# eli5 If the photons in light have no mass, why are they refracted by high gravity around stars and black holes in vaccuum, or mediums like water, glass and air?

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eli5 If the photons in light have no mass, why are they refracted by high gravity around stars and black holes in vaccuum, or mediums like water, glass and air?

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for gravity, light follows spacetime and it’s curvature.

For mediums like glass and water, the speed of light becomes smaller. This is in fact due to light acquiring mass in those media.

Because Newton was wrong.

Newton derived the force of gravity using the formula of (G*m1*m2)/(d^2). At that formula works for basic calculations. But he was wrong.

Einstein proved that gravity isn’t a force attracting objects of mass but rather a warping of space time as a result of mass. Gravity functions because mass bends space. As a result light is effected by gravity because light travels in a straight line through curved space and thus follows the curve.