Normal matter interacts with light through electromagnetic interactions. This interaction occurs because normal matter is composed of particles called atoms, which consist of a positively charged nucleus (made up of protons and neutrons) surrounded by negatively charged electrons. When light, which is an electromagnetic wave, passes through normal matter, the electric field component of the light wave exerts a force on the charged particles in the atoms. This force causes the electrons to oscillate, absorbing and re-emitting the light, which gives rise to various phenomena like reflection, refraction, and absorption.
Dark matter, on the other hand, is a hypothetical form of matter that does not interact with light or other forms of electromagnetic radiation in the same way that normal matter does. It does not have an electric charge and does not possess the necessary charged particles, such as electrons, that can be affected by the electric field of light. Dark matter primarily interacts with normal matter and itself through gravitational forces, which means it can influence the motion of galaxies and galaxy clusters through its gravitational pull, but it does not emit, absorb, or reflect light.
The exact nature of dark matter is still unknown, and it remains a subject of active research in astrophysics and particle physics. While its interactions with normal matter are primarily gravitational, there are ongoing efforts to understand the properties and possible additional interactions of dark matter with the known particles and forces in the universe.