What does cause refraction of light in vacuum?

[swansont]

There is no refractive index, because it is not refraction, as you have been told several times.

[DimaMazin]

There is no refractive index, because it is not refraction, as you have been told several times.

Does variable deflective index exist there?

[swansont]

What is a variable deflective index?

[DimaMazin]

What is a variable deflective index?

Can we define deflection angle on short part of photon path in gravitational field?

[Strange]

Can we define deflection angle on short part of photon path in gravitational field?

 

See post #6.

[DimaMazin]

 

See post #6.

I think deflection angle of photon approaching(under some angle) to mass on short part of the photon path = r_s/r₂ - r_s/r₁

_{Can we define the travel time of photon on the part of photon path in seconds of far observer?}