The unification of gravitation and quantum physics is a still unsolved problem. A convincing solution is not in sight and a simple solution is virtually excluded. It seems that modern physics entered into a dead end here. Most of the proposals for solution try to enforce a breakthrough in the pursued direction with ever more complexer approaches. However, there is a path to circumvent these difficulties. By abandoning one of the prerequisites of the General RelativityTheory, a new degree of freedom is won in return. With that, a theory of gravitation can be formulated, wherein the unification of the forces is possible. In the following, we start with the assumption, that gravitation can be understood as secondary effect of electromagnetic interaction. In doing so, the unification of the forces is taken as a prerequisite and is imposed as a new basic postulate. The covariance principle, a pillar of the General Relativity Theory, is abandoned instead. Under these assumptions, a consistent model of gravitation can be established and justified. It describes gravitation with a variable index of refraction of the vacuumand leads, as a consequence, to a system of variable scales. In weak gravitational fields, the theory agrees well with the General Relativity Theory. In strong fields, however, fundamental differences arise.