Test Result: the light speed is constant to better than 1.5cm/sec in all directions.
(Measurement uses one-directional test, NOT round-trip test like Michelson-Morley did)
The light speed measurement was performed in 1964 -1969 at the University of Birmingham, England sponsored by The Royal Society. The experiment utilized the Mössbauer effect and a high-speed ultracentrifuge specifically built for this application.
The original work was written up in 1968 by Ekhard Preikschat for his Ph.D.Thesis, with the work done jointly with and supervised by George R. Isaak. It established a low limit (on any anisotropy of light propagation) of 2.0 +/- 5.2 cm/sec.
Additional work done in 1969 by the two scientists further increased the accuracy of this test to establish a new low limit on the “aether drift” of 1.5 cm/sec. This result is the most accurate one-way measurement of light propagation ever conducted and as such is one of the most critical tests of the special theory of relativity. The experiment involves nuclear decay processes, gravitational forces and thus is also partly a test of the general theory of relativity.
