Another famous experiment that supports General Relativity is the deflection of light by the sun. Previous theories of gravity held that light would not be affected by gravity since it has no mass. However, Einstein thought otherwise. His Equivalence Principle predicts that light will curve in the presence of a gravitational field. The principle states that the effects of a gravitational field are the same as the effects of those in an accelerated frame of reference. Gravity would cause a person in a gravitational field to accelerate with g, the acceleration due to gravity. However, if the person’s frame of reference were to be accelerated at g when they were not in a gravitational field, all of the effects on them would be “equivalent” to how they would be in a gravitational field. Thus, in essence, a gravitational field can be created. Now, if a person was in the accelerating frame of reference and was to shine a beam of light out into an inertial reference frame of space, it would appear as though the light is curving downward since the particles of light emitted earlier would be lower than those emitted as the acceleration proceeds higher. And since this accelerated reference frame is equivalent to a gravitational field, the same thing would apparently happen in a gravitational field; light would curve. But according to classical physics, the force due to gravity is mass times acceleration… so how would light be affected since it has zero mass? And the curvature of spacetime explains this problem perfectly since light doesn’t need mass to follow the curve of spacetime. Thus, according to Einstein, light is deflected by gravity.