The increase in wavelength (shift toward red) of electromagnetic radiation as it climbs out of a gravitational field, caused by gravitational time dilation. Light loses energy as it escapes from massive objects, making it appear redder to distant observers.
Combines 'gravitational' (Latin 'gravitas') with 'redshift' (coined in early 20th century astronomy from the shift toward the red end of the spectrum). Einstein predicted this effect in 1907, and it was first observed in laboratory tests in 1959 by Pound and Rebka.
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