Here's why:

* Empty space (vacuum): Light travels at its maximum speed in a vacuum, which is approximately 299,792,458 meters per second (approximately 186,282 miles per second). This is often referred to as the speed of light, denoted by the symbol "c".

* Gases: Light travels slightly slower in gases than in a vacuum because the photons interact with the gas molecules, causing a tiny delay.

* Liquids: Light travels even slower in liquids than in gases due to the higher density of molecules and more frequent interactions.

* Solids: Light travels the slowest in solids because the tightly packed molecules cause even more frequent interactions and slow down the photons.

In summary: The speed of light is dependent on the medium it travels through, with the speed decreasing as the density of the medium increases.