Why Light Bends Because of Gravity If It Has No Mass?

Gravity affects light not because light has mass or not, but because gravity disturbs the fabric of spacetime itself. According to Einstein's theory of general relativity, massive objects like stars or planets, even mountains to some extent, bend the space around them.

Imagine space is a flexible, three-dimensional rubber grid. For example: planets like Earth or Jupiter, bend and create an impression in this grid. This curvature makes smaller bodies, their moons, follow the planets around in a circle.

Near massive objects, like a star or a black hole, spacetime is more curved, and objects move along more curved trajectories like an elongated ellipse.

Light, like moons and planets, also follows the curvature of this warped spacetime, causing it to appear as if it's being "bent" by gravity.

Does light have mass?

No, light does not have mass. Light consists of massless particles called photons.

The masslessness of photons is a fundamental property that contributes to some unique characteristics, such as traveling at the speed of light and having no electric charge.

Has general relativity been tested?

Albert Einstein proposed his theory of gravity, known as the theory of general relativity, in 1915 in a sequence of four papers. Time and time again the theory has been proven right, for instance in explaining the rotation of Mercury's orbit.

That's why general relativity is extensively used in modern technological applications such as atomic clocks, GPS, etc.