Recently I argued that Yang's pure-space equations must be supplemented by restrictions on the class of allowable space-times. I now consider time-dependent solutions of the pure-space equations and prove the violation of Birkhoff's theorem. Time-dependent spherically symmetric solutions are displayed, as well as solutions representing plane gravitational waves. The suggestion is made that pure spaces are unphysical and Yang's theory requires the explicit presence of a source in vacuum, in contrast to general relativity.

• Received 7 January 1976

DOI:https://doi.org/10.1103/PhysRevLett.37.961