At the end of the presented investigations, the various presentations of special relativity (SRT) available in the literature are discussed and evaluated
in brief form. For this purpose, first the two central preconditions "principle of relativity" and "constancy of the speed of light" are examined. To represent
the occurring range used in the literature, the possible representations were divided into "objective observation criterion" and "axiom". In recent publications
very often the axiomatic approach is chosen. The earlier presentations, e.g. of Einstein, were mostly using the objective observation concept.
The common interpretation of the SRT today includes the aspect that there can be no system of absolute rest. The chains of reasoning used in the literature
concerning this matter are quoted and evaluated. It is shown that none of these approaches can deliver a generally valid proof.
Einstein has chosen a top-down approach for the formulation of the SRT. For this purpose, the principle of relativity and the constant speed of light
were defined as basics and the Lorentz transformation and later also the relativistic mass increase were derived from them. Now, with the "modified
Lorentz theory", a bottom-up concept is presented where the relativity principle is the result; the validity was proved by a multitude of examples.
With free choice of the base system, both approaches are completely equivalent. However, the Theory of Special Relativity has the disadvantage that it
excludes the existence of a system of absolute rest in principle, but this can be integrated without problems into the modified Lorentz concept by a
simple choice of the base system. From today's point of view, it seems reasonable to use for it the system which is the basis for the uniform cosmic background
radiation in the universe. However, since up to now no experimental proof has succeeded, a decision cannot be made at present. In the context of this
elaboration a proposal was made, how an experiment could be arranged, which makes a clear decision possible concerning the different approaches (chapter 12.1).