How does gravity affect light in general relativity?

In general relativity, gravity can bend light, causing it to follow a curved path rather than a straight line.

In the theory of general relativity, proposed by Albert Einstein, gravity is not seen as a force but as a curvature of space-time caused by mass and energy. This curvature affects the path of objects moving through it, including light. This is a significant departure from Newtonian physics, where light, having no mass, would not be affected by gravity.

When light passes near a massive object, the space-time around the object is curved due to its gravity. This curvature causes the light to follow a curved path, a phenomenon known as gravitational lensing. This effect has been observed in numerous astronomical studies, where light from distant stars or galaxies is bent as it passes near a massive object, causing the light source to appear distorted or in a different position than it actually is.

The bending of light by gravity can also lead to an effect known as gravitational redshift. This occurs when light or other electromagnetic radiation is emitted from a source in a strong gravitational field. The energy of the light is reduced by the gravitational field, causing the light to shift towards the red end of the spectrum. This effect has been confirmed by experiments and is used in technologies such as GPS, which need to account for the gravitational redshift caused by the Earth's gravity.

In extreme cases, such as around a black hole, the curvature of space-time can be so intense that light cannot escape, leading to the formation of an event horizon. This is the boundary around a black hole beyond which nothing, not even light, can escape the gravitational pull.

In summary, general relativity predicts that gravity can affect light by causing it to follow a curved path, leading to phenomena such as gravitational lensing and gravitational redshift. These predictions have been confirmed by numerous experiments and observations, providing strong support for Einstein's theory.