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

Light travels fastest in empty space due to the absence of matter, which can impede its movement. In a vacuum, there are no particles to scatter or absorb the light, allowing it to maintain its speed of approximately 299,792 kilometers per second. The density of a medium affects how light propagates; less dense mediums, like a vacuum, allow light to travel more freely compared to denser materials, which can slow it down.

Both the concepts of density and the nature of a vacuum contribute to this phenomenon. A vacuum signifies a complete absence of matter, and when light travels through it, there are no physical barriers or interactions with other particles, which could otherwise hinder its progress and reduce its speed. Thus, in empty space, the lack of density combined with the vacuum condition creates the optimal environment for light to travel at its maximum speed.