Light travels slower in mediums like water compared to a vacuum, but the presence of virtual particles does not impede its speed in a vacuum. Virtual particles are considered non-physical and do not affect the movement of real particles, despite their interactions in quantum electrodynamics (QED). The discussion touches on concepts like Hawking radiation, suggesting that the behavior of particles near black holes does not necessarily require the existence of virtual particles. Some participants argue that virtual particles are essential for understanding phenomena like Lamb's shift, while others maintain they do not influence light speed. Overall, the connection between light and virtual particles remains a complex topic in quantum physics.