Gravitational redshift is a phenomenon predicted by general relativity, where light or electromagnetic radiation loses energy as it escapes from a strong gravitational field—such as near a black hole or a massive star. This loss of energy causes the light’s wavelength to increase, shifting it toward the red end of the spectrum.
The effect occurs because gravity affects not just the path of light, but also the rate at which time flows. Clocks tick more slowly in stronger gravitational fields. As a result, light emitted from a region deeper in a gravitational well appears lower in frequency—or redshifted—when observed from a region with weaker gravity.
Gravitational redshift has been confirmed experimentally, such as in the Pound-Rebka experiment and by observing light from white dwarfs and the edges of black holes. It plays a crucial role in GPS satellite calibration, astrophysical observations, and in understanding how gravity influences time and light.