The speed of light depends on the medium through which light travels. Why does light travel through empty space faster?

Light travels faster in empty space primarily because it is a vacuum, which inherently has no matter to impede its propagation. A vacuum is defined as a space devoid of matter, which means there are no atoms or molecules to interact with the light. This lack of obstacles allows light to move unimpeded, resulting in its maximum speed.

Additionally, the concept of density plays a significant role in understanding light's speed in different media. In less dense media, such as air or vacuum, light can maintain its higher speed compared to denser substances like water or glass. If a medium is denser, light interacts more with the particles present, which can slow it down.

Together, these aspects highlight why light travels fastest in empty space — it is a vacuum (having no matter) and is less dense compared to substances containing particles. Therefore, combining both reasons results in the correct answer consisting of both the characteristics of density and vacuum.