Does light have mass ; If not, why is it effected by gravity?

This is a magnificent inquiry…

On the principal occasion, it's replied by Einstein's hypothesis of general relativity. It's likewise fascinating because there is some sense wherein light has "mass" we would say, light appears to go in straight lines, unaffected by gravity. Obviously, light can twist when it goes through the point of interaction between two media - consider light refracting as passes from air into water, which is the peculiarity that makes a straw in a glass of water seem crimped at the point0 interaction. In any case, that twisting isn't gravitational; it's electromagnetic.

In any case, light curves while going around gigantic bodies like neutron stars and dark openings. This is clarified by Einstein's hypothesis of general relativity.

We are for the most part acquainted with huge articles being affected by gravity. For example, consider a planet circling the sun. As the planet moves, a centripetal power follows up on it, which bends the movement. Without gravity, the planet would go in an orderly fashion. General relativity places an alternate point of view on the circumstance. Rather than portraying the item as moving along a bend in a level spacetime, the article is depicted as moving along exceptional "lines" in a bent spacetime. The bends are a result of attractive energy. The spacetime bends are called geodesics, and they sum up the idea of straight lines to bent spacetime.

Light likewise goes along geodesics (called invalid geodesics), thus ways of light are additionally bent by gravitational power, despite the light not having any mass.

There is some real state-of-the-art research connected with this response. There is motivation to accept that light itself bends spacetime similarly to that enormous items do. This is here and there alluded to as the self-attraction of light. The thought is that an electromagnetic wave has a non-zero energy-force tensor, and ought to hence bend spacetime, but in a little and odd way. Thusly, the conditions of general relativity suggest that the spacetime arch made by spreading light should impact the engendering of that light itself.