Pound-Rebka experiment

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The Pound-Rebka experiment is a well known experiment in general relativity. It was the last of the classical tests of general relativity proposed by Albert Einstein to be verified, in 1959. It is a gravitational redshift experiment, which tests the redshift of light moving in a gravitational field, or, equivalently, a test of the general relativity prediction that clocks should run at different rates at different places in a gravitational field. It is considered to be the experiment that ushered in an era of precision tests of general relativity.

The test was carried out at Harvard University's Jefferson laboratory. The frequency of photons emitted by two iron (Fe⁵⁷) sources were compared at a fixed location. They were located twenty-two meters apart, one on the roof of the building and the other in the basement. These sources were chosen because the frequency of the photons they emitted were particularly tightly defined by the Mössbauer effect.

The result confirmed that the predictions of general relativity were borne out at the 10% level. This was later improved to better than the 1% level by Pound and Snider.

References

R. V. Pound and G. A. Rebka Jr., Gravitational Red-Shift in Nuclear Resonance, Phys. Rev. Lett. 3, 439 (1959). [link] This paper proposed the experiment.
R. V. Pound and G. A. Rebka Jr., Apparent weight of photons, Phys. Rev. Lett. 4, 337 (1960). [link] This paper was the first measurement.
R. V. Pound and J. L. Snider, Effect of Gravity on Nuclear Resonance, Phys. Rev. Lett. 13, 539 (1964). [link] The more accurate measurement with Snider.
Physical Review focus story [link].
R. F. C. Vessot, M. W. Levine, E. M. Mattison, E. L. Blomberg, T. E. Hoffman, G. U. Nystrom, B. F. Farrel, R. Decher, P. B. Eby, C. R. Baugher, J. W. Watts, D. L. Teuber and F. D. Wills, "Test of Relativistic Gravitation with a Space-Borne Hydrogen Maser", Phys. Rev. Lett. 45, 2081-2084 (1980).

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