The Michelson-Morley experiment and the cosmic velocity of the Earth

Abstract

The Michelson-Morley experiment was designed to detect the relative motion of the Earth with respect to a preferred reference frame, the ether, by measuring the fringe shifts in an optical interferometer. These shifts, that should have been proportional to the square of the Earth's velocity, were found to be much smaller than expected. As a consequence, that experiment was taken as an evidence that there is no ether and, as such, played a crucial role for deciding between Lorentzian Relativity and Einstein's Special Relativity. However, according to some authors, the observed Earth's velocity was not negligibly small. To provide an independent check, we have re-analyzed the fringe shifts observed in each of the six different sessions of the Michelson-Morley experiment. They are consistent with a non-zero observable Earth's velocity $v_{\rm obs} = 8.4 \pm 0.5 km/s$. Assuming the existence of a preferred reference frame and using Lorentz transformations, this $v_{\rm obs}$ corresponds to a real velocity, in the plane of the interferometer, $v_{\rm earth} = 201 \pm 12 km/s$. This value, which is remarkably consistent with 1932 Miller's cosmic solution, suggests that the magnitude of the fringe shifts is determined by the typical velocity of the solar system within our galaxy. This conclusion is consistent with the results of all classical experiments (Morley-Miller, Illingworth, Joos, Michelson-Pease-Pearson,...) and with the existing data from present-day experiments.