Question

Why is it said that dark matter or anti gravity can curve light?

Answer 1

Gravity cannot bend light. The observation is correct and passing light rays are a bit curved towards Stars but it is not because of Gravity. Medium Density at Stars is a bit higher than the normal vacuum and hence light rays are bent a bit due to refraction.
That phenomenon seems to have misinterpreted by the Scientists of the late century.It is not Gravity of Dark Mater who centralise Matter in a Contracting Galaxy. And also, it is not Gravitywho decentralise Matter in an Expanding Galaxy.

We are living in an expanding galaxy and we are not orbiting the Galactic Center just as planets orbit round Sun. Instead we are pushed spiral way outgradually with all other solar systems in the Milky Way by the galactic vortex.Theory of Spherical Vortex and due vortex dynamics has to be addressed by the Scientists of the 21st century or unless the phenomenon how Dark Matterinteracts in creation of Galaxies could never be described realistically in certainty.