In this image, we can see the bending of light by gravity. Suppose I put a big glass (it almost has zero weight) of considerable thickness near sun (near the split of the two light paths) which will refract light coming from the star and will change the direction of light.
We can predict the path of light in first case using general relativity. But to predict path of light in the second case, we need general relativity and electromagnetism.
I don't want to use geometrical optics, I want answer using Electromagnetism and General relativity.
Now my question is, to predict path of light in second case do we need Electromagnetism (or QFT) in curved spacetime or do we need to unify Electromagnetism (or QFT) with General relativity into one single theory to predict the path of light?