains as to how...