The effect was first described by Einstein in 1907, eight years before his publication of the full theory of relativity. Gravitational redshift can be interpreted as a consequence of the equivalence principle (that gravity and acceleration are equivalent and the redshift is caused by the Doppler effect) or as a consequence of the mass-energy equivalence ('falling' photons gain energy), though there are numerous subtleties that complicate a rigorous derivation.
Light escaping from the surface of the sun was predicted by Einstein in 1911 to be redshifted by roughly 2 ppm or 2 × 10−6.
The first accurate measurement of the gravitational redshift of a white dwarf was done by Popper in 1954, measuring a 21 km/s gravitational redshift of 40 Eridani B.
Such an effect was verified in the 1959 Pound–Rebka experiment.
Independent analyses by the GRAVITY collaboration (led by Reinhard Genzel) and the KECK/UCLA Galactic Center Group (led by Andrea Ghez) revealed a combined transverse Doppler and gravitational redshift up to 200 km/s/c, in agreement with general relativity predictions. ===Terrestrial tests=== The effect is now considered to have been definitively verified by the experiments of Pound, Rebka and Snider between 1959 and 1965.
The Pound–Rebka experiment of 1959 measured the gravitational redshift in spectral lines using a terrestrial 57Fe gamma source over a vertical height of 22.5 metres.
Brault, a graduate student of Robert Dicke at Princeton University, measured the gravitational redshift of the sun using optical methods in 1962.
Independent analyses by the GRAVITY collaboration (led by Reinhard Genzel) and the KECK/UCLA Galactic Center Group (led by Andrea Ghez) revealed a combined transverse Doppler and gravitational redshift up to 200 km/s/c, in agreement with general relativity predictions. ===Terrestrial tests=== The effect is now considered to have been definitively verified by the experiments of Pound, Rebka and Snider between 1959 and 1965.
The accuracy of the gamma-ray measurements was typically 1%. An improved experiment was done by Pound and Snider in 1965, with an accuracy better than the 1% level. A very accurate gravitational redshift experiment was performed in 1976, where a
in 1971, obtaining the value for the gravitational redshift of 89±19 km/s, with more accurate measurements by the Hubble Space Telescope, showing 80.4±4.8 km/s. James W.
The accuracy of the gamma-ray measurements was typically 1%. An improved experiment was done by Pound and Snider in 1965, with an accuracy better than the 1% level. A very accurate gravitational redshift experiment was performed in 1976, where a
In 2020, a team of scientists published the most accurate measurement of the solar gravitational redshift so far, made by analyzing Fe spectral lines in sunlight reflected by the moon; their measurement of a mean global 638 ± 6 m/s lineshift is in agreement with the theoretical value of 633.1 m/s.
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