The metric was published by István Ozsváth and Engelbert Schücking in 1962.
This stands in contradiction to a claimed strong Mach principle, which would forbid a vacuum solution from being anything but Minkowski without singularities, where the singularities are to be construed as mass as in the Schwarzschild metric.
, define the following tetrad: It is straightforward to verify that e(0) is timelike, e(1), e(2), e(3) are spacelike, that they are all orthogonal, and that there are no singularities.
That is sufficient to conclude that it is a vacuum solution distinct from Minkowski spacetime.
Under a suitable coordinate transformation, the metric can be rewritten as and is therefore an example of a pp-wave spacetime.