Einstein deduced that gravity will bend light by imagining a flashlight shining in a lift that is accelerating upwards (Figure 5.10). As the lift goes up, the light will curve relative to it, so if gravity equates to acceleration, the sun’s gravity should bend the light passing by it, and astronomers observe that it does, but why?
Einstein’s explanation was that light passing the sun bends because, from its perspective, it is going in a straight line, just as light in the lift is. The sun then doesn’t pull the light towards itself, but changes the space around to make it bend.
Gravity as a processing gradient acts the same way, by changing the distribution around light not the light itself. It works like refraction (3.6.2), where light is bent by water because it spreads more slowly in it. It changes direction because if one side of a spreading wave slows down, it skews that way. Light then refracts in water because it is a denser medium, not because a force acts upon it..
Likewise, the gravity gradient of the sun slows down the spread of light towards it, which bends it. A photon of light is a spreading wave, so if space closer to the sun has a denser field, it bends that way. Light has no mass for gravity to attract but processing waves still bend when processing increases, just as light bends when entering water that slows it down.
This model then supports relativity, that gravity bends light by changing the space around it, but the quantum field not space causes it, so the gravity gradient bends light by refraction.