The success of this experiment owed much to the care of Pound and Rebka in preparing the source. In the early 60's physicists Pound, Rebka,and Snyder at the Jefferson Physical Laboratory at Harvard measured the shift to within 1% of the predicted shift.īy just using the expression for gravitational potential energy near the Earth, and using the m in the relativistic energy expression, the gain in energy for a photon which falls distance h isĬomparing the energy shifts on the upward and downward paths gives a predicted difference Is just 4.92 x 10 -15, but the Mossbauer effect with the 14.4 keV gamma ray from iron-57 has a high enough resolution to detect that difference. In just 22.6 meters, the fractional gravitational red shift given by Gravity and the photonApplications: Harvard tower experiment This form made practical some laboratory experiments using nuclear sources with the gravitational term expressed in terms of the gravitational acceleration g on the Earth's surface.įor the Harvard Tower experiment, the shifts in radiation frequency in the gravitational field were related to the relativistic doppler shift experienced from an accelerating light source. Where υ 0 represents a photon emitted closer to the gravitational mass. To express the frequency shift between two locations as For weak gravitational fields or small displacements in a gravity field, one can make use of the approximation: Which is valid for even strong gravitational fields. The result of general relativity using the Schwarzschild metric is If observed at a great distance, we could denote the observed frequency as υ ∞. If a photon of frequency υ 0 is emitted radially outward from the surface of a gravitational mass M, then the photon energy observed at a distance from the mass will be observed to be lower, or "red shifted". General Relativity Gravitational Red ShiftĪccording to the principle of equivalence from general relativity,any frequency shift which can be shown to arise from acceleration of a radiating source could also be produced by the appropriate gravitational field.
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