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Gravitational redshift can be interpreted as a consequence of the equivalence principle (that gravitational effects are locally equivalent to inertial effects and the redshift is caused by the Doppler effect) [5] or as a consequence of the mass–energy equivalence and conservation of energy ('falling' photons gain energy), [6] [7] though there ...
Gravitational blueshift contributes to cosmic microwave background (CMB) anisotropy via the Sachs–Wolfe effect: when a gravitational well evolves while a photon is passing, the amount of blueshift on approach will differ from the amount of gravitational redshift as it leaves the region. [97]
The gravitational redshift of a light wave as it moves upwards against a gravitational field (caused by the yellow star below). Einstein predicted the gravitational redshift of light from the equivalence principle in 1907, and it was predicted that this effect might be measured in the spectral lines of a white dwarf star , which has a very high ...
Due to gravitational redshift, its image reddens over time as the object moves closer to the horizon. [6] In an expanding universe, the speed of expansion reaches — and even exceeds — the speed of light, preventing signals from traveling to some regions.
Gravitational redshift has been measured in the laboratory [65] and using astronomical observations. [66] Gravitational time dilation in the Earth's gravitational field has been measured numerous times using atomic clocks, [67] while ongoing validation is provided as a side effect of the operation of the Global Positioning System (GPS). [68]
The gravitational redshift of a light wave as it moves upwards against a gravitational field (caused by the yellow star below) The first new effect is the gravitational frequency shift of light. Consider two observers aboard an accelerating rocket-ship.
Gravitational redshift measurements provide a direct measure of LPI. Of the three hypotheses underlying the equivalence principle, LPI has been by far the least accurately determined. There has been considerable incentive, therefore, to improve on gravitational redshift measurements both in the laboratory and using astronomical observations. [11]
Gravitational waves are not easily detectable. When they reach the Earth, they have a small amplitude with strain approximately 10 −21, meaning that an extremely sensitive detector is needed, and that other sources of noise can overwhelm the signal. [93] Gravitational waves are expected to have frequencies 10 −16 Hz < f < 10 4 Hz. [94]