Gehrcke believes that the Special Theory of Relativity contains a logical contradiction:

Of the two clocks, where one remains on Earth and the other is sent into space, it can be argued that each clock is moving with respect to the other. Thus each clock is slow relative to the other.

On the other hand, Thirring argues that the difference due to the fact that one clock is accelerated with respect to the other can be explained without contradiction within the framework of the general theory of relativity and thus is described without contradiction.