The Wonderful World of Hammar’s Experiment

In a rather terse note, published in 1935, G.W. Hammar explained his brilliant experiment destined to put away, once and for all, the notion of “aether entrainment”. Certain physicists, such as Dayton Miller, insisted that the null result of the Michelson-Morley experiment and its repetitions could be explained in the framework of Galilean relativity as an artifact of the lab (and the interferometers) “dragging” with them the medium (“aether”) necessary for light propagation. Today, this very clever experiment is almost forgotten, taking a backseat to the more famous pillars of special relativity tests: Michelson-Morley, Kennedy-Thorndike and Ives-Stilwell. Maybe the stark parsimony of Hammar’s note (one page, no figures, no calculations) is the reason for overlooking this wonderful experiment.