Measurement of Relativistic Time Dilatation using the Mössbauer Effect

THE Mössbauer effect allows of some of the most direct tests of certain simple relativistic predictions, and in this connexion we wish to report on the progress of some experiments similar in principle to those first reported by Hay, Schiffer, Cranshaw and Egelstaff^1,2. These authors measured the relativistic frequency shift between a cobalt-57 source of 14.4-keV γ-radiation, near the centre of a rotating disk, and a resonant iron-57 absorber around the periphery of the disk. On spinning the disk the resonance absorption was found to decrease, giving increases in transmission of up to 6 per cent. This was shown to correspond to a relative frequency shift the magnitude of which agreed, to within an accuracy of about 2 per cent, with that predicted by the relativistic expression (Δν/ν) = (v_a² - v_s²)/2c², where v_a and v_s are the velocities of the absorber and source. This expression may be obtained either in terms of the time dilatation of special relativity or in terms of the pseudo-gravitational potential difference between source and absorber.